Abstract:

The cambium of Populus tomentosa Carr. trees planted in Beijing have entered resuming phase before bud swelling. However, initiation of cambial activity with cell proliferation and increase in immature phloem cells was about a week later than bud sprouting. In active phase, phloem differentiation got rapid before mid-April and then continued up to early September with a slow speed. On the contrary, the xylem production commenced in late April (three weeks after appearance of immature phloem cells) and increased fleetly during June before declining in August. Meanwhile, the appearance of mature xylem cells was about a month later than that of mature phloem cells. Different from results of other researches, the cell number of immature and mature xylem of Populus tomentosa Carr. increased rapidly between late April to late June as cambium and immature phloem declined. The cambial tissue entered dormant phase from late September and remained till the following spring. After electrophoresis, there were totally eight peroxidase isozyme bands in dormant cambial region. The number and deepness of bands in zymogram during cambial activity phase were lower than that in other phases. Especially, POI₁, POI₂, POII₁ and POII₂ in peroxidase isozyme bands probably had a mutual relation with activity of cambial cell and differentiation of xylem. The result of histochemical reaction also showed that distribution and activity of peroxidase in different type of tissues or cells had significant difference. These indicated that peroxidase isozyme in cambial region was related to the level of endogenous IAA and differentiation of vascular tissues.

Key words: Populus tomentosa Carr., Cambium, Periodicity of activity, Peroxidase isozyme