PT  - JOURNAL ARTICLE
AU  - Xinyi Wu
AU  - Sheng Shu
AU  - Yu Wang
AU  - Ruonan Yuan
AU  - Shirong Guo
TI  - Exogenous putrescine alleviates photoinhibition caused by salt stress through increasing cyclic electron flow in cucumber
AID  - 10.1101/301762
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 301762
4099  - http://biorxiv.org/content/early/2018/04/16/301762.short
4100  - http://biorxiv.org/content/early/2018/04/16/301762.full
AB  - When plants suffer from abiotic stresses, cyclic electron flow (CEF) is induced for photoprotection. Putrescine (Put), a main polyamine in chloroplasts, plays a critical role in stress tolerance. To elucidate the mechanism of Put regulating CEF for salt-tolerance in cucumber leaves, we measured chlorophyll fluorescence, P700 redox state, ATP and NADPH accumulation and so on. The maximum photochemical efficiency of PSII (Fv/Fm) was not influenced by NaCl and/or Put, but the activity of PSI reaction center (P700) was seriously inhibited by NaCl. Salt stress induced high level of CEF, moreover, NaCl and Put treated plants exhibited much higher CEF activity and ATP accumulation than single salt-treated plants to provide adequate ATP/NADPH ratio for plants growth. Furthermore, Put decreased the trans-membrane proton gradient (ΔpH), accompanied by reducing the pH-dependent non-photochemical quenching (qE) and increasing efficient quantum yield of PSII (Y(II)). The ratio of NADP+/NADPH in salt stressed leaves was significantly increased by Put, indicating that Put relieved over-reduction pressure at PSI accepter side. Taken together, our results suggest that exogenous Put enhances CEF to supply extra ATP for PSI recovery and CO2 assimilation, decreases ΔpH for electron transport related proteins staying active, and enable the non-photochemical quenching transformed into photochemical quenching.