有花植物触敏柱头的闭合行为及其适应意义

Closure Behavior of the Touching-sensitive Stigmas in Flowering Plants and Its Adaptive Significance

有花植物触敏柱头的闭合行为一直是传粉生态学和进化生物学研究的热点问题之一。植物花的多裂片柱头在传粉者接触后迅速闭合的现象主要存在于玄参目的一些类群中。早在上个世纪初,植物学家就对花的柱头闭合现象进行过初步的研究,认为柱头闭合主要是由于花粉在柱头上萌发时吸收水分导致柱头细胞膨压降低而引起的;并对柱头闭合的适应性提出了一些假说。近年来,许多学者研究证实柱头闭合能促进花粉萌发及花粉管伸长,或减少花粉散出与柱头接受花粉间的相互干扰,提高传粉者访问过程中花粉的散播量,并且柱头的状态会直接影响传粉者的取食行为。到目前为止,对柱头闭合的机制及其避免自交的假说还存在许多争议。关于触敏柱头的闭合行为,尤其是其适应机制及其生态学意义还有待更加系统和深入的研究。本文概述了触敏柱头的研究进展,并对研究中尚存在的一些问题进行了讨论。

Studies on the closure behavior of the touch-sensitive stigmas in flowering plants are one of the hotspots in pollination ecology and evolutionary biology. Examples of closure behavior of bi- or multi-lobed stigmas in response to being touched by animal pollinators were mainly studied in some taxa of the order Scrophulariales. Such phenomenon had been studied at the beginning of 1990s. Generally, stigma closure has been attributed to the loss of turgor in cells comprising the stigmatic tissues, during pollen germination and subsequent pollen tube growth absorbing water from surrounding tissues in the pistil. Various hypotheses addressing the adaptive significance of stigma closure have been proposed. Recent years, studies indicated that stigma closure may increase pollen capture and receipt, improve pollen germination and pollen tube growth, and prevent intra-floral selfing. It was also suggested that stigma closure can reduce interference between pollen receipt and pollen dissemination. Stigma closure affects pollen deposition and reduces interference between pollen dispersal and stigmatic receipt as well. Foraging behavior of pollinator is strongly influenced by the status of the stigmas. Until now, the mechanism of stigma closure and the hypotheses of avoiding self-polhnation have been still uncertain. Some experiments with male-female interference and the intra-floral selfing should be carried out to test the adaptive significance of stigma closure. In this paper, recent advances in the sensitive stigma are summarized, and some problematical issues are also discussed.