Differences In Drought Tolerance Research Articles

Drought-triggered false ring formation in a Mediterranean shrub

Recently, the Mediterranean region has experienced unprecedented drought. Climate models continue to predict an increase in drought frequency and duration, which increases the importance of quantifying the response of already drought-tolerant Mediterranean plants to increased drought. We examined the wood anatomy and dendroecological features of a Mediterranean shrub, Arbutus unedo L., at a xeric and a mesic site on the Italian island of Elba to identify shrub growth response to drought. Cross-sectional microsections of A. unedo stems were stained, described, and crossdated. Annual ring widths of radial microsections were measured and compared with regional climatic variables. False rings (intra-annual bands of latewood typically formed in response to a specific stressor) were visible in the wood samples when viewing radial microsections under high magnification. False ring formation coincided with below-average rainfall in late summer at the xeric site, and below-average rainfall and high temperatures in spring and summer at the mesic site. If increased drought occurs in the Mediterranean region, it is likely that plants in this region will experience a drought-induced growth response similar to that seen in A. unedo, and slight differences in drought tolerance may become more important as plants compete for moisture under drier conditions.

PEROXIDASE, GUAIACOL PEROXIDASE AND ASCORBATE PEROXIDASE ACTIVITY ACCUMULATION IN LEAVES AND ROOTS OF WALNUT TREES IN RESPONSE TO DROUGHT STRESS

Peroxidase isozymes (POX, POD and APX) activity were determined in 1-year-old walnut plants grown in environmental conditions characterized by high temperatures and high photosynthetic photon flux density levels and subjected to withholding irrigation for a 20-day period. These mechanisms have been investigated over both irrigated and drought-stressed plants in order to investigate the plant response under stressed conditions and its ability to recover. Before and during the experimental period, leaf and root samples were collected and their POD was analyzed. Significant increases of POD especially APX isozyme activity were also observed during the progressive increment of drought stress in both leaf and root tissues of tolerant genotypes at the seventh day after the beginning of the drought period. The differences in drought tolerance may be closely related with efficient photo protective systems as well as the increased capacity of the anti oxidative system to scavenge reactive oxygen species.

Intraspecific variation in growth and allocation patterns in seedlings of Pinus pinaster Ait. submitted to contrasting watering regimes: can water availability explain regional variation?

• Interpopulation variation in key functional traits of Pinus pinaster Ait. is well recognized. However, the relative importance of drought tolerance to explain this regional variation in the species remains elusive. • Here, we raise the question whether water availability constitutes a likely driver of regional variation in biomass allocation, growth and morphological traits of ten populations that cover the distribution range of P. pinaster. We carried out an experiment where seedlings of five families per population were submitted to two contrasting watering treatments. • The effects of water availability and population were significant for relative diameter and height growth rate, biomass allocation and number of lateral stems and dwarf shoots. Total dry mass significantly differed between watering treatments but it did not among populations. Populations could be clustered into four main groups. Root mass fraction explained most of the variation and significantly correlated to altitude but not to aridity. • The geographical pattern of genetic variation found in morphology and biomass allocation did not translate into population differences in drought tolerance or phenotypic plasticity to water availability, indicating that water availability is not a likely driver of the regional variation observed in the studied traits of P. pinaster at the seedling stage. Mots-cles : altitude / tolerance a la secheresse / Bassin mediterraneen / modeles mixtes / performance du plant entier

Morpho-anatomical and micromorphometrical evaluations in soybean genotypes during water stress

In a greenhouse experiment, morpho-anatomical and micromorphometrical analyses of two soybean cultivars, MG/BR46 (Conquista) and BR16-tolerant and sensitive to drought, respectively-were used to study their water-deficit-tolerance strategies. Drought treatments were applied at reproductive stages from R2 to R7, where evaluations were conducted at 30 days and 45 days after stress started, respectively. The total length of Conquista plants (shoot + root) was greater than of BR16 plants. Pod dry weight was adversely affected due to the lack of moisture, decreasing productivity even of Conquista plants. Both the cultivars had normal development of root hairs; however, it was observed a decrease in the cortex:central cylinder ratio in BR16 stressed for 30 days, and they also showed similar leaflet thickness and stomata distribution. Differences in drought tolerance observed between the two cultivars seemed to be related to factors other than morphological traits since this species has a short lifecycle.

Differential antioxidative responses of indica rice cultivars to drought stress

The present study investigated the linkages between drought stress, oxidative damages and variations in antioxidants in the three rice varieties IR-29 (salt-sensitive), Pokkali (salt-tolerant) and aromatic Pusa Basmati (PB), to elucidate the antioxidative protective mechanism governing differential drought tolerance. Water deficit, induced by 20% (w/v) polyethylene glycol (PEG-6000), provoked severe damages in IR-29 and PB in the form of huge chlorophyll degradation and elevated H2O2, malondialdehyde and lipoxygenase (LOX, EC 1.13.11.12) levels as compared to Pokkali. The protein oxidation was more conspicuous in IR-29. Increment in antioxidants, particularly flavonoids and phenolics was several folds higher over control in Pokkali, while much lesser in IR-29 and PB. The activity of catalase (CAT, EC 1.11.1.6) and superoxide dismutase (SOD, EC 1.15.1.1) were decreased in IR-29 and PB, but unaltered in Pokkali. However, marked drought-induced increase in guaiacol peroxidase (GPX, EC 1.11.1.7) activity was noted in both IR-29 and PB. Induction in radical scavenging activity, being the maximum in IR-29, and increased reducing power ability in all the cultivars, accompanied with drought stress, were observed as a defense mechanism. The novelty of our work is that it showed the aromatic rice PB behaving more closely to IR-29 in greater susceptibility to dehydration stress, while the salt-tolerant Pokkali also showed effective drought tolerance properties.

Responses of leaf gas exchange, water relations, and water consumption in seedlings of four semiarid tree species to soil drying

To understand the response patterns to soil drying and the water use properties of commonly reforested trees in the semiarid Loess Plateau region of China, a glasshouse experiment was carried out with the seedlings of four species, i.e., Robinia pseudoacacia, Armeniaca sibirica, Syringa oblata, and Quercus liaotungensis. Severe water stress induced by withholding water resulted in permanent wilting of most of the seedlings pot-cultured with sandy soil in 8-12 days. Predawn and midday leaf water potentials and gas exchange characteristics (e.g., stomatal conductance) in the seedlings did not show marked changes until the volumetric soil water content decreased to about 0.05. As the soil water content decreased further, these physiological parameters rapidly declined, approaching their minimal levels at the stage of permanent wilting. The response of each parameter to soil water content changes was fitted with a non-linear saturation curve. Though the results suggested that the general pattern of responses to soil drying was identical among the species, quantitative differences in drought tolerance and water use properties were detected. Leaf stomatal conductance in R. pseudoacacia and A. sibirica showed earlier responses to reduced predawn leaf water potentials. However, water use characteristics and specific leaf area indicated that these two species consumed more water and may not be as drought tolerant as S. oblata and Q. liaotungensis. These results may provide important information to compare the reforestation species with respect to soil drying.

Intraspecific differences in drought tolerance and acclimation in hydraulics of Ligustrum vulgare and Viburnum lantana

An adequate general drought tolerance and the ability to acclimate to changing hydraulic conditions are important features for long-lived woody plants. In this study, we compared hydraulic safety (water potential at 50% loss of conductivity, Psi(50)), hydraulic efficiency (specific conductivity, k(s)), xylem anatomy (mean tracheid diameter, d(mean), mean hydraulic diameter, d(h), conduit wall thickness, t, conduit wall reinforcement, (t/b)(h)(2)) and stomatal conductance, g(s), of forest plants as well as irrigated and drought-treated garden plants of Ligustrum vulgare L. and Viburnum lantana L. Forest plants of L. vulgare and V. lantana were significantly less resistant to drought-induced cavitation (Psi(50) at -2.82 +/- 0.13 MPa and -2.79 +/- 0.17 MPa) than drought-treated garden plants (- 4.58 +/- 0.26 MPa and -3.57 +/- 0.15 MPa). When previously irrigated garden plants were subjected to drought, a significant decrease in d(mean) and d(h) and an increase in t and (t/b)(h)(2) were observed in L. vulgare. In contrast, in V. lantana conduit diameters increased significantly but no change in t and (t/b)(h)(2) was found. Stomatal closure occurred at similar water potentials (Psi(sc)) in forest plants and drought-treated garden plants, leading to higher safety margins (Psi(sc) - Psi(50)) of the latter (L. vulgare 1.63 MPa and V. lantana 0.43 MPa). These plants also showed higher g(s) at moderate Psi, more abrupt stomatal closure and lower cuticular conductivity. Data indicate that the development of drought-tolerant xylem as well as stomatal regulation play an important role in drought acclimation, whereby structural and physiological responses to drought are species-specific and depend on the plant's hydraulic strategy.

Identification of Physiological Traits Underlying Cultivar Differences in Drought Tolerance in Rice and Wheat

AbstractRice is used as a model cereal to study drought response at the molecular level, with the goal of applying results to other cereals. To assess the relevance of results from rice to other species, the kinetics of drought development and plant response of tolerant and susceptible tropical rice (Oryza sativa L.) and subtropical wheat (Triticum aestivum L.) cultivars were compared under vegetative and reproductive stage drought in pot experiments. Water was withheld during reproductive stage until plant available soil moisture content was 30 % of field capacity (FC) or leaf wilting was observed, and then reapplied. Rice reached 30 % FC 9 days after withholding water and wheat after 13 days. Before rewatering, both species reached leaf water potentials of −12 bars and similarly low transpiration rates. Stress reduced leaf relative water content, leaf elongation and membrane stability. When water stress was imposed during reproductive stage, pollen fertility was most affected in wheat, while panicle exsertion and anther dehiscence were severely affected in rice. When water stress was imposed during vegetative stage, wheat was less affected to vegetative stage drought than rice. The nature of differences between tolerant and susceptible cultivars was similar for the two species. However, the differential growth habitats and growth rate of plants needs to be considered in these kinds of experiments.

Drought Tolerance of Kentucky Bluegrass and Hybrid Bluegrass Cultivars

The development of drought-tolerant turf cultivars can have a positive impact on future water resources. The objective of the following research was to evaluate the field drought tolerance of nine Kentucky bluegrass (Poa pratensis L.) cultivars and eighteen hybrid bluegrass (primarily P. pratensis × P. arachnifera Torr.) cultivars. The bluegrass entries were established in the field in Albany, OR, and evaluated under drought stress in the summer of 2006 and 2007. Drought tolerance and recovery following drought were measured using digital image analysis and were defined as the number of days until a cultivar reached 50% green tissue. Several Kentucky bluegrass cultivars, including Mallard, Bluestone, and Arrow, demonstrated significantly better drought tolerance than other Kentucky bluegrass and hybrid bluegrass cultivars. One hybrid bluegrass cultivar, Longhorn, and several experimental hybrids, had excellent drought tolerance in this trial. However, many of the hybrids tested in this trial did not have superior drought tolerance characteristics compared to the Kentucky bluegrasses tested. These results demonstrate that there is wide variability in drought tolerance among both Kentucky bluegrass and hybrid bluegrass and the broad screening of this genetic material under limited water can provide turfgrass managers with selections that can ultimately conserve water. In addition, these results demonstrate that there are no clear differences in drought tolerance between hybrid bluegrasses and Kentucky bluegrass.

The Role of Plasma Membrane Intrinsic Protein Aquaporins in Water Transport through Roots: Diurnal and Drought Stress Responses Reveal Different Strategies between Isohydric and Anisohydric Cultivars of Grapevine

We report physiological and anatomical characteristics of water transport across roots grown in soil of two cultivars of grapevine (Vitis vinifera) differing in response to water stress (Grenache, isohydric; Chardonnay, anisohydric). Both cultivars have similar root hydraulic conductances (Lo; normalized to root dry weight) that change diurnally. There is a positive correlation between Lo and transpiration. Under water stress, both cultivars have reduced minimum daily Lo (predawn) attributed to the development of apoplastic barriers. Water-stressed and well-watered Chardonnay had the same diurnal change in amplitude of Lo, while water-stressed Grenache showed a reduction in daily amplitude compared with well-watered plants. Hydraulic conductivity of root cortex cells (Lpcell) doubles in Chardonnay but remains unchanged in Grenache. Of the two most highly expressed plasma membrane intrinsic protein (PIP) aquaporins in roots (VvPIP1;1 and VvPIP2;2), only VvPIP2;2 functions as a water channel in Xenopus laevis oocytes. VvPIP1;1 interacts with VvPIP2;2 to induce 3-fold higher water permeability. These two aquaporins are colocated in the root from in situ hybridization and immunolocalization of VvPIP1 and VvPIP2 subfamily members. They occur in root tip, exodermis, root cortex (detected up to 30 mm), and stele. VvPIP2;2 mRNA does not change diurnally or with water stress, in contrast to VvPIP1;1, in which expression reflects the differences in Lo and Lpcell between cultivars in their responses to water stress and rewatering. VvPIP1;1 may regulate water transport across roots such that transpirational demand is matched by root water transport capacity. This occurs on a diurnal basis and in response to water stress that corresponds to the difference in drought tolerance between the cultivars.

Effects of Severe Drought on Freshwater Mussel Assemblages

AbstractWe examined changes in freshwater mussel abundance and species composition at eight sites in Alabama and Mississippi in response to a severe drought in 2000. Five small‐stream sites in Bankhead National Forest were heavily impacted by drought; one site dried almost completely, and four sites experienced total or near cessation of flow but retained water in their channels to a large extent. In contrast, three large‐stream sites retained flow and experienced only minor streambed exposure, primarily along the stream margins. In small streams, overall mussel density before and after the drought declined by 65‐83%, and the magnitude of the decline did not differ among streams regardless of whether the channel dried or remained wetted. Introduced Corbicula fluminea (Asian clam) experienced near total mortality and declined to a greater extent than native unionids. The magnitude of decline was similar among unionid species, and the likelihood of surviving the drought was mostly a function of predrought abundance; differences in drought tolerance among species were not evident. Consequently, assemblage composition changed primarily because of the loss of rare species, resulting in drainagewide homogenization and convergence on a shrinking species pool. In contrast, we found no evidence for changes in the total abundance or composition of mussel assemblages in large streams that continued to flow during the drought. Our results show that mussels are highly sensitive to the secondary effects of drought—most likely the low levels of dissolved oxygen caused by low flow, warm temperatures, and high biological oxygen demand—in addition to the direct drying of their habitat. The postdrought abundances of some species in Bankhead National Forest may now be below the minimum necessary for successful reproduction. These populations, which are isolated by reservoirs, may be in a downward spiral from which they will have difficulty recovering in the absence of immigration.

Evaluation of Drought Tolerance and Avoidance Traits for Six Creeping Bentgrass Cultivars

The objectives of this study were: 1) to compare drought responses between the more recently developed creeping bentgrass cultivars to standard cultivars and 2) to determine differential drought tolerance and avoidance characteristics associated with cultivar variation in drought resistance. Six cultivars of creeping bentgrass (Agrostis stoloniferia) (‘Penn A-4’, ‘Independence’, ‘Declaration’, ‘L-93’, ‘Penncross’, and ‘Putter’) were maintained in growth chambers at 20 °C day/15 °C night either well-watered or exposed to drought stress by withholding water for 17 days. Cultivars varied in turf performance and physiological responses (leaf relative water content and photochemical efficiency) to drought stress, which was reflected in their differences in drought tolerance (osmotic adjustment) and drought avoidance traits (water use rate and efficiency, root viability, root length, and number). ‘Penn A-4,’ ‘Independence,’ and ‘L-93’ generally performed better than other three cultivars under drought conditions, mainly through maintaining higher water use efficiency, root viability, root elongation, or root production. The majority of physiological parameters evaluated suggested that of the six creeping bentgrass cultivars examined in this study, the three cultivars with better ability to survive drought stress used mainly avoidance traits related to water use and water uptake.

Adaptive responses to progressive drought stress in two Populus cathayana populations

The young, vegetatively propagated cuttings of Populus cathayana Rehder were exposed to a progressive drought stress for 12 weeks in a greenhouse to characterize the physiological and biochemical basis of drought adaptation in woody plants. Two contrasting populations were employed in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that the adaptive responses of P. cathayana to drought were affected by drought intensity and poplar genotype (population). The progressive drought stress significantly inhibited plant growth, increased carotenoid contents and, at the same time, accumulated soluble sugars and free proline in the plants of both populations tested. On the other hand, the gradually increasing drought also induced antioxidative systems including the increase of the activities of superoxide dismutase (SOD) and guaiacol peroxidase (POD). Moreover, there were different responses to progressive drought stress between the two contrasting populations. Compared with the wet climate population, the dry climate population had lower shoot height and growth rate, higher free proline content, and more efficient photoprotective system (such as higher carotenoid content and Car/Chl) and antioxidant system (such as higher POD activity), as a result of drought stress. These results suggest that the dry climate population possesses better drought tolerance than the wet climate population. The differences in drought tolerance may be closely related with efficient photoprotective system, accumulation of the osmoprotectant proline as well as the increased capacity of the antioxidative system to scavenge reactive oxygen species, and the consequent suppressed level of lipid peroxidation under drought conditions.

Evaluation of drought response of two poplar clones (Populus×canadensis Mönch ‘I-214’ and P. deltoides Marsh. ‘Dvina’) through high resolution analysis of stem growth

Different irrigation effects on stem radius variation (DeltaR) and maximum daily shrinkage (MDS) in Populus deltoides 'Dvina' and Populusxcanadensis 'I-214' were studied to assess differences in drought tolerance between clones. One-year-old trees growing in concrete tanks were submitted to two irrigation regimes (natural rainfall and irrigation) from 24 June to 10 August, and DeltaR was monitored by automatic point dendrometers. Independently of the irrigation regime, 'Dvina' showed a higher stem radial increment than 'I-214'. In both clones, the first response to changed soil water content was a significant increase in MDS, whilst DeltaR decreased about 20 d later when pre-dawn leaf water potential (Psipd) dropped below -0.4 MPa. However, they displayed different strategies to overcome drought. 'Dvina' maintained a positive DeltaR for longer than 'I-214', which had lower leaf Psipd and greater leaf abscission at the end of the drought period. After irrigation resumed, 'Dvina' showed a higher capacity to restore stem growth. 'I-214' was probably unable to recover secondary growth because of higher leaf abscission during drought stress and the production of newly expanded leaves during recovery. It is concluded that the larger radial growth of 'Dvina' derived from a better water use (carbon uptake versus water loss) than 'I-214' under limited water availability.

Realized climatic niches of deciduous trees: comparing western Eurasia and eastern North America

AbstractAim Assessment of cross‐continental similarities and differences in climatic limiting values for deciduous tree species and of the possible deterministic influence of past and present climatic differences on the modern tree flora in two regions.Location The deciduous forest regions of western Eurasia and eastern North America.Methods Based on species distribution data (range maps) and climate site data, the realized climatic niches of 137 deciduous tree species from the two regions were quantified using climatic envelopes. To compare these envelopes on the two continents, a hierarchical cluster analysis was performed, and principal components analysis was used to check cluster consistency.Results Significant differences do exist for upper limits of winter temperatures and for lower limits of summer temperatures between Western Eurasia and eastern North America. Lower limits for the annual water balance also appear different, suggesting that the deciduous trees may be more drought‐tolerant in western Eurasia than in eastern North America. Climatic range types generated by the cluster analysis can be characterized, according to the distribution of the species, as boreal‐temperate, northern temperate, temperate, southern temperate, and Appalachian. Five of the eight clusters contain trees from both regions, but three groups consist only of American species that have no European counterparts.Main conclusions Differences in temperature limitations can be explained by location on the east versus west side of the continents and by the almost complete lack of warm moist areas in western Eurasia. The difference in drought tolerance, on the other hand, is more likely to be the product of a deterministic sorting process that occurred during the Plio‐Pleistocene.

Radial growth responses to drought of Pinus sylvestris and Quercus pubescens in an inner‐Alpine dry valley

AbstractQuestion: Lower montane treeline ecotones such as the inner Alpine dry valleys are regarded as sensitive to climate change. In the dry Valais valley (Switzerland) the composition of the widespread, low altitude Pinus forests is shifting towards a mixed deciduous state. The sub‐boreal P. sylvestris shows high mortality rates, whereas the deciduous sub‐mediterranean Quercus pubescens is spreading. These species may act as early indicators of climate change. We evaluate this hypothesis by focusing on their differences in drought tolerance, which are hardly known, but are likely to be crucial in the current forest shift and also for future forest development.Methods: We used dendroecological methods to detect species‐specific patterns in the growth response to drought. The relationship between radial growth of 401 trees from 15 mixed stands and drought was analysed by calculating response functions using yearly tree‐ring indices and monthly drought indices. PCA was applied to the response ratios to discover spatial patterns of drought response.Results: A species‐specific response to moisture as well as a sub‐regional differentiation of the response patterns were found. While Quercus showed a response mainly to the conditions of the previous autumn and those of current spring, Pinus did not start responding before May, but showed responses throughout the whole summer. Quercus may restrict physiological activity to moist periods; growth of Pinus was much more dependent on prior growth.Conclusions: Given that the climate is changing towards (1) longer summer drought periods, (2) higher mean temperatures and (3) shifted seasonally of moisture availability, Quercus may benefit from adapting better to drier conditions. Pinus may increasingly face problems related to drought stress as it depends on summer moisture and has a smaller adaptive capacity due to its long‐lived photosynthetic tissue.

Cell death in response to osmotic and salt stresses in two rice ( Oryza sativa L.) ecotypes

Cell death in the roots of two rice ecotypes under PEG-induced osmotic and NaCl stresses were assayed by TUNEL and DAPI techniques. Although both ecotypes exhibited cell death in response to the osmotic and salt stresses, they appeared to adapt to the two types of stresses through different timing and tissue specificity of cell death. Under the stresses, the occurrence of cell death was always delayed in IRAT109, a drought tolerant upland line, than in IR20, a drought sensitive lowland line. Under the salt stress, cell death progressed successively in a well regulated manner, starting from the outer layer cells in the epidermis and exodermis of roots and subsequently to the endodermis and stele, suggesting a possible function of the dead cells in preventing the influx of excess Na + ions into the inner parts of roots and into shoots, leading to salt exclusion. In contrast, cell death induced by PEG-induced osmotic stress occurred randomly in roots, allowing a better ability to recover after stress. Thus, the coincidence of the difference in drought tolerance between the two rice ecotypes and their differences in the osmotic/salt induced cell death indicate that cell death may have played an important role contributing to rice tolerances to different abiotic stresses.

Differential photosynthetic and survival responses to soil drought in two evergreen Nothofagus species

We asked if differences in distribution between Nothofagus nitida and N. dombeyi were associated with differences in drought tolerance. Survival, gas exchange and chlorophyll fluorescence were measured on seedlings subjected to a gradual drought. At a predawn leaf water potential (Ψm) of −2.7 MPa, survival of N. nitida was 50%, compared to 100% in N. dombeyi. Under well-watered conditions, the two species displayed similar stomatal conductance (g w ) and transpiration (E), but net photosynthesis (A) and instantaneous water-use efficiency (WUE i ) were slightly higher in N. nitida. A, E and g w declined in N. nitida along the gradual drought but increased in N. dombeyi at a Ψm between −1.5 and −2.5 MPa, and declined then drastically at a Ψm below < −2.5 MPa. As N. dombeyi was able to maintain A at higher levels despite declining g w , this species displayed significantly increased WUE i at Ψm below −2.5 MPa. Photochemical efficiency of PSII in the light (ΔF/Fmr) and photochemical quenching (qP) were always lower in N. nitida and along with the photochemical efficiency in the dark (Fv/Fm) they declined in both species. Non-photochemical quenching (NPQ) increased slowly in N. dombeyi along with the gradual drought, whilst it decreased in N. nitida. These results show that differences in drought tolerance are in agreement with sorting of Nothofagus species along moisture gradients in south-central Chile.

Radial growth responses to drought of Pinus sylvestris and Quercus pubescens in an inner-Alpine dry valley

Question: Lower montane treeline ecotones such as the inner Alpine dry valleys are regarded as sensitive to climate change. In the dry Valais valley (Switzerland) the composition of the widespread, low altitude Pinus forests is shifting towards a mixed deciduous state. The sub-boreal P. sylvestris shows high mortality rates, whereas the deciduous sub-mediterranean Quercus pubescens is spreading. These species may act as early indicators of climate change. We evaluate this hypothesis by focusing on their differences in drought tolerance, which are hardly known, but are likely to be crucial in the current forest shift and also for future forest development. Methods: We used dendroecological methods to detect species-specific patterns in the growth response to drought. The relationship between radial growth of 401 trees from 15 mixed stands and drought was analysed by calculating response functions using yearly tree-ring indices and monthly drought indices. PCA was applied to the response ratios to discover spatial patterns of drought response. Results: A species-specific response to moisture as well as a sub-regional differentiation of the response patterns were found. While Quercus showed a response mainly to the conditions of the previous autumn and those of current spring, Pinus did not start responding before May, but showed responses throughout the whole summer. Quercus may restrict physiological activity to moist periods; growth of Pinus was much more dependent on prior growth. Conclusions: Given that the climate is changing towards (1) longer summer drought periods, (2) higher mean temperatures and (3) shifted seasonally of moisture availability, Quercus may benefit from adapting better to drier conditions. Pinus may increasingly face problems related to drought stress as it depends on summer moisture and has a smaller adaptive capacity due to its long-lived photosynthetic tissue.

Acclimation to drought stress generates oxidative stress tolerance in drought-resistant than -susceptible wheat cultivar under field conditions

Wheat crop may experience water deficit cycles during their life cycle, which induces oxidative stress. Present study was conducted to evaluate the role of oxidative stress management in the leaves of two wheat ( Triticum aestivum L.) cultivars, C306 (drought-resistant) and Moti (drought-susceptible), when subjected directly to severe water stress (non-acclimated) or to water stress cycles of increasing intensity with an intermittent rewatering (drought-acclimation). Mild water stress during vegetative growth enabled C306 to acclimatize better than Moti during subsequent water stress of severe nature during post-anthesis period. The drought-acclimated C306 leaves maintained favourable water relations and lower membrane injury due to low H 2O 2 accumulation than non-acclimated C306 plants during severe water stress. This is due to systematic increase in the activity of H 2O 2 scavenging enzymes particularly APX and POX and maintenance of ascorbate and glutathione redox pool by efficient functioning of GR enzyme in the drought-acclimated C306 plants. In contrast, both acclimated as well as non-acclimated Moti plants exhibited loss in turgor potential, high H 2O 2 levels and poor antioxidant enzyme response leading to enhanced membrane damage during severe water stress conditions. Hence, present study shows that genotypic differences in drought tolerance could be, at least in part, attributed to the ability of wheat plants to acclimate and induce antioxidant defense under water deficit conditions.