High Frequencies of Preprophase Bands in Soybean Protoplast Cultures
Protoplasts derived from a non- regenerable soybean cell line provide an excellent experimental system for studying plant preprophase bands (PPBs). Cultured protoplasts developed PPBs in high frequencies, permitting a detailed analysis of PPB development. From observations of thousands of PPBs, six distinct developmental stages were identified. This classification should prove useful in recognizing developmental stages of PPBs and in comparing results among different tissues and species. Perinuclear fluorescence appeared when PPBs were well developed. It consisted of microtubule strands radiating from the nuclear surface at its early stages and more extensive arrays on the surface at later stages. All protoplast cultures from 0.5 day to 5 days had a PPB index (ratio between number of PPBs and number of phragmoplasts) greater than unity, suggesting that in this cell line a high frequency of PPBs is apparently not related to the potential for organized growth (e.g. embryogenesis). Different methods of quantifying the occurrence of PPBs were evaluated. The PPB value (ratio between % of cells with PPB and the mitotic index) was compared with the PPB index and results indicate that it is a useful new parameter for studies of the distribution of PPBs in plant cells.