Effect Of Elicitors On The Content Of Camptothecin And The Activity Of Tryptophan Decarboxylase(TDC) In Camptotheca Acuminata Seedlings

The elicitors, such as salicylic acid(SA), Methyl jasmonate (MeJa) and Ethrel, have drawn more and more scientists' attention for their effect on resistence to adversity of plant. They act as chemical messengers which may activate special defense genes and improve secondary metabolism in plant in order to resist the stress, such as mechanical injury. Camptothecin (CPT) is a kind of alkaloids, which may respond to a series of environmental stress .We are interested in the regulation of Camptothecm biosynthesis and in the external factors that affect it. In this article we studied the inductive effect of wounding and elicitors on the content of Camptothecin, including the best induction duration and optimal concentration of the elicitors. We also study the effect of UV-B radiation and elicitors on CPT content and activity of the key enzyme, tryptophan decarboxylase (TDC) in Camptotheca acuminata seedlings. From this study, we can discover the proposed regulatory mechanism of elicitors,and find a effective way to raise CPT production capacity.Some important results are as follows:1. Four treatments, mechanical wounding, SA, MeJa and Ethrel,could promote the content of CPT, and the improvement induced by SA and mechanical wounding are more obvious, being 47.7% and 27.2%, respectively. Interestingly,the spraying to wounded seedlings of three elicitors did not result in any additive effect on CPT accumulation, however, mechanical wounding could inhibit the effect of elicitors.2. The ability to increase alkaloid biosynthesis was due to the concentration of elicitors we used, The optimal concentrations of SA, MeJa and Ethrel were 50～100 mg·L^-1,5～10 mg·L^-1, 5～10 mg·L^-1 respectively.3. The sensitivity on elicitors was obviously different in different developmental stage of seedlings. After cotyledon expanding about 10 days, the content of CPT can be increased by 106.3% treated with SA. The improvement induced by MeJa, Ethrel and mechanical wounding are also abvious, being 66.1%,70.2% and 40.6%, respectively. The effect of the inducement declined sharply when elicitors were applied in the later growing stage.It shows that sensitive period of Camptotheca acuminata secondary metabolism to elicitors is in the initial growth stage.4. The elicitors can influence the activity of TDC and the content of CPT in Camptotheca acuminate seedlings. Comparing with the control treatment, the activity of TDC in leaves is lower after UV-B radiation treatment, but seedlings can response rapidly to resist the adverse conditions by increasing the content of CPT in leaves. The three elicitors, SA, MeJa and Ethrel, can remarkably enhance the activity of TDC by 281%,514% and 139% respectively after 24 hours treatment. The content of CPT in Camptotheca acuminate seedlings increase subsequently.5. The results show that, under UV-B radiation treatment, the activity of TDC in seedling pretreated with SA, MeJa and Ethrel, increase by 48%,13%,153%, respectively. And the high activity can keep in 72h. Meanwhile, the camptothecin content increase by 32.8%, 59.2% and 75.3% correspondingly in three of the composite treatments of UV-B radiation with SA, MeJa or Ethrel in Camptotheca acuminate seedlings.6. The increasement of TDC activity under single treatment reached the maximum at 24 hours. However, CPT content get its peak value later. If spraying Ethrel before UV-B treatment, TDC activity and CPT content have peak value at 24h after the composite treatments, but after pretreatments of SA and MeJa, TDC activity and CPT content haven't visible pertinence.