Abstract
Non-thermal plasma holds great potentials as an efficient, economical, and eco-friendly seed pretreatment method for improving the seed germination and seedling growth, but the mechanisms are still unclear. Therefore, a plant model organism Arabidopsis thaliana was used to investigate the physio-biochemical responses of seeds to non-thermal plasma at different treatment times by measuring the plant growth parameters, redox-related parameters, calcium (Ca2+) level and physicochemical modification of seed surface. The results showed that short-time plasma treatment (0.5, 1, and 3 min) promoted seed germination and seedling growth, whereas long-time plasma treatment (5 and 10 min) exhibited inhibitory effects. The level of superoxide anion (O2•−) and nitric oxide (NO) and the intensity of infrared absorption of the hydroxyl group were significantly higher in short-time plasma treated Arabidopsis seeds, and the level of hydrogen peroxide (H2O2) was remarkably increased in long-time plasma treated seeds, indicating that O2•−, ·OH, and NO induced by plasma may contribute to breaking seed dormancy and advancing seed germination in Arabidopsis, while plasma-induced H2O2 may inhibit the seed germination. The intensity of hydroxyl group and the contents of H2O2, malondialdehyde, and Ca2+ in Arabidopsis seedlings were obviously increased with the plasma treatment time. Catalase, superoxide dismutase, and peroxidase activities as well as proline level in short-time treated seedlings were apparently higher than in control. The etching effects of plasma on seed surface were dose-dependent, spanning from slight shrinkages to detached epidermis, which also significantly increased the oxidation degree of seed surface. Therefore, the improved activities of antioxidant systems, moderate ·OH, H2O2, and Ca2+ accumulation and seed surface modification induced by plasma all contribute to the enhanced seedling growth of Arabidopsis after short-time plasma treatment.
Highlights
In the past few decades, atmospheric non-thermal plasma has shown promising applications in the biomedical field, leading to the emergence of “plasma medicine” (Fridman et al, 2010)
The Optical emission spectroscopy (OES) results indicated that abundant excited nitrogen molecules and ion, atomic oxygen and nitric oxide (NO) existed in the air plasma, which can react with each other to form various kinds of RNS and ROS due to their high activity (Liang et al, 2012)
Plasma exhibited a dose-effect on seed germination and early seedling growth of Arabidopsis, ranging from stimulation (≤3 min) to inhibition (≥5 min) depended on the plasma treatment time
Summary
In the past few decades, atmospheric non-thermal plasma has shown promising applications in the biomedical field, leading to the emergence of “plasma medicine” (Fridman et al, 2010). Numerous works have shown that nonthermal plasma is a fast, uniform, economic, effective, and ecofriendly approach for stimulating seed germination and seedling growth compared with the conventional seed pretreatment methods, e.g. ultraviolet and gamma radiation, scarification, hot water soaking, and chemical reagent treatment (Li et al, 2014; Randeniya and De Groot, 2015; Mildaziene et al, 2018; Štěpánová et al, 2018). In the last years many authors studied the stimulation of the seed germination and the plant growth by using plasma generator (Živković et al, 2004; Šerá et al, 2010; Dobrin et al, 2015; Bafoil et al, 2018). The detailed mechanisms underlying the stimulatory effects of plasma on seeds are still not fully understood
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