Aluminium coordination to calmodulin: thermodynamic and kinetic aspects

28-Homobrassinolide Primed Seed Improved Lead Stress Tolerance in Brassica rapa L. through Modulation of Physio-Biochemical Attributes and Nutrient Uptake

Brassinosteroids (BRs) influence a variety of physiological reactions and alleviate different biotic and abiotic stressors. Turnip seedlings were grown with the goal of further exploring and expanding their function in plants under abiotic stress, particularly under heavy metal toxicity (lead stress). This study's objective was to ascertain the role of applied 28-homobrassinolide (HBL) in reducing lead (Pb) stress in turnip plants. Turnip seeds treated with 1, 5, and 10 µM HBL and were grown-up in Pb-contaminated soil (300 mg kg-1). Lead accumulation reduces biomass, growth attributes, and various biochemical parameters, as well as increasing proline content. Seed germination, root and shoot growth, and gas exchange characteristics were enhanced via HBL treatment. Furthermore, Pb-stressed seedlings had decreased total soluble protein concentrations, photosynthetic pigments, nutrition, and phenol content. Nonetheless, HBL increased chlorophyll a and chlorophyll b levels in plant, resulting in increased photosynthesis. As a result, seeds treated with HBL2 (5 µM L-1) had higher nutritional contents (Mg+2, Zn+2, Na+2, and K+1). HBL2-treated seedlings had higher DPPH and metal tolerance indexes. This led to the conclusion that HBL2 effectively reduced Pb toxicity and improved resistance in lead-contaminated soil.

ESTUDOS DA TOXICIDADE DO ALUMÍNIO EM VALORES DE pH 7,0 E 7,5 PARA BRASSICA OLERACEA L. E RAPHANUS SATIVUS L

A toxicidade do alumínio tem sido verificada somente em valores de pH abaixo de 5,5 devido a solubilidade dos íons Al3+ que ocorre em meio ácido. Este trabalho teve o objetivo de estudar a toxicidade do alumínio em valores de pH 7,0 para a espécie Raphanus sativus L. (rabanete) e 7,5 para a Brassica oleracea L. (couve) com a finalidade de verificar se em tais valores de pH o alumínio não apresentava efeitos deletérios observáveis. Foi utilizada uma metodologia em que o meio de cultivo continha sementes como organismos testes e um rígido controle dos valores de pH. Os ensaios toxicológicos empregavam concentrações otimizadas de macro e micronutrientes necessários ao desenvolvimento das plântulas. Com o estudo foi possível verificar elevada Toxicidades Aguda e Crônica dos íons Al3+ em valores de pH 7,0 e 7,5 para as plantas estudadas, comprovando que os efeitos tóxicos do alumínio podem ser verificados também em meio de cultivo com valores de pH neutro e ligeiramente básico.

Label-free detection of protein-protein interactions using a calmodulin-modified nanowire transistor

In this study, we describe a highly sensitive and reusable silicon nanowire field-effect transistor for the detection of protein-protein interactions. This reusable device was made possible by the reversible association of glutathione S-transferase-tagged calmodulin with a glutathione modified transistor. The calmodulin-modified transistor exhibited selective electrical responses to Ca2+ (> or = 1 microM) and purified cardiac troponin I (approximately 7 nM); the change in conductivity displayed a linear dependence on the concentration of troponin I in a range from 10 nM to 1 microM. These results are consistent with the previously reported concentration range in which the dissociation constant for the troponin I-calmodulin complex was determined. The minimum concentration of Ca2+ required to activate calmodulin was determined to be 1 microM. We have also successfully demonstrated that the N-type Ca2+ channels, expressed by cultured 293T cells, can be recognized specifically by the calmodulin-modified nanowire transistor. This sensitive nanowire transistor can serve as a high-throughput biosensor and can also substitute for immunoprecipitation methods used in the identification of interacting proteins.

Aluminum toxicity and Ca depletion may enhance cell death of tobacco cells via similar syndrome

The main objective of this work is to find out whether aluminum (Al) toxicity and Ca depletion cause cell death of tobacco cells via similar sequence of events. Tobacco cell suspension culture exhibited maximum fresh weight in the presence of a wide range of Ca concentrations between 0.1-1.0 mM whereas higher concentrations (>1.0-5.0 mM) gradually lowered cell fresh weight. However, this decrease in fresh weight does not imply a negative impact on cell viability since cell growth recommenced in fresh MS medium with rates mostly higher than those of low Ca. In addition, high Ca seems to be crucial for survival of Al-treated cells. On the other side, tobacco cells exhibited extreme sensitivity to complete deprivation of Ca. Without Ca, cells could not survive for 18 h and substantially lost their growth capability. Evans blue uptake proved membrane damage of Ca-depleted same as Al-treated cells; relative to maintained membrane intactness of calcium-supplemented (control) ones. Percentage of membrane damage and the growth capability (survival) of tobacco cells exhibited a clear negative correlation.Alterations in growth (fresh weight per aliquot) could not be ascribed neither to cell number nor to decreased dry matter allocation (dry weight/fresh weight percentage) but was mainly due to decreased cellular water content. In this context, Ca-depleted cells lost about half their original water content while 100 microM Al-treated ones retained most of it (ca 87%). This represented the single difference between the two treatments (discussed in the text). Nevertheless, such high water content of the Al-treated cells seems physiologically useless since it did not result in improved viability. Similarities, however, included negligible levels of growth capability, maximum levels of membrane damage, and comparable amounts of NO(3) (-) efflux. As well, both types of treatments led to a sharp decline in osmotic potential that is, in turn, needed for water influx. The above-mentioned sequence of events, induced by Al application looks, to a great extent, similar to Ca depletion syndrome leading finally to cell death of tobacco cells.

Interactions of bovine serum albumin with aluminum polyoxocations and aluminum hydroxide

Interactions of aqueous solutions of aluminum polyoxocations (Al13-mers and Al30-mers) and aluminum hydroxide suspensions of varying particle sizes (26, 55, and 82 nm) with a model protein, bovine serum albumin (BSA), have been investigated using potentiometry, conductometry, viscometry, 27Al solution NMR, UV-vis spectroscopy, dynamic light scattering, zeta-potential measurements, thermogravimetry, X-ray diffraction, and scanning electron microscopy. Increasing amounts of BSA partially convert Al13-mers and, to a larger extent, Al30-mers into amorphous Al hydroxide without gel formation. At the same time, BSA molecules can form unstable aggregates in the Al polyoxocation solutions which redisperse easily upon standing. In the case of Al hydroxide sols, BSA addition causes substantial gelation, the extent of which is proportional to the amount of BSA added and inversely related to the Al hydroxide particle size. Upon freeze-drying or centrifugation of Al species-BSA solutions, an interesting sheetlike morphology with 150-200 nm wide nanoribbons is observed for pure Al hydroxide nanoparticles and for solutions of Al polyoxocations with the highest amount of BSA studied. On the basis of the combined solution, colloidal and solid-state characterization of model Al species-BSA systems, a qualitative model of possible interactions in the Al polyoxocation-BSA and Al hydroxide-BSA systems is proposed wherein core-shell hybrid nanoparticles are formed from protein "core" and Al polyoxocation "shell" or Al hydroxide "core" and protein "shell".

Recent advances in aluminum toxicity and resistance in higher plants

Aluminum toxicity is a major soil constraint to food and biomass production throughout the world. Considerable advances in the understanding of the mechanism of resistance involving exudation of organic acids have been made in recent years. However, despite intense research efforts, there are many aspects of Al toxicity that remain unclear. This article reviews the features of the chemistry of Al relevant to its toxicity followed by an examination of the mechanisms of toxicity and resistance. Emphasis, however, is given to the mechanisms of Al toxicity, since resistance has been covered recently by several reviews. Some topics which are specifically discussed in this review are: a) The possible role of cellular effects of low pH in Al toxicity, which has been largely ignored and needs to be addressed; b) The relevance of non-genotypic (cell-to-cell) variations in sensitivity to Al; c) Evidence indicating that although Al may well exert its toxic effects in the cell wall, it is highly unlikely that Al does so in a non-specific manner by mere exchangeable binding; and d) The hypothesis that the primary target of Al toxicity resides in the cell wall-plasma membrane-cytoskeleton (CW-PM-CSK) continuum has the potential to integrate and conciliate much of the apparently conflicting results in this field.