Investigation Of Endosperm Cell Development For Four Rice Varieties

In order to explore the development of rice starch endosperm and aleurone layer, in this research, the rice Nipponbare, Yangdao6, Wuyunuol6and Yangfunuo4are used as the experimental material with its caryopsis development days carefully recorded and its caryopsis development closely observed. Starch accumulation and physiological activity were observed by I2-KI, TTC and Evan’s blue staining. Structure changes of rice starch endosperm cells and aleurone layer cells during caryopsis development were observed by embedding the samples in resins, followed by cutting the resins into thin sections, and then observing the samples under light microscopes. The ultrastructure of full ripe rice caryopsis was observed under scanning electron microscope. The results are as follows:(1)The pericarp of rice is green in the development of prometaphase. Along with the increase of filling time, pericarp chlorophyll gradually disintegrated, the green color turns yellow-white, then transparent at last. The growth curve of rice caryopsis is "S" type. The length of rice caryopsis growed fastest and the thickness growed slowest. Rice caryopsis water content and the growth rate of fresh and dry weight was high at the primary stage, then decreased gradually with the increase of the developmental process and the accumulation of storage substance. Rice caryopsis was mature when the water content, fresh and dry weight was constant.(2)The epidermic endosperm cells differentiate into aleurone cells eventually. Aeurone cells contain many small vacuoles and spherosomes during the early development stage. With the accumulation of mineral elements and protein, small vacuoles became aleurone granules in the middle and late stage of development. The formation of aleurone layers is connected with the accumulation of lipids, mineral elements and other "filling wastes"(substances not stored in endosperm)in peripheral endosperm cells. So, the layers of aleurone cells in dorsal caryopsis which transport more nutrients are more than the layers of aleurone cells in ventral caryopsis. (3)The inner endosperm cells differentiate into starch endosperm eventually. The nuclei of starch endosperm cells degenerate with the enlargement of amyloplasts and proteoplast, while the nuclei of aleurone cells do not degenerate at that stage. Amyloplast continue enlarging and growing after the degeneration of nucleus, which shows that the development of amyloplasts is relatively independent.(4)Rice endosperm amyloplasts are multi-granular amyloplasts that contains several starch granules. The amyloplasts were round or elliptic at the beginning of development, and then they became multilateral. The development of amyloplast is related to certain qualities of endosperm. Maldevelopment of amyloplasts is the main cause of the chalkiness in rice endosperm.(5)Dorsal vascular bundle was the channel for the transportation of nutrients. Nutrients from dorsal vascular bundle was unloaded at the nucellar projection. Most of the nutrients were transported into endosperm by aleurone cells in dorsal caryopsis and others were transported to the nucellus tissue around endosperm, then the nutrients was transported into endosperm by aleurone cells in side and ventral. Aleurone layer was the layer by which the endosperm assimilated nutrients.