大豆种子吸胀冷害抗性与其质体膜脂不饱和度正相关

吸胀冷害是干种子在吸胀阶段遭受低温造成不萌发的现象，结果可能造成农作物损失严重。虽然吸胀过程中细胞膜的修复是关键事件，而且细胞膜在响应水分和温度胁迫中扮演重要角色，但是种子吸胀过程中膜变化的过程，特别是膜流动性变化过程研究较少。本文比较了吸胀冷害耐受型（LX）和敏感型（R5）两个大豆品种在吸胀冷害过程中膜脂不饱和度（double bond index, DBI）的变化，结果发现，LX和R5在常温（25℃）吸胀时变化趋势一致，质体膜脂DBI升高，质体外膜脂中磷脂酰甘油(phosphatidylglycerol, PG)分子DBI下降。LX和R5在低温（4℃）吸胀时DBI变化有很大差异，低温吸胀仅仅延缓了耐受型LX中质体膜脂DBI的升高，但是敏感性R5质体膜脂DBI不仅没有升高反而下降。用浓度33%的聚乙二醇 (polyethylene glycol, PEG)引发没有直接引起DBI变化，但是所引起的细微而显著的变化可能为萌发做好准备。PEG引发处理后的R5在吸胀冷害后第二和第三阶段质体膜脂DBI迅速增加，这个增加模式与LX的DBI增加相似。结果表明，吸胀冷害延缓或者阻滞了质体膜脂不饱和度的升高，大豆种子的吸胀冷害抗性与质体膜脂不饱和度正相关，提高质体膜质DBI可以提高吸胀冷害抗性。

The Degree of Unsaturation of Plastidic Membrane Lipids is Positively Associated with Tolerance to ImbibitionalChilling in Soybean Seeds

 Injury caused by imbibitional chilling is a common phenomenon during rehydration of desiccated seeds, and usually causes seriously compromises seedling emergence and crop yield. Restoration of the cell membranes is a critical event during imbibition, moreover it is very important in responses to water and temperature stress. However, the changes in membrane structure during seed imbibition, especially those related to membrane fluidity, have yet to be investigated. This study compared changes in the level of unsaturation of membrane lipids  (double bond index, DBI) between chilling tolerant ‘LX’ and chilling sensitive ‘R5’ soybean cultivars during imbibitional chilling. After imbibition at normal temperature (25℃), seeds of LX and R5 showed similar changes in the level of lipid unsaturation, with increased DBI values for plastidic lipids and reduced levels of extraplastidic phosphatidylglycerol (PG). In contrast, there were dramatic differences in the changes of DBI between LX and R5 following imbibition under chilling conditions (4℃). Chilling only delayed the increase of plastidic DBI in seeds of the tolerant cultivar LX, whereas plastidic DBI did not increase or even decreased in the sensitive cultivar R5 under these conditions. Priming of seeds by incubation in 33% polyethylene glycol (PEG) did not directly cause changes in DBI, however, the subtle but significant changes in DBI that it induced prepared the soybean strain for germination. Plastidic DBI increased during phases II and III of germination in PEG osmoconditioned R5 seeds under imbibitional chilling stress; this increase was similar to the patterns of increase in DBI of LX. Our results suggest that chilled imbibition delays or prevents the increase of the degree of unsaturation in plastidic membrane lipids, that tolerance to imbibitional chilling in soybean is positively associated with an increase in the level of unsaturation of plastidic membrane lipids, and that increased plastidic DBI could improve tolerance of imbibitional chilling.