NDH Complex And Its Role Under Salt Stress In Soybean(Glycine Max.)

Soybean is an important economic crop, and the main source of plant protein and oil for human being. Meanwhile, about 20% available cultivated land and 1/2 irrigation field have been affected by saline at the different levels in the worldwide. Therefore, studying the photosynthetic physiological mechanisms of soybean under salt stress, and improving the ability of stress tolerance and photosynthesis of soybean will be important topic in this research field.Chloroplast NAD(P)H dehydrogenase (NDH) complex is originated from cyanobacteria, and was first found in tobacco. In cyanobacteria and higher plants, NDH complex reduces PQ in the light and is involved in the cyclic electron flow around PSI (CEF1), supplying extra ATP for photosynthesis and enhancing the fitness to environment, particularly under environmental stress conditions. So, in order to define the roles of NDH complex in improving the stress tolerant of soybean, G. max Melrose (cv.Melrose) and somatic hybrid descendants S111-9 were used in our research. According to the analysis by two type of yeast two hybrid, we study the relationships between all subunits that consist of NDH complex, and the relationships between NDH complex and PSI complex. At the same time, we also study the photosynthetic physiological characteristics, activities of CEF1 induced by NDH, the amounts and subcellular localization of NdhB, NdhH and Rubisco in Melrose and S111-9 under salt stress. And results are as follows:According to yeast two hybrid, we first find that NdhB subunit interacts with four hydrophilic subunits NdhH, NdhI, NdhJ and NdhK respectively, NdhH subunit interacts with NdhI and NdhJ, and NdhD subunit interacts with NdhK. Based on these results, we suggest that NdhB subunit is a core subunit in NDH complex and NdhH subunit may be a core subunit in the hydrophilic part of NDH complex. In addition, we also find that a thylakoid transit peptide of ndhB with 36 amino acids in S111-9. And our results first show that PsaA and PsaB, two core subunits in PSI complex, interact with NdhH, NdhI and NdhJ, and NdhH, NdhI respectively.Compared with the phenotype and photosynthetic physiological characteristics in Melrose and S111-9 under salt stress, we find that S111-9 have a higher salt tolerance than Melrose. Meanwhile, the results of photochemical efficiency of PSI and PSII, postillumination transient increase and re-reduction of P700+, which all show that higher activity of CEF1 induced by NDH is the main reason for having high salt tolerance in S111-9. And the results of GFP fusion protein coexpression, the amounts and subcellular localization of NdhB and NdhH, which also infer that the thylakoid transit peptide of ndhB in S111-9 may play an important role in the translocation and localization of NdhB subunit, and resulting in the accumulation of NDH complex, further improving the activity of CEF1 under salt stress. Besides, the results of the amounts and subcellular localization of Rubisco always suggest that the high salt tolerance of S111-9 may be related to the amounts and activity of Rubisco.Meanwhile, we still accidentally find that salt stress will affect the degradation and transport of starch in soybean's chloroplast. Under salt stress conditions, the results of the contents of available phosphorous also suggest that there is a close relationship between the Pi concentrations and the degradation and transport of starch in chloroplast.In conclusion, our results first clarify the interaction relationship between the subunits of NDH complex, NDH complex and PSI complex. Moreover, we also confirm that the CEF1 induced by NDH functions in improving the salt tolerance of soybean. And the function of thylakoid transit peptide of ndhB in S111-9 also will give us a new vision for deeply studying the physiological function of NDH complex.