In wheat (Triticum aestivum L.), water deficit during meiosis in the microspore mother cells (MMCs) induces pollen abortion, resulting in the failure of fertilization and a reduction in grain set. In stressed plants, meiosis in MMCs proceeds normally but subsequent pollen development is arrested. Unlike normal pollen grains, which accumulate
starch during the late maturation phase, stress-affected anthers contain pollen grains with little or no
starch. Stress also alters the normal distribution of
starch in the anther wall and connective tissue. To determine how
starch biosynthesis is regulated within the developing anthers of stressed plants, we studied the expression of
ADP-glucose pyrophosphorylase (AGP), which catalyzes the rate limiting step of
starch biosynthesis. Two partial-length cDNAs corresponding to the large subunit of AGP were amplified by RT-PCR from anther
RNA, and used as probes to monitor AGP expression in developing anthers of normal and water-stressed plants. These clones, WAL1 and WAL2, had identical deduced amino acid sequences and shared 96% sequence identity at the
nucleic acid level. 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 anthers 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 of stressed pollen could be the result of a lower expression of AGP. However, this inhibition of AGP expression is unlikely to be the primary cause of
male sterility because anatomical symptoms of pollen abortion are observed prior to the time when AGP expression is inhibited.