Stress-resistance And The Allelopathy Of An Invasive Plant, Galinsoga Parviflora Cav.

Galinsoga parviflora Cav(.gallant-soldier), native to South America, was first recorded in Yunnan and Sichuan in 1915. Now it has already become an invasive plant in China. Knowledge of the physiological response in stressful environments and allelopathy are very useful in determining the invasive mechanism of this plant.By using the artificial constitution temperature steps and natural dry method in this paper, the varieties of proline, soluble protein, antioxidant enzymes and monodehydroascorbate (MDA) in G. parviflora were studied by environmental stresses such as temperature and drought. The result showed that changes of antioxidant enzymes of G. parviflora were difference from 10℃to 30℃while MDA was found no significant changes and antioxidant enzymes were damaged and MDA contents sharply increased at 5℃,30℃and 35℃. For the drought treatments, the antioxidant enzymes increased at the beginning and decreased later, while MDA increased only at later stage. These results indicated that G.parviflora had a better adaptation to low temperature than the heat and drought stress. Using Fuzzy synthetic evaluation, we evaluated the developments of the antioxidant enzymes, finding that 15-30`C was the optimum temperature for the growth of G.parviflora.By using bioassay method, the allelopathy of aqueous extracts of the G.parviflora. to seed germination, seedling growth and antioxidant enzymes of rice (Oryza sativa L), wheat (Triticum aestivum L)and rape (Brassica napus L)were studied. The results showed the allelopathic effect of gallant-soldier. High concentration aqueous extracts inhibited evidently seed germination and the seedling growth, and this effect was concentration dependent, increasing with increase of aqueous extracts concentration. Under the effect of the aqueous extract, the active oxygen metabolism system and cell membrane permeability were destroyed, and the balance of the protective enzyme system was broken. With the action time of aqueous extracts prolong, the SOD active and the content of MDA of rape in leaf increased at the beginning and decreased later, but the POD active had an opposite tendency.The effect of low temperature stress on allelopathy of G.parviflora was studied by using micronucleus test in Vicia faba root tip cell. The results showed that allelopathic effects of the aqueous extracts of G.parviflora on mitotic index, micronucleus and aberration rates were changed under low temperature stress. Mitotic index decreased, while micronucleus and aberration rates increased by the aqueous extracts of G.parviflora before low temperature stress. After the low temperature stress, however, mitotic index changed in accordance with the concentration of the aqueous extracts of G.parviflora low aqueous extracts concentration of the weed led to mitotic index increase, and high concentration resulted in mitotic index decrease. In addition, micronucleus and aberration rates were significantly higher than those before the stress. Low temperature stress disturbed metabolic cooperation. When G. parvi- flora was stressed by low temperature, on the one hand, this species could enhance absorbing ability of root on mineral substance and water by increasing amount and type of allelopathic substance, on the other hand, it could strengthen its competitive ability by releasing allelopathic substance into the environment to inhibit and supplant other plants.