Revisiting hydropotes of Nymphaeaceae: ultrastructural features associated with glandular functions

ABSTRACT Hydropotes are specialized epidermal structures involved in water and mineral flux into and out of the plant body. We analyzed hydropote morphology of four species of Nymphaeaceae: Nymphaea caerulea, Nymphaea lotus, Nymphaea rubra, and Victoria amazonica. Leaf samples were processed following conventional techniques for plant anatomy and for scanning and transmission electron microscopy. We observed hydropotes comprising an elongated apical sharp-pointed portion with a base composed of two to three short specialized cells. In a later developmental stage the apical sharp-pointed portion was detached and the mature hydropotes comprised an upper lens-shaped cell, a bowl-shaped cell and a large foot cell. Ultrastructural analysis revealed that the lens-shaped cell possesses labyrinthine projections in its outer periclinal wall and abundant plasmodesmata in its inner periclinal wall. Several mitochondria were present in the cytoplasm of both the lens-shaped and the bowl-shaped cells. The cytoplasm of the foot cell was reduced and possessed plastids with starch grains. The ultrastructure of the hydropotes is typical of cells involved in transporting substances and corroborates their role in the flux of substances into and out of the cell. These findings contribute to a better understanding of the functioning of hydropotes and shed light on this little-explored issue.

摘要 水孔（hydropote）是一类特化的表皮结构，参与植物体内外水分与矿质元素的转运过程。本研究针对睡莲科（Nymphaeaceae）的4个物种展开水孔形态学分析，分别为蓝睡莲（Nymphaea caerulea）、埃及白睡莲（Nymphaea lotus）、红睡莲（Nymphaea rubra）以及亚马逊王莲（Victoria amazonica）。叶片样品按照植物解剖学常规方法以及扫描电子显微镜、透射电子显微镜制样流程进行制备。研究观察到，幼期水孔由细长的顶端尖状结构构成，其基部由2~3个短特化细胞组成。在发育后期，顶端尖状结构脱落，成熟水孔由上部透镜状细胞、碗状细胞以及大型基足细胞构成。超微结构分析显示，透镜状细胞的外平周壁具有迷宫状突起，其内平周壁富含胞间连丝。透镜状细胞与碗状细胞的细胞质中均分布有大量线粒体。基足细胞的细胞质较为缩减，且含有内含淀粉粒的质体。水孔的超微结构符合物质转运细胞的典型特征，证实了其在细胞内外物质转运中的功能。本研究结果有助于更深入地理解水孔的运作机制，为这一鲜有探索的研究领域提供新的学术视角。