西瓜胚乳衰退过程中的超微结构变化及其对胚发育的作用

The ultrastructure changes of endosperm during degeneration process and its function to development of embryo in watermelon

西瓜胚乳细胞衰退过程中 ,质膜、液泡膜突起、形成体积较大的囊泡 ,内质网断裂形成体积较小的囊泡 ;细胞质和细胞核降解形成电子致密的碎片沿细胞壁分布 ;细胞壁在衰退过程逐渐变薄 ,由于部分区域分解而使整个壁呈波浪型 ,细胞降解后的物质可直接穿越薄壁处或通过宽约 5 0 nm的胞间连丝向近胚端的胚乳细胞转移。胚乳与珠心组织分界壁 -胚囊壁上有发达的壁内突 ,有利于珠心组织内的物质向胚乳内转运 ;胚乳发育早期与胚共有的壁上内外两侧均有胼胝质沉积 ,壁上无外连丝型的胞间连丝存在 ,胚乳发育后期共有壁上的胼胝质消失 ,胚乳细胞降解物可穿越共有壁进入胚细胞内。实验结果表明西瓜胚乳在发育后期对胚的发育具有重要的作用。

The endosperm of watermelon( Citrullus lanatus ) begins to degenerate from micropylar end to chalazal end at the stage of heart shaped embryo. At first, plasmalemma, vacuoles membrane and endoplasmic reticulum disintegrate into many cisterns. Then most of the electronic dense remnants locate near cell walls become thinner during cells degeneration. Some remainders directly traverse through the thinner wall or by plasmodesmatas and migrate to another cell near the embryo. There are many wall ingrowths in the boundary wall between endosperm and degenerated nucellus, which is benefit to the material transport from degenerated nucellus to endosperm. At the stage of small global embryo, the deposition of discontinuous calloses which have intense fluorescence in the boundary wall between endosperm and embryo indicates that the endosperm maybe have not any functions in feeding embryo at early stage of embryo development. But when endosperm cells near embryo degenerate, calloses disappear and some remnants of degenerated cells migrate into embryo cells, which shows endosperm playing an important role in supporting the rapid development of embryo at late development stage of embryo.