Study On The Relationship Of Chlorophyll Fluorescence Characters And Salt Resistance Of Different Salt-resistant Wheat Varieties

Salinity is one of the major abiotic stressors in the world, which affects the plant growth and crop production. The plants which grow in the saline soil are affected by salt stress in different degree. Chlorophyll fluorescence analysis technology is a new in vivo measurement and diagnostic techniques in plant science, and it is based on the photosynthesis theory to detect the subtle impact of various external factors on the plant photosynthesis using the chlorophyll as a natural probe. So it is of great significance to study on how to make use of chlorophyll fluorescence to detect the degree of injury of plants under salt stress and whether there is any relationship between chlorophyll fluorescence characters and salt resistance. Salt-reistant (DK961) and salt-sensitive (LM15) wheat cultivar were used to study the effects of salt treatment on growth and chlorophyll fluorescence parameters. The main results are as follows:1. Effects of NaCl treatment on the growth, water content and soluble solutesNaCl treatment 3 days inhibited the growth of different wheat varieties. Fresh weight and water content of two cultivar shoot treated with NaCl was lower than those of controls, while dry weight did not change significantly. It suggests that wheat seedlings by reducing their initial moisture content, raising the soluble solute concentration of cells to reduce their water potential for maintaining water absorption and avoiding the damage caused by salt stress during the beginning of salt stress. The treatment of NaCl markedly increased leaf Na+ content and reduced K+ content of two varieties leading to a significant increase of the ratio of Na+/K+. It caused a series of damages such as lower chlorophyll content, membrane lipid peroxidation, membrane selective permeability and so on. The result indicated that DK961 is more tolerant to salt tress than LM15.2. Effects of NaCl treatment on osmotic adjustment ability of wheat seedlingsProline and soluble sugar content of two wheat varieties leaves were significantly increased after salt treatment for 3 days. Proline might be the major osmotic adjustment substance in the leaves of wheat during the beginning of salt stress. The rate of accumulation osmolytes of salt-resistant wheat cultivar (DK961) was faster than that of salt-sensitive one (LM15). It was better to regulate cell osmotic potential and maintain osmotic potential of the cells, in order to maintain internal water balance and the normal proceeding of physiological and biochemical process. Osmotic adjustment ability of salt-resistant wheat cultivar (DK961) was significantly higher than that of salt-sensitive one (LM15) under salt stress, which was one of the reasons for higher salt resistnce of the former than the latter.3. Effects of NaCl treatment on chlorophyll fluorescence of wheat seedlings.The treatment with 200 mmol/LNaCl for 3 days has no effect on the Fv/Fm two cultivars. Fo of salt-sensitive wheat cultivar (LM15) seedlings decreased significantly and no obvious changes were observed in that of salt-resistant one (DK961). Salt treatment for 3 days enhanced PSⅡantenna thermal dissipation in the leaves of salt-sensitive wheat cultivar (LM15), but there was no effect on PSⅡpotential activity of two varieties wheat leaves. At the same time,φPSⅡand qP decreased while NPQ increased in various degrees. All the results showed that the treatment of 200 mmol/LNaCl for 3 days was not caused the reaction center inactivation, but photosynthetic electron transfer process was inhibited. The increase of non-photochemical energy dissipation would help the dissipation of excess excitation energy, thus easing the impact of the environment on photosynthesis. Under condition of salt stress, salt-resistant wheat cultivar (DK961) maintained high potential photochemical efficiency, more energy dissipation, thus avoiding the injury from excess light intensity on the photosynthetic apparatus and ensuring the normal photosynthesis, maintaining a more high photosynthetic oxygen evolution rate. To some extent, the propertites of DK961 decribed above improved salt teolerance.4. Effects of NaCl treatment on chlorophyll transient fluorescence of wheat seedlings.Salt treatment had little effect on the chlorophyll transient fluorescence of two wheat varieties seedlings. The results showed the normal O-I-J-P curve, and there was no special inflection point.5. Effects of NaCl treatment on chlorophyll fluorescence of flag leaves of wheat cultivars and the yield.The field experiments showed that there was no effect on Fo and Fv/Fm in flag leaves of salt-resistant wheat cultivar (DK961) under condition of salt treatment for 15-20 days. But Fo of salt-sensitive wheat cultivar (LM15) very significant increased, and Fv/Fm dropped significantly. It indicated that reversible inactivation or irreversible damage of PSⅡreaction center occurred, thus affecting maximal photochemical efficiency of PSⅡ, making some injury to the photosynthetic apparatus. So Fv/Fm could accurately reflect the change of photosynthetic reaction center. Actual photochemical efficiency (φPSⅡ) decreased under salt stress in the leaf of the two wheat varieties.Therefore,φPSⅡcould accurately reflect that the plant was subject to injury or not and the extent of the injury. Comparing with that of the salt-sensitive LM15, fluorescence parameters of salt-resistant wheat DK961 had little changes under salt stress. Inhibited photosynthesis in plants limited the provision of energy and reduction ability for carbon assimilation, further affecting the accumulation of biomass. In the field, LM15 was also more sensitive to salt stress than DK961. It was shown especially in plant height, spike length, grains per spike and 1000-grain weight all significantly reduced. At the same time, the inhibition degree of growth of salt-resistant wheat cultivar (DK961) was significantly lower than that of salt-sensitive one (LM15). Taken together, to some extent, chlorophyll fluorescence parameters are related to salt resistance of wheat cultivars.In conclusion, 200 mmol/L NaCl treatment inhibited the growth of different salt-resistant wheat varieties. Comparing with the salt-sensitive wheat LM15, the salt-resistant wheat DK961 suffered less damage under salt stress. The reason was that not only the salt-resistant wheat cultivar (DK961) had stronger osmotic adjustment ability, but also it could better protect photosystem II from salt injury induced by the salt stress. So it had higher PSⅡactivity and light energy transform efficiency, which could turn the absorbed light energy into chemical energy effectively, and then increased the transmitting rate of photosythetic electrons, thereby enhancing biomass. In one word, there were some relationship between the chlorophyll fluorescence and the salt resistance of wheat cultivars. Therefore, chlorophyll fluorescence of wheat under a certain NaCl concentration might be a useful index to screen salt-resistant cultivars.