Studies On Content, Allelopathy Activity And Inducing Effects Of DIMBOA In Wheat Seedlings

DIMBOA(2,4-dihydroxy-7-methoxy -2H-1,4-benzoxazin-3 (4H)-one)is an important secondary metabolite in wheat seedlings. It has been paid much attention to because it was closely associated with wheat resistance to insects and pathogens. In this thesis, the content and activity of DIMBOA in wheat seedlings and its biological and chemical induction effects were studied. 1. The pure DIMBOA was isolated and purified, and DIMBOA detection methods were established. DIMBOA crystals were analysed with HPLC mounted with ODS C-18 reverse phase column employing an external standard quantitative method. The mobile phase of MeOH:H₂O (50:50, V/V) was pumped at 1.0 mL/min and monitored at 220nm wavelength. The HPLC condition was optimized to giving satisfactory separation, high sensitivity and good repetition (RSD for peak area 1.18% and retention time 0.319%).The formula of DIMBOA external standard curve: Area = 9.96212164*Amt + 0.3635223; R=0.999995. The analysis methods for wheat seedlings tissues and hydroponic solution have the advantages of high accuracy (recoveries > 90%) and good precision (CV < 5%), all complying with the requirement of micro-analysis. 2. HPLC quantitative analyses were carried out on DIMBOA contents in aerial parts and root parts of wheat seedlings of 31 test wheat cultivars as well as in the hydroponic solution. DIMBOA contents. The higher the DIMBOA content of wheat cultivar was, the stronger its resistance to insects and pathogens. A positive correlation exists between DIMBOA content and the resistance to insects and pathogens of wheat seedlings 3. The allelopathic effects of wheat remnants aqueous extracts were also studied. According to inhibitory IC50, the root-length inhibitory effects of aqueous extracts of Zhongfu 9507 wheat remnant to different target plant seedlings: Digitaria sanguinalis (L.) Scop> Poa annua L. > Amaranthus retroflexus L.> Echinochloa crusgalli (L.) Beauv.> Avena fatua L >Pharbitits purpurea (L.) Voigt; the stem-length inhibitory effects: Poa annua L.> Amaranthus retroflexus L.> Digitaria sanguinalis (L.) Scop. > Avena fatua L> Echinochloa crusgalli (L.) Beauv. > Pharbitits purpurea (L.) Voigt. No inhibitory effects to corn and Lolium multiflorum Lam.were detected. The IC₅₀ to the roots and stem of P. annua, A.retroflexus and D. sanguinalis fell below 1.5 dwmg/mL; IC50 to the stem and root of the other weed with medium-size seeds was smaller than 3.00 dwmg/mL. 4. The tested living wheat cultivars were mixed to sow in vermiculite matrix with either one of six weeds (D. sanguinalis, P. annua, E. crusgalli, L. multiflorum, A.retroflexus and A.fatua). Although there was no high correlation between the number of wheat seeds per square metre and the seed germination rate of weed seeds, wheat plants did show certain allelopathic effects on the germination of seeds of weeds or corn. Their germination rate decreased with increase in the number of wheat plants. 5. The overall inhibitory effects of DIMBOA to weeds with different seed size were: A. retroflexus >D. sanguinalis> A. fatua (in terms of IC50). The effects of DIMBOA and aqueous extracts of wheat seedlings were determined as follows, DIMBOA > aqueous extracts (in terms of γ2 value of weeds seed germination inhibitory effects and the value of IC50 to the root and stem elongation of the 3 target weeds). 6. According to the analytical results of DIMBOA content in aerial parts, the 6-day-old seedlings of 3 wheat cultivars (Zhongfu 9507, Jing411 and Zhongbeizhong 39) were sprayed with different concentration of methyl jasmonate (JA), methyl salicylate (SA), triadimefon, phosphate potassium dihydrogen (KH2PO4) and cupric chloride (CuCl2) The DIMBOA content of aerial parts were analysed and DIMBOA induction effects of these chemicals were determined to be methyl jasmonate > methyl salicylate > triadimefon > phosphate potassium dihydrogen > cupric chloride. At the most effective concentration of 561.0μg/mL (2.5μmol /mL), methyl jasmonate's inducement effect was far higher than any other chemicals. This might be related to the activation of the expression of resistant gene. 7. The biological induction effects of 6 kinds of weeds on DIMBOA production from root exudates and aerial parts of wheat seedlings were studied for the first time. The results of hydroponic experiments of 6 test weeds (D. sanguinalis, A. retroflexus, E. crusgalli, L. multiflorum, P. annua, A. fatua) on 3 wheat cultivars (Zhongfu 9507, Jing411 and Zhongbeizhong 39) showed that, DIMBOA content in both root exudates and aerial parts of wheat seedlings were significantly induced by 3 of tested weeds——D.sanguinalis, A. retroflexus and A. fatua L. Significant difference was detected between the induction effects on roots and aerial parts of 3 different wheat cultivars by the 3 kinds of weeds as above stated. The other 3 weeds E. crusgalli, L. multiflorum, P. annua, showed weak induction effects on DIJBOA in root exudates and aerial parts.