秋冬季节泡桐顶芽形态及显微结构变化分析

Morphology and Microstructure Changes of Terminal Buds of Paulownia in Autumn and Winter

为研究泡桐停止生长及顶芽死亡过程中顶芽形态结构的变化。以生长在郑州地区的1年生毛白33泡桐埋根苗为研究材料,8-12月份每隔10d对泡桐顶芽的外部形态变化进行观察,同时制备顶芽石蜡切片进行显微结构分析。综合毛白33泡桐埋根苗顶芽外形变化和显微结构变化特征,可将该过程划分为4个阶段:1)顶芽分化生长期:9月上旬之前,顶芽细胞分化能力强,能不断分生出新叶。2)顶芽生长分化停止期:9月中旬至9月末,泡桐顶芽细胞壁稍厚,成熟区的维管形成层出现导管,顶芽已不再萌发新叶,顶芽颜色由浅绿色变为绿褐色。3)顶芽死亡发生期:10月上旬到11月上旬,顶芽分生区细胞间开始出现层状裂隙,伸长区的形成层已有导管,芽的木质化程度加深,顶芽颜色褐化程度加深,并有干瘪的趋势。4)顶芽死亡后期:11月中旬到12月中旬,细胞之间裂隙普遍,形成层中导管众多,大多数顶芽细胞已基本死亡。泡桐生长停止前后,泡桐顶芽并未形成芽鳞,之后顶芽细胞间开始出现层状间隙,细胞开始老化死亡,并随着时间推移而程度加深。从芽的形态结构变化分析来看,泡桐顶芽芽鳞的缺失是泡桐顶芽死亡的主要原因。

In order to understand the changes of morphological structures of Paulownia terminal buds in the process of growth cessation and terminal bud＇s death, the buried root seedlings of Paulownia tomentosa × Paulownia fortunei 33 which grew well in Zhengzhou area were used as research materials,the morphology of terminal buds were observed every 10 days from August to December,and the microstructures of terminal buds were analyzed by preparation of paraffin section of terminal bud at the same time. The process could be divided into four stages based on the changes of morphology and microstructures of terminal buds： 1） the period of growth and differentiation of terminal bud： until early September,the terminal buds had strong differentiation ability and could gradually put out fresh leaves. 2） The period of stop growth and differentiation of terminal bud： from mid September to the end of September,the cell walls of terminal buds were slightly thick, vessels were formed in the vascular cambium of the mature region, the terminal buds could not sprout fresh leaves and its color changed from light green to greenish brown. 3） The period of death occurrence of terminal bud. from early October to early November,lamellar gap began to appear among cells in meristematic zone,vessels were formed in the cambium of the elongation zone, the lignification degree of buds was deepened,the terminal buds did＇t enlarge and became shriveled with the browning level increasing. 4） The late period of death of terminal bud. from mid November to mid December,most cell walls of meristematic zone ruptured and cytoplasm exosmosis, the nucleus of a few cells were visible and resided in the side of the cell, lamellar gap existed among cells widely, there were many vessels in the cambium of the elongation zone,most cells of terminal bud were basically dead. The terminal buds of Paulownia did not form bud scale before and after stop growing,then lamellar gap began to appear among cells of terminal buds, cells began to aging and dying, and the level of aging and death became more serious with the course of time. Lack of bud scales was the major cause of the terminal bud＇s death based on the analysis the morphological changes of buds.