Jarosław Gzyl

The new insights into cadmium sensing

Cadmium (Cd) is non-essential heavy metal, which in excess, exhibits deleterious effects to the most of the organisms. Mobilization of defense mechanisms against this toxic agent requires rapid activation of signaling pathways. The article presents recent advances in the research concerning cadmium signal transduction in plants. New insights into the involvement of reactive oxygen species (ROS), nitric oxide (NO), plant growth regulators, and Cd-induced protein modifications are reviewed. Moreover, the role of recently recognized Cd-associated signal elements, including micro RNAs and several cis- and trans-acting elements is discussed.

Nitric oxide implication in cadmium-induced programmed cell death in roots and signaling response of yellow lupine plants.

The sequence of events leading to the programmed cell death (PCD) induced by heavy metals in plants is still the object of extensive investigation. In this study we showed that roots of 3-day old yellow lupine (Lupinus luteus L.) seedlings exposed to cadmium (Cd, 89μM CdCl(2)) resulted in PCD starting from 24h of stress duration, which was evidenced by TUNEL-positive reaction. Cd-induced PCD was preceded by a relatively early burst of nitric oxide (NO) localized mainly in the root tips. Above changes were accompanied by the NADPH-oxidase-dependent superoxide anion (O(2)(·-)) production. However, the concomitant high level of both NO and O(2)(·-) at the 24th h of Cd exposure did not provoke an enhanced peroxynitrite formation. The treatment with the NADPH-oxidase inhibitor and NO-scavenger significantly reduced O(2)(·-) and NO production, respectively, as well as diminished the pool of cells undergoing PCD. The obtained data indicate that boosted NO and O(2)(·-) production is required for Cd-induced PCD in lupine roots. Moreover, we found that in roots of 14-day old lupine plants the NO-dependent Cd-induced PCD was correlated with the enhanced level of the post-stress signals in leaves, including distal NO cross-talk with hydrogen peroxide.

Selection in vitro and accumulation of phytochelatins in cadmium tolerant cell line of cucumber (Cucumis sativus)

Cucumber (Cucumis sativus L.) cells from suspension culture were selected for their ability to grow and divide rapidly in toxic concentration of cadmium. As a result of selection a cell suspension tolerant to 100 μM cadmium chloride (CdCl2) was initiated. The selected tolerant line exhibited stable and repeatable increase in fresh and dry weight of cells in the presence of cadmium. The accumulated level of phytochelatins in cadmium sensitive (unselected) and tolerant cell line was measured by high performance liquid chromatography (HPLC) after 3, 24 h and 5 days of cadmium treatment. It was shown that in both cell lines Cd induced accumulation of phytochelatins and simultaneous glutathione depletion occurred. No distinct changes were found after 3 and 24 h of cadmium treatment whereas after 5 days of exposure to the metal, the level of phytochelatins was two times higher in the sensitive cell line as compared to the tolerant one. The accumulation of phytochelatins was correlated with cadmium concentration that increased in both cell lines during the course of cell exposure to metal. However, the level of cadmium was always lower in the tolerant cell line. The results showed no direct correlation between the tolerance of cucumber cells to Cd and the accumulated level of phytochelatins. Other mechanisms responsible for the increased tolerance of cucumber cells exposed to Cd are discussed.

Cadmium affects microtubule organization and post-translational modifications of tubulin in seedlings of soybean (Glycine max L.)

Cadmium (Cd) is a non-essential heavy metal, toxic to all living organisms. The microtubule (MT) cytoskeleton appears to be one of the main targets of Cd action. In this study we present, with the use of various immunological approaches, the effect of Cd at moderate (85 μM) and high (170 μM) concentrations on the structure and functioning of the MT cytoskeleton in the root cells of soybean seedlings. As the result of heavy metal action, root growth was significantly diminished and was accompanied by a reduction in mitotic activity and disturbance in the structure of the MT arrays, including randomization of the cortical MT arrangement, distorted mitotic arrays and complete depolymerization of the MTs. Biochemical analysis revealed decreased levels of various α- and β-tubulin isoforms with a parallel down-regulation of most examined α-tubulin genes. Simultaneously, Cd treatment led to differentiated changes in the level of tubulin post-translational modifications, including tyrosination, detyrosination, acetylation, and polyglutamylation. Decreased tyrosination and polyglutamylation of particular tubulin isoforms accompanied by increase in the level of specific detyrosinated and acetylated isoforms implies augmented stability and reduced turnover of the MTs during stress conditions. Taken together, the obtained results indicate the significant impact of Cd on gene expression levels and subsequent post-translational processing of tubulin, which may be related to the impairment of MT cytoskeleton functioning in root cells.

Homocysteine over-accumulation as the effect of potato leaves exposure to biotic stress

Homocysteine (Hcy) is a naturally occurring intermediate metabolite formed during methionine metabolism. It has been well documented that its excess can be extremely toxic to mammalian, yeast and bacterial cells. In spite of the metabolic value of Hcy known for decades, the role of this amino acid in the plant response to stress has not been recognized yet. In the presented study, using potato plant (Solanum tuberosum L.) and Phytophthora infestans as a model system, the presence and tissue localization of Hcy in leaves was examined by an immunohistochemical method. The over-production of Hcy was more evidenced in the susceptible than in the resistant genotype of potato starting from 48 hpi. Furthermore, the elevated level of Hcy was correlated in time with the up-regulation of genes engaged in its biosynthesis, e.g. cystathionine β-lyase and S-adenosyl-l-homocysteine hydrolase. The pharmacological approach with exogenous Hcy resulted in significant rise in lipid peroxidation and more potent late blight disease development in leaves of susceptible potato as well. Finally, it has been found that key defense enzymes, i.e. phenylalanine ammonia lyase and β-1,3-glucanase were up-regulated early in the resistant potato genotype, starting from 1st hpi. In turn, in the susceptible potato the time-lag in expression of these enzymes tuned with excess production of Hcy might facilitate leaf tissue colonization by pathogen. Based on obtained results it should be stated that Hcy over-accumulation is engaged in pathophysiological mechanism leading to the abolishment of the resistance and might be an informative disease hallmark both in plant and in animal system.

The infl uence of the selected ratios of trees stability on the wall thickness of tracheids in the Scots pine (Pinus sylvestris L.)

The study comprised an analysis of two tree stability indexes, i.e. slenderness factor (H/D1.3) and crown inclination index (DK/H) of thirty six pines coming from twelve mature stands growing at diff erent sites. Apart from stability for each tree tracheid wall thickness was determined at breast height in early and late wood. Results showed that examined trees belong to a group considered to be stable (Figs. 2, 3), while investigated stability indexes are negatively correlated (−0.64). Next tracheid wall thickness was determined in early wood to be 2.11 ±0.21 μm and for late wood at 6.84 ±1.08 μm. No signifi cant diff erences were found between examined plots in terms of investigated indexes or tracheid wall thickness in late wood. In contrast, statistically signifi cant dependencies were observed between the analysed indexes and tracheid wall thickness in early and late wood. Slenderness factor was most strongly correlated with tracheid wall thickness in late wood. Moreover, a dependence was also found between crown inclination index and tracheid wall thickness in early wood, which most probably may be explained by the relationship between the tree crown, which width was one of the variables in DK/H and hydraulic functions of anatomical elements. With an increase in the crown inclination index the mean tracheid wall thickness decreased, most probably leading to an increase in their lumen, which has a positive eff ect on their effi ciency in conductivity of water and minerals.