The mechanism of zinc tolerance in grasses

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Abstract
The mechanism of zinc tolerance in non‐tolerant and tolerant clones of Deschampsia caespitosa and Anthoxanthum odoratum has been investigated. Analysis of non‐tolerant and tolerant clones of these two grasses showed that the tolerant roots accumulated more zinc than the non‐tolerant ones. The zinc contents of the shoots of both clones were similar and contained less zinc than the roots. Compartmental flux analysis using 65Zn suggested that both clones of D. caespitosa were capable of actively pumping zinc across the plasmalemma into the external medium. However, only the tolerant clone was capable of actively pumping zinc out of the cytoplasm of root cells into vacuoles when exposed to levels of zinc up to 1mM, this process was inhibited above 0.1mM zinc in the non‐tolerant clone. Analysis of D. caespitosa for organic acids showed that only the tolerant clone, grown in the presence of zinc accumulated high levels of malic acid. Cytoplasmic sensitivity to zinc was measured by estimating the effect of zinc upon 1‐malate and 1‐glutamate dehydrogenases extracted from roots of non‐tolerant and tolerant clones. No significant differences were found between the two clones. The implications of these observations are discussed in relationship to the mechanism of zinc tolerance in grasses.