Cell-cycle-related variation in proteins in suspension-cultured rice cells.

To understand the cell cycle process in plants, we searched for proteins that quantitatively change during the cell cycle in suspension-cultured rice ( Oryza sativa L.) cells. The proteins were analyzed by a two-dimensional polyacrylamide gel electrophoresis image-analysis system. We detected 11 proteins that quantitatively changed during the cell cycle, among which beta-tubulins and a calreticulin-like protein were identified. The amounts of beta-tubulin proteins were low in the M phase and high in the G1 phase. In contrast, mRNAs for two of the three types of beta-tubulin were high in the M phase of the cell cycle. The addition of protease inhibitors MG132 or E64d to the cells decreased the beta-tubulin proteins during 24 h, suggesting that beta-tubulin proteins are degraded in vivo by proteases other than those whose activities are inhibited by MG132 or E64d.

Spatial distribution of the 26S proteasome in meristematic tissues and primordia of rice (Oryza sativa L.).

The 26S proteasome is known to play central roles in the growth of many eukaryotes. However, little is known regarding its distribution in higher plants. Here, we report the spatial distribution pattern of Rpn3 (a regulatory PA700 subunit) and C2 (a subunit of the 20S proteasome) in rice ( Oryza sativa L.) seedlings as determined by in situ hybridization. The transcripts were abundantly co-expressed in the apical and marginal meristems of shoots and roots. Interestingly, these transcripts also accumulated in the leaf and ligule primordia of the shoot apex. Our results suggest that the 26S proteasome is spatially distributed among various tissues and may be involved not only in cell division but also in organ formation in higher plants.