Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 30, 2001
Publication Date: January 2, 2002
Citation: Mckenzie, C.L., Shatters, R.G., Mayer, R.T. 2002. Effect of geminivirus and bemisia infestation on induction of pathogenesis-related proteins in tomato. Archives of Insect Biochemistry and Physiology. 2002. v. 49: p. 203-214. Interpretive Summary: Pathogenesis-related proteins (PRs) in plants have been defined as those proteins that are uniquely induced in pathological or related situations. PRs such as chitinases, B-1,3-glucanases and peroxidases are speculated to play a role in plant defensive systems by raising the resistance level to plant pests and phytopathogens. Phytophagous insects (e.g. whiteflies) have been shown to induce these proteins as a result of direct feeding. Control strategies for insect pests can be developed that utilize biological control agents in concert with plant defensive enzymes. Our objective was to compare the effect of tomato mottle virus (ToMoV) and whitefly infestation on induction of PR proteins (chitinase, B-1,3-glucanase, peroxidase, P2 and P4) in tomato over time. Under our experimental conditions, it is clear that the whitefly-ToMoV complex is a much stronger inducer of tomato PR-proteins response than whiteflies alone. Because of the increased nymph production by the viruliferous whiteflies, the cause of the increased PR-protein response when the virus is present may be the result of either increased feeding pressure of viruliferous whiteflies or direct interactions of virus and plant.
Technical Abstract: The effect of tomato mottle virus (ToMoV) and whitefly infestation on induction of PR proteins (chitinase, B-1,3-glucanase, peroxidase, P2 and P4) in tomato was compared. Tomato PR protein response was measured over time in plants divided into 3 treatments: untreated controls, plants infested with healthy whitefly, and plants infested with ToMoV carrying whitefly. Six- to seven-leaf plants were infested with 5 adult whitefly per leaf. Subsequent plant samples were pulled prior to whitefly infestation and at 14, 28, 42, and 56 days post-infestation for protein and enzyme analyses. By 56 days, there were 3-fold more whitefly nymphs on plants infested with viruliferous whiteflies than on healthy whitefly infested plants. Significant increase in the enzymatic activity of all measured PR-proteins, as compared to control plants, was only seen in viruliferous whitefly infested plants. No significant difference was observed in enzyme activities between uninfested and healthy whitefly infested plants; however a trend for healthy whitefly induced increases in PR protein activities was observed. Foliar protein in tomato did not differ significantly among treatments for any of the sample dates indicating that any significant changes in enzyme levels was a result of differences in the specific measured enzymes. The greatest differences for all PR proteins assayed was observed 42 days after treatment initiation. Western blot analyses showed that the differences in PR- protein activities among the treatments were due to changes in specific enzyme levels within the plant and were associated with concomitant increases in levels of P2 and P4 PR-proteins; however, the level of viral induction of PRs was variable among virus infected plants.