Varying water deficit stress (WDS) tolerance in grain amaranths involves multifactorial shifts in WDS-related responses

In this study, water deficit stress (WDS)-tolerance in several cultivars of grain amaranth species ( Amaranthus hypochondriacus [Ahypo], A. cruentus [Acru] and A. caudatus [Acau]), in addition to A. hybridus (Ahyb), an ancestral amaranth, was examined. Ahypo was the most WDS-tolerant species, whereas Acau and Ahyb were WDS-sensitive. Data revealed that the differential WDS tolerance observed was multifactorial. It involved increased proline and raffinose (Raf) in leaves and/ or roots. Higher foliar Raf coincided with induced Galactinol synthase 1 ( AhGolS1 ) and Raffinose synthase ( AhRafS ) expression. Unknown compounds, possibly larger RFOs, also accumulated in leaves of WDS-tolerant amaranths, which had high Raf/ Verbascose ratios. Distinct nonstructural carbohydrate (NSC) accumulation patterns were observed in tolerant species under WDS and recovery, such as: i) high Hex/ Suc ratios in roots coupled to increased cell wall and vacuolar invertase and sucrose synthase activities; ii) a severer depletion of starch reserves; iii) lower NSC content in leaves, and iv) higher basal hexose levels in roots which further increased under WDS. WDS-marker gene expression patterns proposed a link between amaranth’s WDS tolerance and abscisic acid-dependent signaling. Results obtained also suggest that AhTRE , AhTPS9 , AhTPS11 , AhGolS1 and AhRafS are reliable gene markers of WDS tolerance in amaranth. Highlight Differential water deficit stress tolerance in grain amaranths and their ancestor, Amaranthus hybridus , is a multifactorial process involving various biochemical changes and modified expression patterns of key stress-related genes.