Blue Light Enhanced Respiratory Activity Under Photosynthetic Conditions In Chlorella; A Mass Spectrometric Analysis

Mass spectrometric analysis shows that blue light enhances oxygen uptake during photosynthesis in Chlorella fusca. Assays in which all of the normal 16O2 of air has been substituted by 18O2 permit discrimination between photosynthetic O2-evolution (measured as 16O2, i.e. mass 32) and O2-uptake (measured as 18O2, i.e. mass 36). A chlorophyll-free Chlorella kessleri mutant for which in earlier studies the occurrence of blue light enhanced oxidative carbohydrate degradation has been demonstrated (W. Kowallik, H. Gaffron, Planta 69, 9 2 -9 5 (1966); W. Kowallik, Ann. Rev. Plant Physiol. 33, 5 7 -7 2 (1982)) has been used for comparison in the present study. The light intensity dependencies of the observed effect seem to differ in mutant and wild type cells. In the mutant a fluence rate of 1 .5 -2 .0 (μE m -2·s-1 of blue light yields saturation, whereas in the wild type even ten times this value does not. A wavelength dependence of the effect measured with equal fluence rates at 422 nm, 457 nm, 488 nm, 555 nm and 649 nm shows maximal efficiency around 460 nm and no significant effect of red light. This agrees with earlier studies on the chlorophyll- free mutant. As a result of this correspondence, we think that the enhanced oxygen uptake during photosynthesis concerns oxidative carbohydrate degradation. The putative mechanism and significance of the observed blue light enhanced respiration in photosynthesizing Chlorella are discussed