Green leaf volatiles, fire and nonanoic acid activate MAPkinases in the model grass species Lolium temulentum

Dombrowski and Martin BMC Research Notes 2014, 7:807 http://www.biomedcentral.com/1756-0500/7/807 RESEARCH ARTICLE Open Access Green leaf volatiles, fire and nonanoic acid activate MAPkinases in the model grass species Lolium temulentum James E Dombrowski* and Ruth C Martin Abstract Background: Previously it has been shown that mechanical wounding, salinity and heat activated a 46 kDa and 44 kDa mitogen-activated protein kinases (MAPKs) in forage related grasses. Forage and turf related grasses are utilized in diverse environments where they are routinely subjected to herbicides and exposed to fire and volatiles after cutting, however very little is known concerning the perception or molecular responses to these different stresses or compounds. Results: In the model grass species Lolium temulentum (Lt), a 46 kDa mitogen-activated protein kinase (MAPK) was activated in the leaves within 5 min and a 44 kDa MAPK 15 min after exposure to green leaf volatiles released from grass clippings. When the tips of leaves of Lt plants were scorched by fire, the 46 kDa MAPK and 44 kDa MAPK were rapidly activated within 5 min and 20 min respectively in the treated leaf, and 15 min systemically in an adjacent untreated tiller after exposure to fire. Nonanoic acid (pelargonic acid), a component in herbicides used on grasses, activated a 46 kDa MAPK in the treated leaves within 5 min of exposure and 15 min in systemic tissues. At concentrations normally used in the herbicides, nonanoic acid was found to only weakly activate the 44 kDa MAPK after an hour in treated leaves, but strongly activated it in the systemic tillers 30 min after treatment. Acetic acid, HCl and NaOH also were found to activate these MAPKs in treated tillers. Conclusion: The rapid activation of these MAPKs to a wide range of stress stimuli, suggest that these MAPKs play a role in the perception and response to these stresses and compounds. The activation of the MAPK by green leaf volatiles indicates a role for these compounds in wound signaling in grasses. Keywords: Fire, Green leaf volatile, Grass, Herbicide, Lolium, MAPK, Systemic Background The most common abiotic stresses forage and turf related grasses are exposed to in the field are drought, herbicides, fire and grazing/cutting. Drought stress is and has been the most extensively studied of these stresses [1-8]. However much less is known on the molecular responses to the various components in herbicides, to fire and from grazing or cutting in forages and turf related grasses. Herbicides are pervasively used around the world and the most extensively used herbicide is glyphosate [9,10]. Glyphosate is a broad-spectrum herbicide that disrupts * Correspondence: USDA-ARS, National Forage Seed Production Research Center, Oregon State University, 3450 SW Campus Way, Corvallis, Oregon 97331-7102, USA aromatic amino acid production by inhibition of the enzyme 5-enolpryruvylshikimate-3-phosphate synthase. There has been a great deal of research on the biochemical and molecular responses to glyphosate application, such as the genome wide profiling and analysis of miRNAs and transcriptomes in the forage grass tall fescue [11]. The molecular and physiological mechanisms of glyphosate resistance in grasses, such as Lolium, is also being vigorously investigated [12-16]. However much less is known on the other components utilized with glyphosate in its different formulations. Pelargonic acid is a nine-carbon fatty acid that is commonly used in conjunction with glyphosate [17]. It is a contact nonselective herbicide that disrupts intercellular pH and membrane integrity resulting in rapid cell death [17,18]. While some physiological analyses have been done, very © 2014 Dombrowski and Martin; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Dombrowski and Martin BMC Research Notes 2014, 7:807 http://www.biomedcentral.com/1756-0500/7/807 little is known on the plant’s molecular response to this compound. In rice, a cytochrome P450 gene was isolated from rice and expressed in yeast, and the enzyme was shown to catalyze the NADPH-dependent (ω-1)hydroxylation of pelargonic acid, reducing its herbicidal activity, suggesting that it may participate in detoxification of the contact herbicide [19]. Fire is another type of stress grasses are exposed to, grass fields are routinely subjected to prescribed burning as a management practice and wildfires occur regularly in rangelands [20-25]. There has been a great deal of research investigating the ecological impact of fire on soil quality and composition, regrowth of grasses and plants, the effects of fire on composition of plant communities and species succession, disease and pests as well as the economic factors associated with burning of grass fields and rangelands. However, despite grasses frequent exposure to fire, there is virtually nothing known on the molecular responses to fire related stress in grasses or most other plant species. In tomato leaves, exposure to flame damage resulted in the activation of proteinase inhibitors genes locally and systemically [26,27]. Furthermore the research suggested that in addition to chemical signals the systemic signalling had hydraulic and electrical components. Recently, it was reported that prescribed burning in pine was shown to affect the composition of secondary metabolites in the needles [28]. Forage and turf grasses are utilized and exposed to a wide range of environmental conditions in diverse geographical regions of the world. In addition to being exposed to various environmental stresses, these grasses are also routinely subjected to mechanical wounding and grazed upon by animals. Currently there is very little information available on the wound response in forage and turf grass species. Recently a few wound related signalling components have been identified in forage and turf grasses; a wound induced oxidative burst was shown in ryegrass lead blades [29], and a MAPK was rapidly activated within 5 minutes of wounding, both locally and systemically [30], and temperature was also shown to affect the wound activation of the MAPKs [31]. In tufted hairgrass, mechanical wounding was shown to release a characteristic complement of green leaf volatiles, however this blend of volatiles was significantly different than the profiles released when plants were treated with jasmonic acid [32]. In plants, grazing herbivores, pathogens, feeding insects, and mechanical wounding result in the release of a variety of volatiles for inter- and intraplant communicatio (...truncated)