龙眼花蜜腺的形态结构和发育

通过电镜扫描、石蜡切片、半薄切片显微观察和超薄切片电镜观察等方法, 研究了龙眼花蜜腺的形态、结构和发育过程。龙眼花蜜腺位于雌、雄蕊与花瓣、花萼之间的花托上, 呈边缘凹陷的扁平盘状。成熟蜜腺由分泌表皮、泌蜜组织和只具韧皮部的维管组织构成, 为典型的结构蜜腺。蜜腺表面密被单细胞的表皮毛, 具多个气孔。表皮细胞外具角质层, 多数细胞内含颗粒状酚类物质。泌蜜组织由大小两类细胞组成, 小细胞中细胞质浓, 大细胞中含酚类物质。维管组织较为发达。雌、雄花蜜腺是在花的各部分分化后, 开始从花托表面分化。在蜜腺发育过程中, 液泡呈现有规律的变化, 预示着液泡可能参与了蜜汁的合成与分泌过程。泌蜜组织中的大型特化细胞所含的酚类物质在泌蜜过程中存在着分解现象, 因而其除形成蜜腺自身的保护机制外, 也可能作为蜜汁的前体物质。

Structural and Developmental Characteristics of Floral Nectaries of Dimocarpus longan

The structure and development of floral nectaries of Dimocarpus longan were studied with scanning electron microscopy(SEM),paraffin section,thin resin sections and transmission electron microscopy(TEM).The floral nectaries of male and female flowers of Dimocarpus longan were located on the surface of floral receptacle,which formed a convex disc-like nectary.The nectary was located at the outer part of the pistil and stamen and at the inner part of corolla and calyx.The male and female flower nectaries,composed of epidermis,nectariferous tissue and vascular tissue containing only phloem elements,belong to typical structural nectaries.The epidermis of floral nectaries was covered with numerous epidermal hairs consisting of single cell with thickened wall and cuticle.In addition,some small stomata were observed at the top surface of nectaries.There were a lot of granulose phenolic compounds within most epidermis cells.Two types of cells could be distinguished in nectariferous tissue,one was smaller and had densely stained cytoplasm,another was larger and contained phenolic compounds.The former consisted of more cells than the later.The nectaries had well-developed vascular tissues,which derived from the branches of the vascular bundle of floral receptacle,then they terminated nearby epidermis.Normally the nectaries's primordia of male and female flower of D.longan were found to initiate in surface of receptacle after other floral organs were differentiated.During the development of floral nectaries,especially before and after the nectar secretion,the vacuole volume of most of nectariferous tissue cells changed regularly,which imply that they may be involved in the process of nectar synthesis and secretion.Some phenolic compounds in specialized cells of nectariferous tissue were disintegrating during nectar secretion,so besides its protective function in floral nectaries,the phenolic compounds were likely to take part in synthesis of nectar.