Studies On The Structure Of Dwarf And Sheathed Mutant Of Rice

The variation of dwarf and sheathed mutant A846 in its morphology and anatomic structure is studied in this thesis. There are many differences between the wild type and the mutant both in the vegetative organ and reproductive organ..The main results we obtained are shown as following:1.The height of the mutant A846 is about 38.64 cm on average. It belongs to half-dwarf mutant, which excess the half of the normal height. The agronomic characters were not as good as the wild-type, besides the tillering capacity and grain-weight.2.Dwarf traits manifest in the stage of elongating . The length of internodes in mutant is not as long as in the wild type, especially the uppermost internode, which reduced length is about 89.65% of the entire shorten length.3.The uppermost internode in the mutant is much short compared with the wild type. Which results in the sheathed panicle and the abnormal structure of the sheath. The abnormity as follows: parenchyma cells don′t exist between the lower epidermis and aerenchyma; aerenchyma become flat; the layers of parenchyma cell among the aerenchyma are reduced.4.There is no difference between the mutant and the wild type in the structure and cell length of intercalary meristem observed under light microscop . But the elongation of the parenchyma cells is restricted by some way, especially in the uppermost internode.5.The uppermost internode shortens distinctly. One reason is that the number of cells reduces by the reason of IM division is limited. Which reduced 60% the total reduced length .Another reason is that the prolongation of cell is restricted. There is differentia of position and time. Researches indicates that the middle of uppermost internode is the main position and tassel phase is the main time.6.Abnormality of microspore: At middle microspore stage, a serious of abnormal phenomenons began to appear in the microspore of the mutant A846, including the shrink of cytoplasm, the atresia of cytoplasm and nuclear.7.Abnormality of tapetum: In A846, the tapetum cells disintegration is postponed on pollen plenum stage, which agglomerates as massif. The powder chamber wall of anther on every stage thicker than the wild-type.8.Stage of pollen abortion : with the fact that most of mature pollens are typical abortive pollens and the observation on the structure of microspore, we identified that the critical period for pollen abortion was from late microspore stage to early bicellular pollen stage, and many crucial changes occurred just at that period.9.Abnormality of ovary: ovaries develop into pseudograins in mutant A846. No granulose, embryo and endosperm exist in them.