There have been a lot of reports on the number and morphology of somatic chromosomes in Magnoliaceae plants, but there are few studies on the structure and behavior characteristics of chromosomes during meiosis. In the embryological study of Manglietia honghuaensis and Manglietia xiangensis, it was found that although some sporogenous cells, microspore mother cells and diploids were aborted during microsporogenesis, no abnormal chromosome behavior was reported. The process of microsporogenesis is normal, and a large number of microspores with normal development can be produced. Chinese scientists have found some abnormal phenomena in the study of meiosis cytology of some plants in Magnoliaceae, such as the variation of chromosome secondary structure in microspore mother cells of Magnolia grandiflora, micronucleus in tetrads and so on. The chromosome number and karyotype formula of Manglietia yuyuanensis and Manglietia patongensis are the same, and the results of meiosis comparison show that the results of Manglietia patongensis and Manglietia yuyuanensis are obviously different without any human factors. The metaphase ⅰ configuration of Manglietia patongensis is different from that of Manglietia lactiflora. The metaphase I and anaphase I configurations of Manglietia patongensis are complex, and the average metaphase I configuration of single cell is 0.30 IV18.33 II0.15i, including univalent, bivalent and multivalent. The formation of its multivalent is a definite multivalent connected by chromosome cross force, which may be related to the existence of inverted heterozygotes in the same arm, certain heterozygosity in chromosome structure and spontaneous breakage of chromosomes into fragments. The latter configuration is relatively simple, and the average metaphase I configuration of a single cell is 19 bivalents.
The spontaneous chromosome breakage of Manglietia patongensis may be related to the formation of inverted heterozygotes on the same arm. The frequency of chromosome abnormalities such as late ⅰ and late ⅱ chromosome delay between Manglietia patongensis and Manglietia lactuca is obviously different. Taking the late stage of II as an example, 8.8% of milkvetch has delayed chromosomes, and the number of delayed chromosomes does not exceed 2. In the mitotic stage of Manglietia patongensis, the frequency of delayed chromosomes and fragments is as high as 29.3%, except that the number of delayed chromosomes can be1-1. The existing research results show that cells with micronucleus die in the earliest tetrad period. During the meiosis of Manglietia patongensis, the abnormal phenomena of chromosome delay and high frequency breakage may affect the development of pollen (male gametophyte) to some extent. The basic characteristics of meiosis of pollen mother cells of Manglietia patongensis and its related species Manglietia lactiflora were compared. Manglietia yuyuanensis and Manglietia patongensis have the same chromosome number and karyotype, but they are not induced by any human factors, and there are obvious differences in chromosome behavior during meiosis.
The configuration of (1) Manglietia patungensis in metaphase Ⅰ is 0.30Ⅳ18.33Ⅱ 0.15i, which is different from that of Manglietia patungensis from milk. Manglietia patongensis may have an inverted heterozygote on the same arm, and its chromosome structure has certain heterozygosity.
(2) The frequencies of chromosome behavioral abnormalities in late stage ⅰ and late stage ⅱ are obviously different. Take the later stage ⅱ as an example, 8.8% of the cells in the meiosis stage of Manglietia glauca have delayed chromosomes, with no more than two delayed chromosomes. 29.2% of Manglietia patongensis cells have abnormal phenomena such as chromosome delay, and the most delayed chromosomes are 1 1, and the chromosomes also break into fragments. During meiosis of Manglietia patongensis, abnormal chromosome heterozygosity and high frequency chromosome breakage may affect the development of male gametophyte to some extent.
The flower development and embryo development of Manglietia Manglietia were systematically studied. Manglietia patongensis has terminal flowers, and its floral organs began to differentiate at the end of the first year, and differentiated into perianth and pistil in March of the next year until it matured in June. When the pistil is mature, the ovule is inverted, with double integuments, thick nucellus and megaspore tetrad arranged linearly, and the chalazal end develops into functional megaspore, and three micropyle ends degenerate, and the megaspore is monospore. The embryo sac development mode belongs to Polygonum type. The lateral wall of stamen anther is rose red, there are four white pollen sacs inside, and there are 1 layer multinucleated cells in tapetum. The tetrad arrangement of microspores is mostly symmetrical cross-shaped, tetrahedral, even T-shaped and linear, and mature pollen grains are two-cell type. There are no abnormal phenomena in the process of flower development, megasporogenesis and the formation of male and female gametophytes of Manglietia patongensis, so the author thinks that the development of flower organs and male and female gametophytes of this species does not constitute the factors leading to the endangered species. Manglietia patongensis is an endemic plant in China, which belongs to the national key protected plant. In order to find out the risk factors in its propagation, the author studied the morphology and germination characteristics of Manglietia patongensis seeds during dormancy and post-ripening. The results showed that the incomplete development of Manglietia patongensis seed embryo may be the main reason for seed dormancy, and the embryo continued to differentiate and mature during the post-ripening process. The seed coat has good permeability and has little to do with dormancy; There are germination inhibitors in different parts of seeds, and the high content of germination inhibitors in endosperm is an important factor affecting embryo germination.
Endogenous hormones ABA and IAA play an important role in seed dormancy and germination of Manglietia patongensis. ABA is the key factor leading to seed dormancy, IAA is helpful to seed germination, and the change of IAA/ABA relative content has an important influence on seed dormancy and germination. The dormancy of Manglietia patongensis seed is a comprehensive dormancy caused by the morphological and physiological characteristics of the seed itself, and its morphological and physiological after-ripening process can only be completed under the condition of low temperature and moisture preservation at 4℃. However, under natural conditions, Manglietia patongensis seeds mature in autumn when there is little rain, and it is easy to lose water, which may be an important reason for the difficulty of natural regeneration of this species.
Manglietia (Manglietia) is the most primitive group of Magnoliaceae plants, and its modern distribution center is located in tropical and subtropical Asia. There are 30 species of this genus, with 2 1 species in China, mainly distributed in the south and southwest of the Yangtze River. Manglietia patongensis is an endangered species, which is distributed in the evergreen broad-leaved forest with an altitude of 700- 1000m in Hubei (Lichuan, Badong, Xianfeng), Hunan (Yongshun, Sangzhi, Dayong) and Chongqing (Nanchuan), and the distribution area is located in the northern edge of Manglietia. The spatial structure of allozyme genetic variation in Manglietia patongensis, 40 individuals in Xiaoxi population and 28 individuals in Mulberry population was studied by spatial autocorrelation analysis, in order to reveal the spatial pattern of genetic variation in the two populations and explore its formation mechanism and its relationship with the endangered reasons and processes. According to the detected 19 enzyme sites of 8 enzyme systems, alleles with gene frequencies greater than 0. 1 and less than 0.9 were selected, and the spatial autocorrelation coefficients of Moran's were calculated by two methods of equal sample frequency and equal geographical distance interval. The results show that the genetic variation of alleles in small-scale population lacks spatial structure and is a random distribution model.
The fragmented mulberry population in Manglietia patong habitat is the opposite result, and the genetic variation has obvious spatial structure, and the spatial distribution of genetic variation is patchy. The reason for this difference may be the limitation of gene flow caused by the fragmentation and geographical isolation of mulberry population. The above results provide a scientific theoretical basis for further formulating effective protection measures for Manglietia patongensis.