Source-sink carbon movements in grapevine under drought stress and following rehydration.

Allocation kinetics of carbon in the different sinks competing in drought stressed and rehydrated grapevines have been investigated. A plant growth chamber for stable isotope labeling has been set in an environmental control system, basing on pulse-chasing isotopic strategy to trace carbon phloem flows. In addition, an open-air plant/soil growth system consisting in twelve independent plant/pot balloons with computing-adjustable air flows allowing continuous gas exchange detection between plants / soil and atmosphere has been set. Water stress led to a drastic decrease in the photosynthesis rate and a decrease in the respiration rate of the soil by about 50%; after rehydration the plants fully recovered the photosynthetic capacity in the morning, while the photosynthetic capacity in the afternoon remained compromised. Sugar accumulation in berries decreased in plants subjected to continuous stress, while the acidity was higher for both plants subjected to continuous stress and rehydrated plants. Grape production was lower in plants subjected to continuous stress. Plants under water stress had a low and constant microbial biomass throughout the season, whereas irrigated and rehydrated plants remained similar in the first days of the experiment, and an explosion of microbial biomass was recorded in plants rehydrated 15 days after rehydration. This may indicate a higher contribution of carbon allocated by the rehydrated plant to the microbial mass of the rhizosphere, thanks to an increase in root respiration. Delivery of labeled carbon in different sinks is discussed in parallel with the expression of genes involved in carbohydrate transport. Genes encoding proteins that regulate the delivery of sucrose to the sinks and which catalyze the hydrolysis of the sucrose discharged to trigger respiration or carbon storage are analyzed.