APHIDS PICK THEIR POISON: SELECTIVE SEQUESTRATION OF PLANT CHEMICALS
DRIVES HOST PLANT SELECTION IN A SPECIALIST HERBIVORE
NICOLE A. GOODEY1, HANNAH V. FLORANCE2, NICHOLAS SMIRNOFF2 and *DAVE J.
HODGSON1
1
Centre for Ecology and Conservation, Biosciences, College of Life and Environmental Sciences
University of Exeter, TR10 9FE, Penryn, UK
2
Biosciences, College of Life and Environmental Sciences, University of Exeter, EX4 4QD,
Exeter, UK
*Dave Hodgson: D.J.Hodgson@exeter.ac.uk
Comparison of Glucosinolate Extraction Methods. After harvest, plant material was immediately
frozen in liquid nitrogen and lyophilized to dryness. Leaf material (10mg) from 50 randomly
selected plants was combined and ground to a powder using tungsten beads with a diameter of
2 mm and a vibrating-ball micro mill (based on the Retsch MM300 ball mill). 10mg aliquots of
combined leaf tissue were transferred into 24 1.5 ml microcentrifuge tubes, and 12 samples
were randomly assigned to one of two extraction methods: Hot extraction in 70% methanol or
cold extraction in 80% methanol. Tissue disruption was carried out for 4 min at a vibration
frequency of 25 s–1. 400 µl of extraction medium (80% or 70% methanol containing internal
standards umbelliferone, 7.2 µg/ml, and linamarin1.25 µg/ml) were added to plant samples.
Glucosinolate analysis was conducted as stated in Material and Methods.
We compared peak abundances across five identified glucosinolates using paired t-tests. No
difference was found between hot and cold treatments for sinigrin; t = -0.65, df = 11, P = 0.53;
progoitrin; t = 1.50, df = 11, P = 0.16; gluconapin; t = 1.59, df = 11, P = 0.14; or
gluconapoleiferin; t = 1.537, df = 11, P = 0.15. However, peak abundances for glucobrassicin
were significantly higher in the cold extraction treatment (t = 2.57, df = 11, P = 0.02).
Figure 1: Log transformed concentrations of aliphatic and indolic
(glucobrassicin) glucosinolates in paired samples of Brassica oleracea leaves
(N=20) under two different extraction methods, hot 70% methanol and cold,
80% methanol. Boxplots show range (whiskers), interquartile range (boxes)
and median (thick line).