Zinc accumulation and distribution over tissues in Noccaea Naerulescens in nature and in hydroponics: a comparison

Zinc distribution at the tissue level is studied almost exclusively in lab-grown plants. It is essential to establish to what extent the patterns observed in lab-grown plants are corresponding with those in nature. To this end, we compared Zn localization in Noccaea caerulescens growing in its natural environment, a zinc/lead mine tailing, with that in hydroponically grown plants of the same origin. Zinc concentrations in plants and soil were determined by flame AAS and Zn localization in leaf tissues was studied using Zn indicators Zincon and Zinpyr-1. The mean Zn concentration in plants at the mine tailings was around 15,000 mg/kg DW, which corresponded well with the Zn concentration in the leaves of plants grown at 1600 mu M Zn in the nutrient solution. The Zn distribution patterns in leaves of plants sampled from the mine and plants grown in hydroponics were identical. Zn-dependent staining was the most intensive in water-storage epidermal cells, guard cells and vascular bundles, and less intensive in subsidiary and mesophyll cells. Zinc distribution in hydroponically grown plants is representative for plants in nature. Preferential Zn sequestration in leaves, particularly in water-storage epidermal cells, restricts metal accumulation in mesophyll and contributes to Zn hypertolerance.