Effect of different temperature on starch synthase activity in excised grains of wheat cultivars

Excised grains of wheat (Triticum aestivum) varieties HD 2285 (relatively tolerant) and HD 2329 (susceptible type) were incubated for 1 hr at 15 degrees, 25 degrees, 35 degrees and 45 degrees C. In an another treatment, excised grains were incubated for 1 hr at increasing temperature (15 degrees, 25 degrees, 35 degrees and 45 degrees C) continuously, thus exposing the grains to gradual rise in temperature. The above treated grains were then analysed for the activity of soluble starch synthase (SSS) and granule bound starch synthase (GBSS) assayed at 20 degrees C. SSS activity decreased as the pre-exposure temperature was higher, though the tolerant variety showed lesser decrease. Decrease in SSS activity was lesser when excised grains were exposed to gradual rise in temperature from 15 degrees to 45 degrees C as compared to direct exposure to 45 degrees C. Pre-exposure of excised grains to different temperatures however, had no significant effect on GBSS activity.