Leonardite-based biostimulants are a large class of compounds, including humic acid substances. Foliar application of biostimulants at field level improves plant growth, yield and quality through metabolic changes and stimulation of plant proton pumps. The present study aimed at identifying optimum dosage of BLACKJAK, a humic acid-based substance, which is able to modify genes involved in sugar beet growth. Thirty-three genes belonging to various biochemical pathway categories were tested in leaves of treated sugar beet (Beta vulgaris L.) samples to assess gene expression profiling in response to BLACKJAK. Seedlings of a diploid and multigerm variety were grown in plastic pots and sprayed with two dilutions of BLACKJAK (dilution 1:500–1.0 mg C L−1 and dilution 1:1000–0.5 mg C L−1). Leaf samples were collected after 24, 48, and 72 h treatment with BLACKJAK for each dilution. RNA was extracted and the quantification of gene expression was performed while using an OpenArray platform. Results of analysis of variance demonstrated that, 15 genes out of a total of 33 genes tested with OpenArray qPCR were significantly affected by treatment and exposure time. Analysis for annotation of gene products and pathways revealed that genes belonging to the mitochondrial respiratory pathways, nitrogen and hormone metabolisms, and nutrient uptake were up-regulated in the BLACKJAK treated samples. Among the up-regulated genes, Bv_PHT2;1 and Bv_GLN1 expression exerted a 2-fold change in 1:1000 and 1:500 BLACKJAK concentrations. Overall, the gene expression data in the BLACKJAK treated leaves demonstrated the induction of plant growth–related genes that were contributed almost to amino acid and nitrogen metabolism, plant defense system, and plant growth.

This work aimed to investigate the interaction between salt stress and the application of silicon dioxide-nanoparticles. In this study, gerbera plants grown in soilless culture were supplied with nutrient solutions with different NaCl concentrations (0, 5, 10, 20 and 30 mM) in combination with SiO2-NPs spray (0, 25 and 50 mg · L−1). Exposure of gerbera to salinity increased sodium concentration but decreased potassium and calcium concentrations in leaf as well as stem length/diameter, fresh/dry weight, leaf/flower number, flower diameter and leaf area. It also increased the activities of antioxidant enzymes and electrolyte leakage. Results indicated that SiO2-NPs could improve growth, biochemical and physiological traits. It increased stem thickness but slightly affected stem length. Flower diameter was not affected by salinity rates up to 10 mM of NaCl. However, a significant difference was observed between controls and plants treated with 30 mM of NaCl. Salinity increased the electrolyte leakage (32.5%), malondialdehyde (83.8%), hydrogen peroxide (113.5%), and the antioxidant enzyme activities such as ascorbate peroxidase (3.4-fold) and guaiacol peroxidase (6-fold) where SiO2-NPs activated them more, except for superoxide dismutase. Under salinity (30 mM), the increase in SiO2-NPs (especially at 25 mg · L−1) led to the increase in the uptake of Ca2+ (25.3%) as well as K+ (27.1%) and decreased absorption of Na+ (6.3%). SiO2-NPs has potential in improving salinity tolerance in gerbera. It seems that the sensitivity threshold of gerbera to the salinity was 10 mM and the use of SiO2-NPs is also effective in non-saline conditions.

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Background Drought is a major abiotic stress that restricts plant growth and efficiency although some nutrients such as silicon improve drought tolerance by regulating the biosynthesis and accumulating some osmolytes. In this regard, a completely randomized factorial design was performed with three factors including two genotypes (‘Maragheh’ and ‘Kashan’), three concentrations of silicon dioxide nanoparticles (SiO2-NPs) (0, 50, and 100 mg L− 1), and five concentrations of PEG (0, 25, 50, 75, and 100 g L− 1) with three replications. Results The findings showed that drought stress decreased protein content and it was improved by SiO2-NPs, so the genotype of ‘Maragheh’ treated with 100 mg L− 1 SiO2-NPs had the highest protein content. Under severe drought stress, had a higher membrane stability index (MSI) than ‘Kashan’, and the ‘Maragheh’ explants subjected to 100 mg L− 1 SiO2-NPs exhibited the uppermost MSI. The explants supplemented with 100 mg L− 1 SiO2-NPs sustained their photosynthetic parameters more in comparison with other treatments under drought stress conditions and as well as 100 mg L− 1 SiO2-NPs showed higher content of protein and proline of ‘Maragheh’ than ‘Kashan’. Drought stress reduced Fm, Fv/Fm, and Fv, while SiO2-NPs treatment enhanced these parameters. SiO2-NPs also improved water deficit tolerance by enhancing the activity of antioxidant enzymes such as catalase (CAT), peroxidase (POD), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) and reducing lipid peroxidation and H2O2 concentration. Conclusions According to the findings, the genotype ‘Maragheh’ was more tolerance to drought stress than ‘Kashan’ by improving water balance, antioxidant enzyme activities, and membrane stability as it was obtained from the unpublished previous evaluation in in vivo conditions and we concluded based on these results, in vitro culture can be used for drought screening in Damask rose plants. The results of the current study revealed that the induced drought stress by polyethylene glycol (PEG) in two Damask rose genotypes was ameliorated with SiO2-NPs and the tolerance genotypes were better than the sensitive ones in response to SiO2-NPs treatment.

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