Cytochemical Study of Cell Cycle Parameters in Two Cultivars ofHelianthus AnnuusL. Dry Mass Increase as a Possible Factor Regulating Cell Cycle Duration

Abstract

SUMMARYIn root meristem cells of two cultivars of Helianthus annum L., which slightly differ in 2C DNA content, a comparison was made on the following parameters: heterochromatin content, duration of the cell cycle and of some of its particular phases, growth and sizes of cells in the course of interphase, frequency of proliferating cells, RNA, protein and dry mass content in nucleus, nucleolus and cytoplasm, as well as the content of condensed chromatin in consecutive phases of the cell cycle. It was found that in cv. Pionier—which is characterized by lower content of DNA and heterochromatin, smaller cells and a greater increase in dry mass and protein during the G2 phase—the cell cycle lasts 14 h, whereas in cv. Jadalny it lasts 10 h. In both cultivars, the content of condensed chromatin and RNA is similar. The frequency of ring nucleoli increases at the G1/S, S/G2, and G2/M transitions of the cell cycle. It is assumed that an increase in dry mass content may play the role of regulatory factor of the ce...