Manganese (Mn) is an essential element in photosynthesis, acting as a catalyst for water photolysis in photosystem II (PSII). Previous studies have shown that manganese-deficient plants (grown in manganese-depleted media) are more sensitive to photoinhibition and exhibit reduced activity in photosystems I and II.
In a study published in Physiologia Plantarum, two researchers from B3S/I2BC examined the impact of manganese deficiency on the regulation of photosynthetic electron transport. To do this, they used two well-known Arabidopsis thaliana mutants, pam71 and cmt1, which are deficient in Mn transporters. The PAM71 protein is localized in the thylakoid membrane, while CMT1 is found in the inner membrane of the chloroplast envelope.
They quantified the metal content in the thylakoids and leaves of wild-type and mutant plants (using inductively coupled plasma atomic emission spectrometry). In both mutants, manganese content was reduced in the thylakoids, whereas the content of other cations (calcium, copper, magnesium, and iron) was increased.
Several fluorescence parameters were measured as a function of light intensity. The results show that photosystem II is impaired in both mutants, but there are differences in regulation. The pam71 mutant has a reduced ability to dissipate excess light energy through non-photochemical quenching and to perform state transitions, processes essential for balancing light absorption between the two photosystems and optimizing photosynthesis. The cmt1 mutant adapts better and maintains a balance between the two photosystems. Additionally, the relative amount of PSI compared to plastocyanin, a protein essential for electron transport between the two photosystems, is reduced in pam71 but not in cmt1.
Thus, cmt1, unlike pam71, may adapt better to Mn deficiency by maintaining a stoichiometric balance between the components of the photosynthetic chain (PSII, PSI, plastocyanin, cytochrome b6f, etc.), allowing it to retain effective redox and pH control. This stoichiometric balance could be achieved through transcriptional regulation
Contact Institut des sciences du vivant Frédéric-Joliot : anja.liszkay@i2bc.paris-saclay.fr