Studies On Embryological And Seed Dormancy Mechanism Of Allium Mongolicum Regel.

Alliummongolicum(Allium mongolicum Regel.) is a liliaceous, genus allium plant, its alias is alliummongolicum mongolicum regel or mongolian onion, it is endemic to the Mongolian Plateau, and it's the perennial xerophytic herbaceous plant. It has the important ecological value of fixing sand and preventing water loss and soil erosion, and it's a kind of vegetable growing in the desert area with high nutritional value and medicinal value. At present, the research reports about alliummongolicum are increasing, but its megasporogenesis, microsporogenesis and development of female and male gametophyte haven't been reported. The dormant nature of the alliummongolicum seeds causes physical barriers of low rate of emergence and uneven emergence to artificial cultivation. Therefore, this report has a systemic research on the embryology and seed dormancy mechanism of the alliummongolicum, the main conclusions are as follows:1. The study about alliummongolicum's megasporogenesis, microsporogenesis and development of female and male gametophyteAlliummongolicum's ovule is tenuinucellate, anatropous, archespore's volume is larger, the mother cell of megaspore makes reduction division for the first time to form dyad, the cell close to the micropyle gradually degenerates and disappears, the other cell close to the chalazal makes reduction division for the second time to form embryo sac with dinuclear, which is a bispore-allium type embryo sac.The meiosis and cytokinesis of microspore mother cell are simultaneous, the tetrads are mostly bilateral symmetrical type, rarely are tetrahedral type. Anther wall has five layers, they are secretory tapetum. Mature pollen is 2-cell type, no 3 - cell type.2. The study about alliummongolicum seed's dormancy mechanism2.1 Both water permeability and air permeability of the alliummongolicum seed coat are poor, but the former is not enough to be the main cause of seed dormancy, the latter is one of the main causes of seed dormancy.The seed coat and micropyle of alliummongolicum are composed of the thick-walled cells, strong keratinization, compact structure, there is a strong effect of mechanical restraint after the seeds absorbing water, which is one of the main causes of seed dormancy.2.2. The leach liquor of alliummongolicum seed has inhibitory effect on germination rate of cabbage seed, which not only can inhibit seed germination, effect on seedling growth, but also can cause seedling teratogenesis, etc., it illustrates that intrinsic inhibitor contained in alliummongolicum seed which can inhibit germination is one of the causes of dormancy.2.3 The embryo of alliummongolicum seed is cultured in the MS basic medium, the embryo can germinate fast, and the germination rate is up to 85%, so the embryo is not the main cause of alliummongolicum seed dormancy, and at the same time it illustrates that intrinsic inhibitor is mainly contained in the seed coat.2.4 The inhibitor of germination is contained in various organic phases of dormant alliummongolicum seed, which not only can inhibit germination rate, seedling height and root length of the cabbage seed, but also can inhibit its seed itself, the seed which dormancy is broken also contains inhibitor of germination which is less than the dormant seed, but mainly focuses on the methanol phase.2.5 GC-MS analysis shows variety of germination inhibitory material is isolated and identified from organic-phase leach liquor of the alliummongolicum seed, mainly organic acids, esters, phenols, benzenes, aldehydes, alcohols, ketones, etc.2.6 The content of endogenous ABA in the seed increases rapidly firstly and then decreases with the extension of lamination time, GA content increases rapidly firstly and then decreases, IAA becomes fluctuant, the content increases considerably one day before dormancy is broken, ZR content shows a downward trend overall. The ratio of (GA+IAA)/ABA and IAA/ABA shows a similar variation trend, both ratio increase with the extension of lamination time, both ratio come up to the maximum when it is the 12th-day lamination, and it is the time when the seed dormancy is relieved.To sum up, alliummongolicum seed's dormancy mechanism is: the structure of the seed coat and micropyle result in poor air permeability, there is a strong effect of mechanical restraint on seed's germination, the inhibitor of germination contained in the seed and endogenesis ABA inhibit the seed's germination, thus they result in dormancy.This study not only fills the blank of alliummongolicum embryology and seed physiology field, but also provides theoretical guidance of formulating breaking dormancy measures, which has theoretical significance and prospect of application.