Distribution and Toxic Effects of Cadmium and Lead on Maize Roots

Two-day-old seedlings of maize (Zea mays L.) were incubated on Cd and Pb nitrate solutions at the concentrations that inhibited root growth approximately by 50% after two-day-long incubation (LC₅₀; 10^–4 and 10^–3 M, respectively) or completely terminated growth of the primary root after one-day-long incubation (LC; 5 × 10^–4 and 10^–2 M, respectively). Cd and Pb contents were measured using an anodic inversion voltammetric technique in a flow injection system and a histochemical method. At LC₅₀, Cd and Pb were discerned, by histochemical techniques, in all root apical tissues, whereas in the root hair zone, the heavy metals were primarily accumulated in the apoplast of the rhizodermis and cortex and to a lesser extent, in the vascular tissues and parenchyma cells surrounding the metaxylem vessels. Insignificant accumulation of Cd and Pb in the pericycle probably explains why root branching was tolerant to these agents. At LC, Cd and Pb were found in the apoplast of all root tissues, in accordance with the practically complete inhibition of root growth and branching. Irrespectively of Cd and Pb concentrations in the external solution, the metal contents in the root apex exceeded those in the basal region. Procion dyes were used to assess cell death inflicted by Cd and Pb. At LC, the root cap and meristematic cells perished, together with the rhizodermal cells and the outer cortical cells of the root apex, whereas only the rhizodermal cells in the root apical region died at LC₅₀. The evidence that Cd and Pb cross the endodermal barrier at LC presumes that, at lower metal concentrations, the Casparian strip and plasmalemma of the endodermis regulate the transport of these metals into the central cylinder. The authors conclude that the identical barriers control Cd and Pb transport in root tissues.     

Micellar electrokinetic chromatography with polyelectrolyte complexes as micellar pseudo-stationary phases

The separation of dansyl (DNS-AAs) and carbobenzoxy (CBZ-AAs) amino acids using micellar electrokinetic chromatography employing polyelectrolyte-surfactant complexes (PSC) formed in the reaction between polyacrylic acid (PAA) and dodecyltrimethylammonium bromide (DTAB) as pseudo-stationary phases was described. The PSCs were stabilized by hydrophobic interactions of alkyl chains of the surfactant ions and converted to an intramolecular micellar-like phase. The running buffer was a 50mM solution of sodium phosphate (pH 6.0) containing 4.6-20.2mM PSC, in which a part of carboxyl groups of PAA was blocked by aliphatic amines. For the systems with 7.9mM of PAA/DTAB complex (phi=0.30, phi-composition of water-soluble polyelectrolyte complex) as a pseudo-stationary phase, the peaks of six dansyl amino acids (DNS-AAs) were baseline resolved. The separation in this case is based on a complex distribution mechanism of the dansyl derivatives between the free buffer and the intramolecular micellar-like phase of the water-soluble PSC. On the other hand, the additives of PAA/DTAB complex (phi=0.30) to the running buffer does not essentially affect on the electrophoretic behaviour of the CBZ-AAs, the variant MEKC is not realized. The influence of the concentration of the complex of PAA/DTAB on the electrophoretic behaviour of analytes was investigated. Relative retentions and relative selectivities were used for describing electrophoretic behaviour of the amino acid derivatives.     

Bionanocompositional chitosan-silica sorbent for liquid chromatography

Preparation of hybrid nanocompositional chitosan/silica sorbent was carried out. It was shown that formation of gel in sol-gel process of hydrolytic polycondensation of tetraethoxysilane (TEOS) with including of chitosan consists of two stages. Suppression of crystallization of chitosan in obtained two-phase system and changes in IR spectra are evidenced of interactions between molecules of chitosan and silanol groups of silica network. The resulting hybrid chitosan/silica sorbent was tested by high-performance liquid chromatography (HPLC).     

Methods to Determine the Chirality Sign for Helical and Superhelical Protein Structures

Biophysics - A method was designed to describe the helical structures of various levels of organization in proteins. The method makes it possible to characterize the sign of chirality/helicity and...     

Lewisite metabolites detection in urine by liquid chromatography-tandem mass spectrometry

A sensitive and simple method for the quantification and for the detection of 2-chlorovinylarsonous (CVAA) and 2-chlorovinylarsonic (CVAOA) acids was developed. CVAA and CVOA are important biological markers in human and rat urine specific to lewisite (chlorovinylarsonous chloride compounds) exposure. The developed assay was based on the use of solid-phase extraction (SPE) followed by liquid-chromatography coupled to electrospray ionization (negative ion-mode) low-energy collision dissociation-tandem mass spectrometry (ESI-CID-MS/MS). The method demonstrated linearity over at least three orders of magnitude and had a detection limit (LOD) of 0.5 ng/ml for CVAA and 3 ng/ml for CVAOA. The relative standard deviations for the quality control samples ranged from 6 to 11%. Application of this procedure was demonstrated in the lewisite animals exposure model. Rats were exposed intravenously by no lethal doses of lewisite and markers levels in urine samples were analyzed for 21 days post-exposure.     

Chirality As a Symmetric Basis of Self-Organization of Biomacromolecules

Biophysics - A review of materials within the concept of chirality as a symmetric basis of self-organization in biomacromolecules is presented. The following topics are considered: methods for...