Effect of Dielectric Barrier Discharge Cold Plasma on Pea Seed Growth

Abstract

Traditional seed pretreatment methods cause secondary pollution for the application of various chemicals. This study investigated the effect of dielectric barrier discharge (DBD) cold plasma on seedling growth. Effects of plasma-activated tap water (PATW) and plasma-activated seeds (PAS) were compared for germination rates, seedling height, dry weight, and chlorophyll content. Results show that compared with controls these growth parameters were all increased by more than 50%. The yields and contributions of hydrogen peroxide, nitrate, nitrite, and ammonium were quantified. Hydrogen peroxide and nitrate have an important role in seedling growth. By etching, the seed epidermis free radicals can reduce the apparent contact angle and increase the water absorption of the seeds. In addition to the low cost of PATW and PAS compared with commercial fertilizers, DBD does not involve any chemical addition. Thus, both PATW and PAS can be an alternative for improvement of agricultural production.

Mechanisms of Plasma-Seed Treatments as a Potential Seed Processing Technology

“…It seems that plasmas may somehow modulate concentrations of hormones and there may be a link with auxin especially considering that this hormone also affects xylem differentiation [173]. It has been observed that plasma treatment modified the diameters of root and stems as well as the differentiation of tissues such as xylem and phloem [51,52,58,174]. These changes in root morphology may then enhance nutrient exchange [68] which was also proposed by Zahoranová et al [97].…”

“…The role of high-energy photons in plasma-seed treatments has been controversial since UV has had a negligible effect so far but the effects of UV on seeds and plants could theoretically contribute to the wettability or growth enhancement effects indirectly; for example, by producing radicals or reactive oxygen species (ROS) such as ozone [60]. Gao et al [52] checked the effects of UV separately from plasma and observed that UV had only a minor contribution toward the seed wettability. Sarinont et al [102] also reported that there was no effect from UV when they saw the lack of growth enhancement effect after they blocked UV with a quartz plate.…”

“…Bafoil et al [61] showed the importance of the seed coat by using mutants of Arabidopsis plant model Ler and Col-0 ecotypes and showed the rearrangement of lipid components, changes in lignin and seed coat erosion. Many, although not all authors have observed with scanning electron microscopy (SEM) that seed surfaces treated with plasma have an eroded appearance [52,83,86,93,96,104], where MildaŽiene et al [128] only saw etching on the seed surface facing plasma treatment and others did not see any changes [29,110,129].…”

“…This principle could likewise work for nitrogen gas but instead of modifying respiration, it may be directed toward other cellular processes such as photosynthesis since it is a major component of chlorophyll or protein synthesis [138]. As mentioned in the paper of Gao et al [52], the presence of CO and O + 2 signals confirmed that chemical etching of the seed surface by plasma played an important role in stimulation of seed germination [139]. These chemical changes may then be responsible for changing the biochemistry and molecular events in the plant and therefore, these will be discussed in the next section.…”

Advantages and Limitations of Surface Analysis Techniques on Plasma-Treated Arabidopsis thaliana Seeds

“…Surface morphology information can be obtained using scanning electron microscopy (SEM). Seed coat erosion in plasma-treated seeds is the most common effect observed by SEM (Stolárik et al, 2015;Junior et al, 2016;Ambrico et al, 2017;da Silva et al, 2017;Guo et al, 2017;Li et al, 2017;Wang et al, 2017;Gao et al, 2019) but this does not necessarily occur in every instance. For example, Mildaziene et al (2016) noticed etching only on the seed surface facing the plasma, while other authors did not remark any (Sera et al, 2010;Bormashenko et al, 2012;Kitazaki et al, 2014).…”