Anther development and formation of dehiscence pore in Rhododendron × pulchrum

Abstract

Flowers of Rhododendron have unique poricidal dehiscence anther, but the formation of the dehiscence pore and the mechanism of pollen releasing are not fully known. The purpose of this research was to study the anther development of Rhododendon × pulchrum through microdissection and paraffin section to find out how the dehiscence pore develops and what tissues are involved in its development. The results were as follows: (1) The tissue forming the apical pore and the main body of the anther diverged from the very beginning of the stamen development. The dehiscence pore is formed by breaking down of parenchyma tissue, which is derived from the apical meristem of stamen primordium. The body part of the anther comes from the archesporial cells and they develop into regular pollen sacs with multi-layered anther walls. (2) The anther wall is fully differentiated at the stages from microspore mother cell to microspore tetrad, with 6-7 layers of cells, including 1 layer of epidermis, 2-3 layers of endothecia, 1-2 layers of middle layers and 1 layer of tapetum. The middle layers soon break down after completion of microspore tetrads and the tapetum disappears before the pollen tetrads are fully mature. The epidermis and 2-3 layers of endothecia remain to the end. (3) Unlike those of longitudinal dehiscent anthers, the endothecia of Rhododendon× pulchrum are not fibrous at maturation. Instead, they are persistent and somewhat elastic through accumulation of polysaccharide granules in cells. (4) The four microspores produced by one microspore mother cell do not separate from each other and the pollens are released as tetrads, with viscous threads between pollens and among tetrads. The authors assume that the thickened multi-layer endothecia reduced the inner volume of the pollen sacs, therefore the pollen tetrads at the top are “squeezed out” from the dehiscence pore, and the viscous threads allow the pollen tetrads to be pulled out in clusters by pollinators.

Keywords

• rhododendron
• rhododendron × pulchrum
• anther development
• poricidal dehiscence
• endothecium
• parenchyma