Non-enzymatic antioxidant accumulation as a potential short-term memory mechanism to drought in M2 grapevine rootstock

Recurrent drought events, exacerbated by climate change, pose a growing threat to grapevine productivity and wine quality worldwide. While long-term structural and epigenetic stress memory in grapevine is well documented, the biochemical mechanisms underlying short-term, within-season memory remain poorly understood. This study investigated short-term drought stress memory in the M2 rootstock genotype under controlled growth chamber conditions. Plants were subjected to four treatments - well-watered, early-short drought, late-long drought, and double drought - across two stress periods separated by a full recovery phase. Gas exchange, relative water content, electrolyte leakage, soluble sugars, total polyphenols, flavonoids, and key stress-responsive proteins were monitored throughout the experiment. Results indicate that prior drought exposure conferred no advantage in stomatal regulation or water status management. However, double drought significantly enhanced membrane integrity compared to late-long drought alone, as shown by lower electrolyte leakage, alongside a markedly higher accumulation of total polyphenols and flavonoids. This non-enzymatic antioxidant response was underpinned by accumulation of the enzymes 5-enolpyruvylshikimate-3-phosphate synthase and chalcone synthase during the early-short stress and recovery, suggesting that the shikimate and phenylpropanoid pathways may serve as the molecular imprint of short-term drought stress memory in grapevine.