The Minimum Photon Requirement for Photosynthesis

Abstract

SUMMARYVariations in the apparent photon requirement for photosynthesis (<l>cb,) o"" (^ol) ^^ *^^ ^^^ô f Warburg & Burk (1950) and Yuan, Evans & Daniels (1955) can be ascribed to changes in O2 uptake and energy-dependent processes which result in aberrant photon requirements in organisms subjected to non-optimal conditions. The increase in 05, with increases in the gas exchange quotient (7) in the observations of Yuan et al. (1955) is consistent with increases in photorespiratory production of glycollate, whilst changes in ^5l ^^^ *^CO2 '^ ^^^ results of Warburg & Burk (1950) can be explained by a variable Kok effect associated with nitrate assimilation at low light levels. When these Og and energy-dependent processes are minimal, the lowest values should be observed. The minimum value obtained when Chlorella is photosynthesizing under optimal conditions is 6 mol photons mol"^ Og. These results provide direct independent evidence for a photon requirement for photosynthesis of less than 8 mol photons mol"^ Og. Such a value is not consistent with the Z scheme of photosynthesis.

Photon requirement for O2‐Revolution in red (λ= 680 nm) light for some C3 and C4 plants and a C3–C4 intermediate species*

“…Unlike the data reported by Bjorkman & Demmig (1987) and Evans (1987) a Kok-effect (Kok 1949) was observed with all the species examined. Whilst the reason for this difference is not known it is unlikely to complicate assessments of 0^ in this work, as these were calculated from measurements made above the light compensation point (see Osbome and Geider 1987a). No correlation was found between leaf absorptance or chlorophyll content and 0^ or 0^, consistent with white light determinations made by Bjorkman & Demmig (1987) and Frost-Christensen & Sand-Jensen (1992).…”

Changes in Net O2 Exchange Induced by Inorganic Nitrogen in the Blue-Green Alga Anacystis nidulans

“…the progressive inhibition of respiration by photosynthesis with increasing light intensity (6). The inflection occurs in this case above the light-compensation point, a situation that usually happens when the CO2 concentration is high (10,14). The Kok effect in cyanobacteria has been reported and studied by several groups, the general idea being that it relies on the fact that the respiratory and the photosynthetic electron transport chains are closely linked and even share some of their components, such as the plastoquinone pool or the Cyt b/c complex (1,3,12,13).…”

Oxygenic Photoautotrophic Growth Without Photosystem I

“…Some conclude that the minimal quantum requirement is 5 to 6 hv/O z in wild-type green algae (17,18). Such values, if correct, cannot be explained by the Z scheme as it predicts a quantum requirement of at least 8 hv/O z .…”

“…Pathway studies with the chemical inhibitors 3 [3,4-dichloropheny 1] -1,1-dimethylurea, 2,5-dibromo-3-methyl-6isopropyl-p-benzoquinone, 2-n-nonyl-4-hydroxyquinoline-N-oxide, and carbonyl cyanide-p-trifluoromethoxyphenylhydrazone indicated that in PSII photosynthesis, electron flow from PSII to Fd/NADP + reduction is through the plastoquinone pool and the cytochrome b/f complex (19). When both practical energy loss (such as a loss of about 15% excitations in PSII antenna) and involvement of PSI activity (such as PSI cyclic photophosphorylation) are considered, a quantum requirement (4 hv/O z ) for PSII photosynthesis can explain the reported values of 5 to 6 hv/O z in wild-type green algae (17,18). The previously reported quantum requirement (5 to 6 hv/0 2 ) may suggest that PSII photosynthesis can occur even in wild-type algae.…”