Abstract:

The physiological and anatomical changes in leaves of Poinsettia (Euphorbia pulcherrima) tube-plantlets occurred in the process of transplantation and acclimation were investigated in this paper. Before transplantation and acclimation, leaves of the tube_plantlets were apparently thin and the vascular system was not well developed, and the net photosynthetic rate of the plantlet was low, but the stomatal conductance and transpiration rate of the leaves were relatively high. At the early stage of transplantation, the tube-plantlet was vulnerable to relative low humidity and intense light that could resulted in wilting of leaves due to excess water loss. During the acclimatization, the net photosynthetic rate of the plantlets increased progressively and the stomatal conductance and transpiration rate decreased gradually, accompanied by an increase in the thickness of the leaves and the size of leaf epidermal cells, together with the fully development of vascular system, palisade and spongy tissues in leaves. The results indicated that the acclimatization could greatly improve the photoautotrophic ability of the tube-plantlets, bring anatomical changes to the plantlets in order to avoid excessive leaf dehydration for the gradual adaptation of the plantlets to natural environment.

Key words: Poinsettia (Euphorbia pulcherrima), tube_plantlet, acclimatization, photosynthetic rate, transpiration rate, anatomical structure