南京地区美洲黑杨雌、雄花芽分化的解剖学研究

Anatomical observations on the male and female floral buds development of Populus deltoides in Nanjing area

【目的】研究多年生木本植物花芽分化进程和特点,揭示树木成花分子调控机制。【方法】分别以南京地区成年美洲黑杨(Populus deltoides)雌株和雄株为材料,详细记录其花芽发育的完整过程,并采用石蜡切片技术对雌、雄花芽发育各阶段进行解剖观察。【结果】在南京地区,每年5月底至6月初成年美洲黑杨的当年花枝上形成肉眼可见的花芽。随后的花芽分化过程可以分为5个阶段:苞片分化期(6月中旬之前)、小花原基起始期(6月中旬至7月中旬)、雌蕊/雄蕊分化期(7月中旬至11月)、休眠期(12月至翌年1月)和雌/雄配子体形成期(翌年2—3月),最终在早春形成单性花。【结论】美洲黑杨雌、雄花均为Ⅱ型单性花,即某一性别花中不存在相反性别花器官的残留。在整个花芽发育过程中,雄花芽较雌花芽大而饱满,雌、雄花芽鳞片外观嫩绿、质地坚硬,花芽长度生长趋势呈"S"形曲线。研究结果可为进一步深入研究杨树花器官发育及性别分化的分子机制提供必要的前提和基础。

【Objective】Characterizing floral bud development in perennial woody plants is critical for revealing the molecular regulatory mechanisms of flowering in trees.【Method】In this study,morphological changes in floral buds were investigated in male and female Populus deltoides.Anatomical structures were observed in paraffin sections.【Result】In Nanjing area,floral buds begin to appear on the floral branches from late May to early June each year.The developmental process can be divided into five stages:bract differentiation(before mid-June),floret primordium initiation(from mid-June to mid-July),gynoecium/androecium differentiation(from mid-July to November),dormancy(from December to January of the following year),and male/female gametophyte development(from February to March).Finally,the differentiation of unisexual flowers occurred in early spring.【Conclusion】Both male and female flowers of P.deltoides belong to the typeⅡunisexual flower,which exhibits no rudiments of the opposite sex.During the entire developmental period,both the bud scales of male and female flowers remained green and rigid,though the male floral buds were larger and plumper than those of females.The growth curve of floral buds exhibited a sigmoid shape.The results obtained in this study provide a necessary foundation for exploring the molecular mechanisms underlying floral organogenesis and sex determination in poplar.