| Harpins are glycine-rich, protease-sensitive, heat-stable, acidic proteins produced by Gram-negative plant pathogenic bacteria, and are required for induction of the hypersensitive response (HR) or hypersensitive cell death (HCD) in nonhost plants of bacteria. Application of harpins to many plants can enhance plant growth, induce resistance to pathogens or insects and improve tolerance to environmental adversity like drought.However,what signaling processes contribute to enhanced plant growth (EPG) or drought tolerance (DT) in plants treated with harpins have been unclear. This study was aimed to address questions on harpin signaling in EPG and DR by determining whether the phenotypes are attributable to activation of signaling pathways. By now, the target sites of harpins on plant cells are not clear.The cellular localization of harpins are closely related to the contituative signal transduction.However as which part of the plant cell is cell wall,cell membrance or cytoplasm ,there is no consistent conclusion from different research. The author tried to use the fluorescent protein labelled harpinxoo and harpinxooc to analyze their cellular localization in rice plant. 1. Harpin enhance plant growthHarpinEa can enhance plant growth in coincidence with relevant physiological responses and expression of several genes involved in ethylene signaling pathway.In the assay on four different kinds of plants treated with harpinEa including Arabidopsis, tomato, tobacoo and rice were taller and their individual weight were higher than those treated with water. Total leaf nitrogen content (TLN),chlorophyll a/b ratio(Chl.a:b) and chlorophyll content (Chi) which were connected closely with photosynthesis of plant were measured at seven days after treatment with harpinEa and CFVP(cell-free vector preparation).These results suggested that harpinEa can improve the TLN ,Chl and Chl.a:b. Application of to Arabidopsis thliana induces expression of the EIN2, ETR1, ERS1,PDF1.2, andPR-3b genes.Whereas PDF1.2,and PR-3b are molecular markers of the ethylene signal transduction pathway,which regulates growth and development and many other processes in plants, ERS1,ETR1 and EIN2 function as ethylene receptors and a transcriptional regulator in the pathway. Further,application of harphiEa induces expression of genes encoding expansin that played significant role in plant growth.2. Harpin -induced DT is mediated by ABA in tobacooHarpinxoo conspicuously increased drought tolerance (DT) of plants which water had been withheld for seven days before treatment with the protein and subsequently grown under water stress conditions for another 10 days. Up to 7 days of water stress (WS),Harpinxoo-treated plants grew well as those regularly watered. In contrast, control plants sprayed with water became wilt and faded away soon.Moreover, microscopic observation showed evident differences in stomatal status between plants treated water and Harpinxoo-By 6 days after the protein application and 7 days after WS, approximately 70% stomata closed. In contrast, during the same period, only 24% stomata closed on leaves of control plants.Harpinxoo effectively reduces some drought severity.Harpinxoo can also induce other physiological characteristics related to drought tolerance.These include: increasing the levels of endogenous proline, reducing cell membrane permeability . improving superoxid dismutase (SOD) activities and decreasing the content of malondialdehyde (MDA).In these responses, harpinx00 acted as similary as did ABA.However harpinx00 kept at lower levels than ABA-control,and no changes are found in the negative control in which the plants were treated regularly with water. In plant grown under water stress conditions,harpinxoo induced the accumulation of endogenous abscisic acid similarly to ABA. However the amount of increase and timing are different between two treatments. Compared to the control plants, faster and larger increase in endo-ABA concentration was found in plants treated with harpinxoo- Genes osmotin, pkll-cl andphi-2 were expre...
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