Leaf Expansion Rate Research Articles

Leaf Expansion and Transpiration Response to Soil Drying and Recovery among Cowpea Genotypes

Sensitivity of leaf expansion to water‐deficit conditions could have a major influence on C assimilation rate and water loss rate under developing drought conditions. While cowpea (Vigna unguiculata L.) is commonly grown in more arid regions, there is no information on the sensitivity of its leaf expansion with drying soil. Three experiments were undertaken in controlled environments to document leaf expansion during increasing soil drying (11–13 d). Eight cultivars of cowpea were studied. It was found that the initiation of the decrease in leaf expansion occurred earlier in the soil drying cycle than the decrease in transpiration rate in all genotypes. Also, the soil water content at which leaf expansion completely stopped was slightly greater than the termination of transpiration. Therefore, both measures of leaf expansion sensitivity to soil water showed greater sensitivity to soil drying than plant gas exchange as measured by transpiration rate. Genotypic differences were observed among the genotypes in their sensitivity to soil drying. In one experiment, the severely stressed plants were rewatered and recovery in leaf expansion rate occurred very rapidly. Leaf expansion rates of all genotypes following rewatering returned to the rates of the well‐watered plants within ∼1 d.

Physiological and morphological responses to permanent and intermittent waterlogging in seedlings of four evergreen trees of temperate swamp forests.

Waterlogging decreases a plant's metabolism, stomatal conductance (gs) and photosynthetic rate (A); however, some evergreen species show acclimation to waterlogging. By studying both the physiological and morphological responses to waterlogging, the objective of this study was to assess the acclimation capacity of four swamp forest species that reside in different microhabitats. We proposed that species (Luma apiculata [D.C.] Burret. and Drimys winteri J.R. et G. Forster.) abundant in seasonally and intermittently waterlogged areas (SIWA) would have a higher acclimation capacity than species abundant in the inner swamp (Blepharocalyx cruckshanksii [H et A.] Mied. and Myrceugenia exsucca [D.C.] Berg.) where permanent waterlogging occurs (PWA); it was expected that the species from SIWA would maintain leaf expansion and gas exchange rates during intermittent waterlogging treatments. Conversely, we expected that PWA species would have higher constitutive waterlogging tolerance, and this would be reflected in the formation of lenticels and adventitious roots. Over the course of 2 months, we subjected seedlings to different waterlogging treatments: (i) permanent (sudden, SW), (ii) intermittent (gradual) or (iii) control (field capacity, C). Survival after waterlogging was high (≥80%) for all species and treatments, and only the growth rate of D. winteri subjected to SW was affected. Drimys winteri plants had low, but constant A and g during both waterlogging treatments. Conversely, L. apiculata had the highest A and g values, and g increased significantly during the first several days of waterlogging. In general, seedlings of all species subjected to waterlogging produced more adventitious roots and fully expanded leaves and had higher specific leaf area (SLA) and stomatal density (StD) than seedlings in the C treatment. From the results gathered here, we partially accept our hypothesis as all species showed high tolerance to waterlogging, maintained growth, and had increased A or g during different time points of waterlogging. Differences in leaf (SLA) and stomata functioning (gs, StD) plasticity likely allows plants to maintain positive carbon gains when waterlogging occurs. The species-specific differences found here were not entirely related to microhabitat distribution.

Causes of ecological gradients in leaf margin entirety: Evaluating the roles of biomechanics, hydraulics, vein geometry, and bud packing.

A recent commentary by Edwards et al. (Am. J. Bot. 103: 975-978) proposed that constraints imposed by the packing of young leaves in buds could explain the positive association between non-entire leaf margins and latitude but did not thoroughly consider alternative explanations. We review the logic and evidence underlying six major hypotheses for the functional significance of marginal teeth, involving putative effects on (1) leaf cooling, (2) optimal support and supply of the areas served by major veins, (3) enhanced leaf-margin photosynthesis, (4) hydathodal function, (5) defense against herbivores, and (6) bud packing. Theoretical and empirical problems undermine all hypotheses except the support-supply hypothesis, which implies that thinner leaves should have non-entire margins. Phylogenetically structured analyses across angiosperms, the El Yunque flora, and the genus Viburnum all demonstrate that non-entire margins are indeed more common in thinner leaves. Across angiosperms, the association of leaf thickness with non-entire leaf margins is stronger than that of latitude. We outline a synthetic model showing how biomechanics, hydraulics, vein geometry, rates of leaf expansion, and length of development within resting buds, all tied to leaf thickness, drive patterns in the distribution of entire vs. non-entire leaf margins. Our model accounts for dominance of entire margins in the tropics, Mediterranean scrub, and tundra, non-entire margins in cold temperate deciduous forests and tropical vines and early-successional trees, and entire leaf margins in monocots. Spinose-toothed leaves should be favored in short-statured evergreen trees and shrubs, primarily in Mediterranean scrub and related semiarid habitats.

Relationship between leaf functional traits and productivity in Aquilaria crassna (Thymelaeaceae) plantations: a tool to aid in the early selection of high-yielding trees.

Physiological traits are frequently used as indicators of tree productivity. Aquilaria species growing in a research planting were studied to investigate relationships between leaf-productivity traits and tree growth. Twenty-eight trees were selected to measure isotopic composition of carbon (δ13C) and nitrogen (δ15N) and monitor six leaf attributes. Trees were sampled randomly within each of four diametric classes (at 150 mm above ground level) ensuring the variability in growth of the whole population was represented. A model averaging technique based on the Akaike's information criterion was computed to identify whether leaf traits could assist in diameter prediction. Regression analysis was performed to test for relationships between carbon isotope values and diameter and leaf traits. Approximately one new leaf per week was produced by a shoot. The rate of leaf expansion was estimated as 1.45 mm day-1. The range of δ13C values in leaves of Aquilaria species was from -25.5‰ to -31‰, with an average of -28.4 ‰ (±1.5‰ SD). A moderate negative correlation (R2 = 0.357) between diameter and δ13C in leaf dry matter indicated that individuals with high intercellular CO2 concentrations (low δ13C) and associated low water-use efficiency sustained rapid growth. Analysis of the 95% confidence of best-ranked regression models indicated that the predictors that could best explain growth in Aquilaria species were δ13C, δ15N, petiole length, number of new leaves produced per week and specific leaf area. The model constructed with these variables explained 55% (R2 = 0.55) of the variability in stem diameter. This demonstrates that leaf traits can assist in the early selection of high-productivity trees in Aquilaria species.

Genetic Diversity of Salt Tolerance in Miscanthus.

Miscanthus is a woody rhizomatous C4 grass that can be used as a CO2 neutral biofuel resource. It has potential to grow in marginal areas such as saline soils, avoiding competition for arable lands with food crops. This study explored genetic diversity for salt tolerance in Miscanthus and discovered mechanisms and traits that can be used to improve the yield under salt stress. Seventy genotypes of Miscanthus (including 57 M. sinensis, 5 M. sacchariflorus, and 8 hybrids) were evaluated for salt tolerance under saline (150 mM NaCl) and normal growing conditions using a hydroponic system. Analyses of shoot growth traits and ion concentrations revealed the existence of large variation for salt tolerance in the genotypes. We identified genotypes with potential for high biomass production both under control and saline conditions that may be utilized for growth under marginal, saline conditions. Several relatively salt tolerant genotypes had clearly lower Na+ concentrations and showed relatively high K+/Na+ ratios in the shoots under salt stress, indicating that a Na+ exclusion mechanism was utilized to prevent Na+ accumulation in the leaves. Other genotypes showed limited reduction in leaf expansion and growth rate under saline conditions, which may be indicative of osmotic stress tolerance. The genotypes demonstrating potentially different salt tolerance mechanisms can serve as starting material for breeding programs aimed at improving salinity tolerance of Miscanthus.

Leaf Demography of Some Evergreen and Deciduous Tree and Shrub Species of Kumaun Himalaya, India

Leaf demography was studied in 9 trees (6 Evergreen (ES), 1 Semideciduous (SD) and 2 Deciduous (DS)) and 10 shrubs (7 Evergreen (ES) and 3 Deciduous (DS)) occurring between 350 to 2500 m elevation in the Kumaun Himalaya, India. Although each species had its own pattern about seasonality of leaf recruitment, it was possible to group the species based on leaf expansion behavior. The result shows the leaf expansion rate was greater for deciduous species compared to Evergreen species. The percent leaf area after four weeks of expansion was also greater for deciduous species.

Comparative effects of water deficit and enhanced UV-B radiation on photosynthetic capacity and leaf anatomy traits of two grapevine (Vitis vinifera L.) cultivars

The effects of drought and enhanced UV-B radiation on photosynthetic and leaf anatomical characteristics were studied in two different grapevine genotypes (Vitis vinifera L. cvs ‘Romeiko’ and ‘Soultanina’), which were grown outdoors in 25 L pots containing a peat:perlite:sand (3:1:1, v/v/v) potting mix. The plants were subjected to three levels of UV-B radiation (i) ambient, (ii) intermediate (ambient plus 15 % UV-B radiation), (iii) high (ambient plus 30 % UV-B radiation) and two irrigation regimes (i) well-watered (irrigated on daily basis to substrate capacity) and (ii) drought-stressed (irrigated daily with the 50 % of the amount of water provided to well-watered plants). Both abiotic stressors induced a significant decrease in net photosynthesis (Pn) while the combination of drought and elevated UV-B radiation appeared to have synergistic effects on photosynthetic rate. At leaf anatomical level, drought resulted in the development of idioblastic cells in leaves of both grapevine varieties as well as in the reduction of leaf expansion rate, total lamina thickness and total biomass per leaf area whereas leaf tissue density considerably increased. On the other hand, enhanced UV-B radiation did not affect leaf anatomical characteristics of both genotypes in a similar way. In particular, different responses, closely depended to UV-B levels applied, were observed concerning the chlorenchymatic tissue and total lamina thickness. Moreover, the stimulation of UV-B absorbing compounds biosynthesis under enhanced UV-B radiation, could not manage to preserve photosynthetic performance. The implication of the watering regime and the UV-B in the induction of leaf anatomical and morphological alterations in net photosynthesis is discussed.

Radiation capture and conversion efficiencies of Miscanthus sacchariflorus, M.sinensis and their naturally occurring hybrid M.×giganteus.

Miscanthus is a rhizomatous C4 grass of great interest as a biofuel crop because it has the potential to produce high yields over a wide geographical area with low agricultural inputs on marginal land less suitable for food production. At the moment, a clonal interspecific hybrid Miscanthus × giganteus is the most widely cultivated and studied in Europe and the United States, but breeding programmes are developing newer more productive varieties. Here, we quantified the physiological processes relating to whole season yield in a replicated plot trial in Wales, UK. Light capture and conversion efficiency were parameterized for four carefully selected genotypes (M. sinensis, M. sacchariflorus and Miscanthus × giganteus). Differences in the canopy architecture in mature stands as measured by the extinction coefficient (k) were small (0.55–0.65). Sensitivity analysis on a mathematical model of Miscanthus was performed to quantify the accumulative intercepted photosynthetically active radiation (iPAR) in the growing season using (i) k, (ii) variation in the thermal responses of leaf expansion rate, (iii) base temperature for degree days and (iv) date start of canopy expansion. A 10% increase in k or leaf area per degree day both had a minimal effect on iPAR (3%). Decreasing base temperature from 10 to 9 °C gave an 8% increase in iPAR. If the starting date for canopy expansion was the same as shoot emergence date, then the iPAR increases by 12.5%. In M. × giganteus, the whole season above ground and total (including below ground) radiation‐use efficiency (RUE) ranged from 45% to 37% higher than the noninterspecific hybrid genotypes. The greater yields in the interspecific hybrid M. × giganteus are explained by the higher RUE and not by differences in iPAR or partitioning effects. Studying the mechanisms underlying this complex trait could have wide benefits for both fuel and food production.

Component traits of plant water use are modulated by vapour pressure deficit in pearl millet (Pennisetum glaucum (L.) R.Br.).

Traits influencing plant water use eventually define the fitness of genotypes for specific rainfall environments. We assessed the response of several water use traits to vapour pressure deficit (VPD) in pearl millet (Pennisetum glaucum (L.) R.Br.) genotypes known to differ in drought adaptation mechanisms: PRLT 2/89-33 (terminal drought-adapted parent), H 77/833-2 (terminal drought-sensitive parent) and four near-isogenic lines introgressed with a terminal drought tolerance quantitative trait locus (QTL) from PRLT 2/89-33 (ICMR01029, ICMR01031, ICMR02042, and ICMR02044). Plant water use traits at various levels of plant organisation were evaluated in seven experiments in plants exposed either transiently or over the long term to different VPD regimes: biomass components, transpiration (water usage per time unit) and transpiration rate (TR) upon transient VPD increase (gH2Ocm-2h-1)), transpiration efficiency (g dry biomass per kg H2O transpired), leaf expansion rate (cm per thermal time unit) and root anatomy (endodermis dimensions)). High VPD decreased biomass accumulation by reducing tillering, the leaf expansion rate and the duration of leaf expansion; decreased root endodermis cell size; and increased TR and the rate of TR increase upon gradual short-term VPD increases. Such changes may allow plants to increase their water transport capacity in a high VPD environment and are genotype-specific. Some variation in water use components was associated with terminal drought adaptation QTL. Knowledge of water use traits' plasticity in growth environments that varied in evaporative demand, and on their genetic determinacy, is necessary to develop trait-based breeding approaches to complex constraints.

Establishing the temperature dependency of vegetative and reproductive growth processes and their threshold temperatures of vineyard-grown Vitis vinifera cv. Semillon vines across the growing season.

A hydrocooling system provided canopy temperature control of Vitis vinifera L. cv. Semillon vines at set points of 30, 35 and 40°C. The impacts on vegetative and reproductive growth over the growing season were assessed. Dynamics and rates of leaf expansion, bunch biomass and sugar accumulation were strongly affected by canopy temperatures - being highest at 30°C and lowest at 40°C. Leaf and stem biomass accumulation at 40°C was detrimentally affected but was otherwise little affected by temperature. Leaf expansion was earliest, leaf sizes greatest and rates of expansion all optimal at 30°C and all were strongly temperature dependent. Bunch biomass accumulation was earliest at 35°C but amount of biomass in bunches and rates were both highly temperature dependent and optimal at 30°C. Rates of sugar accumulation and total amounts accumulated at harvest were both highly temperature-dependent processes: fastest and greatest at 30°C. Many of the temperature-dependent processes decreased in rates and amounts linearly between 30 and 40°C. Despite the effects of temperature on bunch and berry growth, there were no treatment effects on the yield per vine. The study confirms that the threshold temperature for most processes was 35°C, where some depreciation in dry matter and sugar accumulation occurred, whereas 40°C was detrimental to all growth processes.

Evaluation of the Effect of Irrigation and Fertilization by Drip Fertigation on Tomato Yield and Water Use Efficiency in Greenhouse

The water shortage in China, particularly in Northwest China, is very serious. There is, therefore, great potential for improving the water use efficiency (WUE) in agriculture, particularly in areas where the need for water is greatest. A two-season (2012 and 2013) study evaluated the effects of irrigation and fertilizer rate on tomato (Lycopersicum esculentum Mill., cv. “Jinpeng 10”) growth, yield, and WUE. The fertilizer treatment significantly influenced plant height and stem diameter at 23 and 20 days after transplanting in 2012 and 2013, respectively. As individual factors, irrigation and fertilizer significantly affected the leaf expansion rate, but irrigation × fertilizer had no statistically significant effect on the leaf growth rate at 23 days after transplanting in 2012. Dry biomass accumulation was significantly influenced by fertilizer in both years, but there was no significant difference in irrigation treatment in 2012. Our study showed that an increased irrigation level increased the fruit yield of tomatoes and decreased the WUE. The fruit yield and WUE increased with the increased fertilizer rate. WUE was more sensitive to irrigation than to fertilization. An irrigation amount of 151 to 208 mm and a fertilizer amount of 454 to 461 kg·ha−1(nitrogen fertilizer, 213.5–217 kg·ha−1; phosphate fertilizer, 106.7–108 kg·ha−1; and potassium fertilizer, 133.4–135.6 kg·ha−1) were recommended for the drip fertigation of tomatoes in greenhouse.

Quantifying canopy formation processes in fodder beet (Beta vulgaris subsp. vulgaris var. alba L.) crops

Abstract Fodder beet is a highly productive forage crop of expanding use in livestock production systems in temperate regions, notably in Europe and New Zealand. The main determinant of fodder beet productivity is the amount of light intercepted by the crop canopy, which is regulated by temperature and the availability of water and nitrogen (N) for plant development and growth. The quantitative understanding of canopy formation processes under constraining growth conditions is an essential step for the development of biophysical simulation models of new crops for research and predictive purposes. In this study, we provided the first estimates of key canopy formation parameters in fodder beet both under optimum and water- and N-limited supply, in two field experiments in Lincoln, Canterbury, New Zealand. Specifically, the base temperature for leaf appearance in fodder beet was estimated as 0 °C. The range of the critical LAI (c. 90–95% of light interception) was 3–4 m 2 /m 2 . The phyllochron was 48–53 °Cd/leaf in unstressed crops and 60 °Cd/leaf in water stressed crops, with no effect of N supply. Leaf senescence rates varied widely (from 42 to 260 °Cd/leaf) depending on water availability and canopy cover. Leaf expansion, appearance and senescence rates fully recovered following a period of water stress to values similar to those observed in unstressed crops in response to late season rainfall events. Leaf area expansion rates (LAER) ranged from 0.0012 to 0.0034 m 2 /m 2 /°Cd and was reduced both by limited water and N supply. Leaf area senescence rates (LASR) ranged from 0.0005 to 0.0019 m 2 /m 2 /°Cd, with low values recorded during drought periods when crop growth was negligible. Canopy architecture, characterised by the extinction coefficient ( k ), was less sensitive to water stress than canopy expansion or senescence with a conservative value of 0.74. This first quantitative description of fodder beet canopy forming processes can assist the development of predictive approaches, such as biophysical simulation models, for application in research, extension and teaching.

Kinematic evidence that atmospheric nitrogen dioxide increases the rates of cell proliferation and enlargement to stimulate leaf expansion in Arabidopsis

To elucidate the stimulation of leaf growth by atmospheric nitrogen dioxide (NO2), we performed a kinematic analysis of the eighth leaves of Arabidopsis thaliana (accession C24) plants grown for 17–35 days after sowing in the presence or absence of 50 ppb NO2 (designated +NO2 plants and –NO2 plants, respectively). We found that the peak and mean values of the relative rates of leaf expansion, cell division and cell expansion were always greater in +NO2 plants than in –NO2 plants. No evidence for prolonged duration was obtained. Thus, NO2 treatment increased the rates of both cell proliferation and enlargement to increase leaf size. Furthermore, a fold-change analysis showed that cell proliferation and enlargement differentially regulated NO2-induced leaf expansion.

Responses in gas exchange and water status between drought-tolerant and -susceptible soybean genotypes with ABA application

The purpose of this study was to investigate the physiological responses of drought-tolerant and drought-susceptible soybean genotypes to exogenous abscisic acid (ABA) application during progressive soil drying at seedling stages. Five-day old soybean seedlings were transplanted into PVC tubes filled with soil mixture. Seedlings were watered daily with similar water volumes until second trifoliate leaves emerged, and thereafter soil drying with or without exogenous ABA application was imposed. Half of the seedlings of each genotype were left for regular watering as control plants. Soil water status declined significantly over seven days of withholding water supply for both genotypes. Leaf expansion rate, stomatal conductance (gs), leaf water potential (ψw), and relative water content of leaves (%RWC) declined significantly under soil drying as well as soil drying with ABA application, compared to their values for well-watered soybean genotypes. However, a drought-tolerant genotype (C12) responded more rapidly than a drought-susceptible genotype (C08) after imposition of soil drying and soil drying with exogenous ABA. In addition, application of exogenous ABA to water-restricted soybeans resulted in higher %RWC and ψw in the drought-tolerant than in the drought-susceptible genotype. Compared to the drought-susceptible genotype, the drought-tolerant genotype was more responsive to exogenous ABA application, resulting in a higher root-to-shoot ratio.

Relationship between the morphogenesis of Italian ryegrass cv. 'BRS Ponteio' with forage and seed production

This study aims to verify, accurate and precisely, the responses of Italian ryegrass 'BRS Ponteio' cultivar to different frequencies of defoliation for forage production and especially for seed production. For this purpose, a randomized block design experiment with four replications was conducted. Four frequencies of defoliation were applied (zero, one, two, and three) based on the thermal sum, evaluating the rate of leaf appearance (LAR), phyllochron (P), leaf expansion rate (LER), leaf senescence rate (LSR), stems expansion rate (SER), tillering rate (TR), leaf life span (LL), forage production, proportion of leaf blades, stems plus sheaths, senescent material, and inflorescences, as well as seed production. Second defoliation noticeably altered the morphogenic plant responses, reduced expansion rates and leaf appearance, increased rates of tillering and stems expansion. This phenotypic maintained a high seed production and provided a harvest of forage mass 100% higher than the collected mass in the first cutting. Third defoliation led to an increase of 100% of the harvested forage mass; however, it caused drastic and negative changes in the morphogenic characteristics and seed yielding.

Earlier snowmelt and warming lead to earlier but not necessarily more plant growth.

Climate change over the past ∼50 years has resulted in earlier occurrence of plant life-cycle events for many species. Across temperate, boreal and polar latitudes, earlier seasonal warming is considered the key mechanism leading to earlier leaf expansion and growth. Yet, in seasonally snow-covered ecosystems, the timing of spring plant growth may also be cued by snowmelt, which may occur earlier in a warmer climate. Multiple environmental cues protect plants from growing too early, but to understand how climate change will alter the timing and magnitude of plant growth, experiments need to independently manipulate temperature and snowmelt. Here, we demonstrate that altered seasonality through experimental warming and earlier snowmelt led to earlier plant growth, but the aboveground production response varied among plant functional groups. Earlier snowmelt without warming led to early leaf emergence, but often slowed the rate of leaf expansion and had limited effects on aboveground production. Experimental warming alone had small and inconsistent effects on aboveground phenology, while the effect of the combined treatment resembled that of early snowmelt alone. Experimental warming led to greater aboveground production among the graminoids, limited changes among deciduous shrubs and decreased production in one of the dominant evergreen shrubs. As a result, we predict that early onset of the growing season may favour early growing plant species, even those that do not shift the timing of leaf expansion.

Combining field performance with controlled environment plant imaging to identify the genetic control of growth and transpiration underlying yield response to water-deficit stress in wheat.

Crop yield in low-rainfall environments is a complex trait under multigenic control that shows significant genotype×environment (G×E) interaction. One way to understand and track this trait is to link physiological studies to genetics by using imaging platforms to phenotype large segregating populations. A wheat population developed from parental lines contrasting in their mechanisms of yield maintenance under water deficit was studied in both an imaging platform and in the field. We combined phenotyping methods in a common analysis pipeline to estimate biomass and leaf area from images and then inferred growth and relative growth rate, transpiration, and water-use efficiency, and applied these to genetic analysis. From the 20 quantitative trait loci (QTLs) found for several traits in the platform, some showed strong effects, accounting for between 26 and 43% of the variation on chromosomes 1A and 1B, indicating that the G×E interaction could be reduced in a controlled environment and by using dynamic variables. Co-location of QTLs identified in the platform and in the field showed a possible common genetic basis at some loci. Co-located QTLs were found for average growth rate, leaf expansion rate, transpiration rate, and water-use efficiency from the platform with yield, spike number, grain weight, grain number, and harvest index in the field. These results demonstrated that imaging platforms are a suitable alternative to field-based screening and may be used to phenotype recombinant lines for positional cloning.

English

Plants under hydrothermal stress show a variety of responses aimed at reducing leaf growth and total leaf area, thereby reducing physiological processes such as transpiration and photosynthesis. The effects of hydrothermal stress on cassava plant growth parameters were thus investigated. Twenty cassava varieties representing a broad range of genetic diversity were used. Plants were grown in the field, physical measurements were made and percentage changes in growth parameters and biomass accumulation recorded bimonthly. Significant variation among varieties was found for the response to stress of leaf growth rate (losses of between 60 and 100% after stress) and duration (losses within 1 to 2 months) which equally resulted into reduction in leaf area. Variations were also observed in leaf retention (0 to 40%) and expansion rate (lamina width (25 to 33%) and length (14 to 58%) among different varieties. Differences were also observed for the time and rate of leaf loss during stress period. Based on observed differences, varieties were grouped under three distinct clusters including early recovering varieties, stay green varieties and the susceptible varieties. Alterations in leaf properties were highly correlated to harvest index where low harvest index (0.2 to 0.4) was observed for stay green and susceptible varieties compared to early recovering varieties (0.4 to 0.7). From the observation, different coping mechanisms, important in selection of drought stress tolerant genotypes were identified and pointed to specific genetic mechanisms for leaf retention/loss and biomass accumulation. The results suggest that rate of growth and duration differences are due to different physiological mechanisms, and can be combined to select for hydrothermal stress tolerant varieties. Key words: Leaf expansion rate, leaf area, leaf development, recovery mechanisms.

Influence of Drought Stress on Leaf Traits of Different Strawberry (Fragaria ananassa L.) Varieties in Natural Environment

A study was carried out to explore leaf traits analysis of three strawberry varieties under different drought conditions in Malaysian upland environment in 2013. Plants of three strawberry varieties were grown in three different soil moisture levels including 25 percent (severe stress), 50 percent (mild stress), and 75 percent (normal irrigation) and remained for 60 days as a duration of stress to get appropriate observations of plants to drought stress. Significant differences were observed among varieties, treatments, and duration of drought stress in different traits (P < 0.05). Leaf area, leaf number, chlorophyll content, chlorophyll stability index, leaf moisture, leaf expansion rate, and leaf yield were diminished under stress especially when treated with 25 percent of soil moisture level and 60 days of duration. Moreover, there were remarkable differences among plants in terms of leaf thickness in 25 percent, 50 percent, and control. Severe stress reduced leaf thickness significantly compared to other treatments.

Leaf expansion of soybean subjected to high and low atmospheric vapour pressure deficits.

Vapour pressure deficit (VPD) is considered an important environmental factor that might affect leaf expansion and transpiration rate (TR) in plants. Two slow-wilting soybean (Glycine max (L.) Merr.) genotypes PI 416937 and PI 471938 along with commercial cultivar Hutcheson were subjected to low (1.2-1.6 kPa) and high VPD (2.8-3 kPa) environments to study their leaf expansion and TR over five days. Among the three genotypes, PI 416937 had the lowest increase in its TR (34%) at high VPD compared with low VPD and the greatest decrease in leaf area (31%). In contrast, Hutcheson had the highest increase in TR (87%) under high VPD and the lowest decrease in leaf expansion rate (18%). Expansin and extensin genes were isolated in PI 416937 to determine if changes in leaf expansion were associated with changes at the molecular level. The four studied genes were all suppressed after five days in the high VPD environment.