The Structural Characteristics Of Vascular Bundle Of Japonica Rice Caryopsis And Its Relationships With Quality Traits And Grain Filling

Japonica rice Liaojing294 and Yanfeng47 in north China were used as materials to compare the dorsal vascular bundle anatomical structures of caryopsis on primary and secondary rachises during 4-22 days after flowering (DAF). The structures of pericarp and aleuron layer, the morphological change of endosperm starch granules and quality traits and grain filling plumpness of japonica rice during the development of caryopsis were studied, besides, its relationships with traits of the dorsal vascular bundle and the rice quality corresponding to the grain position were also analyzed. The results showed that:1. The transverse section of dorsal vascular bundle of these two varieties were both near ellipse, of which area and short axis length changed as parabola along with the caryopsis development. Caryopsis weight reached max value at 12 DAF for Liaojing294 and at 10 DAF for Yanfeng47, separately. The long axis length showed monotonic increase with the caryopsis development and grain filling. The dorsal vascular bundle, which was composed of centered vascular bundle and circumjacent sieve tube, showed wide to thin from bottom to top. At the same DAF, the vascular bundle transverse section area, long axis length, short axis length, sieve tube width, vessel number, caryopsis volume and caryopsis dry weight of these two varieties were all ranked as follows:grains on top primary rachis> grains on bottom primary rachis> grains on top secondary rachis> grains on bottom secondary rachis. And these values of Liaojing294 were larger than that of Yanfeng47 at the same grain positions.2. The changes of pericarp structure, aleuron layer and endosperm starch granules during the caryopsis development of the two varieties were observed:cells in each layer were clearly observed from outside to inside when the grains were tender:exocarp, mesocarp, cross cell, tube cell layer and endoderm. Aleuron layer had been basically formed during the caryopsis development about 8-10 days, and the cell layers of aleuron layer were various around different parts of the caryopsis:There was 1 layer cell in profile, however, there were more layers near the dorsal vascular bundle, which generally contained 3-6 layers. The endosperm starch granules on the back and abdomen of two Japonica rice varieties were observed by Scanning Electron Microscope, which all revealed polyhedral crystal structure, tightly arranged, with smaller gap between the grains; Nevertheless, the starch granules around the edge of caryopsis were in a state of disorder, which were mostly spherical, loosely arranged, and there were many gaps between the starch granules. Therefore, loose arrangement and undesirable plumpness of the endosperm starch granules were the reasons which lead to rice chalkiness.3. Judging from the grain filling characteristics:to the ultimate growth and maximum filling rate, both of the two varieties on different part of rachises showed that grains on top primary rachis> grains on bottom primary rachis> grains on top secondary rachis> grains on bottom secondary rachis; However, to the time of initial growth potential and maximum filling rate, both of the two varieties on different part of rachises showed that grains on top primary rachis> grains on top secondary rachis> grains on bottom primary rachis> grains on bottom secondary rachis. The change of the two varieties on different part of rachises was analyzed, both of which showed that grains on top primary rachis< grains on bottom primary rachis< grains on top secondary rachis< grains on bottom secondary rachis; The grain weight gain of the two varieties on different part of rachises was also analyzed, at the early weight gain both of which showed that on top primary rachis> grains on top secondary rachis> grains on bottom primary rachis> grains on bottom secondary rachis, but at the plateau weight gain, both of which showed that grains on top primary rachis> grains on bottom primary rachis> grains on top secondary rachis> grains on bottom secondary rachis.4. Correlation analysis showed that, there was significantly negative correlation between the section area of dorsal vascular bundle and its long axis length, the chalky rice rate and chalkiness. A significantly positive correlation between the vascular section area, long axis length, short axis length, sieve tube width, vascular bundle number and caryopsis dry weight, caryopsis plumpness, grain plumpness was identified. The section area of dorsal vascular bundle, long axis length, short axis length, sieve tube width and vascular bundle number were significantly positively correlated with the max grain filling rate and were significantly negatively correlated with the time reached the max grain filling rate; The average of sieve tube width was significantly positively correlated with both initial and final growth potential. So, the structural difference of dorsal vascular bundle was considered as the important morphological and anatomical basis for difference of rice chalkiness, caryopsis plumpness and other accumulation related characters.