李庆军
论文题目：山姜属植物花柱卷曲性异交机制的研究
作者简介：李庆军
，男，1965年08月出生，1998年03月师从于中科院昆明植物研究所许再富教授，于2002年08月获博士学位。
摘
要
植物繁育系统的研究是植物学、生态学和保护生物学等研究中的热点，也是揭示有花植物起源与进化的关键课题。本文以姜科山姜属植物为研究对象，系统地研究了长柄山姜(Alpinia kwangsiensis)和红豆蔻(A. galanga)的繁殖生物学特性及繁育系统的特征，特别侧重于其自交亲和性与自交衰退、促进远交的机制，以及访花动物的拜访行为与花柱卷曲性的互动适应等。
已研究的山姜属植物每个种的各个居群中都具有两种表型的个体，其差异在于开花行为的不同，根据开花过程中柱头的运动方向，分别称为花柱下垂型和花柱上举型：1) 花柱下垂型个体，上午开花时其柱头向上反卷在花药背面，花药腹面的花粉囊开裂，花粉散出。中午时分花柱开始向下卷曲，下午下垂于花药腹面，而此时花粉已经散尽；2) 花柱上举型个体，上午开花时其柱头垂在未开裂的花药腹面，能够接受到拜访者携带的花粉，中午开始向上反卷，当其上举到花药背面时，花粉囊开裂，花粉散出。两种表型在自然居群中的比例为1:1，而且它们的花部运动节律是同步的，与它们的传粉昆虫拜访特性相一致，有效的传粉只能发生在上述两种表型之间。野外实验表明长柄山姜是自交亲和种类，传粉主要依赖于昆虫。这一独特的开花机制被作者命名为“花柱卷曲性”，本文系统的研究了这一远交机制，并建立了中、英文命名系统。
除了花柱卷曲性导致的远交优先以避免近交引起的衰退外，在气候条件不利于传粉或传粉昆虫稀少的情况下，山姜属植物种群中有一半的个体(花柱下垂型个体)具有通过滞后主动自交(delayed autonomous selfing)来实现有性生殖的繁殖保障能力。这在红豆蔻(A. galanga)中表现得尤为明显—套袋后的花柱下垂型花序仍有将近25%的座果率。
不同授粉方式获得的后代，在适应性方面有显著的不同，但这种差异在后代生长的各个生活史阶段的表现程度有所不同。首先，表现在花粉在柱头上的萌发率和花粉管在花柱中的生长速率不同，远交花粉具有明显的优势，花粉萌发率高，萌发速度和花粉管生长速度都较快；其次，在同一种花型内，异交的结实率(fruit set)、结籽率(seed set)均高于自交；最后，异交产生的果实和种子的特性明显优于自交产生的果实和种子。
花蜜是植物为传粉者提供的主要回报物质之一，花蜜分泌量的多少和成分的组成，能够调节拜访昆虫的访花行为，从而对其远交的成功具有很大的决定作用。通过初步的研究表明，长柄山姜根据远交的需要，具有调节花蜜分泌量的能力：在花柱下垂的雌性阶段，分泌的花蜜量相对较多，使得昆虫拜访次数增加，停留时间延长，进而增加了获得足够外源花粉的机会，提高了植物的雌性适合度；而在柱头上举的雄性阶段，分泌的花蜜相对较少，昆虫每次拜访在一个植株或花序上拜访的花朵数和停留的时间就少，这样，一棵植株上的花粉就有可能被更多的传粉者携带到更多、更远的其它植株上去，从而节约了资源，又增加了植物的雄性适合度。
花柱卷曲性异交机制具有和花柱异长异交机制相类似的两型花，具有这一机制的种类，其种群中的个体具有在比例上1:1的花柱上卷型和花柱下垂型两类表型的个体。它们虽然都是两性花，但从其功能上讲相当于具有性别转换能力的雌雄异株。花的二型性分化也许是有花植物从两性花向单性花和雌雄异株进化的必经之路，由此，本文提出了一条两性花经由花柱卷曲性向雌雄异株进化的可能的途径，有待于在今后的研究中进一步验证。
Abstract
Despite the benefits of self-fertilization, the detrimental effects of inbreeding depression that follow repeated selfing have led to strong natural selection for diverse strategies to promote outcrossing in flowering plants. Here, we report a new floral mechanism that ensures cross-pollination by separating within a flower the receptive stigma from the presentation of pollen by extreme stylar movement. This new mating system adds to the diversity of pollination devices that are in part responsible for the great evolutionary success of flowering plants.
Alpinia, a large and primarily tropical Asian genus in the Ginger Family (Zingiberaceae), contains more than 250 species. They are perennial herbs with terminal inflorescences on leafy-shoots made up of congested bracts with each bract subtending a single or group of hermaphroditic flowers. An inflorescence produces two to ten open flowers per day; each flower lasts only a single day. Supporting by NSFC, we made observations on the flowering behavior of nine native and introduced species of Alpinia in a tropical seasonal rain forest in Xishuangbanna, Yunnan, Southwest China.
Each species of Alpinia has two phenotypes that differ in floral behavior present in all populations. When the flowers of form one are fully open (06:00-06:30), the stigma is exserted above the dehisced anther from which pollen is being released. At the same time, the receptive stigma of flowers in form two is curved downward below the indehiscent anther from which pollen has not yet been shed. Flowers of both types retain these respective positions until about mid-day (11:00-12:00). At that time the style of the second form begins to elongate and turns erect above the anther. As the stigma moves upward and out of direct contact with any subsequent floral visitors (170° between the stigma and the anther’s ventral face; 11:45 - 13:30), the anther dehisces and pollen is released (14:30 - 15:00). The movement of the style of the first form is slower: here the stigma begins to move downward and enters the receptive position (about 170° from the anther’s dorsal face) between 14:40 and 15:00 (several minutes after anther dehiscence in form two flowers). Anthesis in both forms ends after dark when the anthers collapse and the corolla limply hangs down. The speed of stylar movement varies depending on different weather conditions, but all the flowers of the same phenotype that open on the same day are strictly synchronous. The anthers of form two never dehisce before all stigmas of the same phenotype have moved out of the receptive position.
Our study describes a new floral mechanism that decreases inbreeding and promotes outcrossing in a tropical plant by temporally and spatially separating the presentation of pollen and receptive stigmas via active floral movement. This mechanism is different than other passive out-breeding devices, such as dichogamy, herkogamy, enantiostyly, and heterostyly, in that it combines some of the characteristics of all of these mechanisms with the unique movement of the floral parts. We have named this new mechanism “flexistyly” to emphasize the radical movement of the style and stigma in the two phenotypic forms: anaflexistyle flowers move their stigmas from a position below an indehiscent anther to one above the dehisced anther; cataflexistyle flowers move their stigmas from an erect to a downward position. We have observed flexistyly in all nine species studied. In a molecular analyses of the phylogenetic relationships within the Family Zingiberaceae, these nine species are distributed in three separate clades in the tribe Alpineae, which suggests that flexistyly has either evolved independently several times in this Alpineae or is widespread, but as yet unrecorded, in many taxa in the tribe (e.g., Amomum).
Key words: Zingiberaceae; Alpinia; breeding system; inbreeding depression; flexistyly
