Pyruvate orthophosphate dikinase gene expression in developing wheat seeds

The amount of pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1) protein in wheat (Triticum aestivum L. var Cheyenne) grains was determined at different stages of development by the protein blot method. The variation in PPDK protein with time in developing wheat grains was similar to that of the enzyme's activity reported by Meyer et al. (1982 Plant Physiol 69: 7-10). The variation in levels of PPDK mRNA with seed development was determined by analysis of polypeptides immunoprecipitated by anti-PPDK serum from in vitro translation products of extracted seed RNA. This mRNA variation was similar to that of the in vivo enzyme levels and the correlation is consistent with the regulation of PPDK gene expression by the level of its mRNA.

The highest level of PPDK in developing wheat seeds occurs later than the highest levels of both ribulose bisphosphate carboxylase (EC 4.1.1.39) and of chlorophyll, which are located in the green pericarp tissue. PPDK was located in both endosperm and pericarp tissue of the seeds. The tissue location and developmental profile of seed PPDK are consistent with a metabolic role of providing phosphoenolpyruvate as a substrate for recapturing respiratory CO₂ in the seed, and possibly for amino acid interconversions during development.