DISSECTION OF THE BLUE-LIGHT-DEPENDENT SIGNAL-TRANSDUCTION PATHWAY INVOLVED IN GAMETIC DIFFERENTIATION OF CHLAMYDOMONAS-REINHARDTII

Gametogenesis of the green alga Chlamydomonas reinhardtii may be viewe d as a two-step process that is controlled by the environmental cues o f nitrogen deprivation and blue light. Initiation of gametogenesis is induced by nitrogen deprivation, resulting in mating-incompetent prega metes, when cells are kept in the dark. For the completion of gametic differentiation light is required. Pregametes were treated with pharma cological compounds to influence the light-dependent conversion to mat ure gametes. Dibutyryl-cyclic 3'5' adenosinemonophosphate, papaverine, and genistein were found to inhibit the progression of gametogenesis in the light. Treatment of pregametes in the dark with either staurosp orine or papaverine resulted in their conversion to mature gametes. Ap parently, papaverine has different effects in the dark and in the ligh t; the effect of staurosporine suggested that a protein kinase C-like component inhibits the conversion of pregametes to gametes, a block th at normally is relieved by illumination. This hypothesis was corrobora ted by the observation that activators of protein kinase C, N-heptyl-5 -chloro-1-naphthalenesulfonamide, (6-phenylhexyl)-5-chloro-1-naphthale nesulfonamide, and the phorbolester phorbol-12-myristate 13-acetate in hibited gametogenesis in the light. Genistein and dibutyryl-cyclic 3'5 ' adenosinemonophosphate were able to inhibit the dark activation caus ed by staurosporine treatment, suggesting that their targets work down stream from the ''protein kinase C-like'' kinase. Surprisingly, stauro sporine and papaverine worked synergystically on the activation of pre gametes in the dark.