Abstract
Paeonia ludlowii (Stern & Taylor) D.Y.Hong, an endangered species, is indigenous to Tibet, China and propagated only by seed under natural conditions. Its natural reproduction is constrained by low fecundity. Excess seed abortion is a key factor restricting its natural reproduction, cultivation, introduction, and protection. Understanding the specific origin and occurrence of aborted ovules is important for the protection of offspring. Using serial sectioning analysis, we studied the process of pollination and fertilization of P. ludlowii and examined the characteristics of aborted ovules, developmental differences after flowering of normal and aborted ovules, and their ratios at different positions in P. ludlowii ovaries. During pollination, fertilization, and seed development, ovule abortion was frequent, with a random abortion position. There were three types of abortion, namely, abnormal pistil, sterile ovules, and embryo and endosperm abortions. Of these, embryo and endosperm abortions could be divided into early abortion and middle abortion. The early aborted ovules stopped growing on day 12, the endoblast and endosperm in the embryo sac aborted gradually. Furthermore, the shape of the embryo sac cavity changed. The volume of aborted ovules was significantly different from that of fertile ovules. At ripening, the external morphology of different types of aborted seeds was significantly different. The possible reasons for the abortion of the ovules are also discussed.
Highlights
Paeonia ludlowii (Stern & Taylor) D.Y.Hong, Paeonia Sect
P. ludlowii propagates through seeds, it needs to produce a large number of seeds and germinate to expand its population
Morphological characteristics of the carpel and embryo sac: The carpel of P. ludlowii consists of three parts: stigma, style, and ovary (Fig. 2a)
Summary
Paeonia ludlowii (Stern & Taylor) D.Y.Hong, Paeonia Sect. Wild P. ludlowii was only distributed in a small area in the eastern Himalayas, Tibet, China; to date, only six wild populations have been reported (Hong et al 2017). P. ludlowii propagates through seeds, it needs to produce a large number of seeds and germinate to expand its population. P. ludlowii is capable of selfing and outcrossing, its rate of seed setting is only approximately 29.01%, germination percentage is 2.3%, and it requires approximately 2–3 years to grow into seedlings (Hao et al 2014; He 2008; Tang et al 2021; Yang et al 2007). Due to over-excavation, catastrophes, and severe anthropogenic environmental destruction, wild P. ludlowii is endangered in China and is listed as a second level species in the newly released list of China’s national key protected wild plants (National Forestry and Grassland Administration of China 2021). It is necessary to study seed abortion in P. ludlowii
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