Light‐Dark Transients in Levels of Intermediate Compounds during Photosynthesis in Air‐Adapted Chlorella

Abstract

The labeling of intermediate compounds and photosynthetic cofactors during photosynthesis and periods of darkness by Chlorella pyrenoidosa in the presence of 32P‐labeled phosphate and 14CO2 have heen investigated. Algae adapted to photosynthesis in air were used, and the level of carbon dioxide was maintained at approximately 0.04 % and at constant specific radioactivity during the course of the experiments. The transient changes which occur in the levels of labeled fructose‐1,6‐diphosphate and in sedoheptulose‐1,7‐diphosphate, and in the corresponding monophosphates when the light is turned off suggest a light activation of the diphosphatase enzymes which decays after about 2 minutes of darkness. It is suggested that a light‐dark switch in enzymic activities permits photosynthesis and glycolysis to occur in light and dark respectively with the same enzymic apparatus. The greatly diminished rate of disappearanec of the carboxylation substrate, ribulose‐1,5‐diphosphate, after about 2 minutes suggests that there is also a light activation of the carboxylation reaction in vivo. Large transient changes in the level of pyrophosphate between light and dark indicate that there may be an unstable cofactor which decomposes to give pyrophosphate during or alter killing of the algal cells. The possibility that this cofactor is involved in an activation of Carbon dioxide for the carboxylation reaction in vivo is suggested. Light‐dark transient changes in labeling of other compounds of the photosynthetic carbon reduction cycle and related compounds were determined, and possible significance of these changes is discussed.(PDF DAMAGED)

Intermediates Of Photosynthesis in Acetabularia mediterranie Chloroplasts

“…The intermediates that were detected, RuDP, HMP, triose phosphate, and PGA all behaved in a similar manner to that reported by Bassham et al (2,13). This further supports observations from other plant sources that chloroplasts fix CO2 by this pathway (9,20).…”

Enhanced Dark CO2 Fixation by Preilluminated Chlorella pyrenoidosa and Anacystis nidulans

“…The (14) came to this conclusion when investigating light-dark transients during photosynthesis in Chlorel1a. Alternatively, it may be that the hexose and pentose phosphates formed in the cytoplasm cannot penetrate the photosynthetic apparatus.…”

“…An "absoluite" light-dark switch controlling the activitv of riibulose 5-P kinase is unlikelx since at least 2 groups have demonstrated sufficient ribulose 5-P kinase in extracts of photosynthetilc organisms kept in darkness to catalyze the observed rates of CO, fixation (16,17 2-fold higher in illuminated leaves ov-er that fotund in the dark coiitrol (E. Latzko, uinpiublished observations). 'Most likely AT P prodiuced in the chloroplast duiring the light phase is consume(d rapidlys in kinase and hydrolytic reactionis (8,14) an(l that ATP other thani that produiced h) photophosphorylation canniot be ultilized by the kinase reactions of the photosynthetic carboln reduiction cvcle. We are not aware of any uinequlivocal evi-(lence ( Literature Cited…”

Generation of Reduced Nicotinamide Adenine Dinucleotide for Nitrate Reduction in Green Leaves

“…Such compounds, termed "transport metabolites" (19), could provide the carbohydrate link that associates light with nitrate reduction. (That is, the migration of the phosphorylated sugars into the cytoplasm would provide the substrates necessary for the generation of NADH by the predominantly cytoplasmically located NAD-dependent 3-PGAId dehydrogenase [16,32,39]). …”