Treatment of plant seeds with electromagnetic fields or non-thermal plasmas aims to take advantage of plant functional plasticity towards stimulation of plant agricultural performance. In this study, the effects of pre-sowing seed treatment using 200 Pa vacuum (7 min), 5.28 MHz radio-frequency cold plasma (CP −2, 5, and 7 min) and electromagnetic field (EMF −5, 10, 15 min) on seed germination kinetics, content of phytohormones, morphometric parameters of seedlings and leaf proteome were assessed. CP 7 min and EMF 15 min treatments caused 19–24% faster germination in vitro ; germination in the substrate was accelerated by vacuum (9%) and EMF 15 min (17%). The stressors did not change the seed germination percentage, with exception of EMF 5 min treatment that caused a decrease by 7.5%. Meanwhile both CP 7 min and EMF 15 min treatments stimulated germination, but the EMF treatment resulted in higher weight of leaves. Stressor-specific changes in phytohormone balance were detected in seeds: vacuum treatment decreased zeatin amount by 39%; CP treatments substantially increased gibberellin content, but other effects strongly varied with the treatment duration; the abscisic acid content was reduced by 55–60% after the EMF treatment. Analysis of the proteome showed that short exposure of seeds to the EMF or CP induced a similar long-term effect on gene expression in leaves, mostly stimulating expression of proteins involved in photosynthetic processes and their regulation.

The effects of Norway spruce (Picea abies) seed treatment with cold plasma (CP), vacuum, and electromagnetic field (EMF) on germination and seedling growth are studied. CP treatments negatively affected germination ‘in vitro’, but for germination in cassettes CP (7 min) and EMF (5 min) significantly increased the germination yield. All treatments increase the germination rate in cassettes except CP (7 min) treatment having a negative effect. Seed treatment with CP and EMF increases the number of paramagnetic centers in dry seeds and modulate H2O2 production in germinating seeds. After the second vegetation season seedlings grown from CP (5 min) and CP (7 min) treated seeds, characterized by negative effects on either the germination rate or yield, have 50–60% larger height and 40–50% increased branching in comparison to the control seedlings.

The effects of seed treatment with cold plasma (2–7 min), vacuum (7 min), and electromagnetic field (5–15 min) on Echinacea purpurea germination and performance are studied. All treatments induce faster germination but did not change the final germination percentage, except the decrease evoked by vacuum treatment. The plants grown from all groups of treated seeds have larger height, develop more leaves, some treatments increase root weight. The content of vitamin C and phenolic acids in extracts of plant leaves from the treated groups is substantially higher in comparison to the control, so that the amount of cichoric acid per plant increased up to 3.8‐fold, and amount of vitamin C per plant – up to 1.9‐fold. Seed treatments induce large increase in radical scavenging activity (up to 114%) in leaf extracts.

The aim of this study was to estimate the effects of treatment with atmospheric cold plasma (CP) on sunflower (Helianthus annuus) seeds on germination kinetics, content of seed phytohormones, early seedling growth, and photosynthetic activity. Seeds were treated with a scalable dielectric barrier discharge device for different durations. Differences in CP-induced changes in the seed phytohormone content in cases of positive or negative effects on germination and/or seedling growth were detected. The eustress response was related to the increased ratio between gibberellin (GA) and abscisic acid (ABA) contents, and the distress response was related to decreased GA/ABA and increased salicylic acid content.

Radiofrequency (5.28 MHz) electromagnetic radiation and low-temperature plasma were applied as short-term (2-15 min) seed treatments to two perennial woody plant species, including Smirnov's rhododendron (Rhododendron smirnowii Trautv.) and black mulberry (Morus nigra L.). Potential effects were evaluated using germination indices and morphometry. The results suggest that treatment with electromagnetic field stimulated germination of freshly harvested R. smirnowii seeds (increased germination percentage up to 70%), but reduced germination of fresh M. nigra seeds (by 24%). Treatment with low-temperature plasma negatively affected germination for R. smirnowii, and positively for M. nigra. The treatment-induced changes in germination depended on seed dormancy state. Longer-term observations revealed that the effects persisted for more than a year; however, even negative effects on germination came out as positive effects on plant morphometric traits over time. Treatments characterized as distressful based on changes in germination and seedling length increased growth of R. smirnowii after 13 months. Specific changes included stem and root branching, as well as increased leaf count and surface area. These findings imply that longer-term patterns of response to seed stressors may be complex, and therefore, commonly used stressor-effects estimates, such as germination rate or seedling morphology, may be insufficient for qualifying stress response. Bioelectromagnetics. 37:536-548, 2016. © 2016 Wiley Periodicals, Inc.

Pre-sowing treatment of red clover seeds with cold plasma (CP) and electromagnetic field (EMF) was applied aiming to evaluate changes induced in germination and early seedling growth under controlled laboratory conditions, and to estimate treatment effects on plant growth, biomass production, nutritional value and the amounts of major leaf secondary metabolites under long-term field experimental conditions. The effects of seed treatment using radio-frequency EMF (5, 10, 15 min) and CP (2, 5, and 7 min) on seed germination kinetics, morphometric parameters of seedlings were assessed for two cultivars of red clover—‘Vyčiai’ and ‘Sadūnai’. Long-term observations revealed that the effects of seed treatments persist for the entire vegetation season, while the observed effects on germination (CP increased germination rate by 4%–20%) do not provide sufficient information to predict the impact on plants on a longer time scale. The effects on morphometric parameters were dependent on plant cultivar, and were much stronger (up to 24% for ‘Sadūnai’ and 49% for ‘Vyčiai’) after growing the plants in the field for 5 months in comparison to the effects (absent or below 10%) observed in the early growth stages. A minor improvement of nutritional value per biomass unit was observed for ‘Vyčiai’. Protein yield per plant increased substantially (up to 70%). Pre-sowing seed treatment with CP and EMF had an obvious impact on the amounts of major isoflavones in leaves, and the nature of these changes strongly depended on the vegetation stage of plants (before flowering or at flowering stage). CP treatment for 5 min was found to be the most effective in this respect in not flowering plants, inducing a strong increase in biochanin A/formononetin ratio in leaves of both cultivars. However, an opposite effect was observed in the flowering plants, where the CP and EMF treatments decreased biochanin A/formononetin ratio.

The effects of presowing treatment of red clover seeds with cold plasma (5 and 7 min) and electromagnetic field (10 and 15 min) on plant agronomic performance were studied. Seed treatments stimulated germination and this effect correlated with changes in the balance of seed phytohormones: a decreased amount of abscisic acid and an increased gibberellin/abscisic acid ratio. Experiments performed in rhizoboxes revealed that seed treatments stimulated root growth and root nodulation. Stressor and dose‐specific changes in the amounts of flavonoids important for communication with nitrogen‐fixing strains of rhizobacteria were detected in the root exudates. The results suggest that besides changes in plant's internal processes, the response of plants to seed treatment involves beneficial modulation of plant communication with microorganisms.

This study aimed to estimate the dependence of the effects of radish (Raphanus sativus) seed irradiation with atmospheric cold plasma (CP) on physiological seed condition or dormancy status. Seeds were treated for different durations with a scalable dielectric barrier discharge (DBD) device. The relationship between the effect of CP on germination kinetics with changes in the content of phytohormones in seeds stored for different periods of time after harvesting (1, 5, and 7 months) was estimated. CP treatment efficiently stimulated germination only in freshly harvested (not after-ripened seeds), and these changes correlated with a decrease in abscisic acid (ABA) and an increase in gibberellin (GA) content. CP treatment induced a fast decrease in ABA content and ABA/GA ratio in after-ripened seeds (5 months after harvesting) but did not stimulate germination. Primary evidence of direct ABA modification by the reactive compounds from the gaseous phase of CP was obtained.