板栗‘燕山早丰’有性生殖过程解剖学研究

An anatomical study on sexual reproduction process of Castanea mollissima 'Yanshanzaofeng'

为揭示板栗结实率低的内在原因，以河北迁西地区12年生‘燕山早丰’板栗为试材，采用石蜡切片、荧光显微观察和扫描电镜法，对其有性生殖发育过程进行了研究。结果表明：①4月下旬在1年生枝条的芽体内已具花原基，柔荑花序形成；5月上旬完成性别分化；5月中旬幼花药分化出表皮、内壁、中层及腺质绒毡层，花药壁发育为基本型；5月下旬小孢子母细胞开始减数分裂，经过胞质同时分裂，形成四分体；6月上中旬花药开裂，花粉粒散出，成熟花粉为二细胞、三沟。②雌花于5月上旬开始形成，分为雌花原基分化期、柱头原基分化期、柱头伸长期、子房形成期和开花期。6月中旬胚珠原基形成，子房8-9室，每室两个倒生胚珠，具双珠被，厚珠心。6月底至7月初胚囊成熟，属蓼型胚囊。③6月上中旬雄花开放后，花粉管经过约2周穿过花柱基部，于6月底至7月初开始进入胚囊，精卵融合为有丝分裂前型；胚乳为核型胚乳；合子经原胚？棒状胚？球形胚？鱼雷型胚？子叶胚，胚胎发育方式为柳叶菜型。8月上旬发育为成熟胚，8月底至9月初种子成熟时胚乳消失。④在雌配子发育过程中，7月中旬出现71．7％败育的胚珠，表现为空腔的胚囊、珠心组织退化等，这可能是‘燕山早丰’结实率低的原因之一。因此，阻止胚珠败育是提高板栗产量的关键。

To investigate the causes of lack of fruit set in Chinese chestnut, a cultivar named ‘Yanshanzaofeng’ was employed in Qianxi County, Hebei province, and the process of sexual reproduction was examined by microscope. The results showed that ①catkins with floral primordia were formed in the buds of oneyear olds shoots in later April. The sex differentiation was completed in early May. Later, the anther wall layers developed completely by midMay and consisted of epidermis, endothecium, middle layers and glandular tapetum, and the anther wall was of the basic type. Microspore mother cells underwent meiosis through simultaneous cytokinesis in later May and gave rise to tetrads of microspores, which were tetrahedrally arranged. Mature pollens contained two cells with three germ pores. Anthers were dehiscent and pollen grains shed between early June and middle June. ②The female flowers were formed in earlyMay, and can be divided into female flower cluster primordium differentiation stage, alabastrum primordium differentiation stage, stigma primordium differentiation stage, stigma elongation stage, ovary formation stage and blooming stage. The ovule primordium was formed in middle June. The ovary has eight or nine locules, and each locule contained two anatropous ovules which were bitegmic and crassinucellate. The embryo sac was mature between later June and early July, and the development of embryo sac conformed to the Polygonum type. ③ When the anthers were dehiscent, the pollen tube passed through the basal style about two weeks. The pollen tube came into the embryo sac between later June and early July, and the syngamy was of premitotic type. The development of the endosperm was nuclear endosperm. The zygote developed from the proembryo to the clavate, globular, torpedoshaped and cotyledon stage embryoid, and the development of embryo was of Onagrad type. ④The mature embryo formed in early August and the endosperm disappeared between later August and early September. The 71. 7% abortive ovules were observed in the development of female gametophytes in middle Julywhich showed the cavity of embryo and degeneration of nucellus tissue. The abortive ovules were identified as one of the major factors causing the low seed set in ‘Yanshanzaofeng’ . Thus, It was the key to prevent the abortive ovules for the chestnut production.