The Biological Basis Of Leaf Morphogenesis Of Zygophyllum Xanthoxylon

Leaves are important part of plant morphology and structure.As an important nutrient organ of green plants,leaf has strong plasticity.External environmental factors and internal genetic factors together affect leaf morphology and leaf properties.Zygophyllum xanthoxylon(Bunge)Maxim.is a strong xerophytic plant with two fleshy leaflets and an incompletely developed terminal leaflet.The dry and salty environment where Zygophyllum xanthoxylon grows may be the reason for shaping this leaf trait.In this study,Z.xanthoxylon was used as the material to research the development and growth of its leaves;We also compared the differences in morphological structure and physiological indexes of Z.xanthoxylon under the conditions of no-Na Cl treatment and appropriate amount of Na Cl treatment,as well as different moisture conditions of 60%?80%,40%?60%,and 20%?40%.Follows are results of the study:(1)In the growth from leaf primordium to mature leaf,the development of the terminal leaflets and lateral leaflets of Z.xanthoxylon is different.Lateral leaflets can develop and grow normally.After a series of divisions and differentiations,leaves with complete structure and function are formed.However,in the early developmental stage of the terminal leaflet,the cell protoplast concentration decreases and the cells stop differentiation,eventually forming a leaf with incomplete polarity development and insignificant differentiation of mesophyll cells.(2)The anatomical structure of mature leaves with different branch ages is different in the original environment.The palisade tissues the young branches are equally distributed in adaxial and abaxial.The small vascular bundles are ring-shaped,and the aquiferous tissue composed of parenchyma cells is located in the center of the leaf;However,the leaves on the old branches are mostly anatomical structures with different components in adaxial and abaxial.Palisade tissues are mainly distributed on the axial side and leaf margin,and small vascular bundles are arranged in an arc on the axial side,and aquiferous tissue are distributed in abaxial.Besides,the arrangement of palisade tissues in leaves is closely related to the distribution of vascular bundles.(3)With the decrease of soil moisture content,leaf length,leaf width,leaf area,stomata opening and stomata length decrease,petiole diameter,leaf thickness,palisade tissue thickness,water storage tissue thickness,cuticle thickness,vascular bundle size and stomata density All have different degrees of increase.Compared to Z.xanthoxylon without Na Cl treatment,50 mmol/L Na Cl treatment can promote the growth of leaves,and make the length,thickness and area of the leaves increase under various water conditions.Na Cl can also enhance the adaptability of Z.xanthoxylon to drought,and reduce the impact of drought on the external morphology and internal anatomical structure of leaves.The leaves of plants without Na Cl treatment under25%?35%moisture conditions are severely shrunk,and the area of the main vessel vascular bundle increased 1 times of the leaves under the condition of 60%?80%moisture;while the leaves of the salt-added group basically maintained their normal shape under this moisture condition,and the area of the main vessel vascular bundle increased by only 1/3.Under different salt and water conditions,there are some changes of the morphological structure in the terminal leaflet of Z.xanthoxylon.The width and thickness of terminal leafletsboth increase under certain drought conditions,which is similar to lateral leaflets.Na Cl treatment also increases the thickness of terminal leaflets.The reduction of soil moisture significantly reduces the length of terminal leaflets(P<0.05),but Na Cl has no effect on the length of terminal lobules.The two conditions of salt and water cannot change the overall development of terminal leaflets.(4)Drought conditions within limits increased the moisture content and fleshiness of leaves,and also increased the activity of PEPCasease and Ru BPCase,and lead to the strengthening of C₄pathway.The right amount of Na Cl can significantly improved the water physiological indicators,chlorophyll and photosynthetic carbon assimilation enzyme activities of leaves.Na Cl can also reduce the impact of leaves in arid environment.In the soil moisture conditions of 60%?80%,40%?60%,and 20%?40%,50 mmol/L Na Cl makes the leaf water content respectively Increased by 19%,11%,19%,and 8%,fleshiness increased by 91%,165%,and 27%,respectively,and total chlorophyll increased by 6%,58%and 26%,respectively,comparing with the plants without Na Cl treatment.Leaves of Z.xanthoxylon do not have the kranz anatomy of C₄plants,but under a certain degree of soil moisture conditions,the activity of PEPCasease was significantly higher than that of Ru BPCase,and the activity ratio of PEPCase to Rubisco was 3:1,which is between C₃plants and C₄plants.It is speculated that Z.xanthoxylon may be an intermediate C₃-C₄ plant.