Grapevine morphological shade acclimation is mediated by light quality whereas hydraulic shade acclimation is mediated by light intensity.

Plants acclimate to shade by sensing light signals such as low photosynthetic active radiation (PAR), low blue light (BL) levels and low red-to-far red ratios (R:FR) trough plant photoreceptors cross talk. We previously demonstrated that grapevine is irresponsive to variations in R:FR and that BL-attenuation mediates morphological and architectural responses to shade increasing light interception and absorption efficiencies. However, we wondered if grapevine respond to low R:FR when BL is attenuated at the same time. Our objective was to evaluate if morphological, architectural and hydraulic acclimation to shade is mediated by low R:FR ratios and BL attenuation. To test this, we carried out experiments under natural radiation, manipulating light quality by selective sunlight exclusion and light supplementation. We grew grapevines under low PAR (LP) and four high PAR (HP) treatments: HP, HP plus FR supplementation (HP + FR), HP with BL attenuation (HP-B) and HP with BL attenuation plus FR supplementation (HP-B + FR). We found that plants grown under HP-B and HP-B + FR had similar morphological (stem and petiole length, leaf thickness and area), architectural (laminae' angles) and anatomical (stomatal density) traits than plants grown under LP. However, only LP plants presented lower stomata differentiation, lower δ13C and hence lower water use efficiency. Therefore, even under a BL and R:FR attenuated environment, morphological and architectural responses were modulated by BL but not by variation in R:FR. Meanwhile water relations were affected by PAR intensity but not by changes in light quality. Knowing grapevine responses to light quantity and quality are indispensable to adopt tools or design new cultural management practices that manipulate irradiance in the field intending to improve crop performance.

Mechanisms underlying photosynthetic acclimation to high temperature are different between Vitis vinifera cv. Syrah and Grenache.

Photosynthesis acclimation to high temperature differs among and within species. Grapevine intra-specific variation in photosynthetic acclimation to elevated temperature has been scarcely assessed. Our objectives were to (i) evaluate the mechanisms underlying long-term acclimation of photosynthesis to elevated temperature in grapevine, and (ii) determine whether these responses are similar among two varieties. A warming experiment with well irrigated Grenache and Syrah field-grown plants was performed during two growing seasons comparing plants exposed at ambient temperature (control) with plants in open-top chambers (heating) that increased mean air temperature between 1.5 and 3.6°C. Photosynthetic acclimation was assessed through the response of net assimilation (An), Rubisco carboxylation rate (Vcmax) and electron transport rate (Jmax), at leaf temperatures from 20 to 40°C. Our results evidenced different mechanisms for photosynthetic acclimation to elevated temperature. Compared with control, Grenache heated increased An, maintaining higher Vcmax and Jmax at temperatures above 35°C. By contrast, Syrah heated and control presented similar values of An, Vcmax and Jmax, evidencing an adjustment of photosynthesis without increasing C assimilation. Both varieties increased the optimum temperature for An, but to a lesser extent when growth temperature was higher. Our study provides evidence that grapevine varieties present different acclimation mechanisms to expected warming.

Non-structural carbohydrates and sugar export in grapevine leaves exposed to different light regimes.

Light is a main environmental factor that determines leaf microclimate within the vine, as well as its photosynthesis and carbohydrate metabolism. This study aimed to examine the relationships between photosynthesis, carbohydrate metabolism, and the expression of related genes in leaves of grapevine grown under different radiation regimes. During the 2014/2015 growing season, an experiment was conducted on a Malbec vineyard (Vitis vinifera L.) in which four radiation exposure treatments were established on the leaves: (1) East, (2) West, (3) Sun, and (4) Shade (i.e., reduction in light intensity). Diurnal dynamics of photosynthesis and non-structural carbohydrates were measured and leaf export rates were calculated. Transcript profiles of leaf sugar transporters (VvHT1, VvHT3, VvSUC27), a sucrose phosphate synthase enzyme (VvSPS), and invertases (VvGIN1, VvCWI) were also examined. We showed that East and Sun leaves had higher daily photosynthetic and export rates than West leaves, which was mainly explained by the environmental conditions (air and leaf temperature, VPDleaf-air ) and leaf water status. Shade leaves accumulated less starch and soluble sugars than exposed leaves, which correlated with a higher expression of hexose transporters and invertases. The hypotheses that these sugars in Shade leaves would play a role as signaling molecules and/or have increased sink strength and phloem unloading are discussed. These results allow us to understand the physiological and molecular behavior of leaves exposed to different radiation regimes, which can be used to design appropriate vineyard management practices.

A functional-structural plant model that simulates whole- canopy gas exchange of grapevine plants (Vitis vinifera L.) under different training systems.

BACKGROUND AND AIMS: Scaling from single-leaf to whole-canopy photosynthesis faces several complexities related to variations in light interception and leaf properties. To evaluate the impact of canopy strucuture on gas exchange, we developed a functional-structural plant model to upscale leaf processes to the whole canopy based on leaf N content. The model integrates different models that calculate intercepted radiation, leaf traits and gas exchange for each leaf in the canopy. Our main objectives were (1) to introduce the gas exchange model developed at the plant level by integrating the leaf-level responses related to canopy structure, (2) to test the model against an independent canopy gas exchange dataset recorded on different plant architectures, and (3) to quantify the impact of intra-canopy N distribution on crop photosynthesis. METHODS: The model combined a 3D reconstruction of grapevine (Vitis vinifera) canopy architecture, a light interception model, and a coupled photosynthesis and stomatal conductance model that considers light-driven variations in N distribution. A portable chamber device was constructed to measure whole-plant gas exchange to validate the model outputs with data collected on different training systems. Finally, a sensitivity analysis was performed to evaluate the impact on C assimilation of different N content distributions within the canopy. KEY RESULTS: By considering a non-uniform leaf N distribution within the canopy, our model accurately reproduced the daily pattern of gas exchange of different canopy architectures. The gain in photosynthesis permitted by the non-uniform compared with a theoretical uniform N distribution was about 18 %, thereby contributing to the maximization of C assimilation. By contrast, considering a maximal N content for all leaves in the canopy overestimated net CO2 exchange by 28 % when compared with the non-uniform distribution. CONCLUSIONS: The model reproduced the gas exchange of plants under different training systems with a low error (10 %). It appears to be a reliable tool to evaluate the impact of a grapevine training system on water use efficiency at the plant level.

Drought will not leave your glass empty: Low risk of hydraulic failure revealed by long-term drought observations in world's top wine regions.

Grapevines are crops of global economic importance that will face increasing drought stress because many varieties are described as highly sensitive to hydraulic failure as frequency and intensity of summer drought increase. We developed and used novel approaches to define water stress thresholds for preventing hydraulic failure, which were compared to the drought stress experienced over a decade in two of the world's top wine regions, Napa and Bordeaux. We identified the physiological thresholds for drought-induced mortality in stems and leaves and found small intervarietal differences. Long-term observations in Napa and Bordeaux revealed that grapevines never reach their lethal water-potential thresholds under seasonal droughts, owing to a vulnerability segmentation promoting petiole embolism and leaf mortality. Our findings will aid farmers in reducing water use without risking grapevine hydraulic integrity.

Changes in leaf stomatal conductance, petiole hydraulics and vessel morphology in grapevine (Vitis vinifera cv. Chasselas) under different light and irrigation regimes.

Hydraulic conductance and water transport in plants may be affected by environmental factors, which in turn regulate leaf gas exchange, plant growth and yield. In this study, we assessed the combined effects of radiation and water regimes on leaf stomatal conductance (gs), petiole specific hydraulic conductivity (Kpetiole) and anatomy (vessel number and size); and leaf aquaporin gene expression of field-grown grapevines at the Agroscope Research Station (Leytron, Switzerland). Chasselas vines were subjected to two radiation (sun and shade) levels combined with two water (irrigated and water-stressed) regimes. The sun and shade leaves received ~61.2 and 1.48molm-2day-1 of photosynthetically active radiation, respectively, during a clear-sky day. The irrigated vines were watered weekly from bloom to veraison whereas the water-stressed vines did not receive any irrigation during the season. Water stress reduced gs and Kpetiole relative to irrigated vines throughout the season. The petioles from water-stressed vines showed fewer large-sized vessels than those from irrigated vines. The shaded leaves from the irrigated vines exhibited a higher Kpetiole than the sun leaves at the end of the season, which was partially explained by a higher number of vessels per petiole and possibly by the upregulation of some of the aquaporins measured in the leaf. These results suggest that not only plant water status but also the light environment at the leaf level affected leaf and petiole hydraulics.

A leaf gas exchange model that accounts for intra-canopy variability by considering leaf nitrogen content and local acclimation to radiation in grapevine (Vitis vinifera L.).

Understanding the distribution of gas exchange within a plant is a prerequisite for scaling up from leaves to canopies. We evaluated whether leaf traits were reliable predictors of the effects of leaf ageing and leaf irradiance on leaf photosynthetic capacity (V(cmax) , J(max) ) in field-grown vines (Vitis vinifera L). Simultaneously, we measured gas exchange, leaf mass per area (LMA) and nitrogen content (N(m) ) of leaves at different positions within the canopy and at different phenological stages. Daily mean leaf irradiance cumulated over 10 d (PPFD(10) ) was obtained by 3D modelling of the canopy structure. N(m) decreased over the season in parallel to leaf ageing while LMA was mainly affected by leaf position. PPFD(10) explained 66, 28 and 73% of the variation of LMA, N(m) and nitrogen content per area (N(a) ), respectively. Nitrogen content per unit area (N(a) = LMA × N(m) ) was the best predictor of the intra-canopy variability of leaf photosynthetic capacity. Finally, we developed a classical photosynthesis-stomatal conductance submodel and by introducing N(a) as an input, the model accurately simulated the daily pattern of gas exchange for leaves at different positions in the canopy and at different phenological stages during the season.

Extrafoveal choroidal neovascularization secondary to wet age-related macular degeneration treated with intravitreal bevacizumab.

Considering the risk of recurrence of extrafoveal or juxtafoveal lesions after thermal laser treatment and the risk of poor response to photodynamic therapy, it seems reasonable to discuss with the patient the risks and benefits of antiangiogenic therapy. A case of age-related macular degeneration with an extrafoveal choroidal neovascularization treated with a single injection of intravitreal bevacizumab is described. The patient showed both anatomic and visual acuity improvement at 1 month following treatment that persisted even at the 8-month follow-up visit. Further studies are needed to validate the real risk-benefit ratio of intravitreal bevacizumab for extrafoveal exudative lesions versus the current treatments available.