Studies On Mechanisms Of Desiccation-sensitivity Of Aesculus Chinensis Seeds

Mechanisms of desiccation-sensitivity of Aesculus chinensis seeds during the process of maturation and mechanisms of deterioration of mature Aesculus chinensis seeds during the process of dehydration were systematically studied. The results were shown as follows:(1) The desiccation tolerance of Aesculus chinensis seeds was produced gradually during the process of maturation, and the peak of desiccation tolerance occurred at the time of shedding. Rapid nutrient accumulation as well as higher ABA content in seed coat and lower GA3/ABA ratio both in seed coat and embryo had significant effect on desiccation tolerance and shallow dormancy of mature Aesculus chinensis seeds during last stage of seed maturation. Although O/D ratio of soluble sugar in Aesculus chinensis seeds not, to some extent, positively correlated with desiccation tolerance of the seeds, the higher content of oligosaccharide and disaccharide played an important role in the production of desiccation tolerance of Aesculus chinensis seeds during the time of seed maturation.(2) The water content of mature Aesculus chinensis seeds was high, up to 1.42g·g^-1DW. The seeds were desiccation-sensitivity after shedding. When water content was higher than 1.0g·g^-1 DW, slight desiccation would increase the seed germination percentage. But further desiccation would have serious detrimental effect on seed vigor. The possible reason was that the mature Aesculus chinensis seeds had no de-differentiated process and had a high level of respiratory metabolism. The results observed by using electronic microscope showed that the radicle cell of mature Aesculus chinensis seeds was fully differentiated, all cell organelles were shown up completely and clearly, the complicated structure of cell organelles was not changed any more, and there were high content of mitochondrion with well developed structure and clear crista and outer membrane. Endoplasmic reticulum in the form of annulate lamellar structure was observed in cells desiccated for 5 days and it became more and larger after 7 days desiccation. The annulate lamellar structure was not repaired after backwater. And autophagic vacuoles in embryonic cell were observed after 7 days desiccation, indicating that the seeds had suffered fatal injury. In addition, seed deterioration might be accelerated by the abnormal increase of POD activity during dehydration.(3) Although embryos would be quickly dried to lower water content by fast dehydration, seed vigor began to reduce when seed water content was as high as 0.78g·g^-1 DW. At the same time, the result of relative conductivity and FT-IR test showed that protein and cell membrane of embryos were harmed by dehydration. And results observed by electronic microscope also showed that cell nucleuses were shrunk and most organelles were disrupted or dimmed in radicle cells that were filled with numerous of vacuous and starch grains.