Rapid accumulation of trihydroxy oxylipins and resistance to the bean rust pathogen Uromyces fabae following wounding in Vicia faba

Abstract

Background and aims: Insect damage to plants leads to wound-activated responses directed to healing of damaged tissues, as well as activation of defences to prevent further insect damage. Negative cross-talk exists between the jasmonic acid-based signalling system that is activated upon insect attack and the salicylic acid-based system frequently activated following pathogen infection. Thus, insect attack may compromise the ability of the plant to defend itself against pathogens and vice versa. However, insect herbivory and mechanical wounding have been shown to reduce fungal infections on some plants, although the underlying mechanisms remain to be defined. This work examines the effects of mechanical wounding on rust infection both locally and systemically in the broad bean, Vicia faba and follows changes in oxylipins in wounded leaves and unwounded leaves on wounded plants.

Methods: The lamina of first leaves was wounded by crushing with forceps, and first and second leaves were then inoculated, separately, with the rust Uromyces fabae at various times over a 24 h period. Wounded first leaves and unwounded second leaves were harvested at intervals over a 24 h period and used for analysis of oxylipin profiles. KEY RESULTS Mechanical wounding of first leaves of broad bean led to significantly reduced rust infection in the wounded first leaf as well as the unwounded second leaf. Increased resistance to infection was induced in plants inoculated with rust just 1 h after wounding and was accompanied by rapid and significant accumulation of jasmonic acid and two trihydroxy oxylipins in both wounded first leaves and unwounded second leaves. The two trihydroxy oxylipins were found to possess antifungal properties, reducing germination of rust spores.

Conclusions: These results demonstrate the rapidity with which resistance to pathogen infection can be induced following wounding and provides a possible mechanism by which pathogen infection might be halted.

Fig. 1.

Effect of wounding first leaves of broad bean on rust infection of first leaves. Leaves were inoculated with rust 1, 4 and 24 h after wounding. Values represent means ± s.e.m. of five replicates. All treatments are significantly different from the unwounded controls at P ≤ 0.01.

Fig. 2.

Effect of wounding first leaves of broad bean on rust infection of second leaves. Second leaves were inoculated with rust 1, 4 and 24 h after wounding. Values represent means ± s.e.m. of five replicates. All treatments are significantly different from the unwounded controls: wounded 1 h P ≤ 0.05; wounded 4 and 24 h P ≤ 0.01.

Fig. 3.

Chemical structures of the two trihydroxy oxylipins.

Fig. 4.

Effect of wounding first leaves of broad bean on concentrations of TriHOE1 in first (open bar) and second leaves (black bar). TriHOE1 was not detected in unwounded plants. Values represent means ± s.e.m. of four replicates.

Fig. 5.

Effect of wounding first leaves of broad bean on concentrations of TriHOE2 in first (open bar) and second leaves (black bar). TriHOE2 was not detected in unwounded plants. Values represent means ± s.e.m. of four replicates.

Fig. 6.

Effect of wounding first leaves of broad bean on jasmonic acid (JA) concentrations in first and second leaves. Values represent means ± s.e.m. of four replicates. Treatments are significantly different from unwounded controls at 4 and 24 h (P ≤ 0.001).

Fig. 7.

Effects of 1–60 μm TriHOE1 and TriHOE2 on germination of uredospores of U. fabae. Values represent means ± s.e.m. of four replicates (each replicate represents 100 counted spores). Significant differences from the control are shown at ^*P ≤ 0.01 and ^**P ≤ 0.001.

Fig. 8.

Effects of 1–60 μm JA on germination of uredospores of U. fabae. Values represent means ± s.e.m. of four replicates (each replicate represents 100 counted spores). Only 60 μm JA was significantly different from control (^*P ≤ 0.01).