Assessment of the Hormetic Effect of Arsenic on Growth and Physiology of Two Cultivars of Maize (Zea mays L.).

Although growth stimulation at low arsenic doses was observed in several plants, few studies have focused on this phenomenon in more detail. The effects of different concentrations of arsenic (0-50 mg kg-1 of soil: As0-As50) on the growth and selected physiological parameters of two maize cultivars (Zea mays L. cvs. Chapalu and MvNK 333) were tested. Cultivar MvNK 333 manifested a generally higher tolerance to As than cv. Chapalu, which may be related to the lower content of As in the tissues. The highest stimulatory effect of As was recorded at doses of As1 and As2 (cv. Chapalu), and at the As5 dose (MvNK 333), there was an increase in shoot elongation, biomass, and relative water content (RWC), as well as the content of photosynthetic pigments. The stimulatory effect of lower doses of As apparently represents an adaptation mechanism that is associated with water content regulation in the given conditions. The stomata of the studied cultivars were involved in this regulation in different ways. While cv. Chapalu exhibited increased numbers of stomata on both sides of leaves, cv. MvNK 333 instead responded to the given conditions with decreased stomata size. Although hormetic manifestations closely related to changes in stomatal number and size were observed, a typical stomatal hormetic response was not observed in the given range of As doses.

The Cell-Wall ß-d-Glucan in Leaves of Oat (Avena sativa L.) Affected by Fungal Pathogen Blumeria graminis f. sp. avenae.

In addition to the structural and storage functions of the (1,3; 1,4)-ß-d-glucans (ß-d-glucan), the possible protective role of this polymer under biotic stresses is still debated. The aim of this study was to contribute to this hypothesis by analyzing the ß-d-glucans content, expression of related cellulose synthase-like (Csl) Cs1F6, CslF9, CslF3 genes, content of chlorophylls, and ß-1,3-glucanase content in oat (Avena sativa L.) leaves infected with the commonly occurring oat fungal pathogen, Blumeria graminis f. sp. avenae (B. graminis). Its presence influenced all measured parameters. The content of ß-d-glucans in infected leaves decreased in all used varieties, compared to the non-infected plants, but not significantly. Oats reacted differently, with Aragon and Vaclav responding with overexpression, and Bay Yan 2, Ivory, and Racoon responding with the underexpression of these genes. Pathogens changed the relative ratios regarding the expression of CslF6, CslF9, and CslF3 genes from neutral to negative correlations. However, changes in the expression of these genes did not statistically significantly affect the content of ß-d-glucans. A very slight indication of positive correlation, but statistically insignificant, was observed between the contents of ß-d-glucans and chlorophylls. Some isoforms of ß-1,3-glucanases accumulated to a several-times higher level in the infected leaves of all varieties. New isoforms of ß-1,3-glucanases were also detected in infected leaves after fungal infection.

Effect of Cadmium Chloride and Cadmium Nitrate on Growth and Mineral Nutrient Content in the Root of Fava Bean (Vicia faba L.).

The present study aimed to analyze the differences in the tolerance of fava bean (Vicia faba cv. Astar) roots to cadmium in nitrate-Cd(NO3)2-and chloride-CdCl2-solutions. The physiological and biochemical parameters were assessed. The tested doses of Cd (50, 100, 150 and 300 mg/L) did not influence the germination of seeds. However, considerable growth inhibition and dehydration were observed after 96 h incubation. The thickness of roots and rupture of cell membranes increased along with the increasing concentration of the metal in the solution. At a Cd dose of 300 mg/L, irrespective of the solution used, increased nitrogen concentration and no change in sodium content were observed. The content of magnesium increased due to the dose of 100 mg/L (cadmium nitrate) and the content of calcium increased due to the dose of 300 mg/L (in either nitrate or chloride). The correlation analyses pointed to a possible effect of nitrates in the applied solutions on the accumulation of Cd and some minerals in the roots of the given variety of fava bean. This may be important for both research and agricultural practice. The identification of crops with high tolerance to cadmium, as well as knowledge about the mechanisms of ion interactions at the soil solution-plant level, is important in terms of such crops' use in the process of the remediation of cadmium-contaminated soils coupled with food production.

Plant chitinase responses to different metal-type stresses reveal specificity.

KEY MESSAGE: Chitinases in Glycine max roots specifically respond to different metal types and reveal a polymorphism that coincides with sensitivity to metal toxicity. Plants evolved various defense mechanisms to cope with metal toxicity. Chitinases (EC 3.2.1.14), belonging to so-called pathogenesis-related proteins, act as possible second line defense compounds in plants exposed to metals. In this work their activity was studied and compared in two selected soybean (Glycine max L.) cultivars, the metal-tolerant cv. Chernyatka and the sensitive cv. Kyivska 98. Roots were exposed to different metal(loid)s such as cadmium, arsenic and aluminum that are expected to cause toxicity in different ways. For comparison, a non-metal, NaCl, was applied as well. The results showed that the sensitivity of roots to different stressors coincides with the responsiveness of chitinases in total protein extracts. Moreover, detailed analyses of acidic and neutral proteins identified one polymorphic chitinase isoform that distinguishes between the two cultivars studied. This isoform was stress responsive and thus could reflect the evolutionary adaptation of soybean to environmental cues. Activities of the individual chitinases were dependent on metal type as well as the cultivar pointing to their more complex role in plant defense during this type of stress.

Cultivar-specific kinetics of chitinase induction in soybean roots during exposure to arsenic.

The kinetics of defense responses was studied in soybean exposed to ecologically relevant concentrations of arsenic for 96 h. In the roots of two soybean cultivars with contrasting tolerance to this metalloid there were observed differences in basal levels of membrane lipid peroxidation as well as a significantly different course of peroxidation upon exposure to As. The different course of stress was reflected in the accumulation of defense components. The responses of individual chitinase isoforms were studied since these enzymes had previously been shown to be stable components of defense against metals. The kinetics and magnitude of accumulation of the three isoforms during exposure to As significantly differed within as well as between the studied cultivars. Furthermore, accumulation of these isoforms appeared to be related to oxidative status in the root tissue. The timing of induced responses is likely to be important for efficient defense against metal(oid) pollution in environment.

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.

Biochemical and physiological comparison of heavy metal-triggered defense responses in the monocot maize and dicot soybean roots.

Defense responses against cadmium, arsenic and lead were compared in two crop plants such as the monocotyledonous maize (Zea mays cv. Quintal) and dicotyledonous soybean (Glycine max cv. Korada). The applied metals caused root growth retardation, membrane damage and subsequent loss of cell viability, while enhanced H(2)O(2) generation, lipid peroxidation and lignification were detected with respect to corresponding controls. The measured data suggest that soybean was in general more tolerant to tested doses of metals and showed more pronounced defense responses than maize. Concurrently, the total activity of ß-1,3-glucanases, a subgroup of so called pathogenesis-related defense proteins, was comparable in root extracts of both plant types. Though in a view of previous comparative genome approaches the ß-1,3-glucanases do not mirror the differences in the cell wall structure and architecture between the monocots and dicots, we show that in both plant types they clearly respond to metal stress. Accumulation patterns of different glucanase isoforms upon exposure to tested metals indicate that they do contribute to plant defense mechanisms during exposure to heavy metals and their biological role is more complex than expected.