Agnieszka Kutrowska

Low-molecular weight organic acids and peptides involved in the long-distance transport of trace metals

Abstract Higher plants evolved mechanisms of uptake, distribution and accumulation of trace metals essential for the proper functioning of the organism (e.g., copper, zinc). Non-essential metals (e.g., cadmium, arsenic, lead) can also enter plant cells using the routes dedicated to the essential ones, because of the shared similar chemical and physical properties. Generally, trace elements are very reactive, able to generate reactive oxygen species and to interact or bind various organic ligands composed of C, H, O, N, P or S. Thus, after entering to the cells, metals are transported and sequestered mainly in a complex form, bound with amino acids, organic acids, peptides or specific metal-binding ligands. Considering diverse properties (e.g., pH value, abundancy of ions, redox state) characterizing cells, tissues and phloem or xylem sap, plants use various ligands to form stable complexes in different conditions. This literature review aims to provide a comprehensive overview on the role of low-molecular weight acids and peptides in trace metals translocation.

Effects of binary metal combinations on zinc, copper, cadmium and lead uptake and distribution in Brassica juncea

The interaction between lead, copper, cadmium and zinc in their binary combinations was investigated in Indian mustard seedlings (Brassica juncea L. var. Malopolska). Fourteen-days-old seedlings were treated with Pb(NO3)2, CuSO4, CdCl2, ZnSO4 at 50μmol of metal ion concentration and at 25μmol of each metal ion in combinations. Metal combinations were generally more inhibiting in terms of biomass production. This inhibiting effect followed an order: Cu+Cd>Cu+Zn, Cd+Pb>Cu+Pb>Zn+Pb, Cu>Cd>Zn>Zn+Cd>Pb. We observed synergistic and antagonistic effects of metal uptake in binary metal treatments, suggesting metal crosstalk at the plant uptake site. Metal content in plant tissues varied among different combinations. The metal concentrations followed an order of Pb>Cu>Zn>Cd in roots, Zn>Cu>Pb>Cd in the stem and Zn>Cu>Cd>Pb in leaves. Presence of metals altered the distribution of micronutrients (Cu, Zn) in plants: Cu concentration was lowered in roots and leaves and increased in stems; Zn content was increased in plants, with stems having up to 4 or 5 times more Zn than in control plants.

High Peroxide Level May Be a Characteristic Trait of a Hyperaccumulator

Under various abiotic stresses, plants overproduce reactive oxygen species (ROS) such as superoxide anion (O2•−), hydroxyl radical (OH•), and hydrogen peroxide (H2O2). When in excess, these highly reactive molecules cause oxidative stress, thus damaging proteins, lipids, and DNA. Therefore, plants evolved an enzymatic defense machinery that involves such enzymes as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APOX). Various plant families, species and even specimens differ in their ability to withstand the abiotic stress. A study has been undertaken to assess the differences in response to trace metals between two species: a resistant hyperaccumulator Indiana mustard (Brassica juncea) and a metal-sensitive pea (Pisum sativum). We observed that trace elements (Cu, Zn, Cd, Pb) changed the activity of antioxidative enzymes (SOD, APOX, CAT) and the rate of ROS generation. However, in the control plants and at a point 0′ of the treatment, we have noticed a large disproportion in the hydrogen peroxide level, with B. juncea maintaining naturally higher H2O2 level (up to 40 times higher). We believe that this may be a distinguishing trait common to plants being resistant to oxidative stress.