Expression of Storage Protein Genes in Developing Wheat (Triticum aestivum L.) Seeds

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Abstract
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.

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