Abstract
BackgroundThe feeding of Bemisia tabaci nymphs trigger the SA pathway in some plant species. A previous study showed that B. tabaci nymphs induced defense against aphids (Myzus persicae) in tobacco. However, the mechanism underlying this defense response is not well understood.Methodology/Principal FindingsHere, the effect of activating the SA signaling pathway in tobacco plants through B. tabaci nymph infestation on subsequent M. persicae colonization is investigated. Performance assays showed that B. tabaci nymphs pre-infestation significantly reduced M. persicae survival and fecundity systemically in wild-type (WT) but not salicylate-deficient (NahG) plants compared with respective control. However, pre-infestation had no obvious local effects on subsequent M. persicae in either WT or NahG tobacco. SA quantification results indicated that the highest accumulation of SA was induced by B. tabaci nymphs in WT plants after 15 days of infestation. These levels were 8.45- and 6.14-fold higher in the local and systemic leaves, respectively, than in controls. Meanwhile, no significant changes of SA levels were detected in NahG plants. Further, biochemical analysis of defense enzymes polyphenol oxidase (PPO), peroxidase (POD), β-1,3-glucanase, and chitinase demonstrated that B. tabaci nymph infestation increased these enzymes’ activity locally and systemically in WT plants, and there was more chitinase and β-1, 3-glucanase activity systemically than locally, which was opposite to the changing trends of PPO. However, B. tabaci nymph infestation caused no obvious increase in enzyme activity in any NahG plants except POD.Conclusions/SignificanceIn conclusion, these results underscore the important role that induction of the SA signaling pathway by B. tabaci nymphs plays in defeating aphids. It also indicates that the activity of β-1, 3-glucanase and chitinase may be positively correlated with resistance to aphids.
Highlights
The term induced plant resistance refers to biochemical, physiological, and developmental changes that take place in plants following stimuli, that can antagonize the settling, growth, development, and host-plant selection behavior of insects [1, 2]
Utilizing transgenic NahG tobacco plants as a contrast, we aimed to answer the following three questions: (1) Is the defense of tobacco against subsequent M. persicae infestation different in WT and NahG plants pre-infested with B. tabaci? (2) Does the salicylic acid (SA) level have a direct relationship with the induced resistance to M. persicae in tobacco plants? (3) What defense enzymes contribute to this induced resistance against M. persicae in tobacco plants?
Based on Cox proportional hazards model, survival of M. persicae on local leaves of infested WT plants did not differ significantly from that of the uninfested control (P = 0.859) (Fig 1A), but it was significantly lower than the control values on systemic leaves (P < 0.001)
Summary
The term induced plant resistance refers to biochemical, physiological, and developmental changes that take place in plants following stimuli, that can antagonize the settling, growth, development, and host-plant selection behavior of insects [1, 2]. These defenses limit damage caused by plant attackers and stimulate resistance to counter future challenges [3]. The molecular mechanisms involved in plant defense are mediated mainly by the salicylic acid (SA) and jasmonic acid (JA)/ethylene (ET)-dependent signaling pathways [5]. The mechanism underlying this defense response is not well understood
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