Response Mechanism Of Zebrina Pendula To Ultraviolet-B Radiation

Sunlight is the main source of energy for the earth,and ultraviolet light is an intrinsic part of sunlight.Its wavelength is short and its energy is high.When ultraviolet-B reaches the ground,it will cause damage to the organism.Therefore,while using solar energy,plants are inevitable to accept UV-B radiation that is harmful to them.In recent years,due to the large-scale emission of HCFCs produced by human activities,the ozone layer in the atmosphere has become thinner,and the UV-B radiation reaching the surface has gradually increased,which has become a global ecological environment problem.Enhancing UV-B radiation can cause a series of damage to plants,such as resulting DNA damage and macromolecular denaturation of proteins;destroying the structure of biological cell membrane,changing its permeability,leading to autolysis of cells;making the content of chlorophyll a and chlorophyll b decreased,the structure of chloroplast is deformed,the arrangement of granules is sparse and disordered,and the activity of photosystem II is inhibited,which affects the photosynthesis efficiency,and further affects the biological processes such as respiration,secondary metabolism,growth and development of plants.Eventually,the plant height,the type and the leaf area will reduce,the leaves will thicken,the wax content of the epidermis will increase,and the biomass will decrease.Then the damage of the plant ultimately causes changes in the structure,function and stability of the ecosystem through the radiation effects of the food chain.In the process of long-term evolution,plants have gradually formed a variety of strategies to protect against UV-B radiation damage,such as photoremediation,excision repair,and so on.Plants adapt or protect against UV-B radiation in the environment through a series of changes in their physiological metabolic activities,and repair structures damaged by ultraviolet light.As a common greening plant,the Zebrina pendula likes sunlight and also shade,it shows strong adaptability to the changes of light.Its leaves and stems will show different colors with different light intensity,and the shape will also change significantly.Therefore,it is an ideal experimental plant for studying plant defense against UV-B radiation.In this paper,the Zebrina pendula were used as experimental materials to study the changes of leaves and stems under three kinds of illumination conditions: shading 50%,artificial sunlight and artificial sunlight+UV-B.The purpose of this study is to explore the mechanism of the Zebrina pendula defense against UV-B radiation through changes in leaf and stem morphology,anthocyanin content and distribution.The results of the research indicate that:1.Under the condition of shading 50%,the leaves of Zebrina pendula are lighter in color,the leaf area is increased,the leaf thickness is thinner,there is no anthocyanin in the upper epidermal cells,and the anthocyanin content in the epidermis cells is decreased,resulting in the color of leaves turns into cyan,the epidermis is shorter and sparse,the surface wax is less,the UV-B blocking rate of the epidermis is low,and the photosynthetic pigment content in the mesophyll cells is less;Under the condition of daylight + UV-B conversely,the area of the leaf is reduced,the thickness of the leaves increases(mainly due to the increase in the thickness of the epidermis and palisade tissue),and the anthocyanin content in the epidermal cells on the leaves increases,making the color of the leaves more red,the epidermal hair grows and the density increases,and the thickness of the cuticle increased,the content of chlorophyll a,chlorophyll b and total chlorophyll increased significantly,and the biomass per unit volume increased slightly.2.Under the condition of 50% shading,the Zebrina pendula has a phenomenon of excessive growth,its internodal length increases,the anthocyanin content in the stem is less,the chlorophyll a,chlorophyll b and total chlorophyll content are lower,so the stem is cyan overall.Under the condition of daylight + UV-B,the plants became shorter,the internode spacing was shortened,the anthocyanin content in the stem was significantly increased,the surface of the stem appeared purple-red spots,and the whole stem appeared red and obviously thickened.In addition,the content of photosynthetic pigment in the stem is also significantly increased,and the biomass per unit volume is increased.In summary,when the UV-B radiation is enhanced,the leaves and stems of the Zebrina pendula are reduced in the amount of receiving UV-B radiation by reducing the leaf area and shortening the internode spacing respectively;reflecting or filtering out part of the UV-B radiation by growing epidermal hair and increasing the thickness of cuticle;by increasing the thickness of the epidermis and the content of anthocyanin to block or absorb part of the UV-B radiation,the UV-B transmittance is effectively reduced,so that the Zebrina pendula can avoid excessive UV-B radiation while also absorb moderate UV-B radiation ensures that it can perform its own necessary physiological metabolic activities normally.Through the above comprehensive defense strategy,the Zebrina pendula effectively avoids the damage of plants caused by UV-B radiation.