Abstract:The soluble protein content in spikelet of Zhenshan 97A of cytoplasmic male sterile rice decreased rapidly after the formation stage of pollen mother cell (PMC). It was 56%, 34.6% and 30.3% at uninucleate, binucleate and trinucleate stages of pollen, respectively, as compared with that at the formation stage of PMC. The content of soluble protein in maintainer line Zhenshan 97B also decreased, but again increased at pollen binucleate stage which showed a pattern with saddle curve The activity of azocasein protease increased in Zhenshan 97A after the PMC formation stage, whereas less change in activity of this enzyme was found in the maintainer line. The activity of endopeptidase in Zhenshan 97A at the stage of first panicle branch differentiation was higher than that in Zhenshan 97B, and it decreased at the stage of pistil and stamen formation in both the sterile and the maintainer lines. The activity of endopeptidase in sterile line was higher than that in maintainer line by 15% to 55.5% at all developmental stages. At the stage of first panicle branch differelltiation, tile activity of aminopeptidase for tile sterile line was higher than that for the maintainer one. After the stage of PMC formation, the activity of aminopeptidase increased rapidly and reached to the maximum level at pollen trinucleate stage for the sterile line. It may implay that more protein in sterile plants was proteolysised at this stage. The results of protease inhibitor test indicated that aminopeptidase in sterile and maintainer lines after the formation stage of pistil and stamen was of cysteine type with 10% of metalloprotease. However, aminopeptidase in maintainer line at trinucleate pollen stage belonged mainly to the cysteine type. Endopeptidase, BAPA, from sterile line at trinucleate stage showed cysteine- and serine types, and also part of type with metalloprotease, but it was the serine type only in maintainer line. The changes in peptidase types may reflect the derepression of the gene coding of peptidase in cytoplasmic male sterile rice.