Localization of sesquiterpene formation and emission in maize leaves after herbivore damage

Abstract

BackgroundMaize (Zea mays L.) leaves damaged by lepidopteran herbivores emit a complex volatile blend that can attract natural enemies of the herbivores and may also have roles in direct defense and inter- or intra-plant signaling. The volatile blend is dominated by sesquiterpenes of which the majority is produced by two herbivore-induced terpene synthases, TPS10 and TPS23. However, little is known about the pattern of volatile emission within maize leaves.ResultsIn this study, we restricted herbivore feeding to small sections of the maize leaf with the aim of determining the patterns of volatile sesquiterpene emission throughout the damaged leaf and in neighboring leaves. Sesquiterpene volatiles were released at high rates from damaged leaves, but at much lower rates from neighboring leaves. Release was restricted to the site of damage or to leaf sections located apical to the damage, but was not seen in sections basal to the damage or on the other side of the midrib. The emission pattern correlated well with the transcript pattern of the respective sesquiterpene synthase genes, tps10 and tps23, implying that biosynthesis likely occurs at the site of emission. The concentrations of jasmonic acid and its leucine derivative were also elevated in terpene-emitting tissues suggesting a role for jasmonates in propagating the damage signal.ConclusionsIn contrast to other defense reactions which often occur systemically throughout the whole plant, herbivore-induced sesquiterpene production in maize is restricted to the wounding site and distal leaf parts. Since the signal mediating this reaction is directed to the leaf tip and cannot propagate parallel to the leaf axis, it is likely connected to the xylem. The increasing gradient of volatiles from the tip of the leaf towards the damage site might aid herbivore enemies in host or prey finding.

Beetle feeding induces a different volatile emission pattern from black poplar foliage than caterpillar herbivory

“…4,[16][17][18] In this study, beetles created more numerous and smaller lesions in poplar leaves than the gypsy moth caterpillars did in our previous work. 9 Thus the overall area affected by beetle damage might be bigger even though the actual area removed is smaller.…”

“…1 Herbivore-induced volatiles are released from the actual site of damage but can also be emitted systemically from adjacent non-damaged tissue. [2][3][4] There is convincing evidence in the recent literature that herbivoreinduced plant volatile emission can be specific to the attacker species. 5 Insects from different feeding guilds (e.g., sucking, chewing, mining or galling insects) are especially reported to induce different volatile blends.…”

“…Such specificity is readily exploited by herbivore enemies in searching for prey and hosts, depending on the diet breadth of the enemy. 4 Both predators and parasitoids possess sensory apparatus that can distinguish between blends based on qualitative differences or quantitative ones involving ratio-specific odor recognition.…”

Selinene Volatiles Are Essential Precursors for Maize Defense Promoting Fungal Pathogen Resistance

“…In addition to roles as phytohormone signals, specialized terpenoids mediate interorganism interactions and serve as chemical barriers (Gershenzon and Dudareva, 2007). In maize, terpene olefins are nearly ubiquitous components of induced aboveground and belowground volatile emissions acting as indirect plant defenses following biotic stress (Turlings et al, 1990;Degenhardt, 2009;Degenhardt et al, 2009a;Köllner et al, 2013). Maize terpene olefins also can serve as precursors for the localized production of nonvolatile antibiotic terpenoid defenses (Schmelz et al, 2014).…”

Rethinking how volatiles are released from plant cells

“…In vegetative organs, VOCs are often synthesized in the secretory cells of glandular trichomes located on the leaf surface [24][25][26][27] and then secreted to a sac created by an extension of the cuticle, where they are stored until mechanical disruption [28][29][30]. When trichomes are not involved in vegetative VOC production, these compounds are often synthesized in mesophyll cells [31,32], mainly in the palisade parenchyma [33], and released through stomata [34][35][36][37], mechanical disruption, or emission through cuticle [36]. Regardless of the tissue and whether they exit via stomata, at the subcellular level, VOCs must move from their site of biosynthesis through the cytosol to the plasma membrane, and then subsequently traverse the plasma membrane, hydrophilic cell wall, and, in some cases, the cuticle to exit the cell.…”