Regulation And Mechanism Of Exogenous Mitigation Substances On Toona Ciliata Under Drought Stress

Toona ciliata Roem.,a deciduous or semi-deciduous tree species of the Meliaceae,is one of the precious fast-growing timber species in the tropical and subtropical regions of China.It is widely distributed in China,but due to its sporadic natural distribution and poor natural renewal ability,it has become a gradually endangered tree species and is classified as a national II key protected wild plant.As a fast-growing tree species,the growth of Toona ciliata is often limited by soil moisture.Drought can not only reduce the yield of Toona ciliata,but also restrict its suitable environment.About half of China’s land area is arid or semi-arid,which puts greater pressure on the survival and growth of Toona ciliata Roem.In order to enhance the artificial cultivation potential of Toona sinensis and expand its planting area,this paper studied the physiological growth characteristics of Toona sinensis under moderate drought stress,and selected three common exogenous drought mitigation substances to study their mitigation effects on drought stress of Toona sinensis,aiming to provide a theoretical basis for the physiological regulation mechanism of Toona sinensis in drought stress habitat and the screening of suitable exogenous mitigation substances.The results are as follows:1.Drought stress can significantly inhibit the growth of Toona ciliata.Among the three mitigation substances,SA could significantly alleviate the growth inhibition caused by drought stress,while MT and Me JA showed plant height inhibition and ground diameter inhibition on Toona ciliata,respectively.SA can effectively maintain the morphology of mesophyll cells under drought stress.2.In the process of physiological regulation of Toona ciliata under drought stress,Proline is an important substance in the osmotic regulation system.SA and MT can significantly increase the content of proline in Toona ciliata leaves under drought stress,while Me JA significantly inhibits the accumulation of proline.The GSH content under drought stress may be the limiting factor in the As A-GSH cycle of Toona ciliata.The three mitigating substances can promote the As A-GSH cycle of Toona ciliata from different aspects.The scavenging effects of three mitigation substances on ROS were different.MT could significantly reduce the content of H₂O₂,but had no obvious scavenging effect on O₂.SA and Me JA could significantly reduce the content of H₂O₂ and O₂.3.The photosynthetic capacity of Toona ciliata was significantly inhibited under drought stress,and the photosynthetic mechanism was damaged to a certain extent.SA has the most significant effect on the promotion of Pn,while Me JA has a significant effect on the gas exchange of Toona ciliata leaves.All three alleviating substances were effective in improving photosynthetic activity of Toona ciliata and had a role in maintaining the operation of the PSII reaction center of Toona ciliata.4.The severity of drought stress on physiology of Toona ciliata was as follows:photosynthetic physiology>antioxidant system>osmotic adjustment system.Chlorophyll,APX activity,Pn and E can be used as reference indexes for evaluating drought resistance of Toona ciliata.Among the three mitigation substances,SA had the best regulating effect on physiology of Toona ciliata under drought stress,and its promoting effect on growth was much higher than that of MT and MJ.5.SA maintains cell morphology and function by regulating cell osmotic potential,promotes the regeneration and accumulation of main substances in the As A-GSH cycle,improves plant antioxidant capacity,maintain a high chlorophyll level,protect the photosynthetic system from damage,and enhance the ability to utilize low light and CO₂ to maintain a high photosynthetic and biomass accumulation capacity to ensure the normal growth of plants;MT can regulate the osmotic system by promoting the accumulation of proline,promote the As A-GSH cycle,have a significant clearance of H₂O₂,and can enhance the photosynthetic capacity of the plant;Me JA has a significant effect on the osmotic regulation of the plant,which can promote the As A-GSH cycle,and has a significant removal effect on O₂.