Distinct root signaling and anatomy associate with convergent leaf responses to drought and salinity in grapevine rootstocks

Drought and salinity seriously threaten grapevine productivity by inducing convergent leaf phenotypes through distinct upstream signals. This study investigated how abscisic acid (ABA) dynamics, root anatomical traits and zeaxanthin epoxidase (ZEP) content influence tolerance strategies in five rootstocks (140 Ruggeri, Kober 5BB, Dog Ridge, M2 and M4) grown in an aeroponic system. Our results reveal that, although both stresses drastically reduce stomatal conductance and net CO2 assimilation, the underlying signalling pathways diverge radically. Drought was closely associated with genotype-dependent accumulation of leaf ABA and increased immunoreactivity of the 65-kDa ZEP band in roots. This was accompanied by marked endodermal suberisation, particularly in M2, M4 and Kober 5BB, favouring a water conservation strategy. In contrast, salinity induced similar physiological declines with minimal ABA induction (except for the high basal levels in 140 Ruggeri), suggesting the dominance of non-hormonal osmotic, ionic and hydraulic constraints. Furthermore, while drought primarily affected water status, salinity triggered plastic remodelling of biomass with increased allocation to the roots. This study demonstrates that leaf phenotypic convergence can mask divergent control architectures modulated by root anatomical traits. These traits help distinguish between water-conservative and water-spending behaviours and provide critical parameters for identifying genotypes with enhanced resilience to environmental stress.