The response of seed germination to environmental factors can be estimated by nonlinear regression. The present study was performed to compare four nonlinear regression models (segmented, beta, beta modified, and dent-like) to describe the germination rate–temperature relationships of milk thistle (Silybum marianum L.) at six constant temperatures, with the aim of identifying the cardinal temperatures and thermal times required to reach different germination percentiles. Models and statistical indices were calibrated using an iterative optimization method and their performance was compared by root mean square error (RMSE), coefficient of determination (R2) and Akaike information criterion correction (AICc). The beta model was found to be the best model for predicting the required time to reach 50% germination (D50), (R2=0.99; RMSE=0.004; AICc=−276.97). Based on the model outputs, the base, optimum, and maximum temperatures of seed germination were 5.19±0.79, 24.01±0.11, and 34.32±0.36°C, respectively. The thermal times required for 50% and 90% germination were 4.99 and 7.38degree-days, respectively

Background: Drought response in plants at molecular level, aiding them to overcome the adverse effects of drought, remarkably depends on the expression of a few regulator genes and signal transduction. For reducing the drought stress, nanoparticles show great promise compared to other commonly used methods, even though the underlying mechanisms are still unknown. Objectives: This study was performed to investigate the expression analysis of genes involved in drought tolerance and the use of zinc oxide nanoparticles (ZnO NPs) to mitigate the undesirable effects of thought stress in wheat. Materials and Methods: A factorial experiment based on completely randomized design (CRD) was performed with three replicates. The experiment was carried out in the greenhouse of Mohaghegh Aniabili University, Ardabil, Iran in 2017. The factorial combination of stress levels of water supply (including 85%, 60%, and 35% field capacity) and ZnO NPs (0, 0.5, and 1.0 g. L-1) were used on flute wheat cultivars (Mihan, Heidari, and Gascogne). Three days after spraying the ZnO NPs in the three-leaf stage, drought stress was applied for ten days and physio-biochemical traits and gene expression of wheat cultivars were investigated. The expression of Wdhn13, DREB2, P5CS, and CAT1 genes in leaves were analyzed by real-time polymerase chain reaction (PCR). Results: Generally. drought stress significantly enhanced total protein and lysine. soluble sugars, chlorophyll. carotenoid contents, antioxidant enzymes activities, and proline accumulation in plants treated with ZnO NPs. Moreover, the ZnO NPs increased the expression of the genes involved in proline biosynthesis (i.e., P5CS), catalase activity (i.e.. CATO, and dehydration-responsive genes DREB2 and Wdhn13, which are known as drought-tolerance parameters. Conclusions: According to our results, ZnO NP-treated wheat induced drought-tolerance genes and effectively facilitated deficiency tolerance. Therefore, under drought stress, we recommend spraying bread wheat with ZnO NPs (1 g L-1) in the growing season, which can improve wheat grain yield under dry conditions.

Water deficit is considered as a major limiting environmental factor for plant growth and yield. To ameliorate the adverse effects of water restriction, an experiment was conducted in the research field of Mohaghegh Ardabili University in two successive years (2014 and 2015). Foliar spraying of different concentration of epibrassinolide (EBL) (0, 10⁻⁸, and 10⁻⁷M) and ascorbic acid (AsA) (0 and 10 mM) was carried out and water-stress trials included 50 and 100 mm evaporation from class A pan. Water stress significantly enhanced essential oil content, but reduced capitula yield and relative water content (RWC) of leaves. Water-stress damage ameliorated by foliar application of 10 mM AsA with 10⁻⁷M EBL and the essential oil yield and antioxidant enzymes activity improved significantly. Enhancing of malondialdehyde (MDA) content and electrolyte leakage indicates that water-deficit stress caused oxidative damage to the membrane by enhancing hydrogen peroxide (H₂O₂) level. Combined-application of regulators significantly declined the amounts of H₂O_2, MDA, and electrolyte leakage under water stress. Antioxidant enzymes activity and also proline and protein content were enhanced by drought stress as well as regulators. Also, the application of EBL and AsA induced tolerance to water deficit and reduced the reactive oxygen species by increasing antioxidant enzymes activity and osmotic adjustment.