Some Plant Enzymes Are Highly Sensitive to Inhibition by Zinc Ions

Abstract

It is well known that excessive zinc accumulation is harmful to plant cells. Though, it is uncertain at which levels of intracellular availability zinc begins to exert its deleterious action on cell physiology, as the current estimations of zinc in vitro acting concentrations seem to be non-physiologically high (micro- or millimolar). Total esterase activity in plant cells is sensitive to different adverse factors and is often used to access cell physiological activity. Therefore, we determined the effect of different zinc availability levels in vitro on the total esterase activity in extracts from rapeseed (Brassica napus L.) roots and leaves. We founded that esterase activity was drastically decreased by different protein-affecting factors, namely chaotropic salts, detergents, elevated temperatures and denaturing agents. The utilization of reaction media with exactly specified concentrations of free Zn2+ ions demonstrated that total esterase activity is substantially reduced already at tens of nM Zn2+, which is several orders of magnitude lower than was described earlier. Total phosphatase activity in extracts was even more sensitive, being drastically reduced at free Zn2+ concentrations of few nM. Therefore, the plant cellular processes can be adversely affected at very low free Zn2+ concentrations.