The Effects Of Exogenous Gibberellin On The Seed Germination And Seedling Physiological Characteristics Of Paulownia Under Salt Stress

In the agricultural production and ecological environment,there are more and more attention with the problem of salinization.The area of saline-alkali land and secondary saline-alkali land in China is increasing day by day.Salt stress is one of the main environmental factors restricting the seed germination and seedling growth of plants,and the plant growth environment is harsh.Paulownia is a kind of deciduous tree,belonging to Paulownia family in China.It has excellent characteristics such as wide distribution,rapid growth,excellent material and wide use.It is an important fast-growing economic forest tree in China.But the seeds and seedlings of Paulownia is extremely sensitive to salt.It have important value to study salt resistance of Paulownia for economy and ecology.GA3 exist in higher plants.It is able to transmit information during biotic and abiotic stresses,regulate plant physiological mechanisms and plays an important role in enhancing plant stress.In this study,the effect of exogenous GA3 on seed germination index,biomass,antioxidant enzyme system,MDA content,Pro content,photosynthetic parameters and ions content under salt stress were determined by paper germination test and seedlings hydroponic test.To explore the mechanism of exogenous GA3 response of seeds and seedlings under salt stress at morphological and physiological levels,to explore the important of GA3 in enhancing salt tolerance of Paulownia.It provide a theoretical basis for the application of exogenous GA3 in Paulownia production.The main research results are as follow:(1)Exogenous GA3 effectively alleviated the inhibitory effect of salt stress on Paulownia seed germination.Salt stress significantly reduced the germination rate,germination potential and radical length of Paulownia seeds.Under 0.3%NaCl salt stress concentration,the seed were soaked with 100,200,400,600 and 1000mg·L-1 GA3 for 12 hours respectively,and then germination test.The results showed that the germination effect of 600mg·L-1 was better,and the indexes decreased at 1000mg·L-1,The appropriate concentration of GA3 could promote seed germination,alleviate salt stress damage,and had a concentration effect on Paulownia seeds,showing a low promotion and high inhibition.(2)Exogenous GA3 can effectively alleviate the effect of salt stress on the growth of Paulownia seedlings.Under 150mmol·L-1 NaCl stress,the morphological indexes and biomass index of Paulownia seedlings decreased significantly.After 100,200,400 and 600mg·L-1 foliar spraying of GA3,each index was significantly improve.The leaves and roots had different declines,and the best alleviating effect was at the concentration of 400mg·L-1 GA3,and the indexes decreased at 600mg·L-1.The results showed that exogenous GA3 could alleviate the salt damage to Paulownia seedlings,and the roots system was more sensitive than the leaves.(3)Exogenous GA3 increased the activity of antioxidant enzymes and the content of osmotic regulate substances in Paulownia seed germination and seedlings under NaCl stress.Under salt stress,the activities of SOD,POD and CAT in Paulownia seeds and seedlings decreased,while the content of MDA and Pro increased significantly.GA3 can increase the enzyme activity,reduce the content of MDA,and increase the content of Pro in seeds.The seeds had the best remission effect under the concentration of GA3 at 600mg·L-1,thus the seedlings at 400mg·L-1.The results indicated that plants had different salt tolerance at different growth stages,and had different responses to exogenous GA3 under salt stress.(4)Exogenous GA3 enhanced photosynthesis and stable ion balance under salt stress.Salt stress inhibited the content of photosynthetic pigment and photosynthetic parameters of Paulownia seedlings,increased the content of Na+in leaves and roots,decreased the contents of K+,Ca2+,Mg2+and the ratio of K+/Na+、Ca2+/Na+、Mg2+/Na+.It caused metabolic disorder in plants.GA3 could partially recover chlorophyll,which showed a trend of increasing at first and then decreasing.Salt stress also significant reduced Pn,Gs,Ci and Tr,which increased first and then decreased with the increase of GA3 concentration.These indexes reached the maximum under 400mg·L-1 GA3 treatment,which also stabilized the balance of various ions and was beneficial to plant growth.In summary,Paulownia seeds and seedlings are sensitive to salt.The appropriate concentration of exogenous GA3 can alleviate the damage caused by salt,improve the germination index and the growth index of Paulownia,effectively activate the antioxidant enzyme system,improve the antioxidant capacity of Paulownia,and enhance the salt resistance of Paulownia.At the same time,exogenous GA3 can promote photosynthesis in plant,reduce the inhibition degree of photosynthesis under salt stress,effectively protect the stability of photosynthesis and function,and balance the content of ions,which is the main reason for the enhancement of salt tolerance of Paulownia.