同源四倍体水稻胚乳发育:糊粉层细胞壁纤维素物质发育、胚乳淀粉积累及胼胝质“套”的形成

 利用荧光显微术观察，发现同源四倍体水稻与其二倍体原种的糊粉层细胞壁纤维素物质都存在一个“充实”的过程。授粉后5～6 d，糊粉层开始分化形成，此时其细胞壁上未观察到纤维素物质；授粉后6～8 d，糊粉层细胞壁上开始积累纤维素物质；授粉后8～9 d，糊粉层细胞壁积累了大量的纤维素物质。胚乳淀粉的积累存在一个变化的过程：初生胚乳核周围可见一些淀粉体，随着胚乳游离核的增多，游离核周围淀粉体的数量逐渐减少，胚乳细胞化后，胚乳细胞内开始大量形成淀粉体。利用苯胺蓝染色连续切片荧光观察，发现同源四倍体水稻及其二倍体原种胚乳发育过程中，在珠心表皮和内珠被之间存在一层胼胝质物质，围绕着胚囊并包裹住珠心呈“套”状。这个结构的形成变化过程为：授粉后30 min在珠孔端珠心表皮细胞与内珠被之间开始积累少量的胼胝质，之后胼胝质逐渐增多并向合点端扩展延伸；授粉后1～2 d包裹着整个胚囊外的珠心而仅在维管束处断开；授粉后9～13 d，胼胝质“套”消失。该结构可能与胚和胚乳在发育期间的水分和养分的调节等有密切关系。同源四倍体水稻还存在糊粉层细胞壁发育不同步、糊粉层细胞壁结构异常以及胼胝质“套”不消失等异常现象。这些现象有可能会影响同源四倍体水稻的结实率。

Endosperm Development in Autotetraploid Rice: The Development of the Cellulose Wall of Aleuronic Layer Cell, Starch Accumulation of Endosperm and Formation of a Callose "Sheath-like" Structure

The formation of the aleuronic layer cell wall in a utotetraploid and its original diploid rice was studied by using the technique of fluorescence microscopy. The aleuronic layer cells form in 5 to 6 days afte r pollination without cellulose observed in their walls. Cellulose begins to ac cumulate in the wall of the aleuronic cells in 6 to 8 days after pollination. T he cellulose wall of the aleuronic layer cell appears to have completely form ed within 8 to 9 days after pollination. The starch grains of the endosperm ti ssue change dramatically during the period of endosperm development. Some small starch grains can be observed around the newly formed endosperm nuclei. The num ber of starch grains gradually decrease around the nuclei and almost disappear in 2 to 3 days after pollination and then increase again rapidly. A callose “ sheath-like” structure was observed between the epidermis of the nucellar tissue and the internal integument after staining with aniline blue. The formation of this structure shows a dynamic change during the endosperm development. Thir ty minutes after pollination, some calloses begin to form between the epidermi s of the nucellar tissue and the internal integument in the micropylar end and t hen extend gradually toward the chalazal end. Nine to 13 days after pollination , the callose “sheath-like” structure disappears. Non-synchronized development of endosperm cells and abnormal aleuronic layer cell wall formation were observed in some autotetraploid rice, suggesting that the malformation of aleuronic layer cell wall may contribute to the failure in the development of some autotetraploid rice. These abnormal phenomena can result in low seed settin g rate in autotetraploid rice.