Effects of light and low temperatures on chlorophyll content and metabolism of Chlorella sorokiniana Shihira and Krauss

Abstract

Chlorophyll bleaching induced by suboptimal temperatures in Chlorella sorokiniana was shown by Marvin and Karlander (5) to require light and molecular oxygen. The present study with various light qualities and quantities showed that bleaching was light intensity dependent and a two-phase process. White fluorescent light was the most efficient in degrading chlorophyll, then in order, blue, incandescent white, and red. Low intensity blue, 2.55–4.0 mW/cm 2, and red light, 2.8 mW/cm 2, produced an initial decline in chlorophyll more rapid than higher intensities of blue or red light. The low intensity blue and red light curve also showed a mid time-course plateau lasting beyond 100 hr. No mid time-course plateau occurred at low intensities of fluorescent or incandescent white light. Oxygen evolution declined with increasing time of incubation at 10°C. Blue light of 4.0 mW/cm 2 was least destructive, extending the duration of oxygen evolution to nearly 4 times that obtained with white light. Cells incubated at temperatures greater than 22°C exhibited patterns of photosynthesis and respiration approaching those of control cells at 39°C. Cells incubated at temperatures less than 22°C showed patterns approaching those of cells subjected to bleaching at 10°C. Hill activity was destroyed during the initial lag phase before much loss of chlorophyll had occurred. Viability of cells was more closely associated with loss of chlorophyll in the accelerated bleaching phase.