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As soil contamination with heavy metals is increasing and polyamines have roles in the growth of mycorrhiza and plants, it is important to study phytoremediation, growth, tolerance, and mycorrhization in Lallemantia iberica as a multi-purpose plant, by the application of putrescine along with mycorrhiza in Pb-contaminated soils. For this purpose, the study was performed in a factorial arrangement with Pb (0, 300, 600, and 900 mg Pb/kg soil), mycorrhiza (non-inoculation, Funneliformis mosseae (Fm), and Rhizophagus intraradices (Ri)), and putrescine (0, 0.5, and 1 mM) in a greenhouse. Results showed that antioxidant activities, plant Pb, and mycorrhizal features enhanced, while transfer factor (TF), biomass, and tolerance decreased under Pb levels. Mycorrhiza improved growth, greenness, defense, and tolerance and reduced TF, Pb, and H 2 O 2 content under Pb stress. Putrescine (0.5 mM) increased catalase activity, biomass, and colonization and reduced Pb content and TF under Pb levels. Combination of 0.5 mM putrescine with Fm increased shoot biomass (13%), peroxidase (17.2%), root P (7.5%), shoot tolerance (14.4%), colonization (5.1%), and hyphal width (5.5%) and decreased malondialdehyde (20.5%) and shoot Pb content (28.1%). Putrescine (1 mM) had negative effects on all traits in combination with Ri but not with Fm. Combination of putrescine and Fm showed more efficiency in decreasing Pb content in L. iberica and was effective in phytostabilization. It is generally concluded that 0.5 mM putrescine was the beneficial concentration in combination with mycorrhiza, Pb stress, and single use to improve plant performance, and Fm was a useful species for improving the growth and tolerance of L. iberica under Pb levels.

The use of growth-stimulating signals to increase the tolerance of plants to water deficits can be an important strategy in the production of plants in dry areas. Therefore, a split-plot experiment with three replications was conducted to evaluate the effects of sodium nitroprusside (SNP) application rate as an NO donor (0, 100, and 200 µM) on the growth and yield parameters of Silybum marianum L. (S. marianum) under different irrigation cut-off times (control, irrigation cut-off from stem elongation, and anthesis). The results of this study showed that with increasing drought severity, leaf RWC, proline content and capitula per plant, 1000 grain weight, plant height, branch per plant, capitula diameter, and the biological and grain yield of S. marianum decreased significantly, whereas the number of grains per capitula increased compared with the control. Also, by irrigation cut-off from the stem elongation stage, the density of leaf stomata at the bottom and top epidermis increased by 64% and 39%, respectively, and the length of the stomata at the bottom epidermis of the leaf decreased up to 28%. In contrast, the results of this experiment showed that the exogenous application of nitric oxide reduced the negative effects of irrigation cut-off, such that the application of 100 µM SNP enhanced RWC content (up to 9%), proline concentration (up to 40%), and grain (up to 34%) and biological (up to 44%) yields in plants under drought stress compared with non-application of SNP. The decrease in the number of capitula per plant and capitula diameter was also compensated by foliar application of 100 µM SNP under stress conditions. In addition, exogenous NO changed the behavior of the stomata during the period of dehydration, such that plants treated with SNP showed a decrease in the stomatal density of the leaf and an increase in the length of the stomata at the leaf bottom epidermis. These results indicate that SNP treatment, especially at 100 µM, was helpful in alleviating the deleterious effects of water deficiency and enhancing the tolerance of S. marianum to withholding irrigation times.

The present research attempted to investigate the role of sodium nitroprusside (SNP) as a NO donor in yield and accumulation of active substances in milk thistle under drought stress in a 2-year farm experiment. In this experiment, two genotypes of milk thistle (Hungarin and Sari) were sprayed with SNP solutions (0, 100, and 200 µM) under water stress (control or withholding of irrigation from the stages of stem elongation and anthesis). Withholding of irrigation decreased the grain and silymarin yield and increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) content. Application of 100 µM SNP decreased the content of MDA and H2O2 in plants submitted to water deficit and as a result, prevented silymarin yield reduction under stress by increasing grain yield. In both years, with increasing the intensity of stress, taxifolin content, silychristin, silybin A and B, as well as isosilybin B were increased in both genotypes. While, exogenous NO further enhanced taxifolin, silychristin, silybin B, and isosilybin B accumulation, compared with plants solely grown under water deficit without SNP. The results of this study indicated that SNP application, especially at the dose of 100 µM, prevented the leaf water loss and reduces irrigation times from eight times to six or four times under drought stress from the stages of anthesis and stem elongation, respectively, and thus improved grain yield in milk thistle. Moreover, exogenous application of SNP to increasing taxifolin synthesis further enhanced secondary metabolites’ performance under conditions with low water availability.

The effects of four plant growth regulators on Crocus sativus L. (saffron) yield and performance were studied in two consecutive years under field conditions. Saffron corms were immersed in solutions of gibberellic acid (GA3), salicylic acid (SA), paclobutrazol (PBZ), chlormequat chloride (CCC), distilled water (hydroprime), and dry corms as the control. Results showed that among the different treatments, plants primed with GA3 500 μM had the highest flower fresh weight and stigma dry weight. In contrast, primed corms with 1000 μM CCC and 100 μM PBZ had the lowest flower dry weight. Furthermore, the plants primed with SA 1400 had the highest leaf numbers, leaf dry weight, and leaf area index (LAI). Plants treated with GA3 induced narrow but the longest leaves, while those treated with SA showed the widest ones. It was also demonstrated that the application of CCC and PBZ can produce shorter leaves. Furthermore, the greatest numbers of daughter corms were obtained in 1400 μM SA. Both PBZ and CCC were reported to have no impacts on the corm numbers but produced larger and heavier daughter corms. The results revealed that the priming of saffron corms with GA3 and then SA improved saffron growth and yield.

Biochar improves soil physical, biochemical, and microbial properties, leading to the amelioration of soil fertility, which, in turn, results in better growth and yield in crop plants. The current study aimed to evaluate whether using different levels of biochar can enhance soil characteristics and plant attributes. Accordingly, an experimental study was conducted in 2022 using a randomized complete block design with four replications (n = 4) in the experimental glasshouse of the University of Zanjan, in which two regimes of irrigation (D0, full irrigation as the control; D1, water scarcity was applied immediately after the flowering stage for two weeks) and four levels of natural mineral biochar (0% as the control treatment, 0.25, 0.5, and 1% of soil weight) were applied. The results indicated that drought substantially decreased the organic carbon content of the soil and the grain yield while increasing the available phosphorous, soil carbohydrate content, and microbial biomass of the soil. Biochar could considerably alter the means of the studied soil quality parameters and the barley grain yield. Adding biochar could be considered a valid strategy to increase the resistance of plants to drought.

Nitric oxide (NO) is recognized as an endogenous signaling molecule that plays an important role in the defence responses of medicinal plants to NaCl stress. In this study, we investigated the effects of sodium nitroprusside (SNP) as an NO donor at three concentrations (0, 100, and 200 µmol l −1 ) to alleviate the deleterious effects of salt stress (100 mM NaCl) on leaf gas exchange and biochemical characteristics of Silybum marianum L. seedlings. This study showed that salt stress significantly decreased relative water content (RWC), chlorophyll b content, endogenous NO concentration, maximum quantum yield (Fv/Fm), leaf gas exchange, stomatal size, K + /Na + ratio, and plant dry weight, and increased malondialdehyde (MDA) content, hydrogen peroxide (H 2 O 2 ) content, proline content, stomatal density, and enzyme activities. SNP treatment increased Fv/Fm, photosynthetic pigments, K + /Na + ratio, and dry weights of the shoots and roots of NaCl-exposed plants. The exogenous application of NO increased the proline content under salinity stress more than under stress conditions without SNP application, so that the proline content increased from 32 to 47 µmol g −1 . Application of 100 µM SNP also increased endogenous NO concentration (up to 43%) and consequently protected plants against salt stress-induced damage by improving enzyme activity and reducing the H 2 O 2 generation rate (up to 14%) and MDA content (up to 50%) compared to plants treated with NaCl alone. Foliar application of NO to salt-stressed plants increased root and shoot respiration rates from 20 and 12%, respectively, under salinity stress to 57% under the application of SNP and stress conditions, and decreased stomatal conductance by up to 70%, resulting in improved RWC. Increased internal NO generation in plants induced by 100 µM SNP application has the potential to mitigate salinity injury in Silybum marianum L. plants.

Althought safflower is a tolerant crop against many environmental stresses, but its yield and performance reduce under stress. The aim of this experiment was to investigate the effect of silicon (Si) application on the possibility of increasing salinity resistance and related mechanisms in safflower. A greenhouse experiment was conducted to investigate the effects of Si spraying (0, 1.5 and 2.5 mM) on safflower plants grown under salt stress condition (non-saline and 10 dS m −1 ). Salinity reduced seedling emergence percent and rate, growth parameters and disrupted ion uptake but increased emergence time and specifc leaf weight. Spraying of Si increased plant height, fresh and dry weight, leaf area, relative water content (RWC), potassium, calcium and silicon content, while sodium absorption was decreased. As a result, the K + /Na + and Ca 2+ /Na + ratios were increased. Elevated ion contents and ratios indicate an enhanced selectivity of ion uptake following silicon application and may increase ion discrimination against Na + . Treatment with 2.5 mM Si showed the most positive effect on the measured growth traits. Decrement in leaf area ratio under salinity indicates a more severe effect of salinity on leaf area compared to biomass production. On the other hand, silicon reduced the specific leaf weight under stress and non-stress conditions, which revalues the positive effects of silicon on leaf area expansion. Improvement of RWC may a reason for the icrease in leaf area and biomass production. Data shows that spraying with Si especialy with 2.5 mM can reduce salinity stress damage to safflower and increase biomass production.

To investigate how and in what amounts biochar and methyl jasmonate can improve drought tolerance of barley. A two-year experimental study was conducted in a factorial randomized complete block design (n = 5) in the research greenhouse of Zanjan University, Iran, to investigate the possible effects of biochar and methyl jasmonate on some traits of winter barley under drought conditions. Two irrigation regimes, D 0 (full irrigation in soil field capacity as control) and D 1 (withholding irrigation immediately after flowering stage), three methyl jasmonate spray densities [0 (M 0 ), 50 (M 50 ), and 100 (M 100 ) μM] and four levels of biochar in soil [0% (B 0 ), 0.25% (B 0.25 ), 0.5% (B 0.5 ), 1% (B 1 ) per soil weight] were used in this experiment. In this study, drought reduced two-year average leaf area (LA) by 96%, stomatal conductance (gs) by 84%, and photosynthetic water use efficiency (PWUE) by 64%. In addition, drought reduced chlorophyll-b by 1.5% and 81% and transpiration rate (Tr) by 2.5% and 78% in the first and second years, respectively. However, the application of biochar and methyl jasmonate improved all the traits studied in both D0 and D1 drought-treated plants. For most of the parameters studied, the optimal combination of biochar and methyl jasmonate that optimized water use efficiency and alleviated drought was 0.25% and 50 μM, respectively. The synergistic action of biochar and jasmonates improved the tolerance of barley to water stress.

Soil and water salinization is a global treat for crop production and food security. Apply of phytohormones and nutrient management is a novel approach to reduce the negative impact of salinity. Hence the effects of salicylic acid (0, 600, 1200, and 1800 µM) and silicon (0, 1.5, and 2.5 mM) foliar application on safflower ( Carthamus tinctorius L.) seed yield and quality were investigated under salt stress conditions (1.7, 7.5, and 15 dS m − 1 ). Salinity decreased capitulum number, seed number per capitulum, 100-seed weight, seed yield, oil percentage, oil yield, linoleic acid content, palmitic and linoleic acids yield, and seed potassium content. Application of salicylic acid (SA) and silicon (Si) increased biological and seed yield, oil content, oil yield, linoleic acid content, palmitic and linoleic acid yield but decreased stearic and oleic acid content and oleic acid yield. The harvest index (HI) was decreased with increasing salinity levels, indicating a stronger effect of salinity on seed yield more than biomass production. In contrast, SA and Si, whether alone or together, increased HI. The appropriate concentration of SA in saline and non-saline conditions was 1200 µM, but Si was different in salinity levels. Under non-stress and moderate stress conditions 2.5 mM Si showed better performance, while at severe salinity level, 1.5 mM Si showed an appropriate state. Oil content and quality improved by increasing linoleic acid and reducing stearic and palmitic acids by application of SA and Si. The content of seed elements with the application of salt, SA and Si showed different trends. Nitrogen content increased under salt stress, but potassium content decreased and sodium content did not change under saline and non-saline conditions. The application of SA and Si increased nitrogen and potassium content in stressed and non-stressed conditions, but had no significant effect on the amount of sodium.

To determine the effect of biochar application (BIO) and exogenous spraying of methyl jasmonate (MJ) on some biochemical attributes of winter barley under withholding irrigation at the flowering stage (for two weeks), a two-year glasshouse study was carried out. The drought stress increased the electrolyte leakage by 51.7%, however addition of biochar into the soil and spraying methyl jasmonate decreased this parameter remarkabley. Moreover, drought stress increased the enzymatic activity of catalase in both years (1016% and 716% respectively in the first and the second year), super oxid dismutase in both years (1302% in the first year and 382% in the second year), proline content (256%), total soluble sugar content (366% in the first and 490% in the second year) and Malondyaldehyde (383% and 417% respectively in the first and the second year). However, due to application of biochar and methyl jasmonate, the adverse effects of drought stress on these characteristics were adjusted. The highest (9.51 gr/pot) and the lowest (4 gr/pot) grain yield was recorded as a result of combined application of 0.25% of biochar and 50 μmol of methyl jasmonate. Conclusively, it is deduced that, addition of biochar into the soil and spraying methy jasmonate can be effective in managing water shortage conditions if they are used in appropriate doses which were shown to be 0.25% of biochar and 50 μmol per liter of methyl jasmonate respectively, to optimize water use and minimize drought stress.