Dynamic Activity Of Endogenous Plant Hormones In Zelkova Schneideriana During The Growth Of Seedlings

Zelkova schneideriana Hand.-Mazz., the second-class state-protected species, is a valued hardwood tree. The application of Zelkova schneideriana in daily life is wide and the market demand has kept increasing because of its diversified outstanding properties, causing the uncontrolled commercial cutting, and thus making it a rare and endangered species in China. Z. schneideriana is characterized by crown inclination and divarication at the early stage of growth, which has seriously affected the application. Besides, studies are lacking in selective breeding for this tree, and no reports are found on physiological regulation of the demerits in early growth. It is significant that the relationship between the content of endogenous plant hormones and the seedling growth plus plant hormone regulation of the seedling growth process be studied.In this study, the levels of endogenous IAA, GA3, ZT, and ABA in seedlings and the tap and lateral ramification of divaricated seedlings were detected by RP-HPLC. The main conclusions are as follows:(1) The best chromatogram condition:The mobile phase was a mixture of methanol: 0.8%acetic acid; run with a flow rate of 0.8 ml-min-1 at 25℃; UV detection 254 nm.(2) The gradient elution condition:The mobile phase was programmed to hold,0-5 minutes, the first isocratic elution with a mixture of 8:92 (V/V) methanol:0.8%acetic acid, then followed by a linear gradient elution from 5 min to a composition of 50:50 (V/V) at 18 minutes, another linear gradient elution from 18 min to a composition of 75:25 (V/V) at 21 minutes, holding this mixture for 9 minutes, and finally followed by linear gradient elution from 30.01 min to a composition of 8:92 (V/V) at 40 minutes.(3) Concentration changes of four endogenous plant hormones during seedling growth of Zelkova:There were high levels of IAA and ZT but low levels of GA3 and ABA when the terminal bud was bourgeon. It shows that high levels of IAA and ZT are the basic of the terminal bud germination. However, ABA is not required in this period of development. Compared with the level of ABA in the prophase development, the higher level of ABA which keeps in cool autumn inhibits the growth of bud. During the growth of seedlings, the level of GA3 reached an obvious peak at the end of August. GA3 concent increased with the elongation of bud, our study showed that an increasing level of GA3 stimulates the growth of the seedlings.(4) The ratios of ABA to GA3. The two low points appeared in mid June and late August during the seedlings growth periods. It showed that the endogenous quantity of GA3 in this plant was more than that of ABA, and the seedlings were in bloom. In addition, the peak contents of ABA to GA3 appeared when seedlings grew slowly in October. The result suggests that seedlings come into physiological dormancy.(5) The ratios of IAA to ZT:The two low points appeared from late April to early May and late August during the seedlings'growth periods showing the seedlings are in bloom and May and August are the two flourishing growth periods of Zelkova seedlings.(6) Contents of four endogenous plant hormones in the tap and the lateral ramification of divaricated seedling during seedling growth of Zelkova:The contents of IAA, GA3 and ABA in the lateral ramification were more than the tap ramification, except that IAA level in the lateral ramification was less than the tap ramification from late September to early October. However, ZT level in the tap and the lateral ramification of divaricated seedling showed an alternate change, and the ZT level in the lateral ramification was more than that of the tap ramification at June and August.