Nonuniform distribution of glucosinolates in Arabidopsis thaliana leaves has important consequences for plant defense

Abstract

The spatial distribution of plant defenses within a leaf may be critical in explaining patterns of herbivory. The generalist lepidopteran larvae, Helicoverpa armigera (the cotton bollworm), avoided the midvein and periphery of Arabidopsis thaliana rosette leaves and fed almost exclusively on the inner lamina. This feeding pattern was attributed to glucosinolates because it was not evident in a myrosinase mutant that lacks the ability to activate glucosinolate defenses by hydrolysis. To measure the spatial distribution of glucosinolates in A. thaliana leaves at a fine scale, we constructed ion intensity maps from MALDI-TOF (matrix assisted laser desorption/ionization-time of flight) mass spectra. The major glucosinolates were found to be more abundant in tissues of the midvein and the periphery of the leaf than the inner lamina, patterns that were validated by HPLC analyses of dissected leaves. In addition, there were differences in the proportions of the three major glucosinolates in different leaf regions. Hence, the distribution of glucosinolates within the leaf appears to control the feeding preference of H. armigera larvae. The preferential allocation of glucosinolates to the periphery may play a key role in the defense of leaves by creating a barrier to the feeding of chewing herbivores that frequently approach leaves from the edge.antiherbivore defense ͉ MALDI-imaging ͉ plant natural products M any plant natural products appear to serve as defenses against herbivores because of their toxicity or deterrence in artificial diets or when added as a supplement to plant material (1, 2). However, to evaluate the actual defensive role of these substances in planta, it is necessary to estimate the amount that a potential herbivore would encounter during feeding. Although determining the amount of plant tissue ingested during a feeding bout is relatively straightforward, measuring the quantity of specific defense products in that tissue is not. Nearly all studies to date have quantified the levels of defensive metabolites at the level of the whole plant or organ (3). Little is known about the localization of antiherbivore defenses in individual tissues or parts of organs even though this may be critically important to the behavior of small herbivores and to the effectiveness of the defense.One of the most extensively studied classes of antiherbivore chemical defenses in plants is the glucosinolates, a group of sulfur-rich, amino acid-derived metabolites combining a ␤-Dglucopyranose residue linked via a sulfur atom to an Nhydroxyamino sulfate ester (4) (Fig. 1). Glucosinolates are widespread in the order Capparales, which includes vegetables (cabbage, cauliflower, and broccoli), spice plants supplying condiments (mustard, horseradish, and wasabi), and the model species, Arabidopsis thaliana (5, 6). Upon insect feeding or mechanical disruption, glucosinolates are hydrolyzed by an endogenous glucohydrolase activity known as myrosinase, and the released aglycone rearranges to form isothiocyanates, nitriles, and other pr...

The Arabidopsis Thylakoid ADP/ATP Carrier TAAC Has an Additional Role in Supplying Plastidic Phosphoadenosine 5′-Phosphosulfate to the Cytosol

“…PAPST1 expression corresponds to the sites of biosynthesis and accumulation of known sulfated compounds, for example, GS, and generally overlaps with the expression of several genes of GS biosynthesis and regulation, particularly of APK1 (Mikkelsen et al, 2004;Schuster et al, 2006;Gigolashvili et al, 2007aGigolashvili et al, , 2009bMalitsky et al, 2008). GS are known to be abundant in tissues surrounding the main and peripheral veins (Shroff et al, 2008); correspondingly, high PAPST1 promoter activity was detectable in the vasculature ( Figure 5) as is the case for genes encoding PSK precursors (Kutschmar et al, 2009;Stührwohldt et al, 2011). However, PAPST1 is also localized to developing seeds, which do not produce GS and in which APK expression is limited to the funiculus or radicle .…”

Biosynthesis and bioactivity of glucosinolates and their production in plant in vitro cultures

“…In this sense, Shroff et al (2008) observed that Helicoverpa armigera larvae showed a non-uniform feeding pattern in leaves of A. thaliana, avoiding the midvein and the edge of the leaf, which are glucosinolate-enriched parts. These results suggested that the high amount of glucosinolates on the leaf periphery may act repulsing the insects that start feeding from the edge of the leaf (Shroff et al 2008).…”

Engineering insect-resistant plants by transgenic expression of an insecticidal spider-venom peptide

“…Beekwilder et al (2008) found that weight gain was 2.6-fold higher for larvae fed on double-mutant Arabidopsis (myb28 myb29) completely lacking aliphatic glucosinolates and 1.8-fold higher for larvae fed on single-mutant Arabidopsis with intermediate levels of aliphatic glucosinolates compared to WT plants (Beekwilder et al, 2008). Our results are consistent with the report by Shroff et al (2008) that H. armigera larvae avoid the glucosinolate-rich mid-vein and leaf periphery when feeding on Arabidopsis leaves.…”

“…Glucosinolates are plant secondary metabolites, found in members of the Brassicaceae family, which have insecticidal effects on insect pests such as H. armigera (Hopkins et al, 2009;Muller et al, 2010;Bohinc et al, 2012;Kos et al, 2012;Mithofer and Boland, 2012). Herbivory of Arabidopsis by H. armigera has been shown in induce production of indolic glucosinolates (BadenesPerez et al, 2013) and H. armigera were shown to avoid feeding on the mid-vein and periphery of Arabidopsis rosette leaves where the concentration of the major glucosinolates is highest (Shroff et al, 2008). (C) Photograph of larvae after feeding on WT and gluc-null Arabidopsis for 9 days.…”