The role of vanadium in green plants. III. Influence on cell division of Chlorella.

Vanadium, although essential for growth and chlorophyll formation in unicellular green algae, reveals toxic influences on cell division of Chlorella pyrenoidosa, these disturbances arising in the same range of V-concentrations as the known positive effects of the trace metal. In permanent light, as documented by cell volume statistics, vanadium (4-10(-7) g-at/1 as NH4VO3) causes a significant shift of the distribution maxima to higher values of the algal cell volume, the shift having its optimum at 10(-5) g-at V/1. It is documented in pH-constant liquid culture that this effect is not due to a change of pH in the nutrient medium. Under synchronous conditions of algal cultivation (16:8h), vanadium causes a total arrest of cell division after 3 periods; this stop lasts for the next 3 cycles. Afterwards, asynchronous divisions newly occur and lead to generally larger autospores. Staining of algal cell nuclei revealed an inhibitory V-effect on nuclear division, yielding giant nuclei with multiple sets of chromosomes, and thereby limiting cell division. Under these conditions, Chlorella pyrenoidosa is not synchronizable in presence of vanadium.