Abstract
Ultraviolet (UV) radiation can modulate plant defenses against herbivorous arthropods. We investigated how different UV exposure times and irradiance intensities affected tomato (Solanum lycopersicum) resistance to thrips (Frankliniella occidentalis) by assessing UV effects on thrips-associated damage and host-selection, selected metabolite and phytohormone contents, expression of defense-related genes, and trichome density and chemistry, the latter having dual roles in defense and UV protection. Short UV daily exposure times increased thrips resistance in the cultivar 'Moneymaker' but this could not be explained by changes in the contents of selected leaf polyphenols or terpenes, nor by trichome-associated defenses. UV irradiance intensity also affected resistance to thrips. Further analyses using the tomato mutants def-1, impaired in jasmonic acid (JA) biosynthesis, od-2, defective in the production of functional type-VI trichomes, and their wild-type, 'Castlemart', showed that UV enhanced thrips resistance in Moneymaker and od-2, but not in def-1 and Castlemart. UV increased salicylic acid (SA) and JA-isoleucine concentrations, and increased expression of SA- and JA-associated genes in Moneymaker, while inducing expression of JA-defensive genes in od-2. Our results demonstrate that UV-mediated enhancement of tomato resistance to thrips is probably associated with the activation of JA-associated signaling, but not with plant secondary metabolism or trichome-related traits.
Highlights
Ultraviolet (UV) radiation (280–400 nm), a small fraction of the solar radiation reaching the terrestrial ecosystems, is an important modulator of plant physiology (Paul andGwynn-Jones, 2003)
We demonstrate that UV-mediated enhancement of tomato resistance to F. occidentalis depends on the UV exposure time and irradiance intensity, and that the induction of resistance is not explained by UV-associated changes in the leaf metabolome or trichome-mediated defenses, but it might be explained by reinforcement of jasmonic acid (JA)-associated defenses
We first determined that exposure to 30 min d−1 of supplemental UV had the strongest positive effect on plant resistance to thrips, and this effect decreased with longer exposure times (Fig. 1).These results suggest the existence of specific defenserelated photomorphogenic responses to different UV exposure times
Summary
Ultraviolet (UV) radiation (280–400 nm), a small fraction of the solar radiation reaching the terrestrial ecosystems, is an important modulator of plant physiology UV-B exclusion and supplemental studies have shown that it can decrease preference and/or performance of herbivorous arthropods in diverse plant species (Mazza et al, 1999; Rousseaux et al, 2004; Caputo et al, 2006; Foggo et al, 2007; Demkura et al, 2010; Kuhlmann and Müller, 2010; Mewis et al, 2012; Mazza et al, 2013; Zavala et al, 2015) This has been partially explained by UV-B-mediated effects on constitutive plant defenses, such as increases in secondary metabolites (Escobar-Bravo et al, 2017b). While solar UV positively influences plant resistance to herbivores, this might come at the expense of reduced growth by antagonizing auxin signaling (Hectors et al, 2012; Hayes et al, 2014) These UV-mediated plant responses need to be disentangled when aiming for the efficient use of UV in crop production. Determining how plants respond to sudden UV exposure is crucial in the context of new lighting technologies and greenhouse-grown crops such as tomato (Mariz-Ponte et al, 2018)
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