Effects of brassinazole,an inhibitor of brassinosteroid biosynthesis,on light- and dark-grown<Emphasis Type="Italic"> Chlorella vulgaris</Emphasis>

Treatment of cultured Chlorella vulgaris Beijerinck cells with 0.1–10 M brassinazole (Brz2001), an inhibitor of brassinosteroid (BR) biosynthesis, inhibits their growth during the first 48 h of cultivation in the light. This inhibition is prevented by the co-application of BR. This result suggests that the presence of endogenous BRs during the initial steps of the C. vulgaris cell cycle is indispensable for their normal growth in the light. In darkness, a treatment with 10 nM brassinolide (BL) promotes growth through the first 24 h of culture, but during the following 24 h the cells undergo complete stagnation. Treatment of dark-grown cells with either Brz2001 alone, or a mixture of 10 nM BL and 0.1/10 M Brz2001, also stimulates their growth. The effects of treatment with 10 nM BL mixed with 0.1–10 M of a mevalonate-pathway inhibitor (mevinolin), or a non-mevalonate-pathway inhibitor (clomazone), were also investigated. Mevinolin at these concentrations did not inhibit growth of C. vulgaris; however, clomazone did. Addition of BL overcame the inhibition. These results suggest that the mevalonate pathway does not function in C. vulgaris, and that the non-mevalonate pathway for isopentenyl diphosphate biosynthesis is responsible for the synthesis of one of the primary precursors in BR biosynthesis.Abbreviations Brz Brassinazole - BL Brassinolide - BR Brassinosteroid - Clo Clomazone - DMAPP Dimethylallyl diphosphate - IPP Isopentenyl diphosphate - MVA Mevalonic acid - Mev Mevinoline