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Title: Cytokinin inhibition of senescence and its effect on Nicotiana-Pseudomonas interactions

item Smigocki, Anna
item Baker, Con

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2008
Publication Date: 11/1/2008
Citation: Barna, B., Smigocki, A.C., Baker, C.J. 2008. Cytokinin inhibition of senescence and its effect on Nicotiana-Pseudomonas interactions. Phytopathology. 98:1242-1247.

Interpretive Summary: Plant diseases cause major losses to farmers each year. Better understanding of the biochemical basis for plant resistance to disease will lead to strategies to improve plant health and reduce losses. In many diseases the symptoms that develop often mimic a rapid aging process that ends in the death of the tissue. In this paper we report the discovery that plants that have been genetically engineered to over produce cytokinin, an “anti-aging” chemical that keeps tissue active and juvenile, are less susceptible to bacterial disease. This information will be of use to plant scientists who are devising new strategies to improve disease resistance in plants.

Technical Abstract: Responses of cytokinin overproducing transgenic Nicotiana plants to infections with compatible and incompatible Pseudomonas syringae pathovars were compared. Plants used were transformed with the ipt (isopentenyl transferase) gene that catalyzes the synthesis of cytokinin. In cytokinin overproducing lines that carry the ipt gene fused to the CaMV 35S (Nt+ipt), the wound-inducible proteinase inhibitor II (Ntx+ipt) or the light-inducible Rubisco small subunit protein (Npl+ipt) promoter, the development of hypersensitive response (HR) after infection with incompatible bacteria (Pseudomonas syringae pv. tomato) was significantly inhibited as compared to the untransformed (Nt) controls. The number of colony forming units of P. syringae pv. tomato bacteria was slightly reduced in the cytokinin overproducing Nt+ipt line as compared to the Nt control. When the compatible P. syringae pv. tabaci was used to infect the ipt transformed lines, slight or no significant differences in necrosis development were observed. Following infection, the titer of P. syringae pv. tabaci increased rapidly in both the transgenic and control lines but was higher in Nt+ipt plants. Leaf superoxide dismutase and catalase enzyme activities were about 60 % higher in ipt leaf extracts than in the controls. This augmented antioxidant capacity likely decreased the amount of H2O2 that may be associated with the higher tolerance of plants to pathogen induced necrosis. In addition, the Nt+ipt lines had a significantly lower molar ratio of free sterols to phospholipids. The more stable membrane lipid composition and the higher antioxidant capacity likely contributed to the suppressed HR symptoms in the cytokinin overproducing Nt+ipt plants.