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Cyclic electron flow and light partitioning between the two photosystems in leaves of plants with different functional types.

ABSTRACT: Cyclic electron flow (CEF) around photosystem I (PSI) is essential for generating additional ATP and enhancing efficient photosynthesis. Accurate estimation of CEF requires knowledge of the fractions of absorbed light by PSI (f_I) and PSII (f_II), which are only known for a few model species such as spinach. No measures of f_I are available for C₄ grasses under different irradiances. We developed a new method to estimate (1) f_II in vivo by concurrently measuring linear electron flux through both photosystems [Formula: see text] in leaf using membrane inlet mass spectrometry (MIMS) and total electron flux through PSII (ETR2) using chlorophyll fluorescence by a Dual-PAM at low light and (2) CEF as ETR1-[Formula: see text]. For a C₃ grass, f_I was 0.5 and 0.4 under control (high light) and shade conditions, respectively. C₄ species belonging to NADP-ME and NAD-ME subtypes had f_I of 0.6 and PCK subtype had 0.5 under control. All shade-grown C₄ species had f_I of 0.6 except for NADP-ME grass which had 0.7. It was also observed that f_I ranged between 0.3 and 0.5 for gymnosperm, liverwort and fern species. CEF increased with irradiance and was induced at lower irradiances in C₄ grasses and fern relative to other species. CEF was greater in shade-grown plants relative to control plants except for C₄ NADP-ME species. Our study reveals a range of CEF and f_I values in different plant functional groups. This variation must be taken into account for improved photosynthetic calculations and modelling.

SUBMITTER: Sagun JV

PROVIDER: S-EPMC6874625 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Cyclic electron flow and light partitioning between the two photosystems in leaves of plants with different functional types.

Sagun Julius Ver JV Badger Murray R MR Chow Wah Soon WS Ghannoum Oula O

Photosynthesis research 20190913 3

Cyclic electron flow (CEF) around photosystem I (PSI) is essential for generating additional ATP and enhancing efficient photosynthesis. Accurate estimation of CEF requires knowledge of the fractions of absorbed light by PSI (fI) and PSII (fII), which are only known for a few model species such as spinach. No measures of fI are available for C4 grasses under different irradiances. We developed a new method to estimate (1) fII in vivo by conc ...[more]

PMID: 31520186

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Project description:The Antarctic green alga Chlamydomonas sp. UWO241 (UWO241) survives in the deep photoc zone of the permanently ice-covered Lake Bonney in the McMurdo Dry Valleys. The extreme habitat in its natural environment has given way to unique adaptive mechanisms in this halotolerant psychrophile. One of the most striking phenotype of UWO241 is the constitutive upregulation of cyclic electron flow (CEF) around Photosystem I (PSI). This CEF is associated with the formation of a PSI-cytochrome b6f supercomplex that is stable under conditions of high salinity, corresponding to its natural habitat. Although studies have been done to understand the changes in the photosynthetic apparatus associated with increased CEF, not much is known about the purpose of constitutive CEF in UWO241. In this study, we examined the changes in the metabolism associated with increased in CEF and PSI-supercomplex formation in UWO241 under high salinity. Using Electrochomic Shift (ECS) based spectroscopy we identified a higher NPQ and proton motif flux through ATP synthase associated with UWO241 under high salinity. This higher proton flux was associated with high alternative electron transport when plotted against linear electron flow. We also identified several proteins associated with PSI-cytb6f supercomplex in UWO241 that have not been shown before. A Bestrophin-like protein was identified in the whole cell proteome of UWO241 suggesting high capacity for NPQ. Using comparative shotgun proteomics we identified a total of 98 proteins that were significantly affected under high CEF phenotype in UWO241. Out of the 98 proteins, 46 were upregulated and belonged to Calvin cycle, secondary metabolism and translational machinery. Several enzymes in the secondary metabolic Shikimate pathway were upregulated under high CEF phenotype, with one protein involved in downstream indole acetic acid (IAA) biosynthesis upregulated. Metabolomics revealed upregulation of compatible solutes and downregulation of tryptophan in UWO241 under high salinity. We suggest that UWO241 maintains constitutively high CEF with associated PSI-cytb6f supercomplex under native high salinity conditions to rewire its downstream metabolism towards higher carbon fixation capacity and that fixed carbon is utilized to make secondary metabolites necessary for adaptation in its extreme habitat.

Dataset Information

Cyclic electron flow and light partitioning between the two photosystems in leaves of plants with different functional types.

Publications

Cyclic electron flow and light partitioning between the two photosystems in leaves of plants with different functional types.

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