巴西橡胶树的季节生长与组织分化

Seasonal Growth and Tissue Differentiation of Hevea brasiliensis

对栽培在海南岛儋州地区的成龄巴西橡胶树（ＨｅｖｅａｂｒａｓｉｌｉｅｎｓｉｓＭｕｌｌ．Ａｒｇ．）苗端分生组织和维管形成层的季节活动进行光学和电于显微镜研究，结果表明，橡胶树在冬季叶黄时原来不活动的顶芽顶端分生组织即开始细胞分裂，这可以看作芽萌发的开始，如果不遇阻碍生长的低温（旬平均温度＜１８℃），９ｄ左右即发生肉眼可见的萌发，如遇阻碍生长的低温则肉眼可见的萌发延迟出现。春季新梢叶蓬淡绿末期顶芽顶端分生组织停止细胞分裂进入休眠；这种休眠芽可以在当年经几次活动和休眠形成新的叶蓬，也可以一直到下一个冬春季节才重新萌发。笔者认为顶芽的活动被成熟叶片控制，冬季叶片衰老脱落导致芽的休眠被解除，但由于有阻碍生长的低温而使芽被迫休眠。在冬季无叶期小枝次生韧皮都和维管形成层的超微结构与着叶期比较并无明显变化；这与温带树木不同，后者在准备休眠过程中，细胞结构发生导致获得抗寒性的若干明显改变。

Light-and electro-microscopical observations were made on the seasonal activities ofthe shoot apex meristem and vascular cambium of mature Hevea brasiliensis grown inDanzhou, Hainan, China. It was found that in winter when the leaves of the tree turned yellow the cell division appeared in the shoot apex meristem of the terminal bud which hadbeen inactive. The cell division could be considered as the evidence of the beginning of thebud break. The visible bud break took place in some 9 days but delayed when low temperatures impeding growth (the average temperature in a ten-day period<18℃) occurred. In springwhen the sprout from the breaking bud had its leaves at the end of light green phase thecell division suspended in the apex meristem and the new terminal bud became dormant. Thedormant bud could have many times of flush or did not sprout until the next spring. It wassuggested that the bud activities be controlled by the leaves in that the leaf senescence andabscission led to bud dormancy break but to imposed bud dormancy which may be caused bylower temperatures impeding growth. In comparison with the branchlet in leaf-bearing period,the branchlet in leaf-absent period in winter had no obvious change in ultrasturcture of thesecondary phloem and vascular cambium. This is different from the temperate zone treeswhich made some changes in cell structure for dormancy and thus become cold-resistant.