Action Mechanism Of Xanthomomas L4 Phytotoxin For Weed Control

The chemical and physical characters of Xanthomonas L4 phytotoxin, including its heat stability, liposolubility, molecular weight and effect of pH on weed control activity, then its action mechanism on the cell level was explored, and the inhibitory condition of Xanthomonas L4 phytotoxin was also further studied. Researches on bacterial herbicide are mostly limited to weed control test with phytotoxin from bacterial fermentation broth. However, mechanism of weed control was reported scarcely in the home and abroad. So works reported in this research will provide foundation for developing Xanihomonas L4 phytotoxin as a new kind of bacterical herbicide.The tests of ethyl acetate extraction and dialyzation from Xanihomonas L4 fermentation broth demonstrated the L4 phytotoxin was very liposoluble compound and belonging to micromolecular, further experiments indicated it was very stable under high temperature and phytotoxin have highest bioactivity at pH4. The experiment of selecting adjvant showed that Tween-80, JFC, SDS, Silicone was suitable for Xanthomonas L4 phytotoxin at lower concentration and 1% Tween-80 was best adjvant.After Amaranthus retro/lex (redroot amarant) were infected by Xanthomonas L4 phytotoxin in greenhouse, the variation of soluble protein, DNA, peroxidase (POD) activity, malon dialdehyde (MDA), photosynthetic conversion efficiency, cell memebrane permeability and respiratory ratio of leaves were dertemined with Coomassie Brilliant Blue, UV spectroscopy, guaiacol, thiobarbituric acid, PAM201-pulse modulation fluorometer, conductometry and LI-6400 Portable Photosynthetic System, and the change of cell ultrastructure and epidermis of leaves were also inspected with transmission electron microscope(TEM) and scanning electron microscope(SEM). The experiment results showed respiratory ratio and POD activity increased 106 % and 50 % Respectively after treat 2h, photosynthetic conversionefficiency, MDA and soluble protein was not inhibited. Ultrastructre observationrevealed that the thylakoids of chloroplast and cristae of mitochondria swelled after 2h treating with the poison; however after 3h treating, cell membrane was disrupted,chloroplast was disintegrated and mitochondria was vesiculated, finally respiratory ratio was inhanced, at last stoma was closed, heat of transpiration couldn't be emitted and leaf began to wilt. So the Xanthomonas L4 phytotoxin's target is mitochondria, which disrupted ATP synthesis metabolic process by blocking process of oxidation coupling with phosphorylation.