【作者】 王若涵；

【导师】 张志翔；

【作者基本信息】 北京林业大学 ， 野生动植物保护与利用， 2010， 博士

【摘要】 木兰科Magnoliaceae植物作为被子植物的原始类群,多为珍贵濒危种,也是全球气候变化的敏感类群,在整个植物进化系统上占有重要地位。本试验以木兰科木兰属的白玉兰Magnolia denudata和武当木兰Magnolia sprengeri为主要研究对象,采取形态学研究、组织化学染色、解剖学观测、人工授粉试验以及红外线热偶探针测温、红外线成像等方法,对开花生物学,传粉机制,繁育系统以及开花生热效应中表现出的原始性状和进化机制进行了深入研究,揭示了自然条件下白玉兰M. denudata部分胚珠败育的机理、玉兰亚属Subgen. Yulania心皮不完全发育的机制、木兰属Magnolia植物花芽长绢毛的趋同进化、木兰属生殖过程中的开花生热效应、以及木兰科植物双花粉管萌发的进化作用与机制。主要结论如下：1)白玉兰M. denudata花粉活力在不同散粉阶段具有明显差异。展瓣期(Stage 3)的花粉活力最强,即此时雄蕊群距中轴辐射散开,花药开裂,离心皮雌蕊柱头暗淡。此阶段的花粉萌发速率最快,近1.5小时即萌发；白玉兰柱头可授期时间很短,仅约5小时,因此,可授期的短促和具活力花粉的适时落置,是该属胚珠发育的先决条件。2)白玉兰M. denudata雌雄异熟间隔时间约为36小时,即从柱头具可受性到雄蕊成熟。尽管雌雄异熟避免自花授粉的发生,但北方玉兰早春花先叶的满树绽放,为访花昆虫在同一株树上长时间访花提供了机会,因而提高了同株异花授粉这种广义自花授粉形式的大量发生,进而使得雌雄异熟机制避免自花授粉在木兰属中的作用微乎其微。3)白玉兰生殖过程为严格意义的异株异花授粉。人工授粉试验结果显示,白玉兰异株异花果实与种子发育良好,同株异花授粉胚珠后期败育。同株异花授粉后,花粉管在花柱道内的生长和伸长率与异株异花样本并无明显差异,荧光显微镜下,同株和异株授粉柱头花粉管均可以通过花柱内的引导组织到达花柱道的底端。此后受精卵开始发育,胚乳核分裂,但胚珠发育停滞在鱼雷期,中心细胞消融退化,解剖学观测到的胚珠鱼雷期败育,直接导致低结实率,而败育发生在受精以后,为自交不亲和的滞后表现(Late-acting self-incompatibility)。4)玉兰亚属心皮的不完全发育是由部分胚珠败育导致。玉兰亚属的心皮由于自交不亲和机制,受自花授粉和同株异花授粉的影响,胚珠部分败育,导致部分心皮不完全发育,果序不饱满。玉兰亚属胚珠发生的自交不亲和的滞后表现,即合子后自交不亲和(Post zygotic SI)。由于原始被子植物不是完善的合心皮果,因此导致有效自交不亲和的进化不能得以顺利进行。5)木兰属Magnolia植物在花的生长发育过程中具有明显的生热效应。木兰属花芽外密被长绢毛,红外线测温以及热偶探针测定显示低温天气下,花芽内部温度高于环境温度,密被绢毛的芽鳞片有效保持了花芽发育的内部温度,并防止热量向外扩散；花蕾期,花芽的温度明显高于枝叶温度；开花期,雌蕊的温度在柱头可授期和最佳散粉期中都会维持较高的温度,花期温度的变化中,雌蕊比雄蕊有更强的控制力。植物开花生热,保持较高的温度,不仅能保障植物花粉发育,花粉管生长和受精等一系列生殖发育的顺利进行,而且能促使花部气味挥发,吸引昆虫访花,提高自身的繁殖成功。6)木兰科植物的花粉萌发出现双花粉管现象,是木兰科在植物系统发育中原始性状的表现。双花粉管的萌发类型在木兰属Magnolia、含笑属Michelia、木莲属Manglietia和鹅掌楸属Liriodendron等木兰科植物中普遍存在。结合裸子植物与部分被子植物的比较研究结果,认为木兰科花粉管的生长上保留了部分原始的特征,是探讨裸子植物与被子植物系统进化过程中具有关联作用的表征,可以看作是从裸子植物到被子植物进化的过程中,在花粉萌发中出现的重演现象。更多还原

【Abstract】 Magnoliaceae plants, originated mostly from China, are the endangered and sensitive species to global climate change. This family occupies an important position on the evolution of angiosperm system. By using morphological observation, anatomical and embroyological analysis, hand-pollination, infrared thermometer and infrared imaging, the features in relation to reproductive development and systematic evolution of Magnolia denudata and Magnolia sprengeri were investigated, based on analysis of the floral character, pollination biology, breeding system and thermogenisis occurred in Magnolia. In the present experiments, the mechanism of ovule abortion of M. denudata under natural condition and the reason of incomplete carpel development of Subgenus Yulania were revealed. Furthermore, the co-evolution of Magnolia flower buds with dense trichomes, heat generation occurred at anthesis and evolution mechanism of two pollen tubes occurred in pollen germination in Magnoliaceae were uncovered. The main results were summarized as follows:1) Pollen viability of M. denudata varied at different stages, but was at its highest in stage 3, during which time the stamens detach from the axis, the anthers dehisce, and the gynoecium stigma starts to fade, and pollen germination rate was fastest and nearly 1.5 hours for germination. The duration of pistil receptivity was very short and approximately five hours. These results indicated that poor fertilisation may occur if the optimum period for pollination was missed or the stigma receives poor-quality pollen grains from stages other than stage 3.2) The duration of dichogamy, i.e., from the state of a receptive stigma to mature stamens, was approximately 36 h, although dichogamy avoids selfing, but for the dichogamous M.denudata in early spring in northern China, more numerous floral displays resulted in a longer sequence of visits by pollinators to flowers within the same tree and increased geitonogamous self-pollination. Therefore, protogyny of Magnolia might have little effect in reducing geitonogamy.3) Reproductive process in Magnolia is cross-pollination in a strict sense, and hand-pollination experiments demonstrated that fruits and seeds from cross-pollinated samples grew well, whereas fruits of geitonogamous samples were aborted in later development. The amount and elongation rate of self-pollinated pollen tubes in the styles did not differ from those that were cross-pollinated. Using UV microscopy, both self and cross pollen tubes were found to reach the base of the style along style canal. In addition, zygote and endosperm nucleus developed, but the embryo degenerated in the torpedo stage, our anatomical analysis of ovule and seed development further revealed that fertilisation occurred in samples with geitonogamy, but the embryo degenerated in the torpedo stage, demonstrating that aborted seeds were produced by fertilisation, that is late-acting self-incompatibility.4) Subgenus Yulania carpels are not fully developed due to some ovule sterility. For self-incompatibility mechanism, the incomplete development of carpels was found to be the effect by ovule abortion caused by self-pollination and geitonogamy, and aggregate follicle fruits are not plump. Moreover, the ovule abortion of Subgenus Yulania was late acting self-incompatibility that was post zygotic self-imcompatibility. Incompleted syncarp fruits of primitive angiosperm led to effective self-incompatibility and the evolution can not proceed smoothly.5) There was a significant heat production occurred during anthesis in Magnolia. As the Magnolia plants have dense trichomes on well-developed bracts which tightly packed around floral buds, measurements by thermal couple probe demonstrated that pubescent bracts played a role in keeping the interior of buds warmer than environment, and pubescents avoided the heat spreads out; In its budding stage, the temperature of buds was higher than that of branch and leave buds; In floral stage, the temperature of gynoecium was higher during stigma receptivity period as well as pollen stage. During anthesis, the gynoecium had more control than the stamens. Thermogenisis in plant floral stage, maintain a high temperature, not only to protect pollen development, pollen tube growth, fertilization and etc. during reproduction development, but also can promote evaporation of floral scent, to attract insects visiting flowers, all of which increase their own reproductive success.6) It is commonly observed that there were two tubes from an individual pollen during the germination in Magnolia, Michelia, Manglietia, Liriodendron and other genuses in Magnoliaceae. Given the link between gymnosperm and angiosperm, it is supposed that some original features are maintained in pollen germination pattern in Magnoliaceae. These results have implications for understanding the systematic evolution of primitive angiosperm.更多还原