Generation of reactive oxygen and nitrogen species in pea cultivars under copper exposure

Copper is an essential microelement in plants, but its exposure can induce toxicity symptoms such as growth inhibition, chlorosis or necrosis. The aim of this study was to investigate the physiological responses of two pea cultivars (Pisum sativum L. cv. Rajnai törpe and cv. Lincoln) to long term copper exposure. Seven-day-old pea plants were treated with 25 or 50 μM CuSO4, in nutrient solution for 14 days. We studied the growth parameters, the metal uptake, the levels of different reactive oxygen species (hydrogen peroxide, H2O2 and superoxide radical, O2.-) and reactive nitrogen species (nitric oxide, NO. and peroxynitrite, ONOO-) together with lipid peroxidation and cell death in the meristem cells of pea roots using in vivo and in situ microscopic methods. Long-term copper exposure resulted in a serious decrease in shoot and root growth of both pea cultivars and the root system proved to be more sensitive to the stressful condition. The reason of higher sensitivity of the root system is that the largest proportion of copper accumulated in it, namely, pea plants exclude the toxic metals from their shoot. Copper treatment induced the elimination of O2.- and the concurrent H2O2 generation in root tips of both cultivars. The level of NO significantly decreased as the effect of Cu2+ exposure, while the level of ONOO- (+OH.) enhanced, suggesting the occurrence of the reaction between O2.- and NO yielding peroxynitrite. As the effect of copper, lipid peroxidation and cell death were detected in the root tips which led to growth inhibition and biomass decrease of pea plants

The effect of selenium (Se) on development and nitric oxide levels in Arabidopsis thaliana seedlings

Selenium (Se) is an essential element for many organisms, but its excess leads to toxicity symptoms such as growth inhibition or chlorosis. Since nitric oxide (NO) is a multifunctional signal molecule in plants acting during several physiological plant responses, we examined the effect of selenite treatment on nitric oxide status of Arabidopsis plants during their growth. The effect of selenite on the development and cell viability of seedlings proved to be concentration and time-dependent and it can be explained by the disturbance of protein synthesis, structure and function. Selenite treatment modified the endogenous NO status in the root and the cotyledon of Arabidopsis plants. During the first days after germination the effect of Se was shown to be rather inhibitory on NO content, while during the late developmentin Se-treated plants NO levels increased, which may contribute to growth inhibition

In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 μM) and high (50 μM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants

Comparing the effects of excess copper in the leaves of Brassica juncea (L. Czern) and Brassica napus (L.) seedlings: Growth inhibition, oxidative stress and photosynthetic damage

Hydroponic experiments were conducted to compare the effects of excess copper (Cu) on growth and photosynthesis in young Indian mustard (Brassica juncea) and oilseed rape (Brassica napus). We compared the effects of excess Cu on the two Brassica species at different physiological levels from antioxidant levels to photosynthetic activity. Nine-day-old plants were treated with Cu (10, 25 and 50 μM CuSO4) for 7 and 14 days. Both species took up Cu from the external solution to a similar degree but showed slight root-to-shoot translocation. Furthermore, after seven days of treatment, excess Cu significantly decreased other microelement content, such as iron (Fe) and manganese (Mn), especially in the shoots of B. napus. As a consequence, the leaves of young Brassica napus plants showed decreased concentrations of photosynthetic pigments and more intense growth inhibition; however, accumulation of highly reactive oxygen species (hROS) were not detected. After 14 days of Cu exposure the reduction of Fe and Mn contents and shoot growth proved to be comparable in the two species. Moreover, a significant Cu-induced hROS accumulation was observed in both Brassica species. The diminution in pigment contents and photosynthetic efficiency were more pronounced in B. napus during prolonged Cu exposure. Based on all the parameters, B. juncea appears to be more resistant to excess Cu than B. napus, rendering it a species with higher potential for phytoremediation

Involvement of nitric oxide (NO) and auxin in signal transduction of copper induced morphological responses in Arabidopsis seedlings

Background and Aims Plants are able to adapt to the environment dynamically through regulation of their growth and development. Excess copper (Cu2+ ), a toxic heavy metal, induces morphological alterations in plant organs; however, the underlying mechanisms are still unclear. With this in mind, the multiple signalling functions of nitric oxide (NO) in plant cells and its possible regulatory role and relationship with auxin were examined during Cu2+ -induced morphological responses. Methods Endogenous auxin distribution was determined by microscopic observation of X-Gluc-stained DR5::GUS arabidopsis, and the levels of NO, superoxide and peroxynitrite were detected by ¿uorescence microscopy. As well as wild-type, NO-overproducer (nox1) and -de¿cient (nia1nia2 and nia1nia2noa1-2) arabidopsis plants were used. Key Results Cu2+ at a concentration of 50mM resulted in a large reduction in cotyledon area and hypocotyl and primary root lengths, accompanied by an increase in auxin levels. In cotyledons, a low Cu2+ concentration promoted NO accumulation, which was arrested by nitric oxide synthase or nitrate reductase inhibitors. The 5-mM Cu2+ -induced NO synthesis was not detectable in nia1nia2 or nia1nia2noa1-2 plants. In roots, Cu2+ caused a decrease of the NO level which was not associated with superoxide and peroxynitrite formation. Inhibition of auxin transport resulted in an increase in NO levels, while exogenous application of an NO donor reduced DR5::GUS expression. The elongation processes of nox1 were not sensitive to Cu2+ , but NO-de¿cient plants showed diverse growth responses. ConclusionsIn plant organs, Cu2+ excess results in severe morphological responses during which the endogenous hormonal balance and signal transduction are affected. Auxin and NO negatively regulate each other¿s level and NO intensi¿es the metal-induced cotyledon expansion, but mitigates elongation processes under Cu2+ exposurePetó, A.; Lehotai, N.; Lozano Juste, J.; Leon Ramos, J.; Tari, I.; Erdei, L.; Kolbert, Z. (2011). Involvement of nitric oxide (NO) and auxin in signal transduction of copper induced morphological responses in Arabidopsis seedlings. Annals of Botany. 108(3):449-457. doi:10.1093/aob/mcr176S449457108