SOLUBILITY OF ZINC AND INTERACTIONS BETWEEN ZINC AND PHOSPHORUS IN THE HYPERACCUMULATOR THLASPI-CAERULESCENS

The relationship between Zn and P in the Zn hyperaccumulator Thlaspi c aerulescens J. & C. Presl was investigated using hydroponic culture, T otal concentrations of Zn in the shoots increased from 0.2 to 27 g kg( -1) dry mass when solution Zn increased from 1 to 1000 mmol m(-3). Wat er-soluble Zn accounted for > 80% of the total Zn in the shoots contai ning > 5 g Zn kg(-1) dry mass, Total P was maintained at about 3 g kg( -1) dry mass in the shoots containing < 20 g Zn kg(-1) dry mass, but s ignificantly decreased with higher Zn concentrations, Linear regressio n between insoluble P and insoluble Zn in the shoots produced a small slope, suggesting that co-precipitation of Zn and P was not an importa nt detoxification mechanism in the shoots, In contrast, there was a st rong correlation between insoluble P and insoluble Zn in the roots, wi th a linear slope of 0.3 - close to the P:Zn ratio in Zn-3(PO4)(2). Fo liar sprays of phosphate did not affect shoot dry mass significantly, but decreased root length and root dry mass significantly at Zn concen trations in solution from 10 to 3000 mmol m(-3). Foliar P was transloc ated to roots to enhance co-precipitation of Zn and P, although this d id not enhance Zn tolerance, The results suggest that T. caerulescens possesses mechanisms which allow it to accumulate and sequester huge a mounts of Zn in the shoots without causing P deficiency.