| Trichosanthes Kirilowii. Maxim seed is dormant, which troubles its large-scale production in agriculture. Research on the dormancy characteristics and germination-promoting measures will provide a key to the problem. In this study, we investigated the germination characteristics to get a initial understanding of Trichosanthes Kirilowii's dormant state. Then we resolve the dormant causes from three aspects of seed testa, embryo, and germination inhibitor. Finally, according to the causes, feasible measures of improving germination will be provided to break dormancy.Firstly, we studied the germination characteristics of Trichosanthes Kirilowii. Seeds were put in sand under 25-35℃, and 25days later, germination percentages would be calculated. Seed storde material content and metabolic enzyme activities were tested every 5 days. The results showed that seeds with the viability of 94.7%germinated only 37.5%. The a-amylase activity during Trichosanthes Kirilowii's germination was in a low level, resulting in the less utilization ratio of starch, which was only 26.6%in the germination process. In addition, seed's nitrogen source re-allocation does not make full. From these results we determined that Trichosanthes Kirilowii seed was dormant. Metabolic enzymes have been activated or synthesised to some extent in the early germination period, but most enzymes fell little in the later process except forβ-amylase. Correspondingly, seed's storde material was not fully mobilized and finally resulting in the low germination rate.Secondly, seed dormant causes was resolved. Compared with the complete seed testa, knife-cutting and completely removing was setted as treatments to determine the effect of seed testa on germination percentage. The results showed that removal of testa could quickly make the seeds imbibed, but ultimately made little difference with the control. However, germination tests had shown that despite the increases of germination percentage of knife-cutting was not obvious, the removal of testa was able to get the germination rate of 67.6%. From the perspective of embryo effect, the embyo rate in normal germination condition was monitored, the results showed that seeds which had the embryo rate of 28.2%before germination could only increased to 60.3%in the end of germination. From the point of inhibitor, water, methanol, ether extracts respectively from seed testa and kernel as germination medium, germination percentage, amylase activity, root and sheet length, and fresh weight of cabbage seeds was measured, in order to determine the distribution, polarity and kinds of inhibitors. Methanol extract from seed testa inhibited the germination percentage and amylase activity most. In all the extract from kernel, ether extract inhibited most. Thus, we believed that Trichosanthes Kirilowii. seed dormancy was a comprehensive dormancy, its seed testa and embryo had various degree of their influence to the dormancy. The seed testa limited embryo's breaking though by mechanical obstruction, and the inhibitor in testa inhibited the seeds' growth by metabolism restrictions. Embryo from maternal plant was not fully developed, and the mainly non-polar germination inhibitors also limited the growth of seeds.Finally, according to the causes, we tested some feasible measures to break the dormancy of Trichosanthes Kirilowii. (1) Seed testa was removed or acid etched in order to release the testa effect of seed dormancy.Results showed that seed germination percentage was improved to 67.6%when testa was removed, while acid etching did not have a similar result. The germination percentages improved in each treatment, especially the acid etching. So we believed that mechanical peeling was an effective means to improve Trichosanthes Kirilowii's germination percentage. However, because of the good permeability of the seed testa, acid etching treatment should be considered to reduce processing time. We also believed that, water-washed itself also had significant effect on lifting the seed germination rate. (2) Natural stratificaion, warm stratification, cold stratificaion, cold-warm stratificaion, and warm-cold stratificaion were set in order to release the Trichosanthes Kirilowii's dormancy. The germination percentages were tested after each stratificaion, and changes of amylase activity and embryo rate were monitored. The results showed that cold stratificaion and warm-cold stratificaion both had good effects, especially the latter having the percentage of 63.6%. Accordingly, despite of a reduction when temperature conversed, the embryo rate increased to 43.1%in the end of stratificaion. In addition, stratificaion process affects the a-amylase activity significantly, especially the warm-cold stratificaion, with an increase of 173.7%compared with the control. Thus, we believed that warm-cold stratification had the best effect on Trichosanthes Kirilowii's germination promoting, which may release the dormancy by hormone regulation, embryo morphological afterripening, and testa softering. (3) Seeds were set to be soaked by 100,200,500μmol/L of GA3 or CTK, and 200μmol/L GA3 and CTK to measure the hormonal regulation. Germination percentages of each treatment were tested, changes of a-amylase activity were monitored, and germination inhibitor of testa and kernel were tested. The results showed that,200μmol/L of GA3 and CTK treated together increased the germiantion rate most, reaching 63.6%, the separate treatment of the two hormone had the germination percentage of 50.4%and 53.6%respectively. We concluded that, the a-amylase synthesis or activation of GA had the important meaning to the seed dormancy-release. CTK had its own way to break the dormancy which was different from GA's. CTK's dormancy-breaking might associated with the inhibitor's cancellating. Besides, we made a deduction:there were at lease two ways of GA's dormancy-breaking, besides of metabolism promoting, perhaps it had some effects on the dormancy's physical release. |
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