| Rice direct sowing is one of the main trends of rice production and development in the world. The difficulty of seedling emergence of direct-seeded rice lead to delay the heading time and prolong the ripening stage which also effect full heading and yield. Significant correlation was found between the mesocotyl elongation and the emergence rate of direct sowing. The variety of semi-dwarf cultivated rice have a better emergence capacity with the shallow soil covered because of its shorter mesocotyl and poor elongation capacity. But it influenced the quality of rice shoot seriously at a dry land direct sowing or deep soil direct sowing. Therefore, excavation of the rice germplasm of longer mesocotyl and high emergence rate should be done to overcome the difficult of seeding emergence and then it is to be better breed the variety have longer mesocotyl and promote development of direct seeding.Weedy rice is fine in rice improvement especially in resistance breeding which has preferably genetic variation、adaptability and stress-resistance. Mesocotyl elongation is important for emerging, mesocotyl length materials of WR04-6and WR04-43and mesocotyl short materials of Akihikari of weedy rice were used in this study to discuss the essence of mesocotyl elongation and discuss its regulation of hormone、mechanism of physiology enzyme^response of exogenous hormone and the molecular base. The main findings are as follows:1. To observed the cytomorphology of mesocotyl in the dark condition by artificial climate chamber, the study used varieties as WR04-6、WR04-43and Akihikari,then the result showed that the elongation growth of seedling mesocotyl could occurred only at dark condition; The difference of height between varieties at seedling stage were caused by mesocotyl elongation. To observed mesocotyl cell morphology by the paraffin method and the result showed that the number of mesocotyl cell account for80%of total at whole period and then cell division and proliferation stop. The cell number of longitudinal and cell length of long mesocotyl material of weedy rice were higher100%to Akihikari, and400%than those of short mesocotyl material respectively. The cell division and elongation promoted elongation growth of seedling mesocotyl together during early stage of that and then it depended cell longitudinal extending later. The added cell number and cell elongation promoted mesocotyl elongation together while cell longitudinal extending made a decision effect on elongation growth of mesocotyl.2. Study on endogenous hormone of mesocotyl elongation show that GA、IAA and CTK could promote elongation of mesocotyl. On all stage, GA、IAA and CTK of WR04-6and WR04-43were higher than those of Akihikari. Among these endohormone, GA has the greatest difference than the IAA and CTK. Content trend of these hormonal were different. With seedling growth, GA and CTK were decline but IAA was growing continually. No matter days, differences of hormone content with materials were keep accordance and also the mesocotyl elongation.3. The dynamics research of mesocotyl elongation showed that the materials with long mesocotyl could improve activity of α-amylase and (3-amylase, and had a high content of soluble sugar. The improvement of amylase activity could result in the degradation for starch storage material, as well as priovide abundant energy substrate and carbon frame. Meanwhile, the content of solube sugar had consistent change with amylase activity.a-amylase,(3-amylase and soluble sugar provided powerful energy sources for elongation of mesocotyl.4. Research on the components of cell wall of mesocotyl showed that the content of cellulose had a increase with the seedling growth, and which of weedy rice with long mysocotyl was lower than that of akimitsu with short mesocotyl; Rusults of cell wall enzymology of mesocotyl showed that activity of β-1,3-glucanase had varying increase with seedling growth, WR04-6was the highest, WR04-43took a second place, and akimitsu was the lowest in tested materials, the changes manifested as consistent with length of mysocotyl. The activity of β-1,3-glucanase had a vary influence on elongation of mesocotyl; The changes of activity of cell wall ecllulose presented as a modest increase in the whole growth stage of hypocotyl elongation, it could accelerate hydrolysis of cell wall fiber, make cell wall loosening, and promote cell elongation; IAA oxidase was declined steadily; POD avtivity had a consistent change with IAA oxidase in the whole growth stage of mesocotyl elongation, but the weedy rice of WR04-6and WR04-43were significantly lower than akimitsu. The lower acitivity of cell wall oxidase promoted the transformation rate of conjugated IAA to free IAA. increased more free IAA in cells, and then enhanced content of IAA in mesocotyl.5. Three exogenous hormones such as GA、IAA、CTK can significantly promote mesocotyl of extension, which of GA is playing important role for promotion of WR04-6, secondly for WR04-43; IAA is playing important role for promotion of WR04-43, secondly for WR04-6; CTK was no significant difference for promotion of three materials. On the whole, GA is the most important for promoting extension of mesocotyl, IAA take a second place, effect of CTK is least. Applied GA can stimulate synthesis of IAA and make cell wall relax, extensibility of cell wall increase, and reduce longitudinal extension resistance of cell, accelerate the growth, promoting extension of cell. Applied IAA can promote extension growth of mesocotyl. The main effect was improve activity of cytohydrolist and decrease oxidase activity of cell wall, so as to make cell wall relax, induced elongation growth of cell.6. The depolymerization of mesocotyl cells of weedy rice in rapid elongation in microtube was significant, and microtubules tend t-type perpendicular to the axis of cell elongation. The application of low concentration of oryzalin (25nM) further increases the mesocotyl length in both weedy rice and cultivared rice Akihikari. In contrast, MTs-stabilizing drug taxol significantly inhibit the elongation of mesocotyl at the concentration of1μM or over. Here, we found that several genes encoding MAP65s were downregulated during the later stage of weedy rice mesocotyl elongation which may be closed relationship with the reorganization of MTs in weedy rice mesocotyl elongation. At the same time, morl, a gene coding for microtubule binding protein has higher gene expression. However, p60(1), p60(2) and p80.Which were encoding MT-serving enzymes have significant lower gene expression. In this study, we provided the evidence that dynamic instability of MTs in mesocotyl cells is essential for rice mesocotyl elongation.7. Using an F2population derived from the parents of short-mesocotyl WCVS02428and long-mesocotyl WR04-6and131SSR molecular markers built genetic linkage map.There were131pair primer had polymorphism between parents in all of935pairs SSR primer and its frequency was13.7%.The total distance was1384.4cM of the131markers and cover90.5%of whole genome, mean distance of makers was10.6cM. The four genes control the length of mesocotyl was mapped on chromosome1,2,3and4, the range of LOD was 2.54-3.77, phenotype contribution rate of single QTL was6.39-16.75%. This genetic linkage map established foundation for researching various traits of WR04-6and mesocotyl QTL... |
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