Genotypic Variation for Glycinebetaine Accumulation by Cultivated and Wild Barley in Relation to Water Stress1

Abstract

The accumulation of betaine (glyclnebetalne, N,N,N‐trimethylglycine) in barley (Hordeum vulgate L.) during water stress may be of adaptive value. The objective of this research was to evaluate the variability for betalne level among genotypes of H. vulgare and H. spontaneum C. Koch in preparation for a physiological‐genetic assessment of the adaptive value of betaine accumulation. Betaine was determined using either a pyrolysis/gas chromatographic method or a periodide spectrophotometric assay, specially modified for screening. In controlled environment tests, 339 genotypes were grown to the four‐leaf stage under well‐watered conditions and analyzed for shoot betaine level; 145 of these were also tested under water‐stressed conditions. There were significant differences for betaine level among genotypes, both without and with water stress (approximate ranges of betaine levels: 10 to 40 μmol/g dry wt in well‐watered conditions; 35 to 90 μtmol/g dry wt under stress). The betaine levels of stressed plants were significantly correlated with those of unstressed plants of the same genotype. Thirteen H. vulgare cultivars which were high and low accumulators in controlled environments were grown in the field under simulated dryland conditions and betaine was analyzed in the upper leaves. At the ear emergence stage, significant variation for betaine level was observed among cultivars although there were no significant differences in their water status. Those cultivars that accumulated either high or low levels of betaine in controlled environments accumulated respectively high or low levels in the field, the correlation among cultivars in the two environments was highly significant (r = 0.71). These results indicate that genotypic variability for betaine level is expressed in both controlled environments and in the field, and that this variability is unlikely to be due solely to variability for water status. Physiological‐genetic studies of the adaptive role of betaine may thus be possible.