Defense responses of soybean roots during exposure to cadmium, excess of nitrogen supply and combinations of these stressors.

Heavy metal pollution is a serious environmental problem in agricultural soils since the uptake of heavy metals by plants represents an entry point into the food chain and is influenced by the form and amount of nitrogen (N) fertilization. Here we studied the defense responses in soybean roots exposed to ions of cadmium (applied as 50 mg l(-1) Cd(2+)) when combined with an excessive dose of N in form of NH(4)NO(3). Our data indicate that despite of stunted root growth, several stress symptoms typically observed upon cadmium treatment, e.g. peroxidation of lipid membranes or activation of chitinase isoforms, become suppressed at highly excessive N. At the same time, other defense mechanisms such as catalases and proline accumulation were elevated. Most importantly, the interplay of ongoing responses resulted in a decreased uptake of the metal into the root tissue. This report points to the complexity of plant defense responses under conditions of heavy metal pollution combined with intensive fertilization in agriculture.

Bilayer structures in dioctadecyldimethylammonium bromide/oleic acid dispersions.

This paper reports on the properties of bilayers composed of dioctadecyldimethylammonium bromide (DODAB) and oleic acid (OA) at various molar ratios. The mole fraction of OA, X(OA), was varied in the range of 0-1 and the total lipid content was constant and equal to 10 mM. The DODAB/OA dispersions were extruded at a temperature higher than that of the gel-liquid transition of DODAB. The morphology of bilayer structures formed in the dispersions was inspected using a cryogenic transmission electron microscopy (cryo-TEM) and a differential interference contrast microscopy (DIC). The observations revealed that the incorporation of OA into DODAB bilayer results in a decrease of the membrane curvature. Anisotropy measurements using 1,6-diphenylhexatriene (DPH) as a rotator probe demonstrated that the DODAB/OA membrane microviscosity decreased considerably for X(OA)>0.4. The thermal behavior of DODAB/OA membranes has been studied by differential scanning calorimetry (DSC). In the case of the systems in which X(OA)<0.8, the DODAB/OA membranes are in the gel phase at room temperature. Additionally, Langmuir monolayer experiments of the DODAB/OA mixtures showed that due to the electrostatic interactions between the oppositely charged head groups of DODAB and OA they get close to each other, which results in a decrease of the mean area per molecule. The results were next discussed based on the packing parameter concept. The reduction of the mean area per head group (a) in the DODAB/OA systems leads to subsequent increase in the so-called packing parameter (S), which governs the morphology of surfactant aggregates.