The beneficial effects of silicon (Si) have been shown on plants using reduction-based strategy for iron (Fe) acquisition. Here we investigated the influence of Si on Fe deficiency stress alleviation in barley (Hordeum vulgare), a crop plant which uses the chelation-based strategy for Fe acquisition. Analyses of chlorophyll content, ROS accumulation, antioxidative status, concentrations of Fe and other micronutrients, along with the expression of Strategy II genes were studied in response to Si supply. Si successfully ameliorated Fe deficiency in barley, diminishing chlorophyll and biomass loss, and improving the activity of antioxidative enzymes, resulting in lowered reactive oxidative species accumulation in the youngest leaves. Alleviation of Fe deficiency stress correlated well with the Si-induced increase of Fe content in the youngest leaves, while it was decreased in root. Moreover, Si nutrition lowered accumulation of other micronutrients in the youngest leaves of Fe deprived plants, by retaining them in the root. On the transcriptional level, Si led to an expedient increase in the expression of genes involved in Strategy II Fe acquisition in roots at the early stage of Fe deficiency stress, while decreasing their expression in a prolonged stress response. Expression of Strategy II genes was remarkably upregulated in the leaves of Si supplied plants. This study broadens the perspective of mechanisms of Si action, providing evidence for ameliorative effects of Si on Strategy II plants, including its influence on accumulation and distribution of microelements, as well as on the expression of the Strategy II genes.

Essential micronutrients belonging to the transition metals, such as Fe and Cu, are indispensable for plant growth and stress tolerance; however, when present in excess, they can become potentially dangerous producers of reactive oxygen species. Therefore, their homeostases must be strictly regulated. Both microelement deficiencies and elevated concentrations of heavy metals in the soil are global problems that reduce the nutritional value of crops and seriously affect human health. Silicon, a beneficial element known for its protective properties, has been reported to alleviate the symptoms of Cu toxicity and Fe deficiency stress in plants; however, we are still far from a comprehensive understanding of the underlying molecular mechanisms. Although Si-mediated mitigation of these stresses has been clearly demonstrated for some species, the effects of Si vary depending on plant species, growing conditions and experimental design. In this review, the proposed mechanistic models explaining the effect of Si are summarized and discussed. Iron and copper compete for the common metal transporters and share the same transport routes, hence, inadequate concentration of one element leads to disturbances of another. Silicon is reported to beneficially influence not only the distribution of the element supplied below or above the optimal concentration, but also the distribution of other microelements, as well as their molar ratios. The influence of Si on Cu immobilization and retention in the root, as well as Si-induced Fe remobilization from the source to the sink organs are of vital importance. The changes in cellular Cu and Fe localization are considered to play a crucial role in restoring homeostasis of these microelements. Silicon has been shown to stimulate the accumulation of metal chelators involved in both the mobilization of deficient elements and scavenging excess heavy metals. Research into the mechanisms of the ameliorative effects of Si is valuable for reducing mineral stress in plants and improving the nutritional value of crops. This review aims to provide a thorough and critical overview of the current state of knowledge in this field and to discuss discrepancies in the observed effects of Si and different views on its mode of action.

Extracellular vesicles (EVs) are shown to play an important role in the interaction between bacteria and human cells, as well as between fungi and plants; however, much less is known about their role in plant-bacteria relations. Outer membrane vesicles (OMVs), EVs produced by Gram-negative bacteria, were shown to have both immuno-activating and immuno-suppressive effects on plants, and a direct interaction of OMVs with plant cell membranes was shown for one phytopathogenic bacterial strain. Data on OMVs’ participation in the symbiotic relationship between plant-beneficial bacteria and plants are even more limited, and are mainly related to the rhizobia-legume interaction. To investigate the interaction of OMVs of non-rhizobial phytobeneficial bacteria with plant cells, we isolated and characterized OMVs produced by Paraburkholderia phytofirmans PsJN, a strain well known for its growth-promoting and stress-protective effects in a wide range of plant species. Using OMVs labelled with fluorescent lipid-binding dye Vybrant ^TM DiD and confocal laser scanning microscopy, we showed that PsJN-OMVs interact directly with the root hairs and epidermal cells of Arabidopsis thaliana and tomato. Moreover, by employing octadecyl-rhodamine B chloride (R18), we demonstrated that PsJN-OMVs can fuse with plant cell membranes. The findings presented in our study are an important step in elucidating the potential role of OMVs in the early stages of root colonization and the establishment of symbiotic relationships. Increasing our understanding in this area could pave the way for the use of these nano-vehicles to develop eco-friendly solutions for overcoming environmental challenges and supporting sustainable agriculture.

Maize is one of the most important crop species worldwide, but also extremely susceptible to the effects of increasingly higher temperatures and drought during the summer and its flowering and grain filling stage. Different strategies are being utilized to ensure a satisfying yield potential and quality even in the extremely unfavourable environmental conditions, which are the result of climate change. Some of them are cropping pattern changes and sowing alterations, including earlier sowing. Since this implies the exposure to suboptimal temperatures during early developmental stages, it leads to a demand for developing maize lines tolerant to low temperatures during these stages. This research focuses on the first phase of germination, imbibition. Maize tolerance to low temperatures is a complex trait that includes different mechanisms and strategies that all work together to ensure adaptation and survival, such as cell membrane changes, antioxidative system activation, etc. Additionally, the low temperature response of different maize inbreds varies substantially, so recognizing the different ways in which they respond to low temperatures during imbibition and other earlier stages of development is crucial. To accomplish this, seeds of two maize inbred lines of contrasting susceptibility to low temperatures were selected and exposed to control (20? C) and low temperature (8?C) conditions during the first 24h of imbition and then further analyzed to assess their response. This included germination and tetrazolium assays; ascertaining membrane integrity by evaluating cell leakage and lipid peroxidation; determining the antioxidative capacity by assessing superoxide dismutase (SOD) and catalase (CAT) activity; and expression analysis of four genes included in the low temperature response (gibberellin insensitive dwarf 1 gibberellin receptor, gid1; fatty acid desaturases 2 and 6, fad2 and fad6; plastid-lipid-associated 2 protein, pap2). The results showed that, while there is not a significant difference in their germination rate, they differ in their survival rate, with more seeds of the tolerant genotype surviving the low temperature period. Significant differences between them were found in cell leakage (p<0,01), as well as gid1(p<0,05) and fad6 (p<0,05) gene expression assays. The present research brings light to our understanding of the effect of low temperatures on the first germination stage, - imbibition. It highlights the importance of choosing the right inbreds for earlier sowing and points to certain routes that could be taken for improving and accelerating the breeding process for low temperature tolerance.

Excess copper (Cu) disrupts metal homeostasis and induces oxidative stress in plants. Silicon (Si) is known to mitigate heavy metal toxicity, yet the molecular basis of its protective role under Cu stress remains insufficiently understood. To address this, an exploratory transcriptome-wide screening was performed to identify candidate differentially expressed genes (DEGs), long non-coding RNAs (lncRNAs), and microRNAs responsive to excess Cu and/or Si in cucumber (Cucumis sativus cv. Chinese Long). Genes encoding metal transporters and selected miRNA–target pairs were further analyzed by qRT-PCR. Silicon alone modulated the expression of numerous candidate DEGs, notably enhancing the expression of metal transporter genes. Exposure to excess Cu suppressed genes involved in metal uptake while upregulating those associated with efflux and metal redistribution. Application of Si under Cu stress mitigated these transcriptional alterations. Cu stress repressed miR398 and miR408, concomitantly increasing the expression of their targets: superoxide dismutase (SOD) and plantacyanin (PCY). Furthermore, excess Cu downregulated miR390, resulting in increased expression of its predicted lncRNA target. The addition of Si to Cu-stressed plants further enhanced SOD expression while attenuating the upregulation of PCY and the lncRNA. The results demonstrated that Si modulates both coding and non-coding RNA expression under optimal and Cu-stress conditions, revealing post-transcriptional gene expression regulation as an additional layer of Si’s effect on plants. When integrated with previously reported physiological and biochemical data, these findings advance our understanding of the molecular basis of Si-mediated heavy metal tolerance in plants.