Abstract
Temperature has a major impact on plant development and growth. In temperate climates, the seasonal temperature displays large variations that can affect the early stages of plant growth and development. Sessile organisms need to be capable of responding to these conditions, so that growth temperature induces morphological and physiological changes in the plant. Besides development, there are also important molecular and ultrastructural modifications allowing to cope with different temperatures. The chloroplast plays a crucial role in plant energetic metabolism and harbors the photosynthetic apparatus. The photosynthetic light reactions are at the interface between external physical conditions (light, temperature) and the cell biochemistry. Therefore, photosynthesis requires structural flexibility to be able to optimize its efficiency according to the changes of the external conditions. To investigate the effect of growth temperature on the photosynthetic apparatus, we followed the photosynthetic performances and analyzed the protein and lipid profiles of Lepidium sativum (cress) grown at three different temperatures. This revealed that plants developing at temperatures above the optimum have a lower photosynthetic efficiency. Moreover, plants grown under elevated and low temperatures showed a different galactolipid profile, especially the amount of saturated galactolipids decreased at low temperature and increased at high temperature. From the analysis of the chlorophyll a fluorescence induction, we assessed the impact of growth temperature on the re-oxidation of plastoquinone, which is the lipidic electron carrier of the photosynthetic electron transport chain. We show that, at low temperature, along with an increase of unsaturated structural lipids and plastochromanol, there is an increase of the plastoquinone oxidation rate in the dark. These results emphasize the importance of the thylakoid membrane composition in preserving the photosynthetic apparatus under non-optimal temperatures.
Highlights
Plant metabolism must respond to daily and seasonal temperature variations
The changes in the non-photochemical quenching (NPQ) are symmetrically reflected in the quantum yield of photosystem II photochemistry ( PSII, Figure 2B)
The plants grown at 30◦C had constantly a lower yield of PSII compared to the control growth temperature
Summary
Photosynthesis, which is the main energetic process allowing plants to produce organic carbon, chemical energy, and reducing power, is no exception. Light energy conversion requires a series of pigment– protein complexes, namely photosystem II (PSII), cytochrome b6f (Cytb6f ), and photosystem I (PSI). These complexes are functionally connected constituting an electron transport chain (Rochaix, 2011). The electrons obtained from the water-splitting reaction at PSII are transferred to plastoquinone (PQ), which is reduced to plastoquinol (reduced PQ). Reduced PQ diffuses into the membrane until Cytb6f This complex oxidizes the reduced PQ, splitting the two electrons obtained from the oxidation, one toward the plastocyanin and the other to a second PQ molecule. The water-splitting and the cycle of the PQ during the electron transport increase the proton concentration in the thylakoid lumen generating a pH gradient across the membrane ( pH)
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