Stomata play a key role in plant adaptation to changing environmental conditions as they control both water losses and CO(2) uptake. Particularly, in the context of global change, simulations of the consequences of drought on crop plants are needed to design more efficient and water-saving cropping systems. However, most of the models of stomatal conductance (g(s)) developed at the leaf level link g(s) to environmental factors or net photosynthesis (A(net)), but do not include satisfactorily the effects of drought, impairing our capacity to simulate plant functioning in conditions of limited water supply. The objective of this review was to draw an up-to-date picture of the g(s) models, from the empirical to the process-based ones, along with their mechanistic or deterministic bases. It focuses on models capable to account for multiple environmental influences with emphasis on drought conditions. We examine how models that have been proposed for well-watered conditions can be combined with those specifically designed to deal with drought conditions. Ideas for future improvements of g(s) models are discussed: the issue of co-regulation of g(s) and A(net); the roles of CO(2), absissic acid and H(2)O(2); and finally, how to better address the new challenges arising from the issue of global change.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2010.02181.x

An overview of models of stomatal conductance at the leaf level

This review deals with grapevine responses to water stress by examining perturbations to physiological and molecular processes at the root, shoot, leaf and berry levels. Long-distance signalling among organs is also considered. Isohydric or anisohydric Vitis genotypes are described in relation to their response to drought, which is linked to stomatal behaviour. Stomatal regulation of grapevine under abscisic acid and hydraulic control (the latter being linked to embolism formation and recovery in water pathways upstream the stomata) is reviewed and linked to impairments of photosynthetic assimilation. We define three stages of photosynthesis regulation in grapevines that are subjected to progressive water stress on the basis of the main causes of assimilation decline. Early and late contributions of aquaporins, which play a fundamental role in water stress control, are discussed. Metabolic mechanisms of dehydration tolerance are rewieved, and variation linked to differences in transcript abundance of genes involved in osmoregulation, photosynthesis, photorespiration, detoxification of free radicals and coping with photoinhibition. Results of these defence strategies accumulated in berries are reviewed, together with perturbations of their molecular pathways. Features observed in different organs show that grapevine fits well as a complex model plant for molecular and physiological studies on plant drought avoidance/tolerance.

/pdf/drought-induced-changes-in-development-and-function-of-1x7v890ccr.pdf

Drought-induced changes in development and function of grapevine (Vitis spp.) organs and in their hydraulic and non-hydraulic interactions at the whole-plant level: a physiological and molecular update

The hybrid Richter-110 (Vitis berlandieri3Vitis rupestris) has the reputation of being a genotype strongly adapted to drought. A study was performed with plants of R-110 subjected to sustained water-withholding to induce acclimation to two different levels of water stress, followed by rewatering to induce recovery. The goal was to analyse how photosynthesis is regulated during acclimation to water stress and recovery. In particular, the regulation of stomatal conductance (gs), mesophyll conductance to CO2 (gm), leaf photochemistry (chlorophyll fluorescence and thermoluminescence), and biochemistry (Vc,max) were assessed. During water stress, gs declined to 0.1 and less than 0.05 mol CO2 m 22 s 21 in moderately and severely water-stressed plants, respectively, and was kept quite constant during an acclimation period of 1-week. Leaf photochemistry proved to be very resistant to the applied water-stress conditions. By contrast, gm and Vc,max were affected by water stress, but they were not kept constant during the acclimation period. gm was initially unaffected by water stress, and Vc,max even increased above control values. However, after several days of acclimation to water stress, both parameters declined below (gm )o r at (Vc,max) control values. For the latter two parameters there seemed to be an interaction between water stress and cumulative irradiance, since both recovered to control values after several cloudy days despite water stress. A photosynthesis limitation analysis revealed that diffusional limitations and not biochemical limitations accounted for the observed decline in photosynthesis during water stress and slow recovery after rewatering, both in moderately and severely stressed plants. However, the relative contribution of stomatal (SL) and mesophyll conductance (MCL) limitations changes during acclimation to water stress, from predominant SL early during water stress to similar SL and MCL after acclimation. Finally, photosynthesis recovery after rewatering was mostly limited by SL, since stomatal closure recovered much more slowly than gm.

http://max2.ese.u-psud.fr/publications/Flexas-Palma-JExpBot2009.pdf

Photosynthesis limitations during water stress acclimation and recovery in the drought-adapted Vitis hybrid Richter-110 (V. berlandieri×V. rupestris)

Improving water use efficiency (WUE) in grapevines is essential for vineyard sustainability under the increasing aridity induced by global climate change. WUE reflects the ratio between the carbon assimilated by photosynthesis and the water lost in transpiration. Maintaining stomata partially closed by regulated deficit irrigation or partial root drying represents an opportunity to increase WUE, although at the expense of decreased photosynthesis and, potentially, decreased yield. It would be even better to achieve increases in WUE by improving photosynthesis without increasing water loses. Although this is not yet possible, it could potentially be achieved by genetic engineering. This review presents current knowledge and relevant results that aim to improve WUE in grapevines by biotechnology and genetic engineering. The expected benefits of these manipulations on WUE of grapevines under water stress conditions are modelled. There are two main possible approaches to achieve this goal: (i) to improve CO2 diffusion to the sites of carboxylation without increasing stomatal conductance; and (ii) to improve the carboxylation efficiency of Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The first goal could be attained by increasing mesophyll conductance to CO2, which partly depends on aquaporins. The second approach could be achieved by replacing Rubisco from grapevine with Rubiscos from other C3 species with higher specificity for CO2. In summary, the physiological bases and future prospects for improving grape yield and WUE under drought are established.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1755-0238.2009.00057.x

Improving water use efficiency in grapevines: potential physiological targets for biotechnological improvement.

Spatial and temporal changes to the water regime of a Mediterranean vineyard due to the adoption of cover cropping

The responses of two grapevine cultivars from ecologically different regions, Chardonnay from Burgundy, France and Airen from La Mancha, Spain, to water stress were compared. The plants were grown in weighing lysimeters under two water availability conditions: water stress and nonstress. Leaf area development, photosynthesis, and dry matter production were evaluated. Except for dry matter produced in the first phase and fruit dry matter at harvest, the interaction between cultivar and irrigation treatment was not significant for any of the parameters evaluated. Water stress resulted in a reduction in the total amount of leaf area developed. Water stress resulted in less growth (leaf area formation) during the later stages of vine growth. Leaf area distribution between primary and lateral shoots was not significantly modified by water stress. The capacity to form leaf area and the sensitivity of leaf area development to water stress were apparently under genetic control. Water stress reduced the photosynthetic activity of mature and healthy leaves to a similar degree in both cultivars. No significant differences were found between cultivars in any of the photosynthesis measurements. Water stress modified timing of dry matter accumulation during the growth cycle. Water-stressed grapevines produced a greater amount of total dry matter accumulation from fruit set to veraison, while nonstressed grapevines produced more dry matter after veraison. Grapevine productivity could be modeled as a linear function of average leaf area during the growth cycle. An increase in plant leaf area resulted in an increase in dry matter production at a similar rate for both nonstress and stress conditions. Cultivar and water availability determined leaf area development, and, in turn, leaf area determined the amount of dry matter produced.

Effect of Water Stress on Leaf Area Development, Photosynthesis, and Productivity in Chardonnay and Airén Grapevines

This essay studies the morphological and anatomical properties of the leaves of Garnacha tinta, Tempranillo, Chardonnay and Airen grapevines in order to discover the drought adaptation strategies present in Vitis vinifera L The grapevines were grown under two water availability conditions: water limitation and non-water limitation There was a significantly lower development of leaf area under conditions of water limitation compared to non-water limitation due to a reduction in the size of main and lateral shoot leaves, and a smaller number of leaves on lateral shoots The development of the leaf area under water limitation conditions occurred on earlier dates than under non-water limitation conditions Significantly lower stomatal density was observed under water limitation conditions rather than non-water limitation conditions exclusively in the Airen cultivar

/pdf/drought-adaptation-strategies-of-four-grapevine-cultivars-18n79ojw2q.pdf

Drought adaptation strategies of four grapevine cultivars ( Vitis vinifera L.): modification of the properties of the leaf area

Predawn leaf water potential, night respiration, stomatal conductance, transpiration, and photosynthesis of 4 grapevine cultivars were assessed under irrigated and non-irrigated conditions in July, August and September 1994. Predawn leaf water potential was not significantly related to either stomatal conductance or photosynthesis. Water stress induced distinct stomatal closure in all cultivars at 11 a.m. For a given stomatal conductance rate, photosynthesis of stressed vines was lower than that of nonstressed vines. At similar stomatal conductance rate, photosynthesis was lower in cv. Chardonnay than in any other cultivar. Photosynthesis was the physiological parameter mostly affected by water stress. Dry matter production was linearly related to stomatal conductance, photosynthesis, and the night respiration to photosynthesis ratio for all vines pooled together. In contrast, under stress conditions dry matter production was not related to any physiological parameter.

/pdf/water-stress-induced-physiological-changes-in-leaves-of-four-3boqnwxnie.pdf

Water-stress induced physiological changes in leaves of four container-grown grapevine cultivars ( Vitis vinifera L.)

Four grapevine training systems (single curtain, vertical shoot-positioned, high bush, and short bush) were compared for their effects on physiological performance, yield, vegetative growth, and must composition in Vitis vinifera L. cv. Tempranillo in Mediterranean weather conditions. Net CO2 assimilation rate, stomatal conductance, and transpiration rate were measured at the beginning of bunch closure, veraison, and maturity on fully exposed leaves. At each stage, changes in these values were measured in the morning, at midday, and in the afternoon. Differences in individual leaf responses among treatments were the result of photosynthetically active radiation levels on the outer leaves. Fully exposed leaves of the bush-trained vines had the highest stomatal conductance and transpiration rates and those of the high-bush vines had the highest photosynthetic rates. Grape yield results showed that the vertical shoot-positioned system was the most productive, adjusted for its greater pruning level. Although acceptable grape quality was obtained with all four systems, single curtain and high bush had greater total soluble solids at the expense of lower grape yield.

Ecophysiological and Agronomic Response of Tempranillo Grapevines to Four Training Systems

A comparative study of stomatal responses to rewatering was conducted on grapevines previously subjected to conditions of water stress and no water stress. Two cultivars were grown in 35 L lysimeters: 'Airen', from the dry zone of La Mancha, and 'Chardonnay', from the humid zone of Burgundy. The day after rewatering no significant differences in soil water content were found between water treatments or cultivars. However, predawn leaf water potential was significantly higher under non-stress than under stressed conditions, differences between cultivars were also found. Water consumption during the 5 d after rewatering was directly related to vine leaf area development. Vines grown under water stress conditions showed more uniform stomatal behaviour after rewatering. One day after rewatering rates of leaf conductance, transpiration and net photosynthesis were significantly higher in non-stressed vines, while 3 d after rewatering leaf conductance and transpiration were significantly higher in vines previously subjected to water stress. Net photosynthesis was significantly higher in water-stressed vines 5 d after rewatering. No differences were found between cultivars with regard to leaf conductance. The differences in the relationship between net photosynthesis and leaf conductance between stressed and non-stressed vines before rewatering were not found after rewatering. The only permanent adaptation mechanism to water stress was a lowering of leaf area development, which allowed water-stressed vines to consume less water to maintain a higher water availability and high or constant stomatal conductance.

/pdf/effect-of-previous-water-conditions-on-vine-response-to-5dl03atluj.pdf

C. Ruiz

Papers

Effect of Water Stress on Leaf Area Development, Photosynthesis, and Productivity in Chardonnay and Airén Grapevines

Drought adaptation strategies of four grapevine cultivars ( Vitis vinifera L.): modification of the properties of the leaf area

Water-stress induced physiological changes in leaves of four container-grown grapevine cultivars ( Vitis vinifera L.)

Ecophysiological and Agronomic Response of Tempranillo Grapevines to Four Training Systems

Effect of previous water conditions on vine response to rewatering