Abstract
Summary In nature, herbivorous insects and plant pathogens are generally abundant when plants are flowering. Thus, plants face a diversity of attackers during their reproductive phase. Plant responses to one attacker can interfere with responses to a second attacker, and phytohormones that orchestrate plant reproduction are also involved in resistance to insect and pathogen attack. We quantified phytohormonal responses of flowering plants exposed to single or dual attack and studied resistance mechanisms of plants in the flowering stage.Flowering Brassica nigra were exposed to either a chewing caterpillar, a phloem‐feeding aphid or a bacterial pathogen, and plant hormonal responses were compared with dual attack situations. We quantified phytohormones in inflorescences and leaves, and determined the consequences of hormonal changes for components of direct and indirect plant resistance.Caterpillars were the main inducers of jasmonates in inflorescences, and the phytohormonal profile of leaves was not affected by either insect or pathogen attack. Dual attack increased plant resistance to caterpillars, but compromised resistance to aphids. Parasitoid performance was negatively correlated with the performance of their hosts.We conclude that plants prioritize resistance of reproductive tissues over vegetative tissues, and that a chewing herbivore species is the main driver of responses in flowering B. nigra.
Highlights
During their life time, plants interact with a multitude of organisms, and plant attackers are generally abundant during the flowering period (Lucas-Barbosa et al, 2014; Schlinkert et al, 2015)
We focused on three key phytohormones, abscisic acid (ABA), salicylic acid (SA) and Jasmonic acid (JA), including precursors, active forms and degradation forms of JA
The jasmonates (JA, (+)-7-iso-JA-Ile, (À)-JA-Ile) and their catabolites (12-OH-JA, 12-OH-JA-Ile, 12-COOH-JAIle) as well as ABA were more abundant in inflorescences than in leaves, whereas SA and cis-OPDA were more abundant in leaves than in inflorescences (Fig. 2b)
Summary
Plants interact with a multitude of organisms, and plant attackers are generally abundant during the flowering period (Lucas-Barbosa et al, 2014; Schlinkert et al, 2015). Inducible resistance traits of plants can vary depending on the ontogenetic stage of the plant (Barton & Koricheva, 2010; Erbilgin & Colgan, 2012; Quintero et al, 2014), on the identity of the attacker (Erb et al, 2012; Dicke & van Loon, 2014) and on whether the plant is attacked by a single or by multiple species (Soler et al, 2012; Kroes et al, 2015). Plants are often simultaneously or successively challenged by multiple attackers, and the synergistic or antagonistic nature of phytohormonal responses can shape a plant’s phenotype and determine plant resistance or
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