Differential levels of wheat germ agglutinin (WGA) in germinating embryos of different wheat cultivars in response to osmotic stress

The variability in wheat germ agglutinin (WGA) content of germinating embryos of wheat (Triticum aestivum L.) in response to osmotic stress was studied in nine different cultivars with an objective to study its physiological role in stress adaptation. Germination both in water as well as in 0.75 M mannitol resulted in dramatic decrease in WGA content of the germinating embryos as compared to ungerminated ones in all cultivars except PEW-138, PEW-154, and PEW-299. In these three cultivars, osmotic stress resulted in a dramatic increase in WGA levels relative to ungerminated embryos, thus suggesting that the metabolism of WGA in the germinating wheat embryos of different wheat cultivars is regulated differentially by osmotic stress. The specific WGA content of the ungerminated embryos was substantially higher than the germinating ones, apparently due to increased synthesis of germination associated proteins and increased degradation of WGA in the latter. There was a strong negative correlation (r=-0.772, significant at P less than or equal to 0.001) between germination capacity under stress and stress-induced relative increase in the WGA content. Those cultivars which, relative to water irrigated seedlings, showed higher levels of WGA per embryo in seedlings irrigated with 0.75 M mannitol exhibited lower germination capacity. Based on these results, a possible physiological role of WGA in germination of wheat embryos is discussed.