Moderate Water Deficit Research Articles

Jujube fruit water relations at fruit maturation in response to water deficits

The fruit maturation stage is considered the optimal phenological stage for implementing water deficit in jujube (Zizyphus jujuba Mill.), since a low, moderate or severe water deficit at this time has no effect on yield, fruit volume or eating quality. However, no information exists at fruit water relations level on the mechanisms developed by Z. jujuba to confront drought. The purpose of the present study was to increase our understanding of the relationship between leaf and fruit water relations of jujube plants under different irrigation conditions during fruit maturation, paying special attention to analysing whether fruit size depends on fruit turgor. For this, adult jujube trees (cv. Grande de Albatera) were subjected to five irrigation treatments. Control plants (T0) were irrigated daily above their crop water requirements in order to attain non-limiting soil water conditions in 2012 and 2013. T1 plants were subjected to deficit irrigation throughout the 2012 season, according to the criteria frequently used by the growers in the area. T2 (2012), T3 and T4 (2013) were irrigated as T0 except during fruit maturation, in which irrigation was withheld for 32, 17 and 24 days, respectively. The results indicated that the jujube fruit maturation period was clearly sensitive to water deficit. During most of this stage water could enter the fruits via the phloem rather than via the xylem. From the beginning of water withholding to when maximum water stress levels were achieved, fruit and leaf turgor were maintained in plants under water deficit. However, a direct relation between turgor and fruit size was not found in jujube fruits, which could be due to an enhancement of a cell elasticity mechanism (elastic adjustment) which maintains fruit turgor by reducing fruit cells size or to the fact that jujube fruit growth depends on the fruit growth-effective turgor rather than just turgor pressure.

Effect of water deficit during vegetative growth periods on post-anthesis photosynthetic capacity and grain yield in winter wheat (Triticum aestivum L.)

Determining the effect of water deficit during vegetative growth periods on grain yield will provide reasonable strategy for water-saving management of winter wheat (Triticum aestivum L.). Pot experiment was conducted using winter wheat cultivar (Yangmai16) to investigate the effects of water deficit during vegetative periods on post-anthesis photosynthetic capacity and the relationship with grain yield formation during the growing season of 2013–2014. Water deficit consisted of moderate (leaf water potential of −1.20 to −1.40 MPa) and severe (leaf water potential of −1.80 to −2.20 MPa) levels during tillering and jointing growth stages, respectively. Moderate water deficit during tillering significantly increased grain yield through an enhanced yield capacity per stem and moderate water deficit during jointing resulted in similar grain yields as compared to control, while severe water deficit during both periods significantly reduced grain yield due to strong reduction in number of spikes as compared to control. Moderate or severe water deficit during tillering had no effect on flag leaf area but reduced it significantly when it occurred during jointing. Water deficit treatments during jointing and tillering increased net photosynthetic rate (P n) of flag leaves, the treatment during jointing being the most stimulatory. The maximum photochemical efficiency of Photosystem II, actual photochemical efficiency, the maximum carboxylation rate and photosynthetic electron transport rate increased in ways similar to P n in response to water deficit but non-photochemical quenching decreased. We conclude that improved photosynthetic capacity by moderate water deficit during vegetative growth period highly contributes to grain yield, especially during tillering period, while grain yield decreased by the limitation of leaf area and spikes under severe water deficit.

Water Deficit Alters Cotton Canopy Structure and Increases Photosynthesis in the Mid‐Canopy Layer

Little is known about how water deficit affects cotton (Gossypium hirsutum L.) canopy architecture and the vertical distribution of photosynthesis within the canopy. The objective of this 2‐yr field experiment was to determine the effects of reduced water supply on (i) surface area distribution within a cotton canopy, (ii) the transmission of photosynthetically active radiation (PAR) within the canopy, and (iii) the contribution of leaves and non‐leaf organs at different positions within the canopy to whole‐canopy photosynthesis. The results showed that compared with conventional irrigation, water deficit reduced leaf surface area in the upper canopy layer by 20 to 46% and increased PAR transmission into the mid‐canopy layer by 38 to 73%. Slight water deficit reduced leaf photosynthetic rates in the upper canopy layer by 24%, but increased leaf photosynthetic rates in the mid‐canopy layer by 23% and the lower canopy layer by 79%. Compared with conventional irrigation, slight water deficit had no significant effect on yield, whereas moderate water deficit significantly reduced both variables. Leaves, especially those in the upper canopy layer, were the main drivers of whole‐canopy photosynthesis. On a percentage basis, non‐leaf organs accounted for <26% of whole‐canopy photosynthesis. Future research is needed to learn more about the photosynthetic potential of non‐leaf organs and their response to water deficit.

Anatomical adaptations of the desert species Stipa lagascae against drought stress

AbstractStipa lagascae R. & Sch. (perennial bunchgrass) is one of the most promising steppic species for arid and desert lands of Tunisia. The present study was designed to study the effect of drought on root and leaf anatomy, water relationship, and the growth of three- month-old S. lagascae plants, submitted to water deficit (5, 10, 15, 20, 30 days of withheld irrigation) and grown in pots in greenhouse conditions. The results show that water deficit treatments reduced the biomass accumulation (MS) and leaf water potential (Ψw) of plants. However, leaf relative water content (RWC) decreased significantly only at severe drought. The root’s anatomical features showed reduced root cross-sectional diameter under water deficit. Conversely, epidermis was unaffected by water stress. Moderate and/or severe water deficit (20-30 days) reduced significantly the cortex thickness, cortical cell size, stele diameter, xylem vessel diameter and the stele/root crosssectional ratio, while the number of cortical cells increased for severe water deficit. The cuticles and mesophyll of S. lagascae was thickened by moderate to severe drought and the entire lamina thickness was increased significantly by 5.8% only after 30 days of water deficit while epidermis was unaffected by water deficit. However, severe water deficit (30 days) decreased the width and the length of the bundle sheath. At the same time, the mesophyll cells size and both the xylem and phloem vessels diameter diminished by 12, 16.8 and 17.5%, respectively. Leaf rolling occurs as a response to water deficit and its level increases as the drought period is progressing in plants while reduced bulliform cells size occurred only at severe water deficit. Our findings suggest a complex network of root and leaf anatomical adaptations such as a reduced vessel size with lesser cortical and mesophyll parenchyma formation and increased leaf rolling. These proprieties are required for the maintenance of water potential and energy storage under water stress which can improve the resistance of S. lagascae to survive in extremely arid areas

Effect of seaweed extract (Ulva rigida) on the water deficit tolerance of Salvia officinalis L

The present investigation examined the effect of a seaweed extract (SWE) of Ulva rigida applied at different concentrations: 25, 50, and 75 % to sage plant (Salvia officinalis L.) subjected to drought stress tolerance. Three watering treatments, without stress (WS), moderate water deficit (MWS), and severe water deficit (SWD) corresponding respectively to 82, 18, and 7 % field capacity (FC), were used to understand the metabolic and physiological changes of Salvia plant during water deficit. SWE application enhanced vegetative growth in sage plants under drought stress conditions. The shoot length, total leaf area, and number were significantly reduced under water stress treatment. All SWE concentrations enhanced these growth parameters under water deficit. Maximal shoot number was observed with application of 25 % U. rigida extract under MWD that resulted in increases of 40 % compared to the control plants. Water stress increased glycine betaine (GB) content, that was significantly reduced by all concentration of SWE applied. The maximum reduction of GB was observed with the 50 % SWE treatment. The lipid peroxidation was less pronounced in drought-stressed plants treated with SWE. The lowest content of malondialdehyde (MDA) was in non-stressed plants and 50 % SWE treatment. The total phenolic content was reduced in plants with increased water deficit intensity (30 % reduction of TFC under SWD) but improved by all concentrations of SWE applied. Drought stress increased the superoxide dismutase (SOD) activities when compared to control. There was a significant enhancement of SOD activity and ascorbate peroxydase (APX) activity when sage plants were treated by SWE under deficit water. The beneficial effect of SWE varied with extract concentrations applied. No significant effect was observed with treatment of SWE. Results indicated that seaweed extract of U. rigida application to medicinal plant S. officinalis under water resulted in amelioration of drought stress and helped in enhancement of antioxidant potential and drought tolerance.

MORPHOLOGICAL CHARACTERISTICS AND WATER STATUS OF SOME TUNISIAN BARLEY GENOTYPES SUBMITTED TO WATER STRESS

Tunisia has been qualified as a country vulnerable to climate change that will be unregistered a great drop of annual rainfall and an increase of evaporation. Response strategies of agriculture to drought will be critical because drought is one of the major abiotic stresses which adversely affect crop growth and yield. Among strategies to be developed to cope with the effect of climate change, recourse of genetic diversity and new varietal creation can be a solution among other methods.
 In this study, four barley genotypes were cultivated in semi-controlled conditions and submitted to three levels of water stress. Data were recorded on number of grain per plant (NGP), one thousand grains weight (PMG), total leaf surface (TLS), plant height (HAT), stomata density (DS), leaf water content (RWC) and leaf water potential (LWP).
 Results showed that morphological characteristics (HAT, TLS, DS), yield components (NGP, PMG) and water status (LWP, RWC) of barley genotypes were decreased significantly. However, moderate water deficit didn’t affect significantly the most of parameters studied. Study had demonstrated also that barley genotypes developed different strategies and mechanisms to cope with water deficit, based essentially on their osmotic adjustment capacity.

Comparing different soil fertility systems in Sage (Salvia officinalis) under water deficiency

Sage is a popular medicinal plant which is widely used in cosmetics and pharmaceutical industries. A two years study was conducted to study the effects of different fertility systems on growth and essential oil production of sage under water deficiency. For this purpose, we used a randomized complete block design arranged in split plots with three replications. The maximum of dry matter (2.702±0.15tha−1), essential oil content (1.86±0.10%) and essential oil yield (37.30±3.83lha−1) were obtained in I1 (no stress), I2 (moderate water deficit), and I2 (moderate water deficit), respectively. The highest of dry matter, essential oil content and essential oil yield were obtained in F5 (Vermicompost+N fixing bacteria). Totally, 48 compounds were identified in essential oils of sage by means of GC–MS. 1,8-cineol, α-thujone and camphor were the dominant essential oil compounds which indicated an increasing under I2, F5 and I2×F5 treatments among the three times harvest.

Acclimation mechanisms elicited by sprayed abscisic acid, solar UV-B and water deficit in leaf tissues of field-grown grapevines

The independent and interactive effects of solar ultraviolet-B radiation (UV-B), moderate water deficit and sprayed abscisic acid (ABA) on leaves gas exchange and biochemical aspects of field-grown grapevines of the cv. Malbec were investigated in a high altitude vineyard (1450 m a.s.l.). Two UV-B treatments (ambient solar UV-B or reduced UV-B), two watering treatments (well watered or moderate water deficit) and two ABA treatments (no ABA and sprayed ABA) were given alone and combined in a factorial design. Gas exchange and photosynthesis were reduced by water deficit and highly impaired in the UV-B and water deficit combined treatment. UV-absorbing compounds were stimulated independently by UV-B. The monoterpenes α-pinene, 3-carene and terpinolene, and the sesquiterpene nerolidol were augmented by UV-B, water deficit or sprayed ABA. Levels of the triterpene squalene and the diterpene phytol were significantly higher in the treatment that combined UV-B, water deficit and ABA applications. Environment signals (solar UV-B and moderate water deficit) and sprayed ABA elicited mechanisms of acclimation by augmenting the content of terpenes with antioxidant and antifungal properties, thus enhancing the plant defensive mechanisms towards signals both biotic and abiotic.

Leaf physiological responses of mature pear trees to regulated deficit irrigation in field conditions under desert climate

Regulated deficit irrigation (RDI) affects the physiological process of fruit trees. An experiment was conducted to evaluate physiological responses of pear tree to RDI treatments and its impacts on yield under desert climate in 2009 and 2010. Four water stress treatments consisted of moderate and severe (irrigated with 60% and 40% of pan evaporation, respectively) water deficit in the cell division or slow fruit enlargement stage and well irrigation (irrigated with 80% of pan evaporation) during other fruit growth stages. The results showed that leaf photosynthetic, transpiration rate and stomatal conductance all decreased during water stress cycle, and it took 1 to 4 weeks to recover these responses after the irrigation resuming depend on RDI treatments. After severe water stress in cell division stage or moderate water stress in slow fruit enlargement stage, leaf photosynthetic rate effectively enhanced during the fruit enlargement stage following resumption of well irrigation, resulting in the improvement of fruit yield. The leaf water use efficiency was also improved by RDI treatments. The results contributed to understand mechanisms of the yield improvement by RDI and its high water use efficiency.

WATER STRESS TOLERANCE OF FODDER COWPEA AS INFLUENCED BY VARIOUS ADDED LEVELS OF POTASSIUM SULPHATE

A field experiment was carried out on sandy soil of the Agricultural Research Experimental Station, at Ismailia Governorate (latitude 30o 35ʹ 41.9ʺ N and longitude 32o 16ʹ 48.8ʺ E), Egypt, during two successive growing summer seasons; 2013 and 2014. The study aimed to investigate the effect of applying three levels of water supplied through sprinkler irrigation system representing; 100 %, 75 % and 50 % of water supply which corresponding to 2500, 1875 and 1250 m3 fed-1, on the forage yield productivity and quality of fodder cowpea. Such levels represented commonly practiced irrigation (control), moderate and severe water deficit stress for fodder cowpea, respectively. Also, to evaluate the role of four rates of potassium sulphate fertilization namely, 24, 36, 48 and 60 K2O kg fed-1 in alleviating the adverse effect of water deficit stress on cowpea plants under these conditions. Three cuts were taken throughout the growth season. The obtained results revealed that decreasing the levels of water from 100% to 75 or 50% level markedly reduced all traits under studied; plant height, leaves number per plant, leaves/stem ratio of cowpea, green and dry forage yield (kg fed-1), at the three cuts as well as the total yield of the three cuts. The reduction noticeably appeared more detrimental under 50% of water stress especially at the 3rd cut. The results showed that the total green and dry forage yield of the three cuts of plants treated with 48 kg K2O fed-1, under 50% irrigation level, reduced by 52.4 % and 57.0 %, respectively; compared with the yields obtained by plants received the recommended K rate (48 kg K2O fed-1) under commonly practiced irrigation. Increasing water deficit stress lowered carbohydrate %, crude proteins % and ash content (kg fed-1) in plants as well as K% in leaves. Also, it significantly decreased the contents of Fe, Zn and Mn in plants. Increasing the application rates of K up to 60 K2O kg fed-1 substantially elevated all the aforementioned studied traits under each level of irrigation and the reduction resulted due to water stress, under 75% and 50% levels could be suppressed. Application of the highest K rate (60 K2O kg fed-1) not only considerably heightened all the detected nutrients; carbohydrate % and proteins %, ash and micronutrients (Fe, Zn and Mn) uptake by plants as well as K% in leaves of cowpea, but also it remarkably enhanced the water use efficiency by plants grown under 75% irrigation than all applied K rates treatments under 100% irrigation. From the obtained results, it could be inferred that under moderate water stress 75% of the commonly practiced irrigation application of 60 K2O kg fed-1 could sustain cowpea plant to grow satisfactorily.

MORPHOLOGICAL CHARACTERISTICS AND WATER STATUS OF SOME TUNISIAN BARLEY GENOTYPES SUBMITTED TO WATER STRESS

Tunisia has been qualified as a country vulnerable to climate change that will be unregistered a great drop of annual rainfall and an increase of evaporation. Response strategies of agriculture to drought will be critical because drought is one of the major abiotic stresses which adversely affect crop growth and yield. Among strategies to be developed to cope with the effect of climate change, recourse of genetic diversity and new varietal creation can be a solution among other methods. In this study, four barley genotypes were cultivated in semi-controlled conditions and submitted to three levels of water stress. Data were recorded on number of grain per plant (NGP), one thousand grains weight (PMG), total leaf surface (TLS), plant height (HAT), stomata density (DS), leaf water content (RWC) and leaf water potential (LWP). Results showed that morphological characteristics (HAT, TLS, DS), yield components (NGP, PMG) and water status (LWP, RWC) of barley genotypes were decreased significantly. However, moderate water deficit didn’t affect significantly the most of parameters studied. Study had demonstrated also that barley genotypes developed different strategies and mechanisms to cope with water deficit, based essentially on their osmotic adjustment capacity.

Respostas ecofisiológicas de cafeeiros submetidos ao deficit hídrico para concentração da florada no Cerrado de Minas Gerais

O objetivo deste trabalho foi avaliar o efeito de diferentes períodos de imposição do deficit hídrico sobre a concentração da florada do cafeeiro (Coffea arabica), bem como sobre as trocas gasosas, a produtividade, a maturação e a qualidade dos grãos. As cultivares Catuaí Vermelho IAC 144 e Bourbon Amarelo J9 foram avaliadas conforme os seguintes tratamentos: não irrigado (NI), irrigado continuamente (IC), e suspensão da irrigação em 1/7/2010 (D1) e em 1/8/2010 (D2), com retorno desta em 24/9/2010. Cerca de três dias após a retomada da irrigação, registrou-se a ocorrência de uma "chuva de florada", com precipitação de 69 mm. O potencial hídrico foliar de antemanhã (Ψam) nas cultivares Catuaí Vermelho IAC 144 e Bourbon Amarelo J9, em 22/9, foi de -0,59 e -0,82 MPa, -0,53 e -0,79 MPa, e -0,34 e -0,49 MPa, para os tratamentos NI, D1 e D2, respectivamente. O percentual máximo de botões florais no estádio E4, imediatamente antes da ocorrência da chuva, não foi afetado pelos níveis de deficit impostos durante o inverno, independentemente das cultivares. Os níveis moderados de deficit hídrico impostos pelos tratamentos (Ψam ~ -0,80 MPa) produziram pouco ou nenhum efeito sobre as trocas gasosas, a taxa de florescimento ou a uniformidade de maturação - percentagem de cerejas de 66% -, e a produtividade e a classificação dos grãos, de ambas as cultivares. O efeito dos diferentes tratamentos sobre o status hídrico dos botões florais não se sobrepõe ao efeito da chuva de florada, que foi determinante para sua abertura.

Individual Leaf Area of Early Flowering Arabidopsis Genotypes Is More Affected by Drought than Late Flowering Ones: A Multi-Scale Analysis in 35 Genetically Modified Lines

Plants acclimate to drought optimizing the trade-off between biomass production and water loss while ensuring their survival and reproduction. Plants also modify their growth or phenology as complementary strategies in response to stress. Despite evidence of an interaction between flowering time and plant growth response to environmental stresses, this interaction in response to drought is under debate. To contribute to the analysis of this interaction, leaf growth of 35 genetically modified lines of Arabidopsis thaliana and their common wild-type, Col-0 was analyzed by a quantitative multi-scale phenotyping approach from cellular to whole plant scale both in wellwatered and soil moderate water deficit conditions. These genotypes were selected for the various physiological functions potentially altered by their genetic modification and that could interact with plant growth and/or their drought responses. In all genotypes, leaf expansion decreased in response to drought both at the whole rosette and the individual leaf levels. Additionally, epidermal cell area and/or epidermal cell number decreased in response to the drought treatment. In contrast, the number of rosette leaves was reduced in only half of the genotypes and leaf growth duration was only modified in 4 of them. Despite long photoperiod conditions, the duration of the vegetative phase, i.e. the time elapsed between germination and flowering stage, varied from 12 to 27 days among genotypes under well watered conditions. Our analyses revealed that the differences of flowering time observed in well-watered condition impacted the leaf area response to drought. Early-flowering genotypes slightly decreased their final leaf number, but strongly reduced their

Seaweed extract effect on water deficit and antioxidative mechanisms in bean plants (Phaseolus vulgaris L.)

The effect of seaweed extract (SWE) obtained from two macroalgae species, Ulva rigida and Fucus spiralis, on drought stress tolerance in green bean plants (Phaseolus vulgaris L.) was studied. Examination of growth parameters and some physiological and biochemical parameters showed that SWE extract enhanced vegetative growth in bean plant without stress and in plant under drought stress condition. Maximal plant height and dry weight were observed with application of 25 % U. rigida and F. spiralis extract. Enhanced chlorophyll a (Chl a) and chlorophyll b (Chl b) pigments and glycine betaine (GB) content were also observed with all SWE treatments under water deficit. The lipid peroxidation was low pronounced in stressed plants treated with SWE. Total phenolic content was increased in bean plants under different growth conditions (without stress (WS), moderate water stress (MWD), and severe water deficit (SWD)) and treated with SWE at all concentrations. The highest total phenolic content was attained with the application 25 % U. rigida extract in bean plant subjected to drought stress (MWD and SWD). There was a significant enhancement of superoxide dismutase (SOD) activity and catalase (CAT) activity with SWE treatment in plant under moderate water deficit. Plants stressed and treated with SWE showed maximal ascorbate peroxidase (APX) activity. The increased total phenolic content and the enhancement of antioxidant enzymatic activity by SWE in stressed bean plants may contribute to protection against peroxidation and reduce the severity of water deficit.

Drought priming at vegetative growth stages improves tolerance to drought and heat stresses occurring during grain filling in spring wheat

Plants of spring wheat (Triticum aestivum L. cv. Vinjett) were exposed to moderate water deficit at the vegetative growth stages six-leaf and/or stem elongation to investigate drought priming effects on tolerance to drought and heat stress events occurring during the grain filling stage. Compared with the non-primed plants, drought priming could alleviate photo-inhibition in flag leaves caused by drought and heat stress episodes during grain filling. In the primed plants, drought stress inhibited photosynthesis mainly through decrease of maximum photosynthetic electron transport rate, while decrease of the carboxylation efficiency limited photosynthesis under heat stress. The higher saturated net photosynthetic rate of flag leaves coincided with the lowered non-photochemical quenching rates in the twice-primed plants under drought stress and in the primed plants during stem elongation under heat stress. Compared to the non-priming treatment, drought priming either applied once or twice alleviated the grain yield reduction by drought stress during grain filling, and priming during the stem elongation stage alleviated yield loss by heat stress at grain filling. The higher concentration of abscisic acid in primed plants under drought stress could contribute to higher grain yield compared to the non-primed plants. Taken together, the results indicate that drought priming during vegetative stages improved tolerance to both drought and heat stress events occurring during grain filling in wheat.

Anatomical adaptations of Astragalus gombiformis Pomel. under drought stress

Abstract The present study was designed to study the effect of drought on root, stem and leaf anatomy of Astragalus gombiformis Pomel. Several root, stem and leaf anatomical parameters (cross section diameter, cortex, root cortical cells, pith, leaf lamina and mesophyll thickness) were reduced under moderate to severe water deficit (20–30 days of withheld irrigation). The stele/cross section root ratio increased under moderate water deficit. The root’s and stems vascular systems showed reduced xylem vessel diameter and increased wall thickness under water deficit. In addition, the root xylem vessel density was increased in these drought conditions while it was unchanged in the stems. The stomata density was increased under prolonged drought conditions whereas the stomata size was untouched. The leaf vascular system showed reduced xylem and phloem tissue thickness in the main vein under moderate to severe water deficit. However, in the lamina the vascular tissue and the distance between vascular bundle were unaffected. Our findings suggest a complex network of anatomical adaptations such as a reduced vessel size with increased wall thickness, lesser cortical and mesophyll parenchyma formation and increased stomata density. These proprieties are required for the maintenance of water potential and energy storage under water stress which can improve the resistance of A. gombiformis to survive in arid areas.

Assessment of Grape Yield and Composition Using Reflectance‐Based Indices in Rainfed Vineyards

Spectral vegetation indices such as the normalized difference vegetation index (NDVI) have proved to be useful in estimating berry yield and composition in irrigated vineyards that usually experience mild to moderate water deficits. However, their performance is not clear under rainfed conditions. This study explores the relationships between NDVI and berry yield and composition in rainfed vineyards experiencing mild to moderate water stress with respect to the timing of water deficits. The study was conducted on grape (Vitis vinifera L. ‘Chardonnay’). Biophysical variables such as predawn water potential (Ψp), canopy minus air temperature difference (ΔTm), fractional intercepted photosynthetic active radiation (fIPAR) and canopy reflectance measurements were acquired at veraison and were related to berry yield, total soluble solids (TSS), titratable acidity (TA), and maturity index (IMAD) at harvest. In our study, while NDVI provided consistent estimates of TSS (r2 = 0.81) and IMAD (r2 = 0.89) when water deficit conditions had a larger incidence before veraison, the water index (WI)–a reflectance‐based index of water status–was related to TA (r2 = 0.62) and IMAD (r2 = 0.67) under post‐veraison water deficits. Since early and late water deficits (i.e., before and after veraison) have a differential impact on the determinants of vine photosynthetic activity (i.e., leaf area and stomatal conductance), the capability of NDVI to estimate berry yield and composition might be subject to the extent and timing of water deficits in these rain‐fed vineyards.

Nitric oxide increases tolerance responses to moderate water deficit in leaves of Phaseolus vulgaris and Vigna unguiculata bean species.

Drought stress is one of the most intensively studied and widespread constraints, and nitric oxide (NO) is a key signaling molecule involved in the mediation of abiotic stresses in plants. We demonstrated that a sprayed solution of NO from donor sodium nitroprusside increased drought stress tolerance responses in both sensitive (Phaseolus vulgaris) and tolerant (Vigna unguiculata) beans. In intact plants subjected to halting irrigation, NO increased the leaf relative water content and stomatal conductance in both species. After cutting leaf discs and washing them, NO induced increased electrolyte leakage, which was more evident in the tolerant species. These leaf discs were then subjected to different water deficits, simulating moderate and severe drought stress conditions through polyethylene glycol solutions. NO supplied at moderate drought stress revealed a reduced membrane injury index in sensitive species. In hydrated discs and at this level of water deficit, NO increased the electron transport rate in both species, and a reduction of these rates was observed at severe stress levels. Taken together, it can be shown that NO has an effective role in ameliorating drought stress effects, activating tolerance responses at moderate water deficit levels and in both bean species which present differential drought tolerance.

Leaf developmental stage modulates metabolite accumulation and photosynthesis contributing to acclimation of Arabidopsis thaliana to water deficit.

We examined whether young and mature leaves of Arabidopsis thaliana in their response to mild water deficit (MiWD) and moderate water deficit (MoWD), behave differentially, and whether photosynthetic acclimation to water deficit correlates with increased proline and sugar accumulation. We observed that with increasing water deficit, leaf relative water content decreased, while proline and sugar accumulation increased in both leaf-developmental stages. Under both MiWD and MoWD, young leaves showed less water loss and accumulated higher level of metabolites compared to mature leaves. This, leaf age-related increase in metabolite accumulation that was significantly higher under MoWD, allowed young leaves to cope with oxidative damage by maintaining their base levels of lipid peroxidation. Thus, acclimation of young leaves to MoWD, involves a better homeostasis of reactive oxygen species (ROS), that was achieved among others by (1) increased sugar accumulation and (2) either increased proline synthesis and/or decreased proline catabolism, that decrease the NADPH/NADP(+) ratio, resulting in a higher level of oxidized state of quinone A and thus in a reduced excitation pressure, and by (3) stimulation of the photoprotective mechanism of non-photochemical quenching, that reflects the dissipation of excess excitation energy in the form of harmless heat, thus protecting the plant from the damaging effects of ROS.

Implications of the mesophyll conductance to CO2 for photosynthesis and water‐use efficiency during long‐term water stress and recovery in two contrasting Eucalyptus species

Water stress (WS) slows growth and photosynthesis (A(n)), but most knowledge comes from short-time studies that do not account for longer term acclimation processes that are especially relevant in tree species. Using two Eucalyptus species that contrast in drought tolerance, we induced moderate and severe water deficits by withholding water until stomatal conductance (g(sw)) decreased to two pre-defined values for 24 d, WS was maintained at the target g(sw) for 29 d and then plants were re-watered. Additionally, we developed new equations to simulate the effect on mesophyll conductance (g(m)) of accounting for the resistance to refixation of CO(2). The diffusive limitations to CO(2), dominated by the stomata, were the most important constraints to A(n). Full recovery of A(n) was reached after re-watering, characterized by quick recovery of gm and even higher biochemical capacity, in contrast to the slower recovery of g(sw). The acclimation to long-term WS led to decreased mesophyll and biochemical limitations, in contrast to studies in which stress was imposed more rapidly. Finally, we provide evidence that higher gm under WS contributes to higher intrinsic water-use efficiency (iWUE) and reduces the leaf oxidative stress, highlighting the importance of gm as a target for breeding/genetic engineering.