Supplementary Calcium Overcomes Nocturnal Chilling‐Induced Carbon Source‐Sink Limitations of Cyclic Electron Transport in Peanuts

ABSTRACT ‘Calcium (Ca 2+ ) priming’ is an effective strategy to restore efficient carbon assimilation with undergoing unfavourable cold stress (day/night: 25°C/8°C). However, it is unclear how exogenous calcium strengthens the cyclic electron transfer (CET) to attain optimal carbon flux. To assess the nutrient fortification role of Ca 2+ (15 mM) in facilitating this process for peanuts, we added antimycin (AA, 100 μM) and rotenone (R, 100 μM) as specific inhibitors. Our results revealed that inhibiting CET caused a negative effect on photosynthesis. The Ca 2+ treatment accelerated the turnover of non‐structural carbohydrates, and linear electron carriers while balancing the photosystem I (PSI) bilateral redox potential. The treatment also strengthened the PROTON GRADIENT REGULATION5 (PGR5)/PGR5‐LIKE PHOTOSYNTHETIC PHENOTYPE1 (PGRL1) and the NADH dehydrogenase‐like (NDH)‐mediated CET, with plausible crosstalk between thioredoxin (Trx) system and Ca 2+ signalling, to regulate chloroplast redox homoeostasis. Specifically, exogenous Ca 2+ strengthened the PGR5/PGRL1‐mediated CET by providing sufficient ATP and adequate photoprotection during the long‐term exposure; the NDH‐mediated CET served to alleviate limitations on the PSI acceptor side by translocating protons. This study demonstrated the effectiveness of harnessing optimal nutrient supply, in the form of foliar Ca 2+ ‐based sprays to strengthen the eco‐physiological resilience of peanuts against cold stress.