Effects of Cadmium(II) Ions on Early Somatic Embryos of Norway spruce Studied by Using Electrochemical Techniques and Nuclear Magnetic Resonance

Abstract

Studying of metal ions effects on plant cells and whole plants are still topical. Early somatic embryos (ESEs) of spruce represent the unique plant model system, which can be used to study of various types of environmental stresses including metal ions under well controlled experimental conditions. In the paper nuclear magnetic resonance (NMR) and electrochemical techniques were employed to investigate the effect of cadmium(II) ions (0, 50, 150, 250, 500 and 1,000 μM) on early somatic embryos (ESEs) of Norway spruce, clone 2/32. The ESEs were treated with cadmium(II) ions for fourteen days. The increase in cluster area and viability were determined by image analysis and fluorescein diacetate/propidium iodide double staining, respectively. Growth characteristics revealed the ESEs treated with cadmium-ethylene diamine tetra-acetic acid (Cd-EDTA) showed an increase in growth-inhibiting effect due to cadmium(II). Furthermore, total thiol content and certain low molecular mass plant thiols (cysteine, reduced glutathione, oxidized glutathione and phytochelatin2) were determined using Brdicka reaction and liquid chromatography with electrochemical detection, respectively. The highest level of phytochelatin2 synthesis was determined in ESEs treated with 50 μM Cd-EDTA. The average content of phytochelatin2 varied from 850 to 1800 nM/g FW. We also attempted to determine changes in water content in the ESEs treated with cadmium(II) ions using NMR. The highest increase in water content was observed at clusters treated with 250 μM Cd-EDTA. The clusters treated with higher cadmium concentrations (more than 250 μM) demonstrate only slow increase in the water content. Water metabolism at woody plants and their embryos exposed to cadmium(II) ions has not yet been described. Based on the results obtained it can conclude that the cells of embryonic clusters attempted to excrete cadmium(II) ions or, more precisely, decrease its concentration within the cluster. This phenomenon can be considered as one of the detoxification mechanisms of plants use to deal with the presence of heavy metal contamination. The escalation of water uptake continuously progress as long as the thiols are synthesized.