Zinc hyperaccumulation :: science

Zinc hyper accruementZinc hyperaccumulation in Thlaspi caerulescens as a chemical substance self-denial against herbivory ABSTRACT Thlaspi caerulescens is one of several plant species cognize to accumulate heavy metals in excess of 2% of their above object plant biomass. The reasons for hyperaccumulation are unknown, but several studies conclude that it may be a plant chemical defence. This has been of interest to biologists because these metals are usually toxic. The accumulation of these metals may serve as a model for coevolution. We examined the effects of zinc hyperaccumulation in Thlaspi on Xanthomonas campestris and found that the plants containing zinc thrived when inoculated with this bacteria, plot plants not containing zinc showed signs of deterioration. INTRODUCTION There are several unjustifiable plant species that have the ability to accumulate noble quantities of heavy metals in their above ground biomass, up to triplet percent or more. many a(prenominal) of these plants are found in the Brassicaceae family throughout Europe and the British Isles. These plants thrive on mineral outcrops with calamine and serpentine soils rich with high levels of zinc, cadmium, and nickel (bread maker et al, 1994). some(prenominal) theories have been advanced on the reasons for this hyperaccumulation. Boyd and Martens propose that it could be a form of drought resistance, inadvertent uptake, interference, tolerance or garbage disposal of metal from the plant, or a chemical defence against herbivory or pathogens. Several studies have supported the chemical defence hypothesis. Martens and Boyd (1994 and Boyd and Martens, 1994) showed that nickel hyperaccumulation is an effective defence against insect herbivores in two different feeding experiments. Boyd et at (1994) withal demonstrated that nickel hyperaccumulating plants resisted pathogens including Xanthomonas campestris. Thlaspi caerulescens J. and C. Presl (Brassicaceae) is a hyperaccumulating plan t found in the British Isles. It has been shown to accumulate 10,000 ppm (1%) of its biomass in zinc (Bakeret 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 collect in Cloughwood, U. K. These seeds germinated on polyester beads supported in expanded polystyrene tons floating on one-tenth strength Rorisons 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.