EXPRESSION OF A WHEAT ADP-GLUCOSE PYROPHOSPHORYLASE GENE DURING DEVELOPMENT OF NORMAL AND WATER-STRESS-AFFECTED ANTHERS

In wheat (Triticum aestivum L.), water deficit during meiosis in the m icrospore mother cells (MMCs) induces pollen abortion, resulting in th e failure of fertilization and a reduction in grain set. In stressed p lants, meiosis in MMCs proceeds normally but subsequent pollen develop ment is arrested. Unlike normal pollen grains, which accumulate starch during the late maturation phase, stress-affected anthers contain pol len grains with little or no starch. Stress also alters the normal dis tribution of starch in the anther wall and connective tissue. To deter mine how starch biosynthesis is regulated within the developing anther s of stressed plants, we studied the expression of ADP-glucose pyropho sphorylase (AGP), which catalyzes the rate limiting step of starch bio synthesis. Two partial-length cDNAs corresponding to the large subunit of AGP were amplified by RT-PCR from anther RNA, and used as probes t o monitor AGP expression in developing anthers of normal and water-str essed plants. These clones, WAL1 and WAL2, had identical deduced amino acid sequences and shared 96% sequence identity at the nucleic acid l evel. In normal anthers, AGP expression was biphasic, indicating that AGP expression is required for starch biosynthesis both during meiosis and later during pollen maturation. AGP expression in stressed anther s was not affected during the first phase of starch accumulation, but was strongly inhibited during the second phase. We conclude from these results that the reduced starch deposition later in the development o f stressed pollen could be the result of a lower expression of AGP. Ho wever, this inhibition of AGP expression is unlikely to be the primary cause of male sterility because anatomical symptoms of pollen abortio n are observed prior to the time when AGP expression is inhibited.