Investigation of element distributions between the symplasm and apoplasm of cucumber plants by TXRF spectrometry

The lead, iron and manganese distribution between the symplasm and apoplasm of cucumber plant parts (root and leaves) was determined by total reflecti on X-ray fluorescence spectrometry (TXRF). Plants were grown in control or in lead-contaminated (10(-5)M Pb) nutrient solutions containing iron in the chemical form of Fe(III)-EDTA or Fe(III)-citrate. The total concentrations of metals in the dried plant parts were measured after their microwave-ass isted digestion. For the determination of the distribution of the elements investigated between the apoplasm and symplasm, the dried root and leaf sam ples were infiltrated and washed with a solution containing 10 mmol/dm(3) N a,EDTA and 0.5 mmol/dm(3) CaSO4. Elements in the washing solutions and in t he washed plant parts were characteristic of the apoplasm and symplasm, res pectively. It was established that lead accumulated mainly in the root apop lasm. Going up towards the shoot, in the leaves, there was approximately 50 -60% of lead in the symplasm. The iron - similarly to lead - was found main ly in the apoplasm in the root, while in the leaves the symplasm/apoplasm r atio was 55:45%. The distribution of manganese between the symplasm and apo plasm did not show any significant change under the different treatments. I n contrast with lead and iron, there was 70% and 60% of manganese in the sy mplasm of the root and of the leaves, respectively. (C) 2000 Elsevier Scien ce B.V. All rights reserved.