CHLORORESPIRATION - AN ADAPTATION TO NITROGEN DEFICIENCY IN CHLAMYDOMONAS-REINHARDTII

When grown under nitrogen limitation, pronounced chlororespiratory activity develops together with an altered composition of thylakoid membranes in Chlamydomonas reinhardtii. Relative to control cultures, the flash-inhibited, chlororespiration-dependent O2 consumption signal increases 10-fold. Also augmented is the light-sensitive respiratory activity responsible for the "Kok effect," reflecting competitive inhibition of chlororespiratory electron transport by photosystem I. Fluorescence measurements show that the thylakoid plastoquinone pool is extensively reduced in dark-adapted, N-limited cells. Thylakoids of N-limited cells have reduced amounts of cytochrome b6, cytochrome f, and light-harvesting complexes. However, thylakoid-bound NADH-PQ oxidoreductase, with major subunits of 51 kDa and 17 kDa, is increased 7-fold and two novel cytochromes of 34 and 12.5 kDa are highly abundant. Thus, components of photosynthetic and chlororespiratory electron transport pathways are differentially regulated by N availability.