Study On Embryology Of Houttuynia Cordata Thunb

Houltuynia cordata Thunb., a perennial herb, belongs to Saururaceae Houttuynia. The whole grass can be used as a traditional Chinese herbal medicine. It consists of methyl nonyl ketone, decanoyl acetaldehyde and flavonoids compound. And it has important clinically application value as for its heat-clearing, detoxifying, anti-bacterial and anti-inflammatory effects. The young rhizomes and leaves with rich nutrition can be used as special vegetable. And it is one of medicinal and edible plants released in2005by The Ministry of Health. H. cordata widely distribute in East and South Asia and rich wild resources in China. So far, studies on H. cordata have mainly focusd on the chromosome numbers of wild resources, microspore development, active ingredient research, and pharmacological activities etc.. But its embryo sac, embryo, and seed development has been rarely reported.The12wild materials of H, cordata were collected from Hubei, Hunan, Sichuan, Hainan and Zhejiang provinces for the study of embryo sac and embryo development using the whole mounting and paraffin method. The detection of pollen sterility and stigma pollen recognition was also conducted in this study to provide the theoretical basis for the mechanism of male sterility, seed development and germination, and for seeds breeding cultivation techniques of H. cordata. The summary of research results were as follows:1. Detection of pollen fertility was conducted in8different groups of H. cordata. Results showed that Y09SCh had highest pollen fertility97.21%while Y01XSh had the lowest0.38%. The pollen fertility of the other six groups ranged from86.72%to97.13%. The pollen germination was detected in vitro in all groups except Y01XSh. Results showed that6populations had high pollen germination rate ranging from81.80%to95.35%while the rest2populations had lower rate of45.99%and41.55%respectively.The8populations mentioned above were self-pollinated meanwhile cross-pollination after emasculation was conducted between Y09SCh and Y11HN with the same flowering time. Stigma and pollen compatibility were observed respectively. Results showed that the stigma pollen was incompatible by self-pollination in the8populations and cross-pollination in the both populations.2h after pollination, stigma papilla cells produced callose. The fertility pollen grains germinated regularly after10h, but the pollen tube could not grow into the stigma. The anther tissue was observed via paraffin section method for Y01XSh and Y09SCh. Results showed that the anther wall of H. cordata was composed of four layers, which were epidermis, endothecium, middle layer and tapetum. Although the pollen fertility was significant different between the two groups, the tapetum cells degenerated normally providing nutrition for microspore development.2. The embryo sac development of Y01XSh was observed by whole transparent and differential interference microscope. Paraffin section and hematoxylin dyeing technology was used for the observation of Y06XN-1embryo sac development. Both experiments showed the same results. The megaspore mother cells were observed to divide to form a megaspore tetrad. The three megaspore degenerated at the micropyle end. The megaspore developed into the functional megaspore at the chalazal end. Then the functional megaspore underwent three times meiotic division successively resulting in formation of the8-nucleate embryo sac. The embryo sac development of H. cordata belongs to a monospore Polygonum type.3. Analysis of the embryo development for Y06XN-1was conducted using paraffin section and hematoxylin dyeing technology. The results showed that the two polar nuclei fused to form the central cell shortly after eight nuclear embryo sac formation. The one synergid cell first started to degenerate following by degeneration and disappearance of antipodal cells. Most embryos were developed from egg cell and one persistent synergid cell. The central cell didn’t divide and disappeared at last. Therefore the seeds had no endosperm. In addition, endomitosis occurred on about60%of egg cells resulting in formation of multinucleated cells. Cytomixis was observed between few egg cells and synergid cells.The results of embryo development assessed by paraffin section and I2-KI dyeing showed that starch gradually accumulated in nucellus cells during the embryonic development. As a result, nucellar cells of mature seeds were filled with starch grains.