【作者】 俞晓敏；

【导师】 赵桂仿；

【作者基本信息】 西北大学 ， 植物学， 2004， 硕士

【摘要】 太白红杉(Larix chinensis Beissn．)是我国特有种，为松科落叶松属植物，仅分布于陕西省境内秦岭山地海拔2600～3500m的山脊绝顶之上，其生境自然间断，在其分布地常形成小种群；自然种群生长极为缓慢，自我更新能力较差，在多数分布地段，植株常发育不良，更为严重的是自然状态下太白红杉的结实率低，即使球果发育，也常常是干瘪无子。该种已被列为国家二级保护植物。 本文通过对太白红杉雌、雄配子体的形成和胚胎发育的系统观察，阐明其胚胎发育过程，揭示其有性生殖障碍，并根据其生殖生物学特征，为其系统位置的确定提供胚胎学证据；同时利用SSR分子标记分析和检测太白红杉自然居群的遗传多样性，阐明太白红杉自然居群的遗传结构和变异。通过对太白红杉胚胎学和遗传多样性的研究，揭示致濒的可能原因，为进一步预测太白红杉的遗传学命运和对太白红杉的保护提供有益的参考。 对太白红杉胚胎学的研究表明：(1)太白红杉的雄球花7月初开始分化。小孢子囊壁一般包括5～6层细胞：表皮、药室内壁、2～3层中层和绒毡层。绒毡层属于周原质团型。造孢细胞在7月下旬形成，8月上旬形成小孢子母细胞，8月下旬开始减数分裂，于10月上旬进入双线期，并以双线期渡过休眠。翌年3月下旬解除休眠继续进行减数分裂，4月中旬形成四分体，4月下旬到5月初小孢子从四分体内释放出来，小孢子经过连续4次有丝分裂后，于5月中旬形成5-细胞型的成熟花粉粒(雄配子体)并开始散粉。(2)太白红杉雌球花于7月中下旬开始分化：9月上旬至9月中旬形成大孢子母细胞；10月中旬，大孢子母细胞进入休眠期：翌年4月底至5月初解除休眠，大孢子母细胞进行减数分裂，于5月10日左右形成直列四分体，7月初形成成熟卵细胞并受精。太白红杉具简单多胚和莲座胚。9月中旬，太白红杉的成熟胚形成，成熟胚具5～6枚子叶。太白红杉从花芽分化到胚胎成熟历时14个月。(3)太白红杉小孢子母细胞发育表现出不同步现象，部分小孢子母细胞在发育过程中出现退化，在小孢子囊内形成空腔，小孢子囊绒毡层细胞在小孢子母细胞进行减数分裂Ⅰ时发生膨大和增生现象，挤压小孢子母细胞，很有可能导致小孢子母细胞的败育。太白红杉在幼胚时期不少胚珠出现发育异常，有的雌配子体变为半透明状，有的则干瘪萎缩。这可能是导致目前太白红杉有性生殖衰退、结实率低的主要原因。(4)太白红杉小孢子母细胞以减数分裂双线期渡过休眠，成熟花粉粒中包含5个细胞，属于油杉型。大抱子母细胞在9月上旬至9月中旬形成，经过近7个月的冬季休眠，于第二年4月底到5月初进行减数分裂，太白红杉具2弓个颈卵器，2个颈细胞，在幼胚发育阶段产生简单多胚和莲座胚。这些胚胎学特征都为太白红杉归属于落叶松属红杉组提供了证据。 通过利用SSR分子标记对6个太白红衫自然居群的遗传多样性的研究，结果表明:太白红杉自然居群具有较高的遗传多样性水平，平均每个位点的等位基因数A=4.71，每个位点的预期杂合度和观测杂合度分别为He=0.6748，Ho=0.6667，Sharinon多样性指数为I=1 .2818。自然居群平均杂合性基因多样度比率凡了=11.6%，表明有88.4%的遗传变异存在于居群内。根据Nei’s(1978)无偏差估算的太白红杉自然居群间的遗传一致度与遗传距离表明，居群间的遗传一致度平均值为0.7894(变化范围:0.6484一0.9069)，遗传距离平均值为0.2403(变化范围:0.0978一0.4332)。太白红杉自然居群间虽然存在相当程度的基因流(Nm=1.9045)，能够抵制遗传漂变的作用，维持居群间的遗传相似性，但与其它松属、落叶松属植物相比较，基因流水平偏低，暗示太白红杉自然居群间产生了一定程度的遗传分化。 通过本文的研究表明，太白红杉致濒原因首先可能是由于太白红杉对其生境的高度适应，导致竞争力缺乏，自然居群总是限制在较小的范围:其次，太白红杉有性生殖过程中，小抱子母细胞的败育和幼胚发育的异常经常发生，进而可能导致太白红杉结实率降低、种子生活力下降:同时，野外调查还发现，随着近年来高山森林生态旅游资源的开发，太白红杉生境的人类活动日益频繁，人为因素干扰将会加剧太白红杉走向濒危。 根据本文的研究结果，建议太白红衫的保护应以就地保护为主，重点加强对居群内遗传多样性较高的朱雀居群、牛背梁居群的保护。同时应加强对其自然更新、生长发育和繁殖规律的研究，注重保护太白红杉生境，减少森林生态旅游开发对其自然居群造成的破坏。更多还原

【Abstract】 Larix chinensis Beissn., an endemic species to China, belongs to the genus Larix Mill and only distributes on several peaks of Qinling Mountains in Shaanxi Province, with the altitude ranging from 2600 to 3500m. L. chinensis usually forms small populations and the individuals are runtishly in their discontinuous habitats, the natural populations grow very slowly and regenerate poorly. What is worse, L. chinensis has an extraordinarily low seed-setting rate and most seeds are atrophic. It has been listed among Grade II Endangered and Protected Plant Species.Through the systematic observation on the formation of male and female gametophytes and the embryonic development, this paper has given a clear picture of L. chinensis’ embryonic development process and revealed its reproductive obstacle. Embryologic evidences are also provided for the determination of its systematic position according to the traits of its reproductive biology. Meanwhile, the genetic structure and variation of L. chinensis’ natural populations have been illustrated by means of SSR molecular markers. Through all these research work, this paper reveals the possible causes for its endangered situation and provides a helpful reference for the prediction of L chinensis’ genetic destiny and its biological conservation.The results of embryological research reveal that: (1) the male cone of L. chinensis differentiates during early July. The microsporangium wall of L chinensis consists of 5-6 cellular layers, namely the epidermis. the endothecium. the 2-3 middle layers and the tapetum. The tapetum belongs to the periplasmodial type. The sporogenous cell occurs in late July and develops into the microspore mother cell in early August. In early August, the latter starts its meiosis and enters into its diplotene phase in early October and later goes through dormancy in this form. The dormancy ends in late March the next year, and its meiosis continues. In middle April tetrads form and microspores are released between late April and early May. After four times’ continuous mitoses, the microspore develop into the mature pollen (malegametophyte) which consists of five cells and begins shedding in middle May. (2) the female strobilus of L. chinensis Beissn. starts its differentiation in middle and late July;Megasporocyte forms during early and middle September and enters into dormancy in middle October; Between late April and early May the following year, the megasporocyte ends dormancy and begins its meiosis. Linear tetrads form around 10 May, and mature egg cells form and start the fertilization takes in early July. Simple polyembryony and rosette embryo occur frequently in L. chinensis. The mature embryo with 5~6 cotyledons forms in middle September. It takes 14 months from differentiation of female strobilus to formation of mature embryo. (3) the development of the microspore mother cell is nonsynchronous. Degeneration occurs in part of microspore mother cells during the developmental process, resulting in the formation of a large cavity in the microsporangium. Besides, the cells of tapetum undergo abnormal inflation and hyperplasia during the meiosis I of the microspore mother cell, which will probably cause abortion of the microspore mother cell. Some ovules undergo abnormal development in the early embryonic stage, with their megagametophytes becoming semitransparent or atrophic. All these phenomena may be responsible for the sexual reproductive degeneration and low seed-bearing. (4) the microspore mother cell of the L chinensis goes through dormancy in the diplotene stage and the mature pollen consists of five cells; Megasporocytes form during middle and late September, and begins its meiosis between April and May the following year after an approximate 7-month period of winter dormancy. L. chinensis has two to three archegonia per ovule, and each archegonium has two neck cells. Furthermore, during the early embryonic development, simple polyembryony and rosette embryos occur in L. chinensis. These embryological traits support the conclusion that the更多还原