Nowadays open field and protected vegetable cultivation practices require and use genotypes which are precisely tailored to their intended growth environments. Variability of this kind provides a rich source of material to uncover molecular mechanisms supporting the necessarily divergent physiological traits. In this study, typical field-optimized and glasshouse-cultivated cucumber F1 hybrids were investigated, and displayed slower growth (‘Joker’) and faster growth (‘Oitol’) in seedlings. Antioxidant capacity was lower in ‘Joker’ and higher in ‘Oitol’, pointing to a potential redox regulation of growth. The growth response of seedlings to paraquat treatment indicated stronger oxidative stress tolerance in the fast-growing ‘Oitol’. To test whether protection against nitrate-induced oxidative stress was also different, fertigation with increasing potassium nitrate content was applied. This treatment did not change growth but decreased the antioxidant capacities of both hybrids. Bioluminescence emission revealed stronger lipid peroxidation triggered by high nitrate fertigation in the leaves of ‘Joker’ seedlings. To explore the background of the more effective antioxidant protection of ‘Oitol’, levels of ascorbic acid (AsA), as well as transcriptional regulation of relevant genes of the Smirnoff–Wheeler biosynthetic pathway and ascorbate recycling, were investigated. Genes related to AsA biosynthesis were strongly upregulated at an elevated nitrate supply in ‘Oitol’ leaves only, but this was only reflected in a small increase in total AsA content. High nitrate provision also triggered expression of ascorbate–glutathion cycle genes with stronger or exclusive induction in ‘Oitol’. AsA/dehydro–ascorbate ratios were higher in ‘Oitol’ for all treatments, with a more pronounced difference at high nitrate levels. Despite strong transcriptional upregulation of ascorbate peroxidase genes (APX) in ‘Oitol’, APX activity only increased significantly in ‘Joker’. This suggests potential inhibition of APX enzyme activity specifically in ‘Oitol’ at a high nitrate supply. Our results uncover an unexpected variability in redox stress management in cucumbers, including nitrate inducibility of AsA biosynthetic and recycling pathways in certain genotypes. Possible connections between AsA biosynthesis, recycling and nitro-oxidative stress protection are discussed. Cucumber hybrids emerge as an excellent model system for studying the regulation of AsA metabolism and the roles of AsA in growth and stress tolerance.

Effects of waterlogging (WL) stress and its mitigation by nitrate (NO₃ ^–) were investigated in a commercial cucumber hybrid line. WL resulted in a shift toward anaerobic metabolism in roots and development of adventitious roots (ARs). In WL stressed roots exodermal, extracellular H₂O₂ accumulation and protein nitration were detected. Shoot growth was retarded with signs of oxidative stress. Nitrate content decreased in both root and shoot. In the root WL upregulated several genes implicated in hypoxic response, including transcripts of CsRAP2.3, CsRBOHs and the CsHem3 phytoglobin genes. Nitrate supplementation restored shoot growth and mitigated oxidative stress. Fermentative metabolism was reduced in the roots. Nitrate levels increased substantially, expression of NRT1 genes was induced, supporting improved NO₃ ⁻ uptake and delivery. According to chemical analysis and fluorescent microscopy NO accumulated in the vascular cylinder of roots. NO depletion by cPTIO confirmed a role for NO in stress mitigation. cPTIO treatment decreased AR formation and foliar nitrate levels. It decreased protein nitration and strongly downregulated nitrate transporters’ gene expression in roots. Overall, our work revealed nitrate triggered, NO mediated alleviation of WL stress in cucumber. Resolution of WL induced energy crisis in the roots by nitrate treatment was attributed to parallel effects of anaerobic respiration and AR formation. Shoot growth repression was probably alleviated by improved root functions, including elevated nitrate transport. Expression of NRT1 nitrate transporter genes was induced by nitrate, and this induction was found NO dependent in WL stressed cucumber.

Much is unknown about the positive effect of plant growth regulators, such as brassinosteroids, on high-temperature stress tolerance in pepper plants. This study aimed to reveal the effect of exogenous brassinosteroids (BRs) on high-temperature-stressed bell peppers by foliar application. BR treatments (1 µM), in both bulk (Br) and nano-encapsulated (N-Br) forms, were applied to pepper plants subjected to high-temperature stress (35 °C). The results indicated an increase in plant biomass, number of fruits, and relative water content and a significantly lower flower abscission in response to Br and N-Br under high temperatures. Br and N-Br applications at high temperatures resulted in the lowest leaf water potential. Br and N-Br, especially N-Br, were more effective than Br in the upregulation of the antioxidant enzyme activity, such as catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), and the overall antioxidant capacity of heat-stressed plants. MDA and electrolyte leakage significantly declined as a result of BR application and the proline content of the leaves was significantly higher in Br and N-Br treatments at high temperatures. Further analysis of the data pointed to SOD, DPPH, proline, RWC, and leaf water potential in pepper leaves as the most affected traits in response to brassinosteroid application under high temperature. Glucose and fructose levels also increased under high temperature, and only N-Br administration showed a significant effect on reducing the sugar levels. At high temperatures, the ratio of saturated to unsaturated fatty acids was greatest when neither Br nor N-Br was present. N-Br could reduce this ratio effectively. Conclusively, the overall performance of bell pepper improved in response to both types of BR application with no significant discrimination being found to prioritize the encapsulated form of BR application.

Peach cultivars (’Elberta’, ‘Red Top’, and ’Dixie Red’) were studied for their in vitro adoptability and performance in producing virus-free plantlets. The thermotherapy method with increasing temperatures (25 °C to 37 °C) was applied for the elimination of famous peach infecting plum pox viruses (PPVs) and prunus necrotic ringspot virus (PNRSV), and the DS-ELISA test and RT-PCR technique were performed to confirm the production of virus-free microshoots. The application of 30 mg L⁻¹ of Fe-EDDHA treatment resulted in the best performance for culture establishment of all cultivars, where the best subsequent morphological performance in terms of branch and leaf numbers was recorded for the ’Dixie Red’ cultivar in MS medium, supplemented with 0.5 mgL⁻¹ of gibberellic acid (GA₃) and 0.5 mg L⁻¹ of 6-Benzylaminopurine (BAP). At the regeneration stage, the highest (26.96 mm) and lowest (18.43 mm) shoot lengths were obtained from the ’Dixie Red’ cultivar treated with GA₃ (2 mg L⁻¹) + thidiazuron (TDZ) (2.5 mg L⁻¹) and the ’Red Top’ cultivar treated with GA₃ (1 mg L⁻¹) + TDZ (1 mg L⁻¹), respectively. The leaf numbers were affected by the application of growth regulators, where the ’Elberta’ cultivar under GA₃ (2 mg L⁻¹) + TDZ (2.5 mg L⁻¹) treatment showed the highest numbers and the ’Red Top’ cultivar under GA₃ (1 mg L⁻¹) + TDZ (1 mg L⁻¹) showed the lowest mean values. The thermotherapy treatment and micropropagation of shoot tips resulted in 100% virus-free plantlets, as confirmed by both applied diagnostic methods. The result of the application of the rooting stage with growth regulators on ’Elberta’ plantlets showed the best performance (90%) in ½ MS medium supplemented with 0.5–1 mg L⁻¹ of IBA, which was significantly higher than the same treatment in MS medium. The obtained results should constitute the basis for further optimization of the multiplication and rooting of virus-free peach plantlets to be served for nurseries and planation orchards.

Silicon (Si) is a ubiquitous element in soil with well-known beneficial effects under certain conditions, in several plant species, if supplied in available form for uptake. It may alleviate damage in various stress situations and may also promote growth when no obvious stressors are applied. Effects of Si are often linked to mitigation of oxidative stress, in particular to the induction of antioxidant defense mechanisms. In the work presented, the impact of silicon provision on pro-oxidant systems was investigated in cucumber. Plants of the F1 cultivar hybrid ‘Joker’ were grown under in vitro conditions in the absence of any applied external stressor. Silicon provision decreased H₂O₂ content and lowered lipid peroxidation in the leaves of the treated plants. This was paralleled by declining polyamine oxidase (PAO) and diamine oxidase (DAO) activities. Several PAO as well as lipoxygenase (LOX) genes were coordinately downregulated in Si-treated plants. Unlike in similar systems studied earlier, the Si effect was not associated with an increased transcript level of gene coding for antioxidant enzymes. These results suggest an inhibitory effect of Si provision on pro-oxidant amine oxidases, which may decrease the level of reactive oxygen species by retarding their production. This extends the molecular mechanisms linked to silicon effects onto redox balance in plants.

Silicon (Si) has long been considered as non-essential element for plant’s growth and production. Numerous efforts are being made for the discovery of its beneficial effects with large scale studies laying foundation for new findings and hypotheses. Therefore, Si has been suggested to be a quasi-essential element due to its positive effects against biotic and abiotic stresses alike. Though Si is the second most abundant element in the soil profile, its availability to plants is limited to the form of monosilicic acid only. Besides, plants’ ability to take-up Si and use it in their physiological processes also depends on the available transporters associated with it. Thus, the present review covers uptake and transport of silicon in plants as well as Si mediated physiological processes, including mechanisms underlying induced tolerance against biotic and abiotic stresses with a particular emphasis on horticultural species.