濒危植物南方红豆杉大孢子发生和雌配子体发育

南方红豆杉(Taxus chinensis var.mairei)为第三纪孑遗树种,也是我国Ⅰ级保护植物。本文通过对其大孢子发生及雌配子发育过程进行细胞学观察发现,南方红豆杉胚珠多为直立单生,偶见1个苞片内着生2个胚珠;大孢子母细胞减数分裂形成4个大孢子,其中3个退化,仅位于合点端的大孢子发育为功能性大孢子;功能性大孢子经过有丝分裂形成256个游离核;颈卵器单生,2~6个;从传粉到受精约2个月;有16个原胚自由核,原胚为标准型;简单多胚和裂生多胚并存,胚发育不同步。因南方红豆杉胚珠直立单生、游离核数目、传粉到受精间隔期、原胚游离核数目等特征与松科差异较大,而与广义柏科具有许多相似之处,故我们支持将红豆杉科置于广义柏科之下的观点。此外,本研究结果还表明,南方红豆杉大孢子发生与雌配子体发育正常,不是致其濒危的主要原因。

Studies on Megasporogenesis and Development of Megagametophytes in Taxus chinensis var. mairei

Taxus chinensis var. mairei, one of the tertiary relic species, is one of the state first class protected species and endemic to China. Over the course of three years, we observed the external morphological changes from cone bud emergence to seed cone formation and the internal cellular changes during megasporogenesis, gametophyte development and embryo-genesis using paraffin-embedded-sectioning and hematoxylin-staining methods. Most ovules were only orthotropous, but two ovules wrapped within one bract could be seen occasionally. The meiotic division of the megasporocyte produced four megaspores in a linear tetrad formation. The three megaspores near the micropyle disintegrated, while the largest spore near the chalaza developed into a functional megaspore. 256 free nuclei were produced by a series of mitoses of the functional megaspore. The number of the archegonia varied from 2 to 6, and were not grouped together. There was about two months from pollination to fertilization. The pro-embryo was standard. Wall formation was initiated at the stake of about 16 free nuclei in the pro-embryo. Simple and cleaved polyembryony were found frequently, and the development of the embryo was not synchronous. The above characteristic structures of female gametophyte development, including the orthotropous ovule, number of free nuclei, the interval between pollination and fertilization, and the number of pro-embryo free nuclei, were fundamentally similar to Cupressaceae (s.l.), but different from Pinnace. Therefore we support that Taxaceae be under Cupressaceae (s.l.). We found no abnormal phenomena in the megasporogenesis and development of female gametophytes, and thus this is not the cause of this species endangerment.