No abstract

Heavy metals perturbate water balance in plants and hence impact stomatal aperture. After longer exposure, stomatal development also is affected, and stomatal density and size can change. Two soybean (Glycine max) varieties were experimentally selected for contrasting tolerance to arsenic and cadmium. For these cultivars, natural variability in leaf epidermal cell parameters was detected. Pot plants at first assimilating leaf stage were exposed for 10 days to 5 mg kg-1 soil As 3+ and 50 mg kg-1 soil Cd 2+ (respectively). Metals accumulated primarily in roots and exerted relatively low impact on biomass. Despite this, we observed diverse adjustments of stomata and pavement cells. In cv. Bólyi 44 the stomatal size decreased upon stress treatment, possibly to avoid further water loss. In contrast, the other cultivar Cordoba uses larger stomata that might be advantageous in gaining further resources. The observed responses varied depending on leaf type. In addition, dorsoventral stomatal responses in width, yet undescribed under metal stress, were observed. Our data show that leaf epidermal cell adjustments are flexible components of plant defense even at low metal doses, and possibly help to compromise the structural and functional needs of plant (tissue) under metal stress.

Arsenic is a serious soil pollutant with toxic effects on biological systems. Elevated soil concentrations may negatively affect crop production and food safety. The impact of arsenic on plants depends on many factors, including nitrogen availability. Nitrogen (N) as an essential mineral affects overall energetics of plants, while its non-optimal doses have been shown to also impact plant performance and yield, as well as tolerance to environmental constraints. The combined effects of these two factors, however, have been rarely studied. Here we investigated the impact of sublethal doses of As 3+ (5 mM) on wheat plants grown in hydropony, applying a set of 8 different N concentrations spanning from starvation (0 mM N in the media) through optimum (7.5 mM N) to excessive amounts (up to 35 mM N). The results showed that the content of photosynthetic pigments varies depending on N concentration and As 3+ presence. The different energetic status of plants also affected the final As uptake. Establishing nutrition conditions might be important for limiting metal(loid) uptake from soil in contaminated areas.

Cell walls represent the first barrier that can prevent the entrance of toxic heavy metals into plants. The composition and the flexibility of the cell wall are regulated by different enzymes. The ß-1,3-glucanases control the degradation of the polysaccharide callose as a flexible regulation mechanism of cell wall permeability and/or its ability to bind metals under stress conditions. The profile and activity of ß-1,3-glucanases in the presence of heavy metals, however, has rarely been studied. Here we studied these enzymes in four soybean varieties (Glycine max) grown in the presence of cadmium ions. These analyses revealed three acidic and one basic enzyme isoforms in each soybean variety, but only two of the acidic isoforms in the variety Moravians were substantially responsive to the presence of Cd 2+ . Since the responses of certain glucanases were detected mainly in the varieties sensitive to metal and accumulating high amounts of metals, we assume their role in the defense rather than strategic metal sequestration.

Cadmium is a serious environmental pollutant and its uptake by plant represents a serious health risk. Uptake, accumulation as well as sensitivity of soybean plants to metals have been shown to vary with genotype, while the dynamics of this uptake has rarely been studied. Here we studied the uptake and accumulation of Cd to monitor its accumulation continuously at 24 h intervals for 10 days. Our results showed that the uptake rate varied among the cultivars, being the highest in roots of the cv. Moravians and the lowest in the cv. Gallec. We also observed a non-even distribution of radioactivity within the entire plants of individual cultivars. The most of Cd 2+ isotope was translocated into primary leaves and leaves in the cvs. Kent and Moravians; on the contrary, relatively less in the cvs. Cardiff and Gallec. The results were fitted with genetic potential, growth as well as defense parameters such as proline accumulation. Combining uptake dynamics and biochemical data are indicative for different tolerance strategies of soybeans.