Abstract: Dioecious sexual system is widespread in woody plants. There are many researches about male and female differences, which has been a hot research topic. In order to provide a reference for the selection of male and female plants in production practice and theoretical study, this article reviewed differences of woody male and female plants in morphology and anatomy, physiology, molecular biology, and chemical defense. In morphology and anatomy, some perennial male plants show taller plant type, bigger leaf and biomass, less damaged organelle under the condition of stresses, and more obvious architectural feature for adapting adverse environment, all of which endow them a growth advantage; However, some female plants possess bigger aboveground biomass, and more obvious xeromorphic leaf, which are important characters in growth. In physiology, most of plants do not behave significant sexual differences in physiological performance under normal condition, but the differences can be significant under adversity condition. Most of male plants show higher photosynthesis, regulating function, protective enzyme activities than female plants under stresses. Endogenous hormones (such as abscisic acid and gibberellin) contents are significantly different in two sexes, and the difference is closely related to growth stage; abscisic acid content is higher in female plants under adversity condition and female plants are sensitive to adversity. In molecular biology, male plants could up-regulate genes expression levels and high expression of some key proteins in response to adverse environment; And most of the genes are related to hormone biosynthesis, photosynthesis, enzyme system of active oxygen removal, and the proteins, involving in electron transfer, photosystem stability, redox equilibrium, and stress response, have higher abundances. Molecular markers of sex-linked genes have been found in some species, and they can be used to sex determination of dioecism. In chemical defense, it has been recognized that defensive substances such as phenols generally are higher and the leaves are tougher in female plants, therefore they have stronger resistance to herbivores. In the sexual difference research, in natural populations the male and female plants have greater genetic differences, and there exist to some degree genetic variation within a family, thus the best materials are the hybrids with fixed parents. Currently, majority of researches on sexual differences principally focus on a certain growth and development stage, and it has been proved that sexual differences are strongly linked to developmental stage. Thus it is necessary to conduct study on different developmental stages to understand the differences more comprehensively. Moreover, sexual differences in physiological and molecular levels should be enhanced, so as to supply theoretical basis for sex determination of dioecious plants.

Key words: woody plant, dioecism, sexual difference