Increasing cyclic electron flow is related to Na+ sequestration into vacuoles for salt tolerance in soybean.

Yi He,Kaixing Lu,Jian Hong,Xiaoman Wang,Jianping Chen,Chengqi Yan,Qinsu Jiang,Andrew James,Ligen Xu,Gangping Xue,Dean Jiang,Junliang Fu,Chenliang Yu

doi:10.1093/jxb/erv392

Abstract

In land plants, the NAD(P)H dehydrogenase (NDH) complex reduces plastoquinones and drives cyclic electron flow (CEF) around PSI. It also produces extra ATP for photosynthesis and improves plant fitness under conditions of abiotic environmental stress. To elucidate the role of CEF in salt tolerance of the photosynthetic apparatus, Na(+) concentration, chlorophyll fluorescence, and expression of NDH B and H subunits, as well as of genes related to cellular and vacuolar Na(+) transport, were monitored. The salt-tolerant Glycine max (soybean) variety S111-9 exhibited much higher CEF activity and ATP accumulation in light than did the salt-sensitive variety Melrose, but similar leaf Na(+) concentrations under salt stress. In S111-9 plants, ndhB and ndhH were highly up-regulated under salt stress and their corresponding proteins were maintained at high levels or increased significantly. Under salt stress, S111-9 plants accumulated Na(+) in the vacuole, but Melrose plants accumulated Na(+) in the chloroplast. Compared with Melrose, S111-9 plants also showed higher expression of some genes associated with Na(+) transport into the vacuole and/or cell, such as genes encoding components of the CBL10 (calcineurin B-like protein 10)-CIPK24 (CBL-interacting protein kinase 24)-NHX (Na(+)/H(+) antiporter) and CBL4 (calcineurin B-like protein 4)-CIPK24-SOS1 (salt overly sensitive 1) complexes. Based on the findings, it is proposed that enhanced NDH-dependent CEF supplies extra ATP used to sequester Na(+) in the vacuole. This reveals an important mechanism for salt tolerance in soybean and provides new insights into plant resistance to salt stress.

Highlights

Soil salinity represents an increasingly prominent problem 2001; Munns and Tester, 2008)
PCC 6803 (Tanaka et al, 1997), which showed that enhanced cyclic electron flow (CEF) from the cytosol to PSI via NAD(P)H dehydrogenase (NDH) is essential for the adaptation of cyanobacteria to salt stress
The results show that salt stress induced increases in NDH-H at the mRNA and protein levels under from 4 h to 1 d salt stress in both varieties (Fig. 5)

Summary

Introduction

Soil salinity represents an increasingly prominent problem 2001; Munns and Tester, 2008). Salinity affects plant growth by inducing secondary stresses such as metabolic toxicity, attenuated nutrient acquisition, membrane disorganization, accumulation of reactive oxygen species (ROS), and inhibition of photosynthesis (Hasegawa et al, 2000). Salt tolerance in plants requires three interconnected cellular functions that (i) prevent or alleviate damage, (ii) re-establish homeostatic conditions in the new, stressful environment, and (iii) resume growth, albeit at a reduced rate (Zhu, 2001). Maintaining a high photosynthetic rate is important to protect the photosynthetic apparatus from damage by excess light energy and ROS under stress conditions

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Conclusion