Abstract
Little is known about how drought stress influences plant secondary metabolite accumulation and how this affects plant defense against different aphids. We therefore cultivated Arabidopsis thaliana (L.) plants under well-watered, drought, and water-logged conditions. Two aphid species were selected for this study: the generalist Myzus persicae (Sulzer) and the crucifer specialist Brevicoryne brassicae (L.). Metabolite concentrations in the phloem sap, which influence aphid growth, changed particularly under drought stress. Levels of sucrose and several amino acids, such as glutamic acid, proline, isoleucine, and lysine increased, while concentrations of 4-methoxyindol-3-ylmethyl glucosinolate decreased. M. persicae population growth was highest on plants under drought stress conditions. However, B. brassicae did not profit from improved phloem sap quality under drought stress and performed equally in all water treatments. Water stress and aphids generally had an opposite effect on the accumulation of secondary metabolites in the plant rosettes. Drought stress and water-logging led to increased aliphatic glucosinolate and flavonoid levels. Conversely, aphid feeding, especially of M. persicae, reduced levels of flavonoids and glucosinolates in the plants. Correspondingly, transcript levels of aliphatic biosynthetic genes decreased after feeding of both aphid species. Contrary to M. persicae, drought stress did not promote population growth of B. brassicae on these plants. The specialist aphid induced expression of CYP79B2, CYP79B3, and PAD3 with corresponding accumulation of indolyl glucosinolates and camalexin. This was distinct from M. persicae, which did not elicit similarly strong camalexin accumulation, which led to the hypothesis of a specific defense adaptations against the specialist aphid.
Highlights
In their natural growing environment, plants encounter multiple environmental stresses that can alter both their chemical composition and the associated herbivore community
Aphid numbers of the generalist M. persicae on A. thaliana plants differed between water treatments, with significantly higher numbers found on drought-stressed plants (Fig. 2)
Simple correlations were used to explore the likelihood that constitutive metabolite levels in the phloem sap of plants under different water conditions might be a basis of plant suitability for aphid species
Summary
In their natural growing environment, plants encounter multiple environmental stresses that can alter both their chemical composition and the associated herbivore community. Drought is a major environmental stress that directly influences plant physiological processes leading to decreased growth, and changes the allocation of resources and profile of secondary metabolites [1,2,3]. Decreased levels of glucosinolates in drought-stressed brassicaceous crops in connection with the improved performance of generalist aphids has been reported in previous studies [2,3,11]. Unlike generalist aphids such as M. persicae [12], crucifer specialists such as B. brassicae may tolerate to some extent glucosinolates in their host plants. The influence of drought stress on secondary metabolite accumulation in relation to the impact this has on plant resistance against aphids with different feeding specialization is still not well understood
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