Differential volatile emissions and salicylic acid levels from tobacco plants in response to different strains of Pseudomonas syringae

Abstract

Pathogen-induced plant responses include changes in both volatile and non-volatile secondary metabolites. To characterize the role of bacterial pathogenesis in plant volatile emissions, tobacco plants, Nicotiana tabacum L. K326, were inoculated with virulent, avirulent, and mutant strains of Pseudomonas syringae. Volatile compounds released by pathogen-inoculated tobacco plants were collected, identified, and quantified. Tobacco plants infected with the avirulent strains P. syringae pv. maculicola ES4326 (Psm ES4326) or pv. tomato DC3000 (Pst DC3000), emitted quantitatively different, but qualitatively similar volatile blends of (E)-beta-ocimene, linalool, methyl salicylate (MeSA), indole, caryophyllene, beta-elemene, alpha-farnesene, and two unidentified sesquiterpenes. Plants treated with the hrcC mutant of Pst DC3000 (hrcC, deficient in the type-III secretion system) released low levels of many of the same volatile compounds as in Psm ES4326- or Pst DC3000-infected plants, with the exception of MeSA, which occurred only in trace amounts. Interaction of the virulent pathogen P. syringae pv. tabaci (Pstb), with tobacco plants resulted in a different volatile blend, consisting of MeSA and two unidentified sesquiterpenes. Overall, maximum volatile emissions occurred within 36 h post-inoculation in all the treatments except for the Pstb infection that produced peak volatile emissions about 60 h post-inoculation. (E)-beta-Ocimene was released in a diurnal pattern with the greatest emissions during the day and reduced emissions at night. Both avirulent strains, Psm ES4326 and Pst DC3000, induced accumulation of free salicylic acid (SA) within 6 h after inoculation and conjugated SA within 60 h and 36 h respectively. In contrast, SA inductions by the virulent strain Pstb occurred much later and conjugated SA increased slowly for a longer period of time, while the hrcC mutant strain did not trigger free and conjugated SA accumulations in amounts significantly different from control plants. Jasmonic acid, known to induce plant volatile emissions, was not produced in significantly higher levels in inoculated plants compared to the control plants in any treatments, indicating that induced volatile emissions from tobacco plants in response to P. syringae are not linked to changes in jasmonic acid.

Aphid Acceptance of Barley Exposed to Volatile Phytochemicals Differs Between Plants Exposed in Daylight and Darkness

“…Diurnal periodicity of plant volatile release has been reported previously and, in almost all cases, peak emissions were found to occur during the photophase, often with very low emissions during darkness. However, the majority of studies have focussed on the release of volatiles induced by herbivory, 4 pathogen attack 5 or exposure to inducing chemicals, 6,31 rather than from undamaged plants. In one case, certain herbivore-induced volatiles were detected only during darkness.…”

“…3 In other cases, volatile emissions have been found to peak during daylight hours. [4][5][6] However influence of light on plant responsiveness to phytochemicals has not been reported.…”

The Role of Indole and Other Shikimic Acid Derived Maize Volatiles in the Attraction of Two Parasitic Wasps

“…Interestingly, several studies on maize volatiles indicate specific induction of volatile indole by herbivore-derived elicitors and not by excision stress or mechanical damage (Frey et al, 2000;Schmelz et al, 2003b). However, in other studies, many of the common herbivore-induced VOCs, including indole and several terpenoids, have been detected in analyses of VOCs released by plants exposed to other forms of stresses, as for example mechanical wounding (van den Boom et al, 2004), exposure to other VOCs (Ruther and Fürstenau, 2005), or infection by microorganism (Huang et al, 2003). Hence, the emission of various volatiles can be induced by a number of enemies and stresses, yet natural enemies are able to discriminate between different forms of stresses (Takabayashi et al, 1995;De Moraes et al, 1998;Vuorinen et al, 2004).…”

Plants under dual attack : consequences for plant chemistry and parasitoid behavior

“…1). As with herbivores, the induced VOC blend can exhibit attacker specificity, with different strains of a same pathogen inducing quantitatively and qualitatively differing VOC blends (Huang et al, 2003). In comparison to HIPV, the ecological function of pathogen-induced plant volatiles is not very clear yet, though it is thought that they may function as an additional defense mechanism against pathogen attack.…”

“…In comparison to HIPV, the ecological function of pathogen-induced plant volatiles is not very clear yet, though it is thought that they may function as an additional defense mechanism against pathogen attack. Volatile emission from infected plants has been found to correlate with a hypersensitive response (local cell death in the region surrounding the infection site) in the plant (Croft et al, 1993;Huang et al, 2003). Furthermore, several pathogen-induced volatile compounds have been shown to severely inhibit pathogen growth.…”