SYNTHESIS OF MESSENGER-RNAS CODING FOR ABUNDANT ENDOSPERM PROTEINS DURING WHEAT-GRAIN DEVELOPMENT

The expression of mRNAs encoding major endosperm proteins has been investigated during wheat grain development. The synthesis and accumulation of the most abundant endosperm proteins, the prolamins gliadin and glutenin, high molecular weight (HMW) albumins and non-storage proteins were examined by comparing 2-dimensional separations of in vivo and in vitro synthesized proteins. Major changes occur during early stages of grain development. No prolamin mRNA or proteins were observed at 5 days after flowering (5 DAF), but both can be detected at 10 DAF. The amounts of prolamin mRNAs increase sharply until the mid-developmental phase and then decline, but prolamin proteins continue to accumulate until grain maturity. The mRNA level of different prolamin classes during development was measured using various cDNA clones. Although controlled by genetic loci on different chromosomes, the HMW albumins and the so-called non-storage proteins are also synthesized in a very similar fashion to the prolamins. A common transcriptional control mechanism is therefore likely which coordinates mRNA synthesis at different genetic loci. Differences in levels of proteins accumulated were found however by comparing in vivo and in vitro synthesized gliadins and non-storage proteins suggesting an additional level of control of protein synthesis during grain development.