DGDG Is Essential In Maintaining Plant Photosynthetic Membrane Structure And Function

Arabidopsis thaliana dgdl mutant is a mutant deficient in digalactosyl diacylglycerol (DGDG). Previous studies have revealed that the PSII photosynthetic activity of PSII is reduced in this mutant and some significant changes take place in the structure of photosystem components. By using Arabidopsis thaliana Col-2 and dgdl mutant, this study has mainly focused on the role that DGDG played in the accumulation of important photosystem functional proteins and in maintaining the photosystem complex superstructure. The results obtained here were summarized as follows:1. Compared to the wild type, the dgdl mutant has the characteristics of reduced Fv/Fm, low light saturation point (LSP) and decreased whole-chain electron transport activity, reflecting its low photosynthetic capacity and potential. Moreover, 77K fluorescence emission spectra of thylakoid membranes showed a slight blue shift of the PSI emission maximum and an increase in the ratio of F₆₉₅/F₇₃₀ in the dgdl mutant. These can be interpreted as suggesting the possible changes in the photosystem structure.2. Compared to the wild type, the dgdl mutant has the decreased PSII electron transport activity, and the photoinhibition and recovery experiments have showed that more severe photoinhibition under high light and low recovery level has occurred in the dgdl mutant, which possibly suggests that the mutant might have increased photosensitivity of PSII. In addition, experiments revealed the low accumulation of PSII reaction center proteins Dl and D2 in the dgdl mutant — the expression of Dl is limited at both transcription and translation level, which reflect that certain changes have taken place in the structure of PSII.3. Blue native polyacrylamide gel electrophoresis (BN-PAGE) analysis of thylakoid membrane protein complexes has revealed that a new PSI subcomplex occurred in the dgdl mutant. Based on the results of Chaotropic salt extraction of thylakoid membranes experiment, together with the fact that the accumulation of PSI subunits were equally reduced, it can be concluded that the detectionof the PSI subcomplex in the mutant is most likely due to impaired stability of these subunits in the dgdl mutant.4. Although the above findings could support that DGDG plays an important role in maintaining normal photosynthetic structure and function, further studies are needed to illustrate that whether the altered MGDG/ DGDG ratio has also had impact on the changed photosystem structure and the reduced photosynthetic ability of the mutant.