光果甘草二体雄蕊的发育及其适应意义

Diadelphous stamens in Glycyrrhiza glabra: their development and adaptive significance

甘草属(Glycyrrhiza)植物具"9+1"二体雄蕊,其中9枚合生雄蕊的上部花丝分离,分离的花丝在发育过程中存在由早期长、短交错的二组排列方式转变为后期以雄蕊管最长的1枚雄蕊为中心向两边渐次缩短的倒"V"形排列。为了解这种雄蕊发育动态、分化现象及发育成熟后的适应意义,该文以光果甘草(G.glabra)为实验材料,比较了雄蕊发育过程中的形态变化、成熟花粉的理化性质及在传粉中的作用。结果显示:雄蕊发育早期长、短两组雄蕊在花药大小与形状上存在分化,但后期伴随着花丝的快速生长与花粉的成熟、散出,花药大小与形状趋于一致;花粉组织化学成分及授粉成功率无差异,但成熟花粉的数量和花粉活力存在差异;去雄处理虽然使访花者在一天内的两个访花高峰期的访花频次降低,但结实率高于自然对照,说明以异交为主的花去除雄蕊后,降低了雌、雄蕊间的功能干扰,提高了传粉昆虫的授粉率;发育早期长、短交错排列的二组雄蕊到成熟期时发生的倒"V"形排列的转变,使不同数量与活性的花粉分布在花内不同空间,最大化接触访花者,实现了资源节约,提高了雄蕊的雄性适合度,即在有限的空间内用最节约的雄性资源投入、使传粉空间与传粉几率最大化的方式,来提高雄性功能。

Aims The stamens of Glycyrrhiza species are diadelphous, with nine staminal filaments united at the base as a staminal sheath and separated in the upper portion of the staminal sheath. The arrayal shape of the nine stamens changes from two rows at an early stage to an inverted ＂V＂-shaped arrangement at a later stage. Our objectives were to （1） describe development of the stamens in G glabra （from the bud stage to full bloom） to determine dif- ferences in shape development, timing and position of stamens and （2） determine the functional role of long- and short-level stamens in the pollination processes and its adaptive significance. Methods The development of stamens （measurement of the filament, anther, and style lengths at five develop- mental stages） and variability of timing and position of stamens were observed under a dissecting microscope. Scanning electron microscopy recorded pollen morphology. The vitality, quantity and chemical composition of pollen were counted and detected. In addition, the number of seeds following each pollination treatment and the pollinator behavior of insects on different stamen removal treatments were compared to examine differentiation of long- and short-level stamens. Important findings There were differences between the long- and short-level stamens in filament length, anther size and shape early in development, but the differences disappeared when filaments elongated and mature pollen was released. The numbers of pollen grains and pollen vitality between the long- and short-level stamens were different later in development. However, no significant differences were observed in chemical composition of pollen and seed sets among different treatments. Emasculation of the long- and short-level stamens induced reduc- tions in the visiting frequency, but the seed sets of emasculation were higher than without emasculation, which indicates that emasculation reduces the interference between stamens and stigma and improves the pollination rate. The arrayal shape of stamens changed from two rows early in time to an inverted ＂V＂-shaped arrangement at a later stage and resulted in different quantity and vitality of pollen. This indicates that the flower of G. glabrauses fewer male resources to obtain the highest pollination efficiency and to improve male functionality.