INDUCTION OF MALE-STERILITY IN WHEAT BY MEIOTIC-STAGE WATER-DEFICIT IS PRECEDED BY A DECLINE IN INVERTASE ACTIVITY AND CHANGES IN CARBOHYDRATE-METABOLISM IN ANTHERS

Water deficit during meiosis in pollen mother cells of wheat (Triticum aestivum L.) induces male sterility, which can reduce grain set by 40 to 50%. In plants stressed during meiosis and then rewatered, divisio n of pollen mother cells proceeds normally but subsequent pollen devel opment is arrested 3 or 4 d later. An inhibition of starch accumulatio n within the pollen grain suggested that an alteration in carbohydrate metabolism or assimilate supply may be involved in pollen abortion. W e measured levels of various carbohydrates and activities of key enzym es of Suc metabolism and starch synthesis at different stages of polle n development in anthers collected from well-watered and water-stresse d plants. Compared to controls, soluble sugars increased in anthers st ressed during meiosis, then decreased at later poststress stages. Sucr ose and myoinositol accounted for part of the sugar accumulation. The activity of soluble acid invertase declined 4-fold during the stress p eriod and never recovered thereafter. Sucrose synthase activity during starch accumulation in pollen was also lower in the anthers of plants stressed at meiosis. Stress had little negative effect on the activit ies of ADP-glucose pyrophosphorylase or soluble and granule-bound star ch synthase during starch accumulation in pollen, although at the earl ier stages, ADP-glucose pyrophosphorylase activity in stressed anthers was slightly lower compared to controls. The results suggest that car bohydrate starvation per se and inhibition of the enzymes of starch sy nthesis probably were not responsible for the stress-induced pollen ab ortion. Instead, an inability to metabolize incoming sucrose to hexose s may be involved in this developmental lesion.