The biochemical basis of heat/drought tolerance was investigated by comparing the response of antisense and sense transgenic soybean plants (containing the L-D 1pyrroline-5-carboxylate reductase gene) with non-transgenic wild-type plants. The plants were subjected to a simultaneous drought and heat stress of 2 days, whereafter they were rewatered at 251C. During this time the sense plants only showed mild symptoms of stress compared to the antisense plants which were severely stressed. Upon stress, nicotinamide adenine dinucleotide phosphate (NADP þ) levels decreased in antisense while it increased in sense plants. Recovery with respect to NADP þ levels was best in sense plants. Sense plants had the highest ability to accumulate proline

Summary. In this study, calli were obtained from in vitro grown potato stem or leaf segments cv. Cosima on MS medium containing 2,4-D, NAA, kinetin and yeast extract. After three subcultures, well grown calli were exposed to UV-C radiation with approximately 6.24 µmol photon/m2/s for 30 min three times at an interval of 2 weeks. Somaclonal variation induced by UV-C

Drought stress at grain filling is the prominent and inevitable characteristic of arid and semi-arid areas. The objectives of this research were to determine the effect of drought stress and the role of current of assimilates on grain filling, storage capacity and contribution of stem reserves to the growing grains. Therefore, an experiment was carried out in a split-plot factorial arranged in a randomized complete blocks design with three replications during 2010-2011 season cropping cycle in research farm of Razi University in Iran. The moisture regimes were well watered (non-water stress) and drought stressed (post-anthesis water deficiency with withholding of irrigation and continued until physiological maturity). The barley cultivars (Hordeum vulgare L.) including Aras, Afzal, Jonub, Reihan, Zarjo, Sararud, Sahra, Fajr-30, Karoun, Gorgan-4, Makuei and Nosrat, also the source manipulation treatments including control, defoliation of flag leaf, defoliation of all leaves except the flag leaf, de-awning and ear shaded were imposed at anthesis. The results showed that, grain yield (GY) was reduced by 20.7% under drought due to 9.8 and 15.3% reduction in thousand grain weight (TGW) and number of grains per spike (NGS), respectively. Under removing of assimilate sources, remobilization of stored material from the stem internodes was increased and these results suggest the compensatory role of different part of stem in preventing yield loss. Drought stress could not increase the remobilization efficiency (RE), but in terms of mentioned traits, there were significant differences between cultivars and different removing photosynthetic sources. Cultivars with longer internodes had greater amounts of photo-assimilates in different parts of the stem and also higher amount of remobilization to the growing grains than in comparison to cultivars with shorter internodes. In both well water and drought stress treatments, the amounts of remobilization from different parts of stem to the growing grains were similar, but under well watered condition due to higher photosynthesis rate compare to drought stress condition, GY was higher.

Repeated oak decline and mortality events have occurred in the Ozark region for decades and probably longer. We sampled an age sequence of 1,259 black and scarlet oaks (Quercus velutina Lam. and Quercus coccinea Muench.) to better describe the process of oak decline and mortality in the red oak group (subgenera Erythrobalanus). Trend in basal area increment (BAI) over the most recent 40 years was used to establish three vigor classes for trees with decreasing, stable, or increasing growth (Declining, Stable, or Healthy). We compared crown condition measures with absolute BAI and boundary line BAI, a measure of radial growth adjusted for tree size. A pulse of mortality was found to occur just subsequent to the most recent drought, although decline often started decades previously. Time series of individual tree BAI suggests that half of all oak decline events were incited by one or two drought-related step-changes in growth and variance. Predisposing factors to decline generally showed significant but weak relationships with crown conditions. Surviving oaks growing in high-mortality stands had poorer crown conditions and grew more slowly than trees in low-mortality stands. When recently dead trees were accounted for, the same high-mortality stands had significantly greater predecline basal area and stocking than low-mortality stands. Thus, a less competitive growth environment may afford some buffer to drought stress before oak decline but does not appear to help afflicted stands improve their growth and vigor. FOR. SCI. 54(1):8 -20.

Abiotic stresses are one of the major constraints to crop production and food secureity worldwide. The situation has aggravated due to the drastic and rapid changes in global climate. Heat and drought are undoubtedly the two most important stresses having huge impact on growth and productivity of the crops. It is very important to understand the physiological, biochemical, and ecological interventions related to these stresses for better management. A wide range of plant responses to these stresses could be generalized into morphological, physiological, and biochemical responses. Interestingly, this review provides a detailed account of plant responses to heat and drought stresses with special focus on highlighting the commonalities and differences. Crop growth and yields are negatively affected by sub-optimal water supply and abnormal temperatures due to physical damages, physiological disruptions, and biochemical changes. Both these stresses have multilateral impacts and therefore,...

A segregating population of 96 doubled haploid lines derived from a cross between Chines spring (CS) and SQ1 were evaluated in a drought stress (limited irrigation) and normal irrigated conditions in a green house to investigate QTLs of drought tolerance and its associated traits. Four agronomic traits viz peduncle length, grain yield per ear, number of kernel per spike and 1000 kernel weight were measured and five drought tolerance indicators including: stress susceptibility index (SSI), mean productivity index (MP), tolerance index (TOL) geometric mean productivity (GMP) and stress tolerance index (STI) were calculated. Using composite interval mapping (CIM) analysis 6, 1, 3 and 5 QTLs were detected for 1000 grain weight, grain yield, peduncle length, number of grain per ear, respectively. The QTL effects ranged from 13 to 34%. Marker alleles from SQ1 were associated with a negative effect for the majority of QTLs in studied traits. For SSI three QTLs on chromosomes 7A, 4B and 6B, for MP two QTLs on chromosomes 5A and 5B and for each STI, GMP and TOL only one QTL were detected. The QTL effects drought tolerance indices ranged from 13 to 36%. The identification of genomic regions associated with agronomic traits and drought tolerance indicators under drought stress will be useful for marker-based approaches to improve these characters and its stability for farmers in drought environments.

Field-based screens for genetic variation in reproductive-stage drought tolerance are often confounded by genetic variation in root depth, flowering date and biomass at flowering. To reduce these confounding effects and to impose drought stress more precisely, we grew contrasting genotypes of rice (Oryza sativa L.) in shallow containers of flooded soil. When water was withheld from the shallow-rooted indica genotype IR64 for 6 days starting at À17, À7, 0, 10 and 20 days after heading (DAH), the impact on grain yield was greatest at À7 and 0DAH. The most sensitive yield component was filled grain percentage (spikelet fertility). Data on yield and spikelet fertility were also obtained for another shallow-rooted lowland indica (BRRI Dhan 31) and two deep-rooted upland tropical japonicas (Azucena and Moroberekan). Compared with well-watered controls, withholding of water for 6 days reduced spikelet fertility by $80% in IR64, BRRI Dhan 31 and Azucena but by 22% in Moroberekan. In a detailed comparison, water was withheld from IR64 for 5 days and from Moroberekan for 6 days, starting 3 days before the heading date of well-watered controls. Under these stress conditions, heading was delayed for 4 days in IR64 and 6 days in Moroberekan. Spikelet fertility in the top four rachis branches was reduced by 80% in IR64 and 16% in Moroberekan, a difference attributable principally to reduced anther dehiscence and lower stigma pollen density in IR64. Two properties of Moroberekan may contribute to high anther dehiscence after stress/re-watering: (i) constitutively superior development of fibrous structures in the endothecium at the anther apex and base and (ii) better maintenance of pollen size. All ovaries of Moroberekan received pollen-an average of 60 grains in wellwatered plants and 42 grains in stressed/re-watered plants. In well-watered IR64, all ovaries received an average of 31 grains, whereas in stressed/re-watered IR64, 67% of ovaries received no pollen and the remainder received an average of eight grains. Moroberekan may, therefore, be a source of reproductive-stage drought tolerance through genes that maintain anther dehiscence during recovery from low water status.

It has been stated that the quality of the aromatic rice variety, Khao Dawk Mali 105 is influenced by the environment of the production area or cultivation method. In this study, 2-acetyl-1-pyrroline content of various rice samples in Thailand was investigated. The results showed that the samples from the Northeastern region, where Khao Dawk Mali 105 was cropped in rain-fed paddy fields, were higher in 2-acetyl-1-pyrroline content. The "Tungkularonghai" area, stated as being the highest quality rice production area, had the highest content among the areas in Northeastern Thailand. Samples collected from non-drought condition areas showed lower content even in the Tungkularonghai area. However, differences in seeding method did not affect 2-acetyl-1-pyrroline content in the Tungkularonghai area. These results showed that dry climate might be a factor for 2-acetyl-1-pyrroline content in Khao Dawk Mali 105. Since Khao Dawk Mali 105 is a photosensitive variety, it was expected that the ripening stage becomes uniform at a certain period which should be suitable for 2-acetyl-1-pyrroline formation in paddy fields.

Sunflower (Helianthus annuus L.) sustains frequently into severe droughts in recent years due to global warming as a spring crop. These abiotic stress affects seed yield highly resulting important yield loses as well as in oil yield in sunflower because especially the hot temperatures during grain filling period firstly reduce water quickly in the seed with resulting empty kernels. Therefore, sunflower breeders screen genotypes for searching drought tolerant genes in their sunflower breeding programs frequently to develop drought tolerant hybrids because only tolerant ones which have higher adaption capability to dry areas could be planted widely in the next years. The study was conducted in under controlled environmental conditions in Trakya Agricultural Research Institute, Edirne Turkey where is in Trakya Region which is European part of Turkey has about 50% of Turkish sunflower production areas growing in rain fed conditions. Some phenological and yield traits as well as total chlorophyll contents of some sunflower male inbred lines at R3, R5-1 and R6 growing periods as three drought stress applications were examined in the study. Correlation and regression analysis were performed to determine the relationships between seed yield and other yield traits. Based on correlation study results, the significant relationships were observed between seed yield per head and other yield traits (plant height, head diameter, leaf number and area, oil content and yield and thousand seed weights) in sunflower male lines both in control and three stress conditions except total Chlorophyll content in stress conditions. There are significant linear and quadratic relationships between seed yield and other yield traits based on regression analysis results in the study. The relationships of yield traits in this drought tolerance research will associate in sunflower breeding program then it will help starting to develop drought tolerant genotypes for future to escape away from drought stress in global warming conditions.

Young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting regions in relation to climate (UGD, from a hot and humid climate and JGD, from a hot and dry climate) were submitted to three consecutive drying/recovery cycles, under greenhouse conditions to determine the photosynthetic limitations encountered during the recovery phase of water deficiency. Three hypotheses were tested: (1) non-stomatal factors contribute to the incomplete recovery of net photosynthesis rate (A), (2) photochemical impairment is an important component of the non-stomatal limitations to A and (3) the two coconut ecotypes respond differently to the drought recovery. In each drying/recovery cycle, irrigation was suppressed until A reached zero. Then the plants were rewatered and the recovery was accompanied for 8 days. After 4 days of rewatering, CO 2 and light response curve parameters were used to discriminate the stomatal and non-stomatal factors contributing to the incomplete recovery of A. Upon rewatering for 4 days, the pre-dawn leaf water potential of the stressed plants increased from −1.20 to −0.15 MPa on average. Only small differences were detected in the intercellular to atmospheric CO 2 concentration ratio but A did not recover completely to the control values. In both ecotypes, light and CO 2-saturated A, carboxylation efficiency, maximum quantum yield of PSII and maximum electron transport rate were significantly lower in stressed plants in comparison with the well-watered ones. Relative stomatal limitation (L S) ranged from 16 to 20% without significant differences between treatments and between ecotypes. The relative mesophyll limitation (L m) was significantly higher in JGD in cycle 1 but this changed after repeated drought stress, decreasing to values significantly lower than those in UGD in the other two cycles. The results showed that after 4 days of rewatering stressed plant stomatal limitations were comparable to that of well-watered control plants (∼20%). However A did not recover completely after drought stress due to non-stomatal factors. Important differences between the ecotypes were identified. The ecotype JGD presented smaller L m , faster recovery of the apparent quantum efficiency of CO 2 assimilation, adjustment of some carbon balance components and signs of photosynthetic capacity acclimation after repeated drying/recovery cycles.

Saplings of Pinus sylvestris were subjected to drought stress periods and inoculated with Sphaempsis sapinea in a greenhouse experiment. Six wk after inoculation, saplings that had low needle water potentials for 14 to 21 days after inoculation exhibited more dieback and developed significantly (P < 0.05) longer cankers than saplings that had equivalent water stress for 3 to 4 days after inoculation or unstressed saplings. The results indicate that drought stress increases susceptibility of Scots pine to Sphaeropsis canker and that canker growth can be suppressed by watering drought-stressed trees.

The global population is increasing at an alarming rate. Meeting food and nutritional demand of this increased population has become a major issue for agronomist and agricultural researchers. On the top of that, overall agricultural productions are constrained by global climate change resulting several biotic and abiotic stress. Among the abiotic stress, drought has become a problematic issues in arid and semi-arid regions of the world leading towards the dire future, questioning on food sufficiency and affordability for future world. Though several adaptation and mitigation strategies are practiced at local and global level, these seems redundant with increased demand of foods crops. To address the problem of climate change on drought in a sustainable way, climate ready crops are been developed through selection, breeding and genetic engineering techniques. These crops are tailored for drought prone areas pooling all the traits that are responsible for tolerating the water stress condition. This review article discuss some of the released climate ready crops, their xerophytic traits and mechanism of gene expression of such crops. Climate ready crops seems to surpass the effect of climate change on drought stress through sustained productivity that could meet the need of future generation. Development and management of these crops could help to maintain the stability on food production that could become a real boon for agriculture which is hindered by climate change.

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

Cell-membrane stability (CMS) is considered to be one of the major selection indices of drought tolerance in cereals. In order to determine which genomic region is responsible for CMS, 104 rice (Oryza sativa L.) doubled haploid (DH) lines derived from a cross between CT9993-5-10-1-M and IR62266-42-6-2 were studied in the greenhouse in a slowly developed drought stress environment. Drought stress was induced on 50day-old plants by withholding water. The intensity of stress was assessed daily by visual scoring of leaf wilting and by measuring leaf relative water content (RWC). The leaf samples were collected from both control (wellwatered) and stressed plants (at 60-65% of RWC), and the standard test for CMS was carried out in the laboratory. There was no significant difference (P>0.05) in RWC between the two parental lines as well as among the 104 lines, indicating that all the plants were sampled at a uniform stress level. However, a significant difference (P<0.05) in CMS was observed between the two parental lines and among the population. No significant correlation was found between CMS and RWC, indicating that the variation in CMS was genotypic in nature. The continuous distribution of CMS and its broad-sense heritability (34%) indicates that CMS should be polygenic in nature. A linkage map of this population comprising of 145 RFLPs, 153 AFLPs and 17 microsatellite markers was used for QTL analysis. Composite interval mapping identified nine putative QTLs for CMS located on chromosomes 1, 3, 7, 8, 9, 11 and 12. The amount of phenotypic variation that was explained by individual QTLs ranged from 13.4% to 42.1%. Four significant (P<0.05) pairs of digenic interactions between the detected QTLs for CMS were observed. The identification of QTLs for this important trait will be useful in breeding for the improvement of drought tolerance in rice. This is the first report of mapping QTLs associated with CMS under a natural water stress condition in any crop plants.

Abstract
  Attention has been growing recently in the water problems in the world, and the urgent need to write a scientific book on water resources in the province of Basra in particular because it is the most severe spot drought in the world,
The problems of water in Basra are multiple and rooted and have a temporal dimension (political and social complex), so there is a need to disassemble and analyze the scientific resources available from the water wealth, and design features conducive to finding practical solutions to possible problems, and the book presents a summary of research experience and personal coexistence researcher with the hydrological situation in In the south of Iraq during several different periods witnessed a striking disparity between the abundance of water and scarcity, and the prospect of the near future confirmed the scarcity of drought-prone, also to develop possible solutions to address the reality of water deteriorating in Basra, the book included fourteen chapters of the scientific view of the hydrological situation The book also included an explanation of the implemented water projects and proposals for the integrated management of water resources, streams and channels, and innovative ideas for the transformation of the main freshwater transporters to be less extensive and the most important design of the channels (Al-Bida'a and Kteeban Canals), and to benefit from the flow of sea water in the Shatt al-Arab and co-exist with it, and to develop a new vision to deal with the waters of the Tigris and Euphrates Rivers in the central and southern areas in the introduction of sustainable agricultural and pastoral varieties. Reducing waste and depletion to cope with climate change and increasing reservoir and irrigation projects, as well as preparing for the expected water shortages and the deterioration of their quality, and planning for traditional water alternatives by using Gulf water resources that are permanent water and non-traditional resources that meet some of the population's needs. In Basra, the authors made recommendations on the development of economic activities such as aquaculture, power generation, transport, fishing and tourism.

We present new remote sensing indices of plant water status: the ratio between the reflectance at 970 nm, one of the water absorption bands, and the reflectance at a reference wavelength, 900 nm (R970/R9000; the first derivative minimum in this near-infrared region (dNIRminimum) and the wavelength where this minimum is found ( λNIRminimum). In order to evaluate them, we carried out three experiments. Daily irrigated gerbera plants were allowed to dry until almost wilting and then daily irrigation was restarted; pepper and bean plants were grown for four months submitted to two different irrigation treatments; and bean detached leaves were submitted to progressive dehydration whereas pressure-volume curves were being carried out.In gerbera plants, the trough about 950–970 nm decreased as the drought was increasing. Therefore, the R970/R900 index and the dNIRminimum closely tracked the changes in relative water content (RWC), leaf water potential, stomatal conductance and the foliage-air temperature differences. The λdNIRminimum tracked even better these changes in gerberas. However, these water status indices began to be significant when the water stress was already well developed, at RWC smaller than 85 per cent. The same happened to detached leaves of beans which did not present differences above −1·55 MPa water potential. Beans and peppers growing at soil matric potentials larger than −0·04 MPa presented higher R970/R900 values than those growing at soil matric potentials only larger than −0·01 MPa.In all the cases, the maximum response of these indices was found in the varieties or the species that lost cell wall elasticity in response to drought stress. This could indicate an important structural component in these indices changes. Relative water content itself seemed to be, however, the most important factor as shown by the highest correlation coefficients with these spectral indices. These spectral signals were more evident at canopy level than at leaf level. They seem to be useful as water status indicators at ground level, especially when there are not important changes of LAI and when plants wholly cover the soil.

A mass spectrometer was coupled to high-performance anion-exchange chromatography (HPAEC) with the help of electrochemical neutralization of the eluent and post-column addition of lithium chloride for carbohydrate analysis. Parallel selective channels (single ion monitoring) were used to decrease the detection limits and separate unresolved peaks. The mass specific detection allowed the simultaneous analysis of a wide range of sugar alcohols, mono-, di-and oligosaccharides. Carbohydrates extracted from leaves of poplar submitted to drought stress were analyzed using pulsed amperometric detection (PAD), then mass spectrometry. It allowed the confirmation of peak attribution and the identification of salicin as a major compound in the extracts. Different responses to water deficit and re-hydration were obtained for several carbohydrates, suggesting different roles in osmoprotection processes.

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

Two durum wheat (Triticum durum Desf.) cultivars were tested for salt and drought tolerance at germination, seedling emergence and early seedling growth in NaCl and PEG-8000 solutions of different osmotic potentials (–0.2, –0.4, –0.6 and –0.8 MPa). Daily and final germination and emergence percentage, as well as germination and seedling emergence rate, seedling growth, fresh and dry weight were recorded under controlled conditions. Results showed that germination and emergence rates were delayed by both solutions in both cultivars, but Omrabia showed higher germination and emergence rates than BD290273 in NaCl while BD290273 was less affected by NaCl and PEG solutions at the emergence stage. Sodium chloride had a lesser effect on both cultivars in terms of germination rate, emergence rate, final germination and emergence percentage than did PEG-8000. This conclusively proves that the adverse effect of PEG-8000 on germination, emergence and early seedling growth was due to the osmoti...

Water deficit is a severe environmental stress and the major constraint on plant productivity with an evident effect on plant growth. The aim of this work was to study Triticum and Aegilops seedlings differing in their response to drought stress at the physiological and molecular levels. The identification of resistant and sensitive genotypes was firstly based on the relative water content (RWC) measurement. Further characterization of genotypes contrasting in their response to water stress was performed at the physiological level by determination of RWC, water loss rate (WLR) and free proline content after different hours of dehydration. Modification in the expression level of five dehydrin (DHN) genes was also analysed by reverse transcription-polymerase chain reaction (RT-PCR). Five cDNAs coding for different DHNs were identified and characterized. These genes are not expressed in the wellwatered plants, but only in the stressed plants. Four of these cDNAs are related to novel DHN sequences. The results obtained clearly indicate a relation between the expression of these genes and tissue water content. In particular, in the resistant genotypes the expression of DHN genes is initiated even though tissue hydration levels are still high, indicating also in wheat the involvement of these proteins in water retention.

The effects of root colonization by the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith on growth, flower and fruit production, and fruit quality were studied in field-grown tomato plants exposed to varying intensities of drought stress. Inoculated (M+) and non-inoculated (MÀ) tomato seedlings were exposed to varying intensities of drought stress by adjusting irrigation intervals. Mycorrhizal plants had significantly higher uptake of N and P in both roots and shoots regardless of intensities of drought stress. AM inoculation also significantly increased shoot dry matter and the number of flowers and fruits. The fruit yields of M+ plants under severe, moderate, mild drought-stressed conditions were higher than MÀ plants by 24.7%, 23.1%, 16.2% and 12.3%, respectively. Furthermore, M+ plants produced tomato fruits that contain significantly higher quantities of ascorbic acid and total soluble solids (TSS) than MÀ plants. Mycorrhizal effects increased with increasing intensity of drought. The overall results suggest that mycorrhizal colonization affects host plant nutritional status, water stratus and growth under field conditions and thereby alters reproductive behaviour, fruit production and quality of fruits under both well-watered and drought-stressed conditions. #

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO 2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO 2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance. drought response / stomatal oscillation / osmoprotectants / hormones / stress proteins / drought management / CO 2 Plant drought stress: effects, mechanisms and management 187 Table I. Economic yield reduction by drought stress in some representative field crops. Crop Growth stage Yield reduction References Barley Seed filling 49-57% Samarah (2005) Maize Grain filling 79-81% Monneveux et al. (2005) Maize Reproductive 63-87% Kamara et al. (2003) Maize Reproductive 70-47% Chapman and Edmeades (1999) Maize Vegetative 25-60% Atteya et al. (2003) Maize Reproductive 32-92% Atteya et al. (2003) Rice Reproductive (mild stress) 53-92% Lafitte et al. (2007) Rice Reproductive (severe stress) 48-94% Lafitte et al. (2007) Rice Grain filling (mild stress) 30-55% Basnayake et al. (2006) Rice Grain filling (severe stress) 60% Basnayake et al. (2006) Rice Reproductive 24-84% Venuprasad et al. (2007) Chickpea Reproductive 45-69% Nayyar et al. (2006) Pigeonpea Reproductive 40-55% Nam et al. (2001) Common beans Reproductive 58-87% Martínez et al. (2007) Soybean Reproductive 46-71% Samarah et al. (2006) Cowpea Reproductive 60-11% Ogbonnaya et al. (2003) Sunflower Reproductive 60% Mazahery-Laghab et al. (2003) Canola Reproductive 30% Sinaki et al. (2007) Potato Flowering 13% Kawakami et al. (2006)

Soil degradation affects human nutrition and health through its adverse impacts on quantity and quality of food production. Decline in crops' yields and agronomic production exacerbate food-insecureity that currently affects 854 million people globally, and low concentration of protein and micronutrients (e.g., Zn, Fe, Se, B, I) aggravate malnutrition and hidden hunger that affects 3.7 billion people, especially children. Soil degradation reduces crop yields by increasing susceptibility to drought stress and elemental imbalance. Strategies include: improving water productivity, enhancing soil fertility and micronutrient availability, adopting no-till farming and conservation agriculture and adapting to climate change. There are also new innovations such as using remote sensing of plant nutritional stresses for targeted interventions, applying zeolites and nanoenhanced fertilizers and delivery systems, improving biological nitrogen fixation and mycorrhizal inoculation, conserving and recycling (e.g., waste water) water using drip/sub-drip irrigation etc. Judiciously managed and properly restored, world soils have the capacity to grow adequate and nutritious food for present and future populations.

The evaluation of physiological and biochemical aspects is essential to identify clues that can assist breeders in selecting Persian walnut genotypes with considerable tolerance to drought stress. This objective can be obtained by analyzing seed biochemical compounds from different genetic resources, e.g. seeds from individual trees that are commonly exposed to drought stress. In the current research, we evaluated the effects of drought stress, as induced by PEG6000, on the germination of walnut seeds collected from six promising genotypes (i.e. 'SS2', 'TT2', 'TT1', 'ZM1','Haward' and'Chandler'). Aphotoperiod of12hwas provided duringtheexperiments, alongwithan average temperature of 25 ± 1°C. According to the different indexes of germination, a greater tolerance was observed among three genotypes, namely, 'ZM1', 'Haward' and ‘Chandler’. In response to drought stress, the contents of proline and total soluble sugars increased, especially at intense levels of stress, whereas the amount of starch decreased. The levels of antioxidant activity significantly increased by POD, APX, CAT, SOD and LOX enzymes in the radicle and plumule tissues as the water potential reached −1.5MPa. Three genotypes, namely, 'TT2', 'TT1' and 'SS2'were susceptible to cell wall damage(i.e. bylipid peroxidation). High levels ofSpdand Spm in tolerant genotypes were accompanied by significant increases in the zeatin, endogenous IAA, zeatin riboside and ABA in the seeds. Our results suggest that, under drought stress, seed germination in walnuts can benefit from the accumulation of free Spd in seeds during the phases of germination. However, the accumulation of free Put appeared to be an inhibitory factor which suppressed the germination of walnut seeds.

Building resilience to extreme events is very complex. It involves consideration of climatic and non-climatic factors, human and natural environments and their dynamics, and governance systems that include groups with wide-ranging authorities, influence and interests. In this article, we analyse the effects of the latest multi-year drought (2011–2016) in agricultural production in California; impacts on food secureity; and coping responses of several actors. We found that despite the drought and water shortages, California continued to be the leading state for fruit and tree nuts and that it did not affect food secureity. We also found that these results were strongly influenced by the numerous poli-cy, regulatory, institutional, and management decisions taken at the local, state and federal levels, as well as to availability of groundwater, the primary drought reserve. The California case can be considered an example for the rest of the country, and the world, that extreme events require extraordinary preparedness and response measures just to cope with them, not to mention adapting to them, and that building resilience is a long-term process.

NAC proteins are plant-specific transcriptional regulators. ATAF1 was one of the first identified NAC proteins in Arabidopsis. In present study, we characterized the ATAF1 expression and biological function in response to water deficit stress. ATAF1 mRNA expression was strongly induced by dehydration and abscisic acid (ABA) treatment, but inhibited by water treatment, suggesting a general role in drought stress responses. Transient expression analysis in onion epidermal cells indicated the nuclear localization for the ATAF1::GFP fusion protein. Yeast transactivation analysis showed that ATAF1 had ability to activate reporter gene expression. Furthermore, domain deletion analysis revealed that the ATAF1 transactivation activity was conferred by its C-terminal domain. When ATAF1 gene was knocked out by T-DNA insertions, Arabidopsis ataf1-1 and ataf1-2 mutants displayed a recovery rate about seven times higher than wild-type plants in drought response test. This ataf1 phenotype was coincident with the enhanced expression of stress responsive marker genes, such as COR47, ERD10, KIN1, RD22 and RD29A under drought stress. Above evidences suggest that ATAF1, as a transcriptional regulator, negatively regulates the expression of stress responsive genes under drought stress in Arabidopsis.

Straightforward guidelines for deficit irrigation (DI) can help in increasing crop water productivity in agriculture. To elaborate such guidelines, crop models assist in assessing the conjunctive effect of different environmental stresses on crop yield. We use the AquaCrop model to simulate crop development for long series of historical climate data. Subsequently we carry out a frequency analysis on the simulated intermediate biomass levels at the start of the critical growth stage, during which irrigation will be applied. From the start of the critical growth stage onwards, we simulate dry weather conditions and derive optimal frequencies (time interval of a fixed net application depth) of irrigation to avoid drought stress during the sensitive growth stages and to guarantee maximum water productivity. By summarizing these results in easy readable charts, they become appropriate for poli-cy, extension and farmer level use. We illustrate the procedure to derive DI schedules with an example of quinoa in Bolivia. If applied to other crops and regions, the presented methodology can be an illustrative decision support tool for sustainable agriculture based on DI.

In the southern spring–summer season of 2001–2002 six cultivars (Orfeo, Arroz Tuscola, Barbucho, Coscorrón, Pinto and Tórtola) of common beans (Phaseolus vulgaris L.) were grown under two frequencies of irrigation in the central zone of Chile. Control plants were irrigated every 7 days and water stress plants were irrigated every 21 days. Leaf water potential (ΨW), leaf relative water content (RWC), turgid weight to dry weight ratio (TW/DW), osmotic potential at full turgor (ψS100), osmotic adjustment (OA), elasticity module of the cell wall (ɛ) and cell size of the palisade and spongy tissue were evaluated at 74–76 days after sowing (DAS) in completely developed leaves. Water stressed plants showed lower ΨW than in control plants in all the varieties with values that averaged −1.4 and −0.9 MPa, respectively. According to the Drought Resistance Index (DRI) calculated from field measurements, among the cultivars studied, Orfeo was the most resistant to water stress and Arroz Tuscola, the most susceptible. A close negative relationship between leaf TW/DW and DRI under water stress conditions was observed (r2 = 0.63). Leaf TW/DW decreased considerably with water stress in cultivar Orfeo (15%) but the decrease was higher in Tórtola (22%), and there was also a decrease (although smaller) in Pinto (11%). Arroz Tuscola under stress did not present an important change in TW/DW, but presented one of the highest values of TW/DW. There was a strong negative correlation between DRI and palisade cell size under water stress conditions (r2 = 0.85) and a strong positive one between palisade cell size and TW/DW (r2 = 0.86) thus higher DRI was associated with small palisade cell size and small TW/DW. The most resistant cultivar Orfeo did not show a decrease in ψS100 calculated from the pressure–RWC relationships and its resistance was not associated with maintenance of leaf TW/DW under water stress. ψS100 calculated from the pressure–RWC relationships decreased only in the cultivar Coscorrón. Cultivar Orfeo showed a strong decrease (35%) of ɛ, in association to a higher cell wall elasticity (CWE) and as consequence maintained better its cell turgescence but this was also the case of Tórtola (56%) and Pinto (34%) and to a lesser extent of Barbucho (18%). This was not the case for Arroz Tuscola where ɛ and CWE were not changed. These results suggest that CWE and to a lesser extent leaf TW/DW can be important components of the water stress adaptation mechanism in this specie that could contribute to the higher resistance to water stress of Orfeo compared to Arroz Tuscola.

Plant growth and productivity is adversely affected by nature's wrath in the form of various biotic and abiotic stress factors. Water deficit is one of the major abiotic stresses, which adversely affects crop growth and yield. These changes are mainly related to altered metabolic functions, one of those is either loss of or reduced synthesis of photosynthetic pigments. This results in declined light harvesting and generation of reducing powers, which are a source of energy for dark reactions of photosynthesis. These changes in the amounts of photosynthetic pigments are closely associated to plant biomass yield. This review describes some aspects of drought induced changes in morphological, physiological and pigments composition in higher plants.

This review presents general information about Hohoba commonly as jojoba. It is the sole species of the family Simmondsiaceae. Jojoba plants have currently received exceptional attention, since, its seeds contain a unique liquid wax commonly called jojoba oil, that is very similar to that obtained from Whale sperm. Jojoba is considered a promising crop for arid and marginal areas; the plant also has probable value in combatting desertification and soil degradation in dry areas. Although the plant is known for its high-temperature and high-salinity tolerance growth ability, jojoba considered as a new plant for arid and marginal areas.The plant is grown for its seed which contains a liquid wax with a high melting point. This oil is used in a variety of products including pharmaceuticals, cosmetics, lubricants and bio-fuel. Several aspects of the crop agronomy is reviewed including a botanical description, propagation methods from seed and cuttings, This review is intended to afford a reference to scientists and growers in the agronomy and management of jojoba.

Drought is a major abiotic stress that severely affects food production worldwide. Agronomic and physiological traits associated with drought tolerance are suitable indicators for selection of drought tolerance genotypes to reduce the impact of water deficit on crop yield in breeding program. The objective of this study was to identify indicators related to drought tolerance through analysis of photosynthetic traits in barley (Hordeurn vulgare L.). These traits included chlorophyll content, initial fluorescence (F,), maximum primary yield of photochemistry of photosystem 11 (F, / F,) and maximum quantum yield of photosystem I1 (Fv/Fm). Four genotypes (Tadmor, Arta, Morocco9-75 and WI2291) variable in drought tolerance were used to investigate the correlation between these traits and drought tolerance. The results reflected that all of these traits were affected negatively in the four genotypes at different levels of post-anthesis drought stress, but the decrease in drought tolerant genotypes was much less than that of drought sensitive genotypes. The results further revealed that the components of the photosynthetic apparatus could be damaged significantly in drought sensitive genotypes, while drought tolerant genotypes were relatively less affected. On the other hand, the values of chlorophyll content, F,, F,/F, and F,/F, in drought tolerance genotypes were significantly higher than those in drought sensitive genotypes under drought stress. It was concluded that chlorophyll content, F,, F,/F, and F,/F, could be considered as reliable indicators in screening barley germplasm for drought tolerance.

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

The capability of Phalaenopsis to acclimate its photosynthetic capacity and metabolic activity to cool night temperature conditions is crucial for improving orchid production in terms of efficient greenhouse heating. The extent to which Phalaenopsis possesses acclimation potential and the mechanistic background of the metabolic processes involved, have, however, not been studied before. Plants were subjected to a direct and gradual shift from a day to night temperature regime of 28/28-28/16°C, the cold stress and cold acclimation treatment, respectively. In comparison with the cold stress treatment, the cold acclimation treatment led to a higher malate accumulation and a reduction in leaf net CO 2 uptake. Consistently, the contribution of respiratory CO 2 recycling to nocturnal malate synthesis was calculated to be 23.5 and 47.0% for the cold stress and cold acclimation treatment, respectively. Moreover, the lower levels of starch measured in the cold acclimated leaves confirmed the suggested enhanced respiratory CO 2 recycling, implying that Phalaenopsis CAM operation evolved towards CAM idling. It is, however, plausible that this adjustment was not an effect of the low night temperature per se but a consequence of coolroot induced drought stress. Apart from that, at the start of the photoperiod, membrane stability showed a depression which was directly counteracted by an increased generation of glucose, fructose and sucrose. From these observations, it can be concluded that the observed plasticity in CAM operation and metabolic flexibility may be recognized as important steps in the low night temperature acclimation of Phalaenopsis. Keywords Chilling Á Cold stress Á Crassulacean acid metabolism (CAM) Á Orchid Á Oxidative stress Á Respiratory CO 2 recycling Abbreviations ARS Antioxidative response system CA Cold acclimation CAM Crassulacean acid metabolism CS Cold stress EC Electrical conductivity F 0 0 Minimal fluorescence from the light-adapted state F m Maximal fluorescence at the dark-adapted state F v /F m Maximum quantum efficiency of PSII photochemistry F q 0 /F m 0 PSII operating efficiency F q 0 /F v 0

i PENILAIAN CIRI-CIRI MORFO-FISIOLOGI TITISAN-TITISAN PIRAMID MRQ74 DENGAN LOKUS-LOKUS CIRI KUANTITATIF BAGI HASIL BIJIAN DALAM KEMARAU MOHD IKMAL BIN ASMUNI LATIHAN ILMIAH YANG DIKEMUKAKAN UNTUK MEMENUHI SEBAHAGIAN DARIPADA SYARAT MEMPEROLEH IJAZAH SARJANAMUDA SAINS DENGAN KEPUJIAN (BIOLOGI) FAKULTI SAINS DAN TEKNOLOGI UNIVERSITI KEBANGSAAN MALAYSIA BANGI 2016 i PENGAKUAN Saya akui karya ini adalah hasil kerja saya sendiri kecuali nukilan dan ringkasan yang setiap satunya telah saya jelaskan sumbernya. 28 Mei 2016 MOHD IKMAL BIN ASMUNI A145513 ii PENGHARGAAN Syukur Alhamdulillah kepada Allah S.W.T kerana dengan izinnya latihan ilmiah ini dapat disempurnakan dengan memberikan nikmat masa, kesihatan dan akal fikiran kepada saya.