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.

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Surface micro-discharge (SMD) plasma holds great potential as an effective, economical and safe method for the treatment of diverse skin infections. Although the antimicrobial effect of SMD plasma is undisputed, the factors most responsible for the inactivation effect and their corresponding killing mechanisms are still not fully understood. Herein, we evaluate the roles of hydroxyl radicals (•OH), hydrogen peroxide (H 2 O 2 ), oxidation-reduction potential (ORP) and pH in the inactivation of yeast cells on an agarose tissue model by helium SMD plasma over different irradiation distances and time periods. The •OH distribution pattern shows that •OH is mostly produced in the center of every hexagon mesh electrode, whose concentration is closely related to humidity and is markedly increased at a shorter irradiation distance and longer treatment time. Meanwhile, the killing pattern of yeast cells corresponds to •OH distribution and the inactivation efficiency has a similar trend to that of •OH concentration. The results of Pearson correlation analysis reveal that the inactivation efficiency is more dependent on •OH and pH compared with H 2 O 2 and ORP. Furthermore, we investigated the effects of •OH and pH on yeast cell viability, membrane integrity and intracellular ROS and pH homeostasis by using a specific •OH scavenger D-mannitol (D-man) and phosphate buffer solution (PBS). The results showed that D-man could significantly reduce the inactivation efficiency by maintaining cell membrane integrity and intracellular ROS and pH homeostasis, while PBS only slightly mitigates the plasma-caused damage on yeast cells. Based on the results, it is concluded that •OH contributes most to the inactivation of yeast cells on a tissue model by helium SMD plasma studied here.

Heavy metal pollution, as a consequence of rapid industrialization and urbanization, poses a threat to highland barley grown in Tibet. This study investigates the effect of different doses of gamma irradiation (50–300 Gy) on the physio-biochemical and molecular mechanism of highland barley under heavy metal stress. Growth data showed that 50-Gy gamma irradiation had the maximal beneficial effects on the highland barley seedlings under lead/cadmium stress. The results of oxidative parameters demonstrated that 50-Gy gamma-irradiated seedlings had lower hydrogen peroxide and malondialdehyde contents under lead/cadmium stress compared to non-irradiated seedlings. Moreover, the activities of antioxidant enzyme and proline levels in 50-Gy gamma-irradiated seedlings were drastically higher than those in non-irradiated seedlings under lead/cadmium stress. Additionally, transmission electron microscopy results revealed that the 50-Gy gamma-irradiated seedlings exhibited improved chloroplasts ultrastructure compared with non-irradiated seedlings exposed to lead/cadmium stress. Notably, transcriptional expression analysis showed that 50-Gy gamma irradiation could significantly affect the expression of genes related to heavy metal transport and abscisic acid metabolism under lead/cadmium stress. Collectively, these results provide insights into the physio-biochemical and molecular mechanisms of low-dose-gamma-irradiation-enhanced heavy metal tolerance in highland barley seedlings, thus proposing gamma irradiation as a potential technology to mitigate heavy metal toxicity in crops.

The stimulatory effects of atmospheric pressure cold plasma (APCP) on plant growth have attracted much attention due to its great potential as a new approach to increase crop growth and production. However, the transcriptome changes of plants induced by APCP treatment are unknown. Herein, the comparative transcriptome analysis was performed to identify the transcriptional response of Arabidopsis thaliana seedlings to APCP. Results showed that APCP exhibited a dual effect (stimulation or inhibition) on Arabidopsis seedling growth dependent on the treatment time and the maximum stimulatory effects were achieved by 1 min APCP treatment. The metabolic analysis of amino acid, glutathione (GSH) and phytohormone demonstrated that 1 min APCP treatment decreased most amino acids concentrations in Arabidopsis seedling, while the accumulations of GSH, gibberellins and cytokinin were significantly increased. The RNA-Seq analysis showed that a total of 218 differentially expressed genes (DEGs) were identified in 1 min APCP-treated seedlings versus the control, including 20 up-regulated and 198 down-regulated genes. The DEGs were enriched in pathways related to GSH metabolism, mitogen-activated protein kinase (MAPK) signaling transduction and plant resistance against pathogens. Moreover, most of the DEGs were defense, stimuli or stress-responsive genes and encoded proteins with oxidoreductase activity. Expression determination of six randomly selected DEGs by quantitative real-time PCR demonstrated similar pattern with the RNA-Seq data. These results indicated that the moderate APCP treatment may regulate the expression of stimuli/stress-responsive genes involved in GSH, phytohormone/amino metabolism and plant defense against pathogens via MAPK signal transduction pathway, accordingly enhance Arabidopsis seedling growth. This study provides a theoretical basis for the application of APCP in agriculture.