Abstract
Honeysuckle (Lonicera japonica Thunb.) is a popular landscape plant. This study was to explore leaf photosynthetic characterization with emphasis on the coordination between photosystem II (PSII) and photosystem I (PSI) in tetraploid and its autodiploid honeysuckle (TH and DH) upon salt stress (300 mM NaCl). Leaf photosynthetic rate and carboxylation efficiency in DH and TH were significantly decreased under salt stress, and the decrease was greater in DH. PSII photoinhibition was induced in DH under salt stress, as the maximum quantum yield of PSII (Fv/Fm) was significantly decreased. PSII photoinhibition declined electron flow to PSI, but did not prevent PSI photoinhibition, as the maximal photochemical capacity of PSI (MR/MR0) was significantly decreased by salt stress. According to the significant decrease in PSI oxidation amplitude in the first 1 s red illumination, PSI photoinhibition was more severe than PSII photoinhibition. As a result, PSII and PSI coordination was destroyed. Comparatively, salt-induced photoinhibition did not occur in TH, as no significant change was observed in Fv/Fm and MR/MR0. Consequently, PSII and PSI coordination was not significantly affected by salt stress. In conclusion, TH maintained normal coordination between PSII and PSI by preventing photoinhibition and exhibited higher leaf photosynthetic activity than DH under salt stress. Compared with DH, lower leaf ionic toxicity due to greater root Na+ extrusion and restriction of Na+ transport to leaf might be responsible for maintaining higher leaf photosynthetic capacity in TH under salt stress.
Highlights
Salinity is one of the main abiotic stresses which reduce plant growth and development
Gs and photosystem II (PSII) were significantly decreased in the leaves of tetraploid honeysuckle (TH) and diploid honeysuckle (DH) under salt stress, and the decrease was greater in DH than TH (Figures 2A,B,E)
carboxylation efficiency (CE) in the leaves of DH was significantly decreased at day 3, whereas the significant decrease in CE was not recorded in the leaves of TH until day 11, and the decrease was lower than that in DH (Figure 2D)
Summary
Salinity is one of the main abiotic stresses which reduce plant growth and development. The effects of salt stress on plant photosynthesis have been extensively studied. Rapid PSII photoinhibition under high temperature or high light stress protects PSI from photoinhibition by restricting the electron flow to PSI (Herrmann et al, 1997; Yan et al, 2013a,b; Zivcak et al, 2014). PSI photoinhibition usually arises under chilling stress with low light because of the limited restriction on electron flow to PSI, and in particular, rapid recovery of PSII after chilling stress is detrimental to the recovery of PSI (Zhang et al, 2011). PSII and PSI coordination plays an important role in protecting PSI or even the whole photosynthetic apparatus It is still largely unknown about the interaction between PSII and PSI in plants under salt stress
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