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<h2> Mycorrhizal and non-mycorrhizal <em>Lactuca sativa</em> plants exhibit contrasting responses to exogenous ABA during drought stress and recovery</h2> <div> <strong>Ricardo Aroca<sup>1</sup></strong><strong>, </strong><strong>Paolo Vernieri<sup>2</sup></strong><strong> and </strong><strong>Juan Manuel Ruiz-Lozano<sup>1</sup><sup>,*</sup></strong> <p> <em><sup>1</sup>Departamento de Microbiología del Suelo y Sistemas Simbióticos. Estación Experimental del Zaidín (CSIC). Profesor Albareda no. 1, E-18008 Granada, Spain<br><sup>2</sup>Dipartimento di Biologia delle Piante Agrarie, Università degli Studi di Pisa, I-56100 Pisa, Italy </em><br> </p> <p> <em>An open access article from Journal of Experimental Botany 2008 59(8):2029-2041.</em> </p> <p> </p> <p> The arbuscular mycorrhizal (AM) symbiosis enhances plant tolerance<sup></sup>to water deficit through the alteration of plant physiology<sup></sup>and the expression of plant genes. These changes have been postulated<sup></sup>to be caused (among others) by different contents of abscisic<sup></sup>acid (ABA) between AM and non-AM plants. However, there are<sup></sup>no studies dealing with the effects of exogenous ABA on the<sup></sup>expression of stress-related genes and on the physiology of<sup></sup>AM plants. The aim of the present study was to evaluate the<sup></sup>influence of AM symbiosis and exogenous ABA application on plant<sup></sup>development, physiology, and expression of several stress-related<sup></sup>genes after both drought and a recovery period. Results show<sup></sup>that the application of exogenous ABA had contrasting effects<sup></sup>on AM and non-AM plants. Only AM plants fed with exogenous ABA<sup></sup>maintained shoot biomass production unaltered by drought stress.<sup></sup>The addition of exogenous ABA enhanced considerably the ABA<sup></sup>content in shoots of non-AM plants, concomitantly with the expression<sup></sup>of the stress marker genes <em>Lsp5cs</em> and <em>Lslea</em> and the gene <em>Lsnced</em>.<sup></sup>By contrast, the addition of exogenous ABA decreased the content<sup></sup>of ABA in shoots of AM plants and did not produce any further<sup></sup>enhancement of the expression of these three genes. AM plants<sup></sup>always exhibited higher values of root hydraulic conductivity<sup></sup>and reduced transpiration rate under drought stress. From plants<sup></sup>subjected to drought, only the AM plants recovered their root<sup></sup>hydraulic conductivity completely after the 3 d recovery period.<sup></sup>As a whole, the results indicate that AM plants regulate their<sup></sup>ABA levels better and faster than non-AM plants, allowing a<sup></sup>more adequate balance between leaf transpiration and root water<sup></sup>movement during drought and recovery.<sup></sup> </p> <p> Key words: ABA, arbuscular mycorrhiza, drought, recovery, stress-related gene </p> <p> </p> </div>
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