10.5061/DRYAD.M0CFXPP0M
Paschalidou, Foteini
0000-0001-5746-8227
Centre de Versailles Grignon
Eyman, Lisa
Swiss Federal Institute of Technology in Zurich
Sims, James
0000-0003-3472-1642
Swiss Federal Institute of Technology in Zurich
Buckley, James
0000-0003-2264-4096
Swiss Federal Institute of Technology in Zurich
Fatouros, Nina
Wageningen University & Research
De Moraes, Consuelo
Swiss Federal Institute of Technology in Zurich
Mescher, Mark
Swiss Federal Institute of Technology in Zurich
Plant volatiles induced by herbivore eggs prime defenses and mediate
shifts in the reproductive strategy of receiving plants
Dryad
dataset
2020
Dutch Research Council
https://ror.org/04jsz6e67
Vidi grant no. 14854
Swiss National Science Foundation
https://ror.org/00yjd3n13
31003A-163145
2021-03-24T00:00:00Z
2020-04-21T00:00:00Z
en
https://doi.org/10.1111/ele.13509
38608 bytes
4
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Plants can detect cues associated with the risk of future herbivory and
modify defense phenotypes accordingly; however, our current understanding
is limited both with respect to the range of early warning cues to which
plants respond and the nature of the responses. Here we report that
exposure to volatile emissions from plant tissues infested with herbivore
eggs promotes stronger defense responses to subsequent herbivory in two
Brassica species. Furthermore, exposure to these volatile cues elicited an
apparent shift from growth to reproduction in Brassica nigra, with exposed
plants exhibiting increased flower and seed production, but reduced leaf
production, relative to unexposed controls. Our results thus document
plant defense priming in response to a novel environmental cue,
oviposition-induced plant volatiles, while also showing that plant
responses to early warning cues can include changes in both defense and
life-history traits.
Larval performance bioassays The effect of exposure to oviposition-induced
volatiles on plant defenses in both Brassica species was assessed via
larval performance assays. Ten plants from each priming treatment (E, Re,
Rc and C) received 10 neonate P. brassicae. On days three and seven
following the initiation of feeding, larval mass was measured on a
microbalance (accuracy +/- 1μg; Mettler- Toledo AG, Greifensee,
Switzerland) as described in Pashalidou et al. (2013, 2015a, c) Volatile
collection and analysis For both Brassica nigra and Brassica oleracea, we
collected volatiles from plants exposed to the four priming treatments
(N=12 per treatment) and with or without larval damage. For damage
treatments, ten L1 larvae were placed on E, Re and Rc plants. Due to
logistical constraints (and because our previous assays showed no effect
of priming treatment Rc on larval performance) we collected volatiles only
from damaged Rc plants and used C plants as undamaged controls. Larvae
were placed on the adaxial side of the 3rd highest leaf. One damaged plant
was excluded from the damaged Re treatment because of unrelated damage.
Volatile collections were made one day prior to larval emergence and two
hours after the initiation of larval feeding. Pots were wrapped in foil to
minimize plastic contaminants. Two connecting metal plates were closed
around the plant stem (with a hole for the stem to pass), and cotton was
used to seal gaps. A 30 L glass dome was carefully placed over the leafy
parts of the plant, with openings for incoming and outgoing air, which was
filtered through activated charcoal, pulled through the chamber at a rate
of 150 ml/min for 4 h, and collected in a stainless-steel cartridge
containing 200 mg of Tenex TA (20/35 mesh; CAMSO, Houston, TX, USA). Due
to space limitations, volatile collections were conducted in three blocks.
After volatile collection, the aboveground parts of the plant were cut and
weighed. Volatile compounds were eluted from the filter using 150 μL of
internal standard solution (2 ng/μL octane and 4 ng/μL nonyl acetate in
dichlormethane) and the eluant was analysed by gas chromatography-mass
spectrometry (GC-MS). Two μL of the eluant was injected with an automatic
Agilent injector 7693 autosampler (Santa Clara, CA, USA) to an Agilent
7890B GC (Santa Clara, CA, USA) with a pulsed splitless inlet at 250°C,
which was held for 2min and then analyzed on the connected MS Agilent
5977A. Compounds were quantified and identified as described in
supplementary methods (Appendix S1). Volatile emissions per plant were
calculated as mean peak area divide by both the fresh weight of foliage
(in grams) and by 104 the n of samples. Testing effects of exposure to
individual volatile compounds Because the emission of cumene was
significantly elevated on egg-infested plants for B. oleracea (Table S2),
we also explored the defense priming effects of this compound on B.
oleracea and B. nigra. Unfortunately, we were unable to similarly test the
effect of β-thujene—a compound showing elevated emissions following egg
infestation in B. nigra (Table S3)—as we could not obtain this compound.
We made a cumene solution containing 156µg/ml of synthetic cumene
(Sigma-Aldrich) in hexane, a concentration approximating the mean daily
emission of an egg-infested plant with a fresh aboveground mass of 200g.
Over a five-day period, 50µL of this solution was applied daily to
sleeve-stopper septa (Sigma-Aldrich) placed at a distance of 15cm from
focal plants (treatment Cu; Table S1). The septa were placed at the height
of the receiver’s apical meristem to simulate elevated cumene emission
from an egg-infested plant. Control plants were similarly exposed to 50µL
hexane (treatment He). Each of the 10 replicate plants per treatment was
infested with 10 neonate larvae after exposure to cumene for five days,
and larvae were weighed three and seven days after placement. Testing
effects of egg-induced volatiles on plant growth and reproduction To test
whether priming by oviposition-induced volatiles altered plant
reproductive output we focused on Brassica nigra, as this annual species
has been previously shown to respond to egg infestation through changes in
reproductive phenology. We produced new plants using six treatments
described in previous sections (C, E and Re with and without larval
damage; Fig. 1, Table S1), omitting Rc plants which were similar to C
plants in previous assays. Larvae were allowed to feed freely until
pupation, with the larval number reduced from ten to three at the third
instar stage to avoid complete defoliation. When larvae neared pupation,
plants were covered with a fine net (to prevent larvae from leaving the
plant), which was removed following pupation (plant treatments without
larvae were similarly covered). We recorded the number of leaves and
flowers present three weeks after the first flower appeared on each plant.
Once all plants were flowering, commercial bumblebees (Biobest,
Switzerland) were introduced for three weeks to ensure pollination;
previous work indicates that bumblebees do not discriminate between
undamaged plants and those with either P. brassicae eggs or feeding damage
on leaves/flowers (Lucas-Barbosa et al. 2013). After plants had completed
their life cycle, ripe seeds were collected from each plant and measured
with a seed counter (elmor c3 version 1.1, Switzerland). Germination rates
were measured as in Pashalidou et al 2015b.