EN
Treatment exposed to light Chlorella vulgaris Beijerinck (Chlorophyceae) with adenine- (BA, Kin, Z) and phenylurea-type (DPU) cytokinins effects positively on alga viability by 1.5- to twofold increase in cell number, chlorophylls, carotenoids, monosaccharides and glycolate content as well as NADH-dependent hydroxypyruvate reducing enzyme activity (NADH-HPR) extensively involved in carbon metabolism. Cytokinins enhance nitrogen assimilation by stimulation of NADH-dependent glutamate dehydrogenase (NADH-GDH) aminating activity finally leading to higher protein level and its secretion as well as polypeptide accumulation in the range of molecular weight 12–195 kDa. In the dark, cytokinins mimic the regulatory effect of light upon algal cell division, metabolite content and stimulate carbon recycling for Calvin cycle reactions by enhancing of light-dependent NADH-HPR activity. The delaying of protein degradation and stimulation of their secretion to environment, triggering polypeptide accumulation and twofold higher NADH-GDH activity catalysing amino acids biosynthesis are observed in the dark-grown microalgae in response to cytokinins. Chlorella vulgaris exhibits sensitivity on cytokinins in the following order of their stimulating properties: DPU > Z > Kin > BA in both light and dark conditions. Understanding of cytokinin role in lower plants under different light conditions could be a step toward the elucidation of the evolution of hormone regulation and their action at molecular level.