Involvement of sulfoquinovosyl diacylglycerol in the structural integrity and heat-tolerance of photosystem II

To examine the role of sulfoquinovosyl diacylglycerol (SQDG) in thylakoid membranes, we compared the structural and functional properties of photosystem II (PSII) between a mutant of Chlamydomonas reinhardtii defective in SQDG ( hf-2) and the wild type. The PSII core complex of hf-2, as compared with that of the wild type, showed structural fragility when solubilized with a detergent, dodecyl beta- d-maltoside, suggesting that the physical properties of the PSII complex were altered by the loss of SQDG. On the other hand, exposure of the cells to 41 degrees C for 120 min in the dark decreased the PSII activity to 70% and 50% of the initial levels in the wild type and hf-2, respectively, which implies that the PSII activity, in the absence of SQDG, becomes less stable under heat-stress conditions. PSII inactivated to 60% of the initial level by dark incubation at 41 degrees C was reactivated by following illumination even at 41 degrees C to more than 90% in the wild type, but only to 70% in hf-2. These results suggest that PSII inactivated by heat recovers through some mechanism dependent on light, and that SQDG participates in functioning of the mechanism. The conformational disorder of PSII caused by the defect in SQDG might be correlated with the increased susceptibility of its activity to heat-stress.     

Imaging,screening and remote sensing of photosynthetic activity and stress responses

Journal of Plant Research -     

Screening of mutants using chlorophyll fluorescence

Journal of Plant Research - Chlorophyll fluorescence has been widely used for the estimation of photosynthesis or its regulatory mechanisms. Chlorophyll fluorescence measurements are the methods...     

Photoinhibition of Photosynthesis during Rain Treatment: Identification of the Intersystem Electron-Transfer Chain as the Site of Inhibition

Continuous wetness of leaves in the light causes a reductionin the carbon exchange rate (CER) in Phaseolus vulgaris L. [Ishibashiand Terashima (1995) Plant Cell Environ. 18: 431]. In this study,we investigated the initial cause of photoinhibition upon applicationof water, designated rain treatment, and we found a large decreasein the rate of electron transport through the whole chain fromwater to methyl viologen via PSII and PSI. In spite of the decreasein the rate of electron transport, there was no decrease inthe activity of either PSI or PSII when these activities weremeasured separately. The intactness of PSI was also confirmedby the absence of any change in the pho-tooxidizable amountof P-700, the reaction centre of PSI, and the intactness ofPSII was confirmed by measurements of Chi fluorescence. Theresults suggest that the inhibition by the rain treatment, whichoccurs at the site between PSI and PSII, might be a novel typeof photoinhibition, unlike the conventional types of photoinhibitionthat involve PSI and PSII. (Received July 29, 1996; Accepted November 28, 1996)     

Various aspects of inhibition of photosynthesis under light/chilling stress: “Photoinhibition at chilling temperatures” versus “chilling damage in the light”

At chilling temperatures, plants suffer damage to photosynthesis. The sites and the mechanisms involved in this damage differ under different chilling conditions. The current status of our understanding of this damage is reviewed, and how chilling temperatures affect photosynthesis is discussed with emphasis on the role of light and the phase separation of membrane lipids. Recipient of the Botanical Society Award for Young Scientist, 1996