Drought Stress and Leaf Herbivory Affect Root Terpenoid Concentrations and Growth of Tanacetum vulgare

Abstract

Plant responses of both shoots and roots to combined abiotic and biotic stress have been rarely investigated. However, stresses such as drought and aboveground herbivory might lead to conflicting resource allocation patterns and pronounced shifts in shoot vs. root defenses. In the present study, the effects of water availability and leaf herbivory by caterpillars of a generalist on various shoot and root traits of the aromatic plant Tanacetum vulgare L. were investigated. This species contains terpenoids in leaves and roots, which can differ in composition among individuals, forming so-called chemotypes. To test for intraspecific variation, responses were investigated in two chemotypes, the thujone and the carvyl acetate chemotype. Furthermore, effects of differences in plant quality on the herbivores were studied. Shoot biomass significantly decreased due to drought and herbivory, whereas the root/shoot ratio increased following drought but was unaffected by herbivory. No shifts in C/N ratios were found. In contrast to our expectation, leaf terpenoid concentrations decreased only slightly due to drought, whereas root terpenoids were significantly induced by both drought and herbivory. Chemotypes showed distinct responses to drought at least in the root/shoot ratio, with a higher drought sensitivity of the carvyl acetate chemotype. The body mass of the caterpillars was unaffected by the irrigation treatment but depended on chemotype and terpenoid concentration of the plants. Thus, both qualitative and quantitative defenses strongly affect herbivore development. The present results offer new insights into the above- and belowground organ-specific responses of plants. They highlight the importance of roots in response to various environmental challenges.

Plant water stress and previous herbivore damage affect insect performance

“…However, the combined effects of water stress and previous herbivory is often overlooked in studies that examine the effect of water stress on insect performance. Several studies have shown that water-stressed plants are better able to induce resistance traits and reduce insect performance compared with well-watered plants (Tariq et al, 2013;Kleine & Muller, 2014). Another study, however, showed that drought can inhibit the induction of resistance traits (Halpern et al, 2010), while others found no or mixed effects of drought on inducibility (Hale et al, 2005;Gutbrodt et al, 2012;Weldegergis et al, 2015).…”

Transcriptome analysis of Leucaena leucocephala and identification of highly expressed genes in roots and shoots

“…On the other hand, in Cymbopogon winterianus (citronella), whose leaves are known to have antimicrobial properties, shows higher expression of terpenoid biosynthesis genes in leaves compared to roots [45]. Also, terpenoids accumulate in roots in response to drought in many plants, including Tanacetum vulgare (tansy) and maize [46,47]. Most likely these compounds act as antioxidants to protect plants against oxidative stress caused by drought.…”

Production of pyrrolizidine alkaloids and shikonins in Echium plantagineum L. in response to various plant stressors

“…Terpenoids in plant shoots decreased after 12 days of moderate drought exposure in contrast to increasing accumulation in plant roots, suggesting increased root protection against soil insects and pathogens. In this case, belowground plant organs may impact the systemic defense system deployed by T. vulgare through the reallocation of resources critical for regeneration following exposure to stress …”

“…2,16,17 Drought stress in plants can result in accumulation of ROS, 2 and bioaccumulation of bioactive terpenes, terpenoids, phenols and alkaloids in multiple herbaceous and woody species that facilitate defense against insects, pathogens and weeds. 17,18 Many of these metabolites play important ecological or defensive roles against pests following exposure to stress. Terpenoids, for example, play a vital role in plant defense as phytoalexins and also as attractants to insect pollinators.…”

“…In this case, belowground plant organs may impact the systemic defense system deployed by T. vulgare through the reallocation of resources critical for regeneration following exposure to stress. 18 Recently, we have investigated the evolution of allelochemical production along with dispersal of the common weed Echium plantagineum (Boraginaceae L.) in Australia and its native range in the Iberian Peninsula. Echium plantagineum, commonly known as 'Paterson's curse', has successfully adapted to severe and diverse environmental stress in its native range in southern Spain and also in Australia, allowing range expansion over 30Mha of pasture and rangeland.…”