CYTOCHROME f LOSS IN ASTAXANTHIN‐ACCUMULATING RED CELLS OF HAEMATOCOCCUS PLUVIALIS (CHLOROPHYCEAE): COMPARISON OF PHOTOSYNTHETIC ACTIVITY, PHOTOSYNTHETIC ENZYMES, AND THYLAKOID MEMBRANE POLYPEPTIDES IN RED AND GREEN CELLS

Abstract

ABSTRACT Photosynthetic activity, chloroplast enzymes, and poly‐peptides were compared in green and red (ketocarotenoid‐containing) cultures of the microalga Haematococcus pluvialis Flotow. Green cultures, grown at 80 μmol pho‐tons.m‐2. s‐1 in an acetate‐containing medium, had a mean generation time of 27 h. Ketocarotenoid accumulation was induced by transfer of green cultures to PO4‐deficient medium and exposure to 250 μmol photons.m‐2. s‐1. Under these conditions, there was no increase in cell number, and the cultures turned red. Relative amounts of enzymes and thylakoid polypeptides in red and green cells were ascertained by immunoprobing with standardization on a chlorophyll (Chl) basis. In red cultures, the level of cytochrome f was greatly decreased (< 1% of green cell level), which is expected to greatly impair the linear electron flow from photosystem (PS) II to PS I. Also, the levels of apoproteins in red cells, namely, of CPI, D2, CP47, LHC I, and ribulose‐1, 5‐bisphosphate carboxylase were reduced to 15, 18, 29, 48, and 80%, respectively, of those in green cells. Only adenosine triphosphate syn‐thase exhibited no significant change in the two types of cultures. The respiration rate of red cultures was much higher (100 μmoles O2. mg Chl‐1.h‐1) than that of green cells (16 μmoles O2. mg Chl‐1.h‐1). Conversely, net O2 evolution (at Pmax in green cultures was 80 μmoles O2. mg Chl‐1.h‐1 but was —40 μmoles O2. mg Chl‐1.h‐1 in red cultures. PS II activity was demonstrated in broken cells of both green and red cultures, showing activity of 40 and 15 μmoles DCPIP‐mg Chl‐1.h‐1 (with DPC as electron donor), respectively. In contrast, PS I activity measured by the Mehler reaction showed that red rather than green cells had a greater activity (64 vs. 46 μmoles O2. mg Chl‐1.h‐1, respectively). Thus, in spite of the decline of O2 evolution in red cells, the photosystems were still functional. We postulate that the decline of O2, evolution in red cells is largely attributable to an increase in the respiration rate and the impairment of linear electron flow from PS II to PS I and, to some extent, to a decrease in components of the photosystems.