Effects Of Short-term NaCl Stress And Chilling Stress Under Weak Light On Functions Of Photosystems In Leaves Of Two Different Wild Soybeans

Shandong cultivar soybean seedlings (Glycine max (L.) Merr. Zaoshu No. 1), Dongbei wild soybean seedlings (Glycine soja Sieb et Zucc ZYD 00019) and Dongying wild soybean seedlings(Glycine soja Sieb et Zucc ZYD 03262) were used to study photosynthesis, carboxylation efficiency, chlorophyll fluorescence, activities of antioxidant enzymes and changes of Na+ concentration in root, shoot and leaves under short-term NaCl stress. By simultaneously analyzing chlorophyll a fluorescence transient and light absorbance at 820 nm, activities of antioxidant enzymes and glycerolipid compositions of the thylakoid membrane under short-term chilling stress with low light, we studied the salt/chilling tolerance and it's mechanisms of the wild soybeans. The main results are as follows:1. Response to short -term NaCl stress(1) The decrease of photosynthesis was not due to stomatal limiting under short-term NaCl stress in the three soybeans. The simultaneous decrease in carboxylation efficiency further demonstrated that the dark reaction of photosynthesis was inhibited under short-term NaCl stress, which might be the major reason of the photosynthesis decrease in the three soybean seedlings. The Dongying wild soybean seedlings exhibited the slightest decrease in photosynthesis and carboxylation efficiency under the short-term NaCl stress.(2) Actual quantum yield of PSII decreased under the short-term NaCl stress in the three soybean seedlings. The short-term NaCl stress had no significant effect on activities of PSII reaction centers and electron donor side (OEC) in the three soybeans, but damaged PSII electron acceptor side, increasing the accumulation of QA-. Dongying wild soybean seedlings had the slightest accumulation of QA- under short-term NaCl stress.(3) Dongying wild soybean seedlings had the highest activities of antioxidant enzymes and higher Na+ transport efficiency under the short-term NaCl stress, which helped to alleviate the damage of the short-term NaCl stress. (4) The shape of chloroplasts was changed to circular from oval, and the granum stacks twisted under the short-term NaCl stress in the Shandong cultivar soybean leaves whereas, only twisted granum stacks were observed in the Dongbei wild soybean leaves. None of the above changes were observed in the Dongying wild soybean leaves.2. Response to short -term chilling stress with low light(1) The ratio of unsaturated fatty acid in membrane lipids in the two wild soybean leaves was higher than that in the cultivar soybean, which may be related to the higher chilling tolerance in the wild soybeans.(2) Compared with the cultivar soybean, the acceptor side and reaction centers of PSII were less damaged, PSII and PSI matched much better in the two wild soybeans under the short-term chilling stress with low light.(3) The higher activities of antioxidant enzymes in the two wild soybeans under the short-term chilling stress with low light alleviated the damage caused by active oxygen.In conclusion, the wild soybeans were more tolerant to NaCl stress and chilling stress with low light, indicating that they are good resources to improve the stress tolerance of cultivar soybean.