Effect Of Exogenous Brassinolide On The Salt-Tolerance Of Robinia Pseudoacacia Seedlings

Soil salinization is one of the major abiotic stresses limiting the growth of trees. Improving salt tolerance is an important task of scientific and technical workers on forestry. Brassinolide is one of the six plant hormones, which can promote plant growth and increase plant resistance. In this experiment, Robinia pseudoacacia is used as the test material, using different concentrations of Brassinolide for seed soaking, root soaking and spraying leaf, to study the impact of exogenous brassinolide on the morphological index, physiological index, fluorescent characteristic and leaf ultrastructure of Robinia pseudoacacia seedling under salt stress, to explore the impact of different application process and concentration of brassinolide on the salt tolerance of Robinia pseudoacacia, to provide theoretical basis for the application in production.The major results are as follows :(1) Through comprehensive analysis of the morphological index, physiological index,chlorophyll fluorescence parameters and leaf ultrastructure, the results showed that brassinolide could improve the salt tolerance of Robinia pseudoacacia seedling effectively. Among the seed soaking, root soaking, spraying leaf methods of brassinolide, root soaking is the optimum application method to increase salt tolerance. In root soaking, 0.5mg/L is the optimal concentration for improving salt tolerance. The root soaking treatment of 0.5mg/L brassinolide under 50mmol/L, 100mmol/L, 150mmol/L, 200mmol/L salinity can significantly reduce the salt injury index of Robinia pseudoacacia seedling, with the reduction degree of 100%, 57.60%,63.40% and 53.21% respectively.(2) The root soaking treatment of brassinolide inhibits the growth of Robinia pseudoacacia seedlings, but it promotes the growth of ground diameter growth, so that seedlings are relatively stronger. Soaking treatment can simultaneously promote the height growth and ground diameter growth of Robinia pseudoacacia seedling under salt stress. Spraying leaf treatment promotes the height growth of Robinia pseudoacacia seedling but restrains ground diameter growth.(3) 0.5mg / L brassinolide root soaking treatment can improve the proline content, relative water content,chlorophyll a,chlorophyll b content,total chlorophyll content, the maximum photochemical efficiency(Fv/Fm), effective photochemical efficiency(Fv’/Fm’), actual photochemical efficiency( Φ PSII) as well as non-photochemical quenching(NPQ) and reduce relative electrical conductivity under 50-200mmol/L of salt stress.(4) Brassinolide process can effectively repair or alleviate the harm of salt stress on Robinia pseudoacacia seedlings. Whether it is under 100mmol/L or 150mmol/L salt concentration stress,0.3mg/L of brassinolide root soaking treatment can effectively alleviate the harm of salt stress damage to its structure of mesophyll cells, which is mainly reflected in: protecting comparatively complete chloroplast membrane, allaying thylakoid lamella expansion, maintaing chloroplast against the wall and in normal shape.(5) In the 0.3mg/L brassinolide root soaking treatment, middle salt concentrations(100mmol/L) promotes the production of annulate lamellae, high salt concentration(150mmol/L) inhibits the production of annulate lamellae. In this experiment, the normal conditions of Robinia pseudoacacia mesophyll cell has no annulate lamellae, Robinia pseudoacacia mesophyll cells under 100mmol/L salt stress treatment have a small amount of annulate lamellae, 100mmol/L salt stress +0.3 mg /L brassinolide root soaking treatment has a great deal of annulate lamellae;brassinolide under 150mmol/L salt stress treatment has a small amount of annulate lamellae,150mmol/L salt stress+0.3mg/L brassinolide root soaking treatment causes no annulate lamellae.(6) Under 100mmol/L and 150mmol/L salt stress, under 0.3mg/L brassinolide root soaking treatment, the quantity of starch grain increases, the volume increases, the volume of osmiophilic granule decreases but the quantity of which increases; the black densic material(generally considered as lipids) in the vacuole that disappears in salt stress re-emerges. It showed that under salt stress, the brassinolide promotes the composition of matters in the Robinia pseudoacacia cells and enhances the osmotic adjustment ability.