Abstract
It is well established that plants emit, detect and respond to volatile organic compounds; however, knowledge on the ability of plants to detect and respond to volatiles emitted by non-plant organisms is limited. Recent studies indicated that plants detect insect-emitted volatiles that induce defence responses; however, the mechanisms underlying this detection and defence priming is unknown. Therefore, we explored if exposure to a main component of Plutella xylostella female sex pheromone namely (Z)-11-hexadecenal [(Z)-11-16:Ald] induced detectable early and late stage defence-related plant responses in Brassica nigra. Exposure to biologically relevant levels of vapourised (Z)-11-16:Ald released from a loaded septum induced a change in volatile emissions of receiver plants after herbivore attack and increased the leaf area consumed by P. xylostella larvae. Further experiments examining the effects of the (Z)-11-16:Ald on several stages of plant defence-related responses showed that exposure to 100 ppm of (Z)-11-16:Ald in liquid state induced depolarisation of the transmembrane potential (Vm), an increase in cytosolic calcium concentration [Ca2+]cyt, production of H2O2 and an increase in expression of reactive oxygen species (ROS)-mediated genes and ROS-scavenging enzyme activity. The results suggest that exposure to volatile (Z)-11-16:Ald increases the susceptibility of B. nigra to subsequent herbivory. This unexpected finding, suggest alternative ecological effects of detecting insect pheromone to those reported earlier. Experiments conducted in vitro showed that high doses of (Z)-11-16:Ald induced defence-related responses, but further experiments should assess how specific the response is to this particular aldehyde.
Highlights
Abbreviations volatile organic compounds (VOCs) Volatile organic compounds herbivore-induced plant volatiles (HIPVs) Herbivore-induced plant volatiles H2O2 Hydrogen peroxide reactive oxygen species (ROS) Reactive oxygen species Vm Transmembrane potential [Ca2+]cyt Cytosolic calcium concentration CLMS Confocal laser scanning microscrope CAT Catalase ppm Parts-per-million POX Peroxidase superoxide dismutase (SOD) Superoxide dismutase (Z)-11-16Ald (Z)-11-Hexadecenal (Z)-11-16Ac (Z)-11-hexadecenyl acetate
We addressed the following questions (1) does (Z)-11-16:Ald induce detectable defence-related responses in Brassica nigra plants when applied as a volatile chemical to the air surrounding a plant? (2) does exposure to (Z)-11-16:Ald elicit early and late defence-related responses in vitro and (3) is the response specific to the (Z)11-16:Ald component of the sex pheromone? To address question 1, we sampled the volatile emissions of plants after exposure to (Z)-11-16:Ald, and after subsequent feeding by first and second instar P. xylostella larvae, and the amount of feeding by the larvae after 24 h
To determine whether exposure to (Z)-11-16:Ald induced detectable defence-related responses in B. nigra, we investigated the amount of feeding damage to plants and the volatile emissions of plants exposed to volatilised pure compound
Summary
Abbreviations VOC Volatile organic compounds HIPV Herbivore-induced plant volatiles H2O2 Hydrogen peroxide ROS Reactive oxygen species Vm Transmembrane potential [Ca2+]cyt Cytosolic calcium concentration CLMS Confocal laser scanning microscrope CAT Catalase ppm Parts-per-million POX Peroxidase SOD Superoxide dismutase (Z)-11-16Ald (Z)-11-Hexadecenal (Z)-11-16Ac (Z)-11-hexadecenyl acetate. Their work showed that goldenrod Solidago altissima plants exposed to the male sex pheromone of the goldenrod gall fly Eurosta solidaginis had higher concentrations of the defencerelated phytohormone jasmonic acid in their leaves and emitted a greater amount of herbivore-induced plant volatiles (HIPVs) than unexposed p lants[12,13]. In subsequent experiments they identified that (E,S)-conophthorin, the most abundant compound in the sex pheromone of the goldenrod gall fly, was responsible for priming goldenrod defences[14]. We addressed question 3 by measuring the Vm of plants exposed to (Z)-11-hexadecenyl acetate ((Z)-11-16:Ac) another component of the sex pheromone
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