Abstract
The exposure to continuous light causes a rise of the mitotic index in the successive generations of the antheridial filaments of Chara vulgaris, whereas culture in darkness leads to a considerable depression of mitosis, and if prolonged, to its complete cessation. Light reverses the effect of the depression of mitosis caused by darkness: in the 16-, and 32-cell generations mitotic activity reappeares as early as after 3 h, but in the 2-, 4-, and 8-cell generations only after 18 h. The size of the cells in the antheridial filaments of plants exposed to continuous illumination is larger as compared with the control material. After being kept in darkness the cells become smaller. The analysis of the size of the latter suggests the inhibition of growth in initial and final periods of interphase. In all generations continuous light reduces the duration of the cell cycle while darkness protracts it. The duration of S phase is similar in all generations of antheridial filaments (ca. 16 h) and is not modified by the light conditions. Thus, the light factor seems to interfere mainly with G2 phase, and its role in the regulation of the cell cycle is correlated with the duration of this phase. The role of light in the kinetics of the cell cycle of the particular generations of antheridial filaments in Chara is discussed in the aspect of the nutritional requirements of cells, hormonal regulation and phytochrome.
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