Photosynthetic recovery in drought-rehydrated grapevines is associated with high demand from the sinks, maximizing the fruit-oriented performance.

"To understand how grapevine sinks compete with each other during water stress and subsequent rehydration,carbon (C) allocation patterns in drought-rehydrated vines (REC) at the beginning of fruit ripening werecompared with control vines maintained under drought (WS) or fully irrigated (WW). In the 30 days followingrehydration, the quantity and distribution of newly fixed C between leaves, roots and fruits was evaluatedthrough 13CO2 pulse-labeling and stable isotope ratio mass spectrometry. REC plants diverted thesame percentage of fixed C towards the berries as the WS plants, although the percentage was higher thanthat of WW plants. Net photosynthesis (measured simultaneously with root respiration in a multichambersystem for analysis of gas exchange above- and below-ground) was approximately two-fold greater in RECcompared to WS treatment, and comparable or even higher than in WW plants. Maximizing C assimilationand delivery in REC plants led to a significantly higher amount of newly fixed C compared to both controltreatments, already 2 days after rehydration in root, and 2 days later in the berries, in line with the expressionof genes responsible for sugar metabolism. In REC plants, the increase in C assimilation was able tosupport the requests of the sinks during fruit ripening, without affecting the reserves, as was the case inWS. These mechanisms clarify what is experienced in fruit crops, when occasional rain or irrigation eventsare more effective in determining sugar delivery towards fruits, rather than constant and satisfactory wateravailabilities."