Identification of Factors Linked to Higher Water-Deficit Stress Tolerance in Compared to Other Grain Amaranths and , Their Shared Ancestor.

Water deficit stress (WDS)-tolerance in grain amaranths (, and A. ), and , their presumed shared ancestor, was examined. was the most WDS-tolerant species, a trait that correlated with an enhanced osmotic adjustment (OA), a stronger expression of abscisic acid (ABA) marker genes and a more robust sugar starvation response (SSR). Superior OA was supported by higher basal hexose (Hex) levels and high Hex/sucrose (Suc) ratios in roots, which were further increased during WDS. This coincided with increased invertase, amylase and sucrose synthase activities and a strong depletion of the starch reserves in leaves and roots. The OA was complemented by the higher accumulation of proline, raffinose, and other probable raffinose-family oligosaccharides of unknown structure in leaves and/or roots. The latter coincided with a stronger expression of and in leaves. Increased SnRK1 activity and expression levels of the class II and trehalose phosphate synthase genes, recognized as part of the SSR network in Arabidopsis, were induced in roots of stressed . It is concluded that these physiological modifications improved WDS in by raising its water use efficiency.