Studies on the plant growth substances causing the growth and enlargement of tubers in yams (Dioscorea alata L.)

本研究建立了一种新的生物测定方法，利用山药试管块茎，检测诱导块茎生长和膨大的内源生长物质的活性。本文介绍了一种新的测定甘薯块茎的方法--微型块茎试验，该方法能可靠地测定甘薯内源生长物质的作用，并在甘薯叶片提取物的酸性组分中发现了块茎膨大活性。短日照时酶活性增加，长日照时酶活性不增加。在季节变化上，夏季块茎膨大活动基本保持不变，9月中旬以后，在试管薯试验的指导下，用气相色谱法对茉莉酸进行了分离和鉴定，结果表明，短日照条件下，叶片中形成的块茎膨大活性，在地下传递，用5种浓度的赤霉素（GA）对山药进行喷雾处理，处理时间为2 ~ 4个月。赤霉素对主茎的伸长没有促进作用，反而略有抑制作用。高浓度GA强烈抑制枝的发育和伸长。与此相反，即使在长日照条件下，GA处理也能促进块茎的生长和膨大。在生长后期叶面喷施GA能显著延长山药块茎的休眠期，这表明山药对GA有特异反应，GA能延长山药块茎的休眠期。

A new bioassay method, using in vitro microtubers of yams, detecting the activity of the endogenous growth substances considered to induce the growth and enlargement of tubers was developed in this studies. The new method "microtuber test" developed is considered to be reliable enough to enable to detect the action of the endogenous growth substances.Using a microtuber test, tuber enlargement activity was found in acidic fraction of extract obtained from leaves in yams. The activity increased under short day length, whereas not incrrease under long day length. In seasonal change, tuber enlargement activity remained almost constant during summer, but after, the middle of September, activity increased gradually and then reached a maximum in early October.Jasmonic acid was isolated with the guidance of microtuber test and identified by gas chromatography.These results seem evidences for the occurrence of the tuber enlargement activity which is formed in leaves under the short day and transmitted to under ground part to induce growth and enlargement of tuber in yams.Yam plants were sprayd with gibberellin (GA) of five concentration levels for two to four months after planting. The application of GA did not promote the elongation of main stem, but instead sligtly inhibited. Highly concentrated GA strongly inhibited the development and elomagation of branches. In contrast, the GA application stimulated the growth and enlargement of tuber even under the long day. It was also observed that foliar spray with GA at the later growth stage significantly extended the period of a dormant state in tubers.These results indicates that yam plants might have a characteristic response to GA and that the application of GA elongates the dormant period of tubers in yams (D.alata).