Expression of Storage Protein Genes in Developing Wheat (Triticum aestivum L.) Seeds: Correlatin of RNA Accumulation and Protein Synthesis

Ribonucleic acid and protein synthesis in developing wheat kernels have been studied through in vivo labeling of wheat heads in culture. In INIA 66R wheat labeled with [5-3H]uridine for 24-hour periods between 9 and 33 days after flowering, the total rate of RNA accumulation in endosperm/testa pericarp tissues was highest in the youngest seeds, and declined with increasing seed age. In contrast, the rate of accumulation of poly(A)+ RNA approximately doubled between 12 and 15 days after flowering, reached a maximum between 15 and 18 days, and declined to half the maximum rate by 24 days. Protein synthetic capacity, measured by in vitro translation of extracted seed RNA, increased in a developmental pattern similar to that of poly(A)+ RNA accumulation, but remained near maximal through 24 days after flowering. Gliadins were prominent in the in vitro translation products. When seed protein was labeled in vivo with L-[3H]leucine, extracted, and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a significant change in the protein synthesis profile was apparent between 12 and 15 days after flowering, and was coincident with a marked increase in storage protein synthesis. Qualitatively similar characteristics were exhibited by the cultivar Cheyenne, although in a shorter developmental period. These results are consistent with a direct relation between levels of mRNA and rates of protein synthesis in developing wheat seeds, with a relatively long storage protein mRNA lifetime, and with control of storage protein gene expression primarily at the level of mRNA transcription.