Abstract
Glycine soja (BB52) is a wild soybean cultivar grown in coastal saline land in Yellow River Delta, China. In order to reveal the physiological mechanisms adapting to salinity, we examined photosynthesis, ion flux, antioxidant system and water status in Glycine soja under NaCl treatments, taking a cultivated soybean, ZH13, as control. Upon NaCl exposure, higher relative water content and water potential were maintained in the leaf of BB52 than ZH13, which might depend on the more accumulation of osmotic substances such as glycinebetaine and proline. Compared with ZH13, activities of antioxidant enzymes including superoxide dismutase, catalase, ascorbate peroxidase and contents of ascorbate, glutathione and phenolics were enhanced to a higher level in BB52 leaf under NaCl stress, which could mitigate the salt-induced oxidative damage in BB52. Consistently, lipid peroxidation indicated by malondialdehyde content was lower in BB52 leaf. Photosynthetic rate (Pn) was decreased by NaCl stress in BB52 and ZH13, and the decrease was greater in ZH13. The decreased Pn in BB52 was mainly due to stomatal limitation. The inhibited activation of rubisco enzyme in ZH13 due to the decrease of rubisco activase content became an important limiting factor of Pn, when NaCl concentration increased to 200 mM. Rubisco activase in BB52 was not affected by NaCl stress. Less negative impact in BB52 derived from lower contents of Na+ and Cl- in the tissues, and non-invasive micro-test technique revealed that BB52 roots had higher ability to extrude Na+ and Cl-. Wild soybean is a valuable genetic resource, and our study may provide a reference for molecular biologist to improve the salt tolerance of cultivated soybean in face of farmland salinity.
Highlights
At present, more than 800 million hectares of lands are affected by salinity in the world and in particular, farmland salinity has become a severe agricultural problem due to unreasonable irrigation and fertilization [1,2]
Photosynthetic rate (Pn), Gs, carboxylation efficiency (CE), E and ΦPSII decreased with increasing NaCl concentration in ZH13 and BB52, and they were higher in BB52 than in ZH13
Salt stress had no significant effect on total rubisco activity in BB52, but when NaCl concentration rose to 200 mM, significant decrease in total rubisco activity appeared in ZH13 (P < 0.05) (Figure 2B)
Summary
More than 800 million hectares of lands are affected by salinity in the world and in particular, farmland salinity has become a severe agricultural problem due to unreasonable irrigation and fertilization [1,2]. G. soja can be considered as a valuable genomic resource for improving salt tolerance of cultivated soybean species by molecular biology means. Up to now, it has been reported about the salt tolerance in G. soja with higher root extrusion and less accumulation in tissues of Na+ and Cl- [21], the systematic salt-adaption physiological mechanisms have not been comprehensively studied in G. soja. We intended to systematically diagnose these mechanisms in G. soja from the aspects of root ions flux, antioxidant system, osmotic regulation and photosynthesis, and the results can enrich the knowledge of plant salt tolerance and may provide a reference for genetic improvement of salt tolerance in cultivated soybean
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