Abstract
Attached leaves of pumpkin (Cucurbita pepo L.) were treated in high or moderate light at room temperature or a 1°C. The symptoms of photoinhibition appearing during light treatments at room temperature could be attributed to a decrease in the primary activity of PSII. However, when the light treatment was given at 1°C, the quantum yield of photosynthetic oxygen evolution decreased much more than would be expected from the decrease in the ratio of variable to maximum fluorescence at 77°K. Also, light treatment at 1°C lowered the chloroplast wholechain electron transfer capacity much more than it affected PSII electron transport (H2O to paraphenylbenzoquinone). Light treatments at both room temperature and 1°C led to an increase in Bmax, which indicates an increase in the proportion of PSIIβ centers. PSI was not affected by the light treatments, and the treatments in the dark at 1°C caused only minor changes in the measured properties of the leaves. We conclude that high light always inhibits the primary activity of PSII, but at low temperature there is greater inhibition of electron transfer from primary electron accepting plastoquinone of PSII to the plastoquinone pool, which leads to a drastic decrease in the quantum yield of oxygen evolution in the chilling-sensitive pumpkin.
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Selected References
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- Arnon D. I. COPPER ENZYMES IN ISOLATED CHLOROPLASTS. POLYPHENOLOXIDASE IN BETA VULGARIS. Plant Physiol. 1949 Jan;24(1):1–15. doi: 10.1104/pp.24.1.1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Azcón-Bieto J. Inhibition of photosynthesis by carbohydrates in wheat leaves. Plant Physiol. 1983 Nov;73(3):681–686. doi: 10.1104/pp.73.3.681. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Melis A., Homann P. H. Heterogeneity of the photochemical centers in system II of chloroplasts. Photochem Photobiol. 1976 May;23(5):343–350. doi: 10.1111/j.1751-1097.1976.tb07259.x. [DOI] [PubMed] [Google Scholar]
- Mäenpä P., Aro E. M., Somersalo S., Tyystjärvi E. Rearrangement of the chloroplast thylakoid at chilling temperature in the light. Plant Physiol. 1988 Jul;87(3):762–766. doi: 10.1104/pp.87.3.762. [DOI] [PMC free article] [PubMed] [Google Scholar]