Summary: Root responses to lack of iron (Fe) have mainly been studied in nutrient solution experiments devoid of silicon (Si). Here we investigated how Si ameliorates Fe deficiency in cucumber (Cucumis sativus) with focus on the storage and utilization of Fe in the root apoplast. A combined approach was performed including analyses of apoplastic Fe, reduction‐based Fe acquisition and Fe‐mobilizing compounds in roots along with the expression of related genes. Si‐treated plants accumulated higher concentrations of root apoplastic Fe, which rapidly decreased when Fe was withheld from the nutrient solution. Under Fe‐deficient conditions, Si also increased the accumulation of Fe‐mobilizing compounds in roots. Si supply stimulated root activity of Fe acquisition at the early stage of Fe deficiency stress through regulation of gene expression levels of proteins involved in Fe acquisition. However, when the period of Fe deprivation was extended, these reactions further decreased as a consequence of Si‐induced enhancement of the Fe status of the plants. This work provides new evidence for the beneficial role of Si in plant nutrition and clearly indicates that Si‐mediated alleviation of Fe deficiency includes an increase of the apoplastic Fe pool in roots and an enhancement of Fe acquisition.

This work was focused on the role of silicon (Si) in amelioration of manganese (Mn) toxicity caused by elevated production of hydroxyl radicals (·OH) in the leaf apoplast of cucumber (Cucumis sativus L.). The plants were grown in nutrient solutions with adequate (0.5 μM) or excessive (100 μM) Mn concentrations with or without Si being supplied. The symptoms of Mn toxicity were absent in the leaves of Si-treated plants subjected to excess Mn, although the leaf Mn concentration remained extremely high. The apoplastic concentration of free Mn²⁺ and H₂O₂ of high Mn-treated plants was significantly decreased by Si treatment. Si supply suppressed the Mn-induced increased abundance of peroxidase (POD) isoforms in the leaf apoplastic fluid, and led to a rapid suppression of guaiacol-POD activity under excess Mn. The spin-trapping reagent 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide was used to detect ·OH by electron paramagnetic resonance spectroscopy. Although supplying Si markedly decreased the accumulation of ·OH in the leaf apoplast with excess Mn, adding monosilicic acid to the Mn²⁺/H₂O₂ reaction mixture did not directly affect the Fenton reaction in vitro. The results indicate that Si contributes indirectly to a decrease in ·OH in the leaf apoplast by decreasing the free apoplastic Mn²⁺, thus regulating the Fenton reaction. A direct inhibitory effect of Si on guaiacol-POD activity (demonstrated in vitro) may also contribute to decreasing the POD-mediated generation of ·OH.

Lignins and lignin-derived compounds are known to have antibacterial properties. The wound healing agents in the form of dressings produce faster skin repair and decrease pain in patients. In order to create an efficient antimicrobial agent in the form of dressing in the treatment of chronic wounds, a composite hydrogel of bacterial cellulose (BC) and dehydrogenative polymer of coniferyl alcohol (DHP), BC-DHP, was designed. Novel composite showed inhibitory or bactericidal effects against selected pathogenic bacteria, including clinically isolated ones. The highest release rate of DHP was in the first hour, while after 24 h there was still slow release of small amounts of DHP from BC-DHP during 72 h monitoring. High-performance liquid chromatography coupled with mass-spectrometry showed that BC-DHP releases DHP oligomers, which are proposed to be antimicrobially active DHP fractions. Scanning electron microscopy and atomic force microscopy micrographs proved a dose-dependent interaction of DHP with BC, which resulted in a decrease of the pore number and size in the cellulose membrane. The Fourier-transform infrared absorption spectra of the BC-DHP showed that DHP was partly bound to the BC matrix. The swelling and crystallinity degree were dose-dependent. All obtained results confirmed BC-DHP composite as a promising hydrogel for wounds healing.

The causal relationship between salinity and oxidative stress tolerance is well established, but specific downstream targets and the role of specific antioxidant compounds in controlling cellular ionic homeostasis remains elusive. In this work, we have compared antioxidant profiles of leaves of two quinoa genotypes contrasting in their salt tolerance, with the aim of understanding the role of enzymatic and non-enzymatic antioxidants in salinity stress tolerance. Only changes in superoxide dismutase activity were correlated with plant adaptive responses to salinity. Proline accumulation played no major role in either osmotic adjustment or in the tissue tolerance mechanism. Among other non-enzymatic antioxidants, rutin levels were increased by over 25 fold in quinoa leaves. Exogenous application of rutin to glycophyte bean leaves improved tissue tolerance and reduced detrimental effects of salinity on leaf photochemistry. Electrophysiological experiments revealed that these beneficial effects were attributed to improved potassium retention and increased rate of Na+ pumping from the cell. The lack of correlation between rutin-induced changes in K+ and H+ fluxes suggest that rutin accumulation in the cytosol scavenges hydroxyl radical formed in response to salinity treatment thus preventing K+ leak via one of ROS-activated K+ efflux pathways, rather than controlling K+ flux via voltage-gated K+-permeable channels.