| Populus euphratica Oliv is the only naturally-distributed tall arbor species in arid desert regions of northwestern China and Central Asia.The tolerance to severe drought and high salinity,high alkalinity soil makes it ecologically important in protecting species diversity and maintaining the ecological balance.The long term adaptation to such desert environment induces the formation of heteromorphic leaves of Populus euphratica,and a single adult tree commonly has ploymophic leaves,such as lanceolate,oval and serrated broad-oval leaves.Special research interest has arisen in understanding the eco-adaptability of Populus euphratica for several years.Comparing the structural and physiological characteristics of the heteromorphic leaves and studying on the relative molecular regulatory mechanism would have both theoretical and practical significance in this area.This paper studied three typical heteromorphic leaves of Populus euphratica,including lanceolate, ovate and serrated broad-oval leaves,and mainly focused on the leaves' anatomical structures, physiological characteristics and proteomics.It will greatly help the understanding of cellular and molecular mechanism during leaves development and elucidating the mechanism of the eco-adaptability of Populus euphratica.Environmental conditions bave close relationships with leave growth and development.Different leaf shape and anatomical structure characteristics can reflect its adaptive capacity to its habitats. Experiments were conducted in leaf shape morphology and anatomical structure of Populus euphratica. The results showed that as the leaf shape changed from lanceolate to serrated broad-oval,the leaf width increased,surface area decreased,the level of carnification enhanced,and petiole extended;the serrated broad-oval leaves had the most well-developed subcortex and palisade tissue,as well as the thickest corneum,while lanceolate leaves' xeromorphic structure was not as well-developed as serrated broad-oval leaves.This demonstrated that the serrated broad-oval leaves were more suitable for arid environments survival compared to the other two types of leaves.The capability of tolerating adverse environment and photosynthesis of leaves can be reflected by several physiological indexes,such as the levels of water potential,bound water,osmolyte,and chlorophyll.Those measurements showed that these three types of leaves had the similar amounts of water,but the serrated broad-oval leaves had lowest water potential,the highest level of bound water, osmolyte and chlorophyll,which explained why the serrated broad-oval leaves had strongest capability of photosynthesis and tolerating adverse environment.The soluble proteins of heteromorphic leaves were separated by SDS-PAGE.Established a suitable Tris-HCl buffer:5%β-mercaptoethanol,2%SDS,0.05mol/L Tris-HCl(pH8.8),10%glycerin, 1mmol/L PMSF。The results indicated that protein expressions were different among leaves in different shapes.The more intuitive and comprehensive understanding on the difference in protein expression can be obtained through proteomics research.Establishing a steady method is very crucial in proteomic study in order to assure the reproducibility of the results.In this paper,by optimizing the extraction method of Populus euphratica leaf proteins(7mol/L urea,2mol/Lthiourea,2%CHAPS,60mmol/L DTT,0.2%Bio-lyte) and the conditions of 2-DE,the electrophoretic techniques specific for proteins from leaves of Populus euphratica's was successfully established and high quality 2-DE maps with less tailing,clearly and well distributed protein spots,and high repetition rate were generated,which laid a solid foundation for further proteomics research on Populus euphratica leaves.The lanceolate and serrated broad-oval mature leaves were collected from the same branch,leaf proteins were separated by 2-DE,and differential proteins were analyzed through tandem mass spectrum.Got 73 different protein spots,51 of them are expression more in the serrated broad-oval leave,and the other are expression more in the lanceolate leaves.Through tandem mass spectrum and Mascot search for 24 of them,successfully identified 13 spots,and representative 12 kinds of proteins, which participate in photosynthesis and respiration etc.The results suggested that lanceolate leaves had stronger capability in compounding active chemical energy from using solar energy,such as ATP etc; while serrated broad-oval leaves had stronger capability in carbon assimilation,and it can change active chemical energy into stable chemical energy,such as sucrose,and provide carbon skeleton and energy for plant growth and development.Meanwhile,the serrated broad-oval leaves had more types of proteins that can enhance its capability to tolerate adverse environment,which allowed them to be able to build a new balance system more efficiently and maintain the normal metabolism when stress occurred,and then satisfy the requirements for the adult Populus euphratica surviving in arid region.Through the studies on the differences in anatomy and physiology of heteromorphic leaves in Populus euphratica,this paper provided more comprehensive understanding in the association between the development and eco-adaptability in Populus euphratica heteromorphic leaves:lanceolate leaves had stronger capability in using solar energy,but it had weaker capability of tolerating adverse environment and carbon assimilation.With the trees growth and environment deterioration,the lanceolate leaves can't meet the requirements for the adult trees.Consequently,the serrated broad-oval leaves,which had stronger capability of photosynthetic carbon assimilation and tolerating the adverse environment,took place of the lanceolate leaves and became the main leaf types in adult trees.Populus euphratica heteromorphic leaves can adapt different environment in different developmental stages through the changes of leaf shape,anatomical structure,physiological metabolism and protein expression,which can be presumed as the major reason for Populus euphratica survival in the arid and semi-arid desert region.
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