Salt adaptability of wolfberry (Lycium chinense) in terms of photosystems performance and interaction

Abstract

At present, photosystems interaction has not been clearly elucidated in halophyte under salt stress. Here, we intended to investigate salt adaptability from photosystems stability and cooperation in a halophytic economic shrub wolfberry (Lycium chinense) by a pot experiment. Under 200 mM NaCl stress, neither PSII nor PSI photoinhibiting occurred according to insignificant changes in Fv/Fm and △MR/MR0, and thus, high tolerance of photosystems was ascertained in wolfberry. Under 300 mM NaCl stress, tremendous increased leaf Na+ content and decreased leaf relative water content induced oxidative stress with significant elevated lipid peroxidation and H2O2 level. Accordingly, PSII and PSI photoinhibition arose upon elevated excitation pressure and declined photosynthetic rate. Earlier PSII photoinhibition restricted electron flow to PSI in line with delayed PSI oxidation in 820 nm reflection transient at day 7. The restricted electron flow helped defend PSI photoihibition, as the simulated interception of electron donation from PSII prevented significant decrease in △MR/MR0. After 12 days of 300 mM NaCl stress, PSI photoinhibition occurred, and PSI damage was more serious than PSII because of significant declined ratio of △MR/MR0 to Fv/Fm. PSI vulnerability was verified by shortened PSI oxidation in 820 nm reflection transient at day 14 upon restricted electron donation from PSII. Considering elevated I step and lowered I2 in prompt and delayed chlorophyll fluorescence transients at day 14, respectively, PQ reoxidation was inhibited, implying greater damage on PSI likewise. PSI photoinhibition could elevate feedback inhibition on electron transport and might aggregate PSII photoinhibition. Consistently, the decrease of Fv/Fm was exacerbated upon the simulated suppression on electron transport beyond primary quinone, so that PSI photoinhibition portended the breakdown of entire photosynthetic apparatus. In conclusion, earlier PSII photoinhibition assisted in protecting PSI under severe salt stress, but this function was limited, as PSI photoinhibition could not be prevented under prolonged stress.