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Arsenic (As) contaminates the food chain and decreases agricultural production through impairing plants, particularly due to oxidative stress. To better understand the As tolerance mechanisms, two contrasting tobacco genotypes: As-sensitive Nicotiana sylvestris and As-tolerant N.tabacum, cv. 'Wisconsin' were analyzed. The most meaningful differences were found in the carbohydrate status, neglected so far in the As context. In the tolerant genotype, contrary to the sensitive one, net photosynthesis rates and saccharide levels were unaffected by As exposure. Importantly, the total antioxidant capacity was far stronger in the As-tolerant genotype, based on higher antioxidants levels (e.g., phenolics, ascorbate, glutathione) and activities and/or appropriate localizations of antioxidative enzymes, manifested as reverse root/shoot activities in the selected genotypes. Accordingly, malondialdehyde levels, a lipid peroxidation marker, increased only in sensitive tobacco, indicating efficient membrane protection in As-tolerant species. We bring new evidence of the orchestrated action of a broad spectrum of both antioxidant enzymes and molecules essential for As stress coping. For the first time, we propose robust carbohydrate metabolism based on undisturbed photosynthesis to be crucial not only for subsidizing C and energy for defense but also for participating in direct reactive oxygen species (ROS) quenching. The collected data and suggestions can serve as a basis for the selection of plant As phytoremediators or for targeted breeding of tolerant crops.
- Publikační typ
- časopisecké články MeSH
BACKGROUND: Methylation of cytosines is an evolutionarily conserved epigenetic mark that is essential for the control of chromatin activity in many taxa. It acts mainly repressively, causing transcriptional gene silencing. In plants, de novo DNA methylation is established mainly by RNA-directed DNA-methylation pathway. Even though the protein machinery involved is relatively well-described, the course of the initial phases remains covert. RESULTS: We show the first detailed description of de novo DNA-methylation dynamics. Since prevalent plant model systems do not provide the possibility to collect homogenously responding material in time series with short intervals, we developed a convenient system based on tobacco BY-2 cell lines with inducible production of siRNAs (from an RNA hairpin) guiding the methylation machinery to the CaMV 35S promoter controlling GFP reporter. These lines responded very synchronously, and a high level of promoter-specific siRNAs triggered rapid promoter methylation with the first increase observed already 12 h after the induction. The previous presence of CG methylation in the promoter did not affect the methylation dynamics. The individual cytosine contexts reacted differently. CHH methylation peaked at about 80% in 2 days and then declined, whereas CG and CHG methylation needed more time with CHG reaching practically 100% after 10 days. Spreading of methylation was only minimal outside the target region in accordance with the absence of transitive siRNAs. The low and stable proportion of 24-nt siRNAs suggested that Pol IV was not involved in the initial phases. CONCLUSIONS: Our results show that de novo DNA methylation is a rapid process initiated practically immediately with the appearance of promoter-specific siRNAs and independently of the prior presence of methylcytosines at the target locus. The methylation was precisely targeted, and its dynamics varied depending on the cytosine sequence context. The progressively increasing methylation resulted in a smooth, gradual inhibition of the promoter activity, which was entirely suppressed in 2 days.
- MeSH
- Caulimovirus genetika MeSH
- estradiol farmakologie MeSH
- malá interferující RNA genetika metabolismus MeSH
- metylace DNA * účinky léků MeSH
- plazmidy genetika metabolismus MeSH
- promotorové oblasti (genetika) MeSH
- RNA interference MeSH
- rostlinné buňky metabolismus MeSH
- tabák cytologie MeSH
- zelené fluorescenční proteiny antagonisté a inhibitory genetika metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Rate of photosynthesis and related plant carbohydrate status are crucial factors affecting plant vigor. Sugars providing carbon and energy sources serve also as important signaling molecules governing plant growth and development through a complex regulatory network. These facts are often neglected when mixotrophic cultivation of plants in vitro is used, where artificial exogenous sugar supply hinders studies of metabolism as well as sugar-driven developmental processes. We compared the growth, selected gas-exchange parameters and sugar metabolism characteristics in four model plants, potato (Solanum tuberosum 'Lada'), tobacco (Nicotiana tabacum 'Samsun'), rapeseed (Brassica napus 'Asgard') and strawberry (Fragaria vesca), under both photomixotrophic (PM) and photoautotrophic (PA) conditions. To ensure PA conditions, we used our improved sun caps that serve as gas and light permeable covers for cultivation vessels. We found bigger biomass accumulation, larger leaf areas, higher stomatal conductance and higher instantaneous water use efficiency and lower root sugar contents in PA plants compared to PM ones. However, for other characteristics (root biomass, root/shoot ratio, pigment contents, leaf sugar and starch levels and transpiration rates), a strong species-dependent reactions to the exogenous sugar supply was noted, which does not allow to create a general view on the overall impact of PM nutrition under in vitro conditions.
- MeSH
- Brassica napus genetika metabolismus fyziologie MeSH
- fotosyntéza genetika fyziologie MeSH
- jahodník genetika metabolismus fyziologie MeSH
- kořeny rostlin genetika metabolismus fyziologie MeSH
- listy rostlin genetika metabolismus fyziologie MeSH
- tabák genetika metabolismus fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
