两性花的雄蕊运动:多样性和适应意义

雄蕊运动指雄蕊在自身能量支持下发生的主动运动,不包括雄蕊在访花者触碰下造成的被动位移。该文总结了雄蕊的应激运动、快速猛烈弹射、缓慢运动以及级联运动等4种主要类型,分析了这些运动类型的系统分布及繁殖适应意义等方面的研究进展。雄蕊的应激运动由访花者或其他外力诱发,可能起到促进散粉和实现繁殖保障的作用;雄蕊快速猛烈的弹射运动可将花粉猛然撒向空中或访花者身上,促进了花粉的风媒或虫媒散布;缓慢运动的雄蕊可能通过在不同花期改变雄蕊的空间位置和雌雄异位程度来调节繁殖策略,或主动将雄蕊花药移至特定部位(如柱头表面)实现自交;雄蕊逐一、依次发生的级联运动较为复杂,主要分布在刺莲花科、梅花草科、旱金莲科和芸香科中,目前还缺乏实验研究;但根据"花粉呈现理论"以及其他类型的雄蕊运动研究结果,雄蕊的级联运动可以将花粉分批呈现给不同的传粉者,通过不同传粉者的分别传粉来提高花粉的输出;而且可避免已散粉雄蕊对即将散粉雄蕊的干扰,同时可能也降低了雌雄功能干扰和(或)花内自交。在芸香(Ruta graveolens)中,级联运动之后的雄蕊还会在花末期再同时向花中央运动;这种多向、多次运动方式是目前发现的最复杂的雄蕊运动类型。雄蕊运动领域值得今后开展进一步实验研究的方向主要有:1)雄蕊运动尤其是级联运动对雌雄功能干扰(性别间干扰)、雄蕊与雄蕊的"性别内干扰"等植物繁殖格局的影响;2)雄蕊运动与雌雄异熟、雌雄异位等花部特征的相互作用;3)雄蕊运动复杂类型的生理与发育机制。

Stamen movements in hermaphroditic flowers: diversity and adaptive significance

In this paper, stamen movement is defined as the movement of stamens with their own energy, either automatically or stimulated by pollinator or other forces, except the forced movement of stamen under the pressure of pollinators. Four main types of stamen movements are classified: stimulated, simultaneous and slow, quick and explosive and cascade. Stimulated movement is normally caused by touching of visiting insects, which can enhance the contact probability of anther/pollen with pollinators or promote contact of anther with self pistil. Simultaneous and slow movement can alter the extent of herkogamy and modify reproductive patterns, and in some plants the stamen can move the anther directly to the self stigma to promote autogamy. Quick and explosive movement can release the pollen rapidly to the air or adhere to visiting insects to promote wind and/or insect dispersal of pollen grains. In cascade movement–in Ruta graveolens (Rutaceae), Tropaeolum majus (Tropaeolaceae), and plants of Loasaceae and Parnassiaceae – the stamens can move one by one and anthers dehisce individually when positioning at the center of flowers. The adaptive significances of cascade movement have not been studied, but, according to ‘pollen presentation theory’, cascade movement can alter the herkogamy and control the pace of pollen presentation and distribute pollen among pollinators by either packaging or dispensing mechanisms, which can greatly enhance pollen removal efficiency. Furthermore, the interferences between stamens and pistil and among individual stamens can be decreased as a result of obvious herkogamy and spatial separation of each stamen caused by cascade movement. In Ruta graveolens, all the stamens move together to the center of flower after the cascade movement, this two-time, multiple-direction stamen movement probably is the most complex stamen movement presently known. Future emphasis in the field of stamen movement should include 1) the effects of stamen movement, especially the cascade movement, on sexual interference and interference among individual stamens, 2) the interaction of stamen movement with dichogamy (temporal separation of male and female funtion)