Sporogenesis and gametogenesis in Chinese chinquapin (Castanea henryi (Skam) Rehder & Wilson) and their systematic implications

Abstract

We provide new embryological information regarding the Fagaceae family. Abortive ovules may be a result of mate choice and be necessary to maximize reproductive success in Chinese chinquapin ( Castanea henryi ). In contrast to most angiosperms, in which fertilization occurs 1–2 days after pollination, fertilization in Fagales is delayed from 4 days to more than 1 year. However, the phenomenon of delayed fertilization in Castanea Miller species (Fagaceae), which are the economically important species of Fagaceae and widely distributed or cultured in many countries of the world, has been consistently neglected, raising questions regarding what the delayed fertilization process is and why fertilization is delayed. To answer these questions, we systematically investigated the micro- and megasporogenesis in addition to male and female gametogenesis in Castanea henryi (Castanea Miller species). Our results show that the ovules primordia are immature at the time of pollination and require 6 weeks to become fully developed. During this 6-week period, 32.30 % of ovules abort because of the inability to form an embryo sac (ES). Approximately 15.79 % of ovules abort because of abnormal development of ES. From 7 to 8 weeks after pollination in which double fertilization occurs, most mature ovules are also aborted because of cell degeneration in gametophytes. Only one ovule can develop into a ripe seed. Thus, the delayed fertilization in Castanea henryi may be necessary to increase the time for mate choice and selective fertilization. A certain number of ovule abortions may be the result of delayed fertilization to maximize reproductive success.