Study On Mechanism Of Male Sterility Induced By Chemical Hybridization Agent SX-1 In Brassica Napus L.

Rapeseed (Brassica napus) is one of the main oilseed crops in China and the world, which is the third largest oil crop in the world after soybean and palm oil. A class of chemical substances that can induce male sterility in plants is called chemical hybridization agent (CHA). Induction of physiological male sterility to emasculation by the chemical hybridizing agent, known as chemical hybridizing. Chemical hybridizing provides a more convenient and efficient way for the breeding and seed production of hybrid rapeseed.In this study, Brassica napus Huyou 15 was treated by chemical hybridization agents SX-1 twice with an interval of 10 days.the first treatment (i.e. preparation 1)was conducted when the plants'biggest bud in main inflorescence up to 1-2mm. The development stage of rapeseed plant under stress induced by SX-1,morphological changes of floral organs, period and characteristic of pollen abortion,Changes of lipid metabolism and the expression of genes involved in regulating cell development and functioning in tapetal cell were investigated.The major results and conclusions are as follows:1.By technique semi-thin sections,the cytological structure of anther from SX-1 treated plant revealed that pollen abortion occur first in sporogenous stage and abnormal developmental state of the pollen and tapetal cell was observed in the various stages of pollen development.Tapetal cell abnormalities classified into two categories: earlier disintegration in advance at microsporogenesis stage and delayed degradation at the male gametophyte formation period.Sudan Black B staining showed lipid metabolism was inhibited in tapetal cell from male sterile anther,causing tapetum can not provide sufficient material for the formation of pollen wall.2.The floral organ of male sterile plants induced by SX-1 with smaller petals,shorter stalk and shorter pistil indicated that the whole plant anabolism was inhibited.Shortened filament was the most significant characteristic,the length of which is only 42.69% of the normal.The inhibition of filaments elongation was occurs primarily in the big buds (>5mm),and many uni-nucleate stage of microspore were observed in anther of big buds,so inhibition of filaments elongation may correlate to pollen abortion.3.By real-time PCR,the result of expression of genes involved in tapetal development and function in male sterile plants induced by SX-1 showed that:(1) expression of genes regulating tapetal development:BnTPD1,BnEMSl and BnDYTl was up-regulated from tetrad stage to the uni-nucleate stagz;BnTDF1 and BnMSl was down-regulated at tetrad stage; (2) expression of genes participating lipid biosynthesis in tapetal cell:BnMS2?BnCYP704B1? BnCYP703A2?BnACOS5?BnCHS1?BnCHS2 is down regulated at tetrad stage.According to the above results, conclusions of the mechanism of male sterility in Brassica napus induced by SX-1 as follows:SX-1 works in rapeseed inflorescence formation stage;The growth of filaments,an junction of maternal plant and the anther, was inhibited;Expression of genes involved in tapetal development and function was influenced, which lead to abnormal development of tapetum cells and obstruction of the synthesis of lipid,so that tapetal cells can not provided enough nutrient for microspore development and the pollen exine formation,as a result the pollen grain aborted.