| (E)-2-hexenal is one of the green leaf volatiles(GLVs), which starts to form after disruption of their tissues and after suffering biotic or abiotic stresses. (E)-2-hexenal has inhibited microbe growth activity and is a part of plant chemical defense. (E)-2-hexenal has the activity to enhance defense genes expression, and is an intercommunion signal molecular between plant self or neighbor. (E)-2-hexenal can induce plant disease resistance against phytopathogenic fungi. However, it hadn't been reported whether (E)-2-hexenal could induce disease resistance to virus in plants.In this paper, we studied the defense responses to TMV and (E)-2-hexenal-mediated defense activation in tobacco seedlings. We also studied the effects of (E)-2-hexenal on physiological and biochemical characteristics in the cucumber seedlings. In addition, allelopathic effects of (E)-2-hexenal on cucumber seeds germination were investigated. The mainly results are as followed:1. The effects of (E)-2-hexenal on the control of TMV in tobacco leaves and the underlying molecular mechanism were investigated.15d after inoculation with TMV, the control leaves had the typical mosaic pattern, while no typical mosaic pattern was observed on the leaves treated with (E)-2-hexenal, and the natural disease incidence and disease index of the leaves treated with (E)-2-hexenal were about 45.9% and 16.0% compared to control leaves. In addition, treating tobacco seedlings with (E)-2-hexenal 24h before inoculation with TMV significantly inhibited TMV multiplication. The level of TMV-CP transcripts in control leaves was about 2.7-fold higher than that in the (E)-2-hexenal treated leaves 48h after inoculation with TMV. These results suggested that (E)-2-hexenal treatment improved the level of resistance to TMV. Our results also indicated that (E)-2-hexenal induced accumulation of H2O2, SA and SA 2-O-β-D-glucoside (SAG) in tobacco leaves. In addition, (E)-2-hexenal improved activities of defense-related enzymes and caused accumulation of tatol phenol and flavonoid in tabacco seedlings, in correlation with the induction of resistance against tobacco mosaic virus(TMV). Therefore, these results strongly suggested that (E)-2-hexenal activated the defense responses and the mode of action of (E)-2-hexenal might have been induction of SAR through H2O2 and SA signal molecules.2. We studied the effects of (E)-2-hexenal on physiological and biochemical characteristics in the cucumber seedlings and plant resistance. The results indicated that (E)-2-hexenal lowerd membrane relative permeability in the cucumber seedlings, about 15.5% to control leaves at 24h treated with (E)-2-hexenal. MDA content of control leaves was about 1.5-fold higher than that in the (E)-2-hexenal treated leaves, at 72h after treatment. The results suggested that (E)-2-hexenal treatment improved the stability of cell membrane, could significantly protect and inhibit the damage to cell membrane. (E)-2-hexenal evoked the Fv/Fm in the cucumber seedlings. Furthermore, the activity of peroxides (POD) was increased, an increase of 86.3% in (E)-2-hexenal treatment compared to the control leaves at 48h treated. These results suggest that (E)-2-hexenal could improve the physiological activities of plants to enhance plant resistance.3. In the experiment, using (E)-2-hexenal as allelopatic donors and cucumber seeds as allelopatic acceptor, the germination energy, the germination rate, the germination index, the vigor index, root length and fresh weigth were tested. Allelopatic effects of different concentration (E)-2-hexenal on seeds germination of cucumber were analyzed. The results showed, except for the positive effect of 1μM (E)-2-hexenal,5,50 and100μM (E)-2-hexenal could inhibit the germination energy, the germination rate, the germination index, the vigor index, root length and fresh weigth of cucumber seeds, compared with controls. Its allelopatic inhibitive effect increased with the concentrations rising. The SEI of 50 and100μM (E)-2-hexenal was-0.232,-0.373, respectively. |
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