Differential changes in grain ultrastructure, amylase, protein and amino acid profiles between Tibetan wild and cultivated barleys under drought and salinity alone and combined stress

Grain phytochemical profiles were compared in Tibetan wild barley XZ5 (drought-tolerant), XZ16 (salinity/aluminum-tolerant) and cv CM72 (salinity-tolerant) in response to drought and salinity alone and combination (D + S) during anthesis. Total antioxidant capacity assessed by determining ferric-reducing antioxidant potential (FRAP) in grains increased significantly as follows: D + S > drought > salinity, and XZ5 > XZ16 > CM72. A marked increase in the total phenol (TP) from individual and combined stresses was observed in XZ5, while a decrease occurred in CM72. Moreover, the activity of α-/β-amylase in the grains under combined stress was 81.8%/16.9% in XZ5 and 48.6%/18.7% in XZ16 higher than that of CM72. Increases in amino acids, protein content and protein fractions of albumin, globulin, hordein and glutelin were maximised under D + S, with larger values in the Tibetan wild genotypes. Observation with a scanning electron microscopy showed a distinct genotypic difference under D + S; for example, XZ5 and XZ16 maintained a relatively integral starch granule with a greater protein deposit/matrix, while CM72 degraded by pitting. This research expands our understanding of barley drought and salt-tolerance mechanisms and provides possibility of Tibetan wild barley in developing barley cultivars with both tolerance to drought and salinity.