Synthesis and deposition of coixin in seeds of Coix lacryma-jobi

Abstract

The synthesis and assembly of prolamins into protein bodies of Coix lacryma-jobi seeds were investigated. Coixins, the Coix prolamins, are grouped into two distinct classes namely α- and γ-coixins. Alpha-coixins are constituted by four size classes, while γ-coixins comprise only one molecular weight class. SDS-PAGE and western blot analysis of prolamins extracted from endosperm during seed development showed that α-coixins are synthesized at earlier developmental stages than γ-coixin. In vitro translation of polysomal RNA attached to protein bodies isolated from mid-maturation endosperm showed that these polyribosomes are highly enriched in coixin messages. Polysomal RNAs isolated from all developmental stages were electrophoresed and probed with cDNA clones representing α- and γ-coixins. The results confirmed the earlier expression of α-coixins and also demonstrated that coixin RNA accumulation in the endosperm occurs mainly at seed mid maturation. Protein bodies isolated from immature endosperm contained all coixin components as determined by SDS-PAGE and western blot analyses. Immunocytochemical analysis by electron and light microscopy revealed that the coixin components are spread all over the protein bodies. The protein bodies are localized in the starchy endosperm cells filling the spaces left by the starch granules. They are surrounded by continuous membranes and are larger than the protein bodies described for maize.