Study On Physiological Mechanisms Of Stress Resistance Of Four Tropical Island Reef Plants Under Salt Stress

Tropical island reef plants grow all year round in high saline alkali,high temperature,strong light,drought,strong wind and barren coastal environments.They have evolved a unique and effective stress response mechanism as the mainstay of the island reef ecology.In the new stage of tropical island reef vegetation restoration and coral island greening,a variety of tropical plants have been screened for ecological restoration and have been very effective.Different plants have different adaptability to high-salt environment,and the growth of the same plant in different coastal areas is also different.Studying its resistance mechanism can provide a strong guide for further introduction.In this study,four representative tropical island reef plants were successfully introduced and represented by Scaevola taccada,Clerodendrum inerme,Phyla nodiflora,and Thuarea involuta to study the differences in salt tolerance of different plants and their specific physiological mechanisms under salt stress.The specific results are as follows:1.Under the short-term stress of 14 days,the height of each plant was inhibited to varying degrees,but none of them reached a significant level.The fresh weight and dry weight of roots,leaves and stems decreased with the increase of salt concentration.The root inhibition was the earliest and most obvious.The inhibitory effect of Scaevola taccada and Clerodendrum inerme with the large biomass are more significant.2.Proline(Pro),the important osmotic adjustment substance of 4 plants increased gradually with the aggravation of salt stress,and there were differences between the 4 plants.The Pro of Thuarea involuta accumulated under low salt stress,and the growth rate was the largest;the other three island reef plants accumulate a large amount of Pro moderate under salt stress and high salt stress,and participate in osmotic regulationc with Pro.The Malondialdehyde content of the 4 plants increased with the increase of salt stress,and the growth rate of Scaevola taccada malondialdehyde(MDA)was significantly higher than that of other plants.3.The activities of superoxide dismutase and peroxidase of 4 kinds of plants increased gradually with the increase of salt concentration.The activities of superoxide dismutase(SOD)and peroxidase(POD)of Thuarea involuta were higher than other plants,but the activities of SOD and POD of Scaevola taccada was the lowest.Reduced glutathione,one kind of the antioxidants participates in the removal of reactive oxygen species in plasma membrane,and reduced glutathione(GSH)plays an important role in the removal of ROS of the Scaevola taccada and Phyla nodiflora under high salt stress.The active oxygen(ROS)of Thuarea involuta was induced under low salt stress,but it was suppressed with the increase of salt stress.4.The biosynthesis and activities of Phenylaine metabolism key enzymes of 4kinds of plants were obviously induced by low and medium salt stress.Enzyme activity of Thuarea involuta grew relatively high,but the enzyme activity decreased under high salt stress,which affected the secondary metabolites such as flavonoids to participate in the plant antioxidant effects.The changes of flavonoid content of the 4plants varied with the increase of salt stress.The flavonoid content of Clerodendrum inerme and Thuarea involuta were reduced with the increase of salt concentration.Low salt stress can induce the accumulation of flavonoids in Scaevola taccada,and high salt stress can promote the accumulation of flavonoids in the Phyla nodiflora.5.The Na~+outflow degree of the 4 plants was increased to different degrees with the increase of salt stress.The Na~+outflow of Thuarea involut was the most obvious under the high salt stress.The Na~+efflux weakened under high-salt stress,and a large amount of Na~+accumulated in cells.In the early stage of stress,K~+efflux of Scaevola taccada and Thuarea involuta was increased with the increase of salt stress,but K~+outflow weakened with the increase of salt stress,promoting Na~+efflux and reducing the toxicity.Under salt stress,the trend of K~+outflow was increased in Clerodendrum inerme and Thuarea involuta and the salt damage increased.The smaller the degree of H~+influx,the more obvious the outflow,reflecting the higher H~+-ATPase activity.The H~+-ATPase activity was increased first and then was decreased with the increase of salt stress,while the H~+-ATPase activity of the other 3 kinds of plants was improved with the increase of salt stress.6.Clerodendrum inerme suffered less from the photosynthesis system under salt stress,which can increase the heat dissipation of the antenna pigment through the PSII electron transfer efficiency and protect the integrity of the original reaction site of the photosynthetic organ.Scaevola taccada and Phyla nodiflora suffered the most damage,and the photosynthetic rate was decreased the most,and Scaevola taccada was basically not carried out under high salt stress.The photosynthetic intensity and damage degree of light and photosynthetic components of Thuarea involuta are lighter than those of the first two plants.