No abstract

This study was performed to investigate mercury (Hg) tolerance, accumulation, and translocation within the genus Salix for the potential use of this plant to remediate Hg-contaminated sites. Six clones of willow (Salix spp.) were tested on tolerance to Hg by treating plants grown in solution culture with 0 to 15 microM HgCl(2). Results showed that willow had a large variation in its sensitivity to Hg. However, the accumulation and translocation of Hg to shoots was similar in the eight tested willow clones as shown by cold vapor atomic absorption spectrometry analysis when plants were treated with 0.5 microM HgCl(2) in a nutrient solution. The majority of total Hg accumulated was localized to the roots, whereas only 0.45 to 0.62% of the total Hg accumulated via roots was translocated to the shoots. Thus, the root system is the main tissue of willow that accumulates Hg and the majority of the Hg in the root system (80%) was bound in the cell wall.

No abstract

Nitrate fertilization has been shown to increase Zn hyperaccumulation by Noccaea caerulescens (Prayon) (formerly Thlaspi caerulescens). However, it is unknown whether this increased hyperaccumulation is a direct result of NO 3 − nutrition or due to changes in rhizosphere pH as a result of NO 3 − uptake. This paper investigated the mechanism of NO 3 − -enhanced Zn hyperaccumulation in N.caerulescens by assessing the response of Zn uptake to N form and solution pH. Plants were grown in nutrient solution with 300 μM Zn and supplied with either (NH 4 ) 2 SO 4 , NH 4 NO 3 or Ca(NO 3 ) 2 . The solutions were buffered at either pH 4.5 or 6.5. The Zn concentration and content were much higher in shoots of NO 3 − -fed plants than in NH 4 + -fed plants at pH 4.5 and 6.5. The Zn concentration in the shoots was mainly enhanced by NO 3 − , whereas the Zn concentration in the roots was mainly enhanced by pH 6.5. Nitrate increased Zn uptake in the roots at pH 6.5 and increased apoplastic Zn at pH 4.5. Zinc and Ca coincreased and was found co-localized in leaf cells of NO 3 − -fed plants. We conclude that NO 3 − directly enhanced Zn uptake and translocation from roots to shoots in N. caerulescens.