Time point- and plant part-specific changes in phloem exudate metabolites of leaves and ears of wheat in response to drought and effects on aphids

Abstract

Alterations in the frequency and intensity of drought events are expected due to climate change and might have consequences for plant metabolism and the development of plant antagonists. In this study, the responses of spring wheat (Triticum aestivum) and one of its major pests, the aphid Sitobion avenae, to different drought regimes were investigated, considering different time points and plant parts. Plants were kept well-watered or subjected to either continuous or pulsed drought. Phloem exudates were collected twice from leaves and once from ears during the growth period and concentrations of amino acids, organic acids and sugars were determined. Population growth and survival of the aphid S. avenae were monitored on these plant parts. Relative concentrations of metabolites in the phloem exudates varied with the time point, the plant part as well as the irrigation regime. Pronounced increases in relative concentrations were found for proline, especially in pulsed drought-stressed plants. Moreover, relative concentrations of sucrose were lower in phloem exudates of ears than in those of leaves. The population growth and survival of aphids were decreased on plants subjected to drought and populations grew twice as large on ears compared to leaves. Our study revealed that changes in irrigation frequency and intensity modulate plant-aphid interactions. These effects may at least partly be mediated by changes in the metabolic composition of the phloem sap.

Root aphid (Aploneura lentisci) population size on perennial ryegrass is determined by drought and endophyte strain

“…These serve as a primary nitrogen source for the aphids. Phloem sap varies in composition throughout the developmental stage of the plant, diurnal cycle, season, as well as abiotic factors such as temperature and water availability (Karley et al 2002;Stallmann et al 2022). The composition and concentration of such amino acids in the phloem is therefore an important indicator of aphid performance and hence populations (Douglas 1993;Karley et al 2002).…”

Revisiting yield in terms of phloem transport to grains suggests phloem sap movement might be homeostatic

“…In wheat, the response of C suc to water deficit is somewhat variable. The water regime has been found to have little effect on sucrose concentration in leaf phloem exudates (Stallmann et al, 2022). Drought was found to increase total sucrose (as well as glucose and fructose) collected from leaf exudates, expressed in mg g −1 FW (Xie et al, 2022) while exudated sucrose was found to decrease (glucose and fructose being unchanged) in another study (Xu et al, 2018).…”

Double trouble : The impact of water availability on plant-insect interactions in Rorippa plant species

“…Per treatment group (i.e., plant species * water treatment * herbivory treatment), there were n = 8 biological replicates (pooled from three plants each, see below). Three days after the aphid infestation had started, phloem exudates of the leaves that had been bagged (either with or without aphids) were collected and analyzed according to Stallmann et al (2022). with some modifications.…”

“…These nutrients will end up in the phloem sap and will thus be taken up by aphids, which might increase their performance Mezgebe and Azerefegne 2021;. Phloem exudation of amino acids like asparagine, leucine and in particular proline were affected by water stress Stallmann et al 2022). However, the extent and direction of these changes depend highly on the plant species and degree of stress the plants are subjected to.…”