Freshly harvested seeds of Arabidopsis thaliana, Columbia (Col) accession were dormant when imbibed at 25°C in the dark. Their dormancy was alleviated by continuous light during imbibition or by 5 weeks of storage at 20°C (after-ripening). We investigated the possible role of reactive oxygen species (ROS) in the regulation of Col seed dormancy. After 24 h of imbibition at 25°C, non-dormant seeds produced more ROS than dormant seeds, and their catalase activity was lower. In situ ROS localization revealed that germination was associated with an accumulation of superoxide and hydrogen peroxide in the radicle. ROS production was temporally and spatially regulated: ROS were first localized within the cytoplasm upon imbibition of non-dormant seeds, then in the nucleus and finally in the cell wall, which suggests that ROS play different roles during germination. Imbibition of dormant and non-dormant seeds in the presence of ROS scavengers or donors, which inhibited or stimulated germination, respectively, confirmed the role of ROS in germination. Freshly harvested seeds of the mutants defective in catalase (cat2-1) and vitamin E (vte1-1) did not display dormancy; however, seeds of the NADPH oxidase mutants (rbohD) were deeply dormant. Expression of a set of genes related to dormancy upon imbibition in the cat2-1 and vet1-1 seeds revealed that their non-dormant phenotype was probably not related to ABA or gibberellin metabolism, but suggested that ROS could trigger germination through gibberellin signaling activation.

Oxidative stress is accepted to play a significant role in stress symptoms, caused by different stressors in a variety of organisms. In this study seedlings of spring barley (Hordeum vulgare L.) were exposed to a wide range of copper, zinc, chromium, nickel, lead and cadmium concentrations in order to determine the relationships between heavy metals-induced oxidative stress and plant growth inhibition. All investigated heavy metals induced an essential increase in lipid peroxidation and a reduction of dry biomass along with an increase in metal concentration in the nutrient solution. A very close and statistically significant exponential relationship between lipid peroxidation and growth inhibition was detected in this study. According to the results of analysis of variance (ANOVA), the intensity of nonspecific oxidative stress is identified as the main factor of barley growth inhibition, explaining 75% of total variance. Almost 10% of growth inhibition is attributed to the specific impact of heavy metals. The most pronounced increase of malondialdehyde content and growth inhibition was observed in Cu and Cd treatments, whereas the lowest changes in observed indicators were detected after exposure to Zn and Pb.

Th e aim of this study was to investigate the possibilities of spring barley (cv. ' Aura DS') cross-adaptation to the impact of diff erent (Cu, Zn, Cr, Ni, Cd and Pb) heavy metals. Th e most effi cient cross-adaptation was detected aft er pretreatment with Cd and Ni. Pretreatment with Cd caused the most essential increase in tolerance to Cr and Ni, was the only stressor to whose impact spring barley was not more tolerant aft er pretreatment with Cd. Aft er pretreatment by Ni, spring barley grew approximately 1.5 times better than not adapted ones, and only Cr was the metal to whose impact spring barley was not more tolerant aft er pretreatment with Ni. Cr and Pb, contrary to Cd and Ni, were detected to be the metals that almost did not stimulate cross-adaptation of spring barley to the other heavy metals and even adaptation to themselves. Cross-adaptive relations among the heavy metals were fou to be not always reciprocal. Cadmium was detected as a heavy metal with the most both-sided cross-adaptive relations with other metals and any reciprocal crossadaptive relation were not detected for Cr and Pb.