拟南芥角果衰老过程中膜脂的变化

角果发育对某些物种的生殖发育具有重要的作用。拟南芥种子附着在角果里，角果在早期发育时进行光合作用，角果成熟后开裂散落种子之前，其细胞会经历一个衰老的过程。一般植物细胞在衰老过程中要经历膜脂降解的过程，但是角果细胞衰老过程仍未知。通过比较角果衰老过程中拟南芥野生型(WS)及与膜脂代谢密切相关的磷脂酶Dδ缺失突变体(PLDδ KO)中膜脂分子的组成情况、膜脂含量、相对含量及双键指数值，结果发现，在拟南芥角果衰老过程中：(i)质体膜脂和质体外膜脂显著下降；(ii)不同膜脂降解速率不一样，质体膜脂的降解比质体外膜脂的降解快；(iii)总的双键指数DBI下降；(iv)磷脂酶Dδ缺失突变体(PLDδ KO)的角果膜脂组成的基本水平和变化样式与野生型(WS)非常相似。结果说明，角果在衰老过程中发生了膜脂的激烈降解。据此推测：(i) 膜脂水解产物可能转移到种子中用于储藏脂三酰甘油的合成；(ii) 质体膜脂相对含量下降和质体外膜脂相对含量上升导致了总的DBI下降；(iii) PLDδ参与了角果衰老中的膜脂代谢。

Changes in Membrane Lipids during Silique Senescence in Arabidopsis

Silique development plays an important role in the reproductive development of many species. In Arabidopsis, the seeds are contained within a silique, which is to photosynthesize in the early stages of development and the cell undergoes a programmed of senescence prior to dehiscence after silique riping. In general, degradation of membrane lipids is an essential process during plant cell senescence, however, the senescence of silique has not been reported. In the present study, the changes of molecular species in membrane lipids, the contents of membrane lipids, relative levels (%), and the double bond index (DBI) during the senescence of siliques were examined in wild type Arabidopsis (ecotype Wassilewskija; WS) and an Arabidopsis mutant deficient in phospholipase Dδ (PLDδ KO). PLDδ is correlated closely with lipid metabolism in Arabidopsis. The present study revealed that during the senescence of siliques of Arabidopsis: (i) levels of both extraplastidic and plastidic lipids decreased significantly; (ii) the degradation of lipids did not occur at the same rate for different lipid species, the rate of decline in levels of plastidic lipids was more rapid than that of extraplastidic lipids; (iii) the DBI of total membrane lipids decreased; and (iv) in siliques of the PLDδ mutant plants, the levels and variations in the levels of membrane lipids were similar to those observed in siliques of WS. These results suggest that severe degradation of lipid molecular species occurred during Arabidopsis silique senescence. Our findings suggest that (i) the products of hydrolysis of membrane lipids may be transferred to seeds for the synthesis of triacylglycerols for lipid storage; (ii) the decline of DBI of total membrane lipids might be caused by the dramatic degradation of plastidic lipids and the relative increase of extraplastidic lipids; and (iii) PLDδ is involved in the metabolism of membrane lipids during silique senescence.