VARIATION IN PROTEIN AND RNA-SYNTHESIS ACTIVITY IN ISOLATED-MITOCHONDRIA OF THE DEVELOPING RICE (ORYZA-SATIVA L.) PANICLE

We have studied variation in mitochondrial protein and RNA synthesis d uring the development of a specialized rice (Oryza sativa L.) reproduc tive organ in a bacteria-free environment. Mitochondria were prepared from the maturing panicle during microsporogenesis when meiosis occurr ed and from etiolated seedlings at two growth stages. We found (1) tha t there was no discernible qualitative difference among the polypeptid es synthesized by these three mitochondrial samples; (2) that the quan tity of proteins synthesized by panicle mitochondria was approximately 3 times that of the seedling mitochondria, while the two seedling sam ples exhibited only a minor quantitative difference; (3) that panicle and seedling mitochondria samples synthesized qualitatively the same R NA but at distinctly different rates and that more RNA products were s ynthesized by panicle than by seedling mitochondria. These results, ta ken together, suggest that either the regulation of mitochondrial tran scription and translation or the copy number of mitochondrial DNA per mitochondrion change discretely in the developing panicle and conseque ntly that the level of mitochondrial gene expression increases conside rably during the development of the reproductive structure in rice.