et at, 1994), and Pollard and Baker (1997) suggest that this is an.
effective defence against herbivory for this species. This paper.
explores the effects of zinc hyperaccumulation in Thlaspi as a.
defence against Xanthomonas campestris.
MATERIALS AND METHODS.
Thlaspi caerulescens seeds were collected in Cloughwood, U. K.
These seeds germinated on polyester beads supported in expanded.
polystyrene rafts floating on one-tenth strength Rorison's solution.
(Hewitt, 1966). These containers were placed in a Conviron E-15.
environmental growth chamber at the following settings: 20 C, 90%.
RH, 16 hr day, and 8 hr night. After three weeks, twenty seedlings.
were transferred to 4 rafts composed of expanded styrene on.
polyethylene, each supporting five plants individually. Ten.
plants floated on one-tenth strength Rorison's, and ten plants.
floated on a solution containing Rorison's and 10ppm zinc, as ZnSO .
The solutions were freshened every four days to inhibit any.
possible algal growth.
After twenty days, each plant was transferred to an individual.
beaker containing 25ml of solution. The ten Rorison's plants.
retained the same solution as did the zinc plants. Parafilm held.
the plants in place. The plants were then inoculated with three.
different strains of Xanthomonas campestris, a bacteria known to.
harm plants. Each plant had each strain inoculated on three.
different leaves. The plants grew in the growth chamber for one.
week and then were examined.
The plants were analyzed with a ranking scale based on.
appearance by three people who did not know which plants contained.
zinc.
RESULTS.
Scale:.
1= Healthy, green leaf with no brown, small puncture hole.
2= Longer puncture hole with some white spots.
3= Some leaf discoloration, expanded hole, some shriveling leaves.
4= Shriveling of several leaves, whole plant not thriving.
5= Many leaves dead, small shriveled plants.
Plant Solution Average .
Rank 1 Non-zinc 5.00 2 Zinc 1.