The phytohormone salicylic acid (SA) has a crucial role in plant physiology. Its role is best described in the context of plant response to pathogen attack. During infection, SA is rapidly accumulated throughout the green tissues and is important for both local and systemic defences. However, some genetic/metabolic variations can also result in SA overaccumulation in plants, even in basal conditions. To date, more than forty Arabidopsis thaliana mutants have been described as having enhanced endogenous SA levels or constitutively activated SA signalling pathways. In this study, we established a collection of mutants containing different SA levels due to diverse genetic modifications and distinct gene functions. We chose prototypic SA-overaccumulators (SA-OAs), such as bon1-1, but also “non-typical” ones such as exo70b1-1; the selection of OA is accompanied by their crosses with SA-deficient lines. Here, we extensively studied the plant development and SA level/signalling under various growth conditions in soil and in vitro, and showed a strong negative correlation between rosette size, SA content and PR1/ICS1 transcript signature. SA-OAs (namely cpr5, acd6, bon1-1, fah1/fah2 and pi4kβ1β2) had bigger rosettes under high light conditions, whereas WT plants did not. Our data provide new insights clarifying a link between SA and plant behaviour under environmental stresses. The presented SA mutant collection is thus a suitable tool to shed light on the mechanisms underlying trade-offs between growth and defence in plants.

Tobacco seedlings (Nicotiana tabacum L cv. Wisconsin 38) were treated for 24 h with colloidal solution of silver and gold nanoparticles (AgNPs and AuNPs) of different size or cultivated for 8 weeks on soil polluted with these NPs. DNA damage in leaf and roots nuclei was evaluated by the comet assay. AgNPs of the size 22–25 nm at concentrations higher than 50 mg·L⁻¹ significantly increased the tail moments (TM) values in leaf nuclei compared to the negative control. Ag nanoparticles of smaller size 12–15 nm caused a slight increase in tail moment without significant difference from the negative control. The opposite effect of AgNPs was observed on roots. The increasing tail moment was registered for smaller NPs. Similar results were observed for AuNPs at a concentration of 100 mg·L⁻¹. DNA damaging effects after growing tobacco plants for 8 weeks in soil polluted with AgNPs and AuNPs of different size and concentrations were observed. While lower concentrations of both types of particles had no effect on the integrity of DNA, concentration of 30 mg·kg⁻¹ of AgNPs caused significant DNA damage in leaves of tobacco plants. AuNPs had no effect even at the highest concentration. The content of Ag was determined by ICP–MS in above-ground part of plants (leaves) after 8 weeks of growth in soil with 30 mg·kg⁻¹. AgNPs and was 2.720 ± 0.408 µg·g⁻¹. Long term effect is much less harmful probably due to the plant restoration capability.

Phytohormone salicylic acid (SA) is a crucial component of plant induced defense against biotrophic pathogens. Although the key players of SA pathway are known, there are still gaps in our understanding of molecular mechanism and regulation of particular steps. In our previous research we showed in Arabidopsis suspension cells that n-butanol, which specifically modulates phospholipase D activity, significantly supresses transcription of pathogenesis related (PR1) gene generally accepted as SA pathway marker. In the presented study, we have investigated the site of n-butanol action in SA pathway. We were able to show in Arabidopsis plants treated with SA that n-butanol inhibits the transcription of defense genes (PR-1, WRKY38). Fluorescence microscopy of Arabidopsis thaliana mutants expressing 35S::NPR1-GFP (nonexpressor pathogenesis related 1) revealed significantly decreased nuclear localization of NPR1 in the presence of n-butanol. On the other hand, n-butanol did not affect nuclear localization of NPR1 in 35S::npr1C82A-GFP and 35S::npr1C216A-GFP mutants constitutively expressing NPR1 monomers. We also observed decreasing effect of n-butanol on ROS production, another important factor in plant response to pathogen attack. Mass spectrometric analysis of plant extracts showed that n-butanol significantly changes metabolic fingerprinting while t-butanol had no effect. We found groups of plant metabolites, influenced differently by SA and n-butanol treatment and we proposed several metabolites as markers for n-butanol action.

Actin cytoskeleton is the fundamental structural component of eukaryotic cells. It has a role in numerous elementary cellular processes such as reproduction, development and also in response to abiotic and biotic stimuli. Remarkably, the role of actin cytoskeleton in plant response to pathogens is getting to be under magnifying glass. Based on microscopic studies, most of the data showed, that actin plays an important role in formation of physiological barrier in the site of infection. Actin dynamics is involved in the transport of antimicrobial compounds and cell wall fortifying components (e.g. callose) to the site of infection. Also the role in PTI (pathogen triggered immunity) and ETI (effector triggered immunity) was recently indicated. On the other hand much less is known about the transcriptome reprogramming upon changes in actin dynamics. Our recently published results showed that drugs inhibiting actin polymerization (latrunculin B, cytochalasin E) cause the induction of genes which are i...