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Responses of Rice Seed Quality to Large-Scale Atmospheric Nonthermal Plasmas

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Responses of Rice Seed Quality to Large-Scale Atmospheric Nonthermal Plasmas

Abstract and Figures

Atmospheric nonthermal plasma (ANTP) is used for various biological applications including seed quality improvements in crop production. However, the underlying mechanisms of plasma-induced seed action are not fully explained and operating large-scale ANTP on seeds is highly challenging. Two large-scale ANTPs, streamer corona plasma (SCP) and dielectric barrier discharge (DBD) plasma, were used to enhance rice seed vigor through surface modification and functionalization. The SCP and DBD plasma were conducted under the same power source and applied to rice seeds to modify their surface from being highly hydrophobic to being highly hydrophilic, as defined by the apparent contact angle measurement. The results show that SCP requires less treatment time (~ 2 min) for surface activation than the DBD plasma process (~ 10 min). Both plasma-treated seeds showed higher seed vigor than non-treated seeds. For 50% of the viable seeds to emerge, the SCP-treated seeds took on average about 62 h., while the untreated rice seeds took around 72 h. The germination percentage of all conditions is ~ 92% which is a typical proportion of good seed quality. The microstructure of the rice seed surface suggests that the bombardment of highly energetic ions and the reaction of reactive oxygen and nitrogen species on the seed surface cause morphological changes via surface etching and functionalization without any adverse effects on seed nutrition. Graphical abstract
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Plasma Chemistry and Plasma Processing (2022) 42:1127–1141
https://doi.org/10.1007/s11090-022-10261-3
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ORIGINAL PAPER
Responses ofRice Seed Quality toLarge‑Scale Atmospheric
Nonthermal Plasmas
ThunyapukRongsangchaicharean1· SiwaponSrisonphan2 ·
DamrongvudhiOnwimol1
Received: 2 December 2021 / Accepted: 9 May 2022 / Published online: 30 May 2022
© The Author(s) 2022
Abstract
Atmospheric nonthermal plasma (ANTP) is used for various biological applications includ-
ing seed quality improvements in crop production. However, the underlying mechanisms
of plasma-induced seed action are not fully explained and operating large-scale ANTP on
seeds is highly challenging. Two large-scale ANTPs, streamer corona plasma (SCP) and
dielectric barrier discharge (DBD) plasma, were used to enhance rice seed vigor through
surface modification and functionalization. The SCP and DBD plasma were conducted
under the same power source and applied to rice seeds to modify their surface from being
highly hydrophobic to being highly hydrophilic, as defined by the apparent contact angle
measurement. The results show that SCP requires less treatment time (~ 2min) for surface
activation than the DBD plasma process (~ 10 min). Both plasma-treated seeds showed
higher seed vigor than non-treated seeds. For 50% of the viable seeds to emerge, the SCP-
treated seeds took on average about 62h., while the untreated rice seeds took around 72h.
The germination percentage of all conditions is ~ 92% which is a typical proportion of good
seed quality. The microstructure of the rice seed surface suggests that the bombardment of
highly energetic ions and the reaction of reactive oxygen and nitrogen species on the seed
surface cause morphological changes via surface etching and functionalization without any
adverse effects on seed nutrition.
Thunyapuk Rongsangchaicharean and Siwapon Srisonphan have contributed equally to the work.
* Damrongvudhi Onwimol
damrongvudhi.o@ku.th
1 Department ofAgronomy, Faculty ofAgriculture, Kasetsart University, 50 Ngamwongwan Road,
Ladyao, Chatuchak, Bangkok10900, Thailand
2 Department ofElectrical Engineering, Faculty ofEngineering, Kasetsart University, 50
Ngamwongwan Road, Ladyao, Chatuchak, Bangkok10900, Thailand
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Graphical abstract
Keywords Nonthermal plasma· Nutrition· Oryza sativa· Seed vigor· Surface
modification
Abbreviations
ABA Abscisic acid
AC Alternating current
ACA Apparent contact angle
ANOVA Analysis of variance
ANTP Atmospheric nonthermal plasma
DBD Dielectric barrier discharge
GA Gibberellic acid
MRET Mean radicle emergence time
OES Optical emission spectroscopy
RONS Reactive oxygen and nitrogen species
SCP Streamer corona plasma
SEM Scanning electron microscope
tRE Radicle emergence time
t50RE The time required for 50% of viable seeds to emerge
Introduction
With the expansion of the global population, the demand for rice as a staple food is rapidly
growing [13]. Various technologies and methods have been introduced to improve rice
seed quality and increase crop yield to meet food security requirements [1, 35]. Numerous
indicators are used to assess seed quality such as seed lot purity, seed viability, and seed
health, however, seed vigor is considered one of the most significant parameters [4, 69].
The level of seed vigor indicates the ability of the seeds to germinate and establish seed-
lings rapidly, uniformly, and robustly in a field across diverse environmental conditions.
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As a result, using seed vigor enhancement technology to achieve rapid and uniform rice
seed germination has proven to be an effective method. Hence, it is a primary objective
within the agricultural industry’s breeding and seed production programs [4]. Several tech-
niques, such as chemical treatments (chemicals, fungicides, and plant growth regulators)
and physical treatments (ultrasonic scratching and electric field treatments), have been used
for seed enhancement [5, 1015]. However, both are labor-intensive, safety concerns, and
costly due to large quantities of chemical consumption and chemical residues [5, 15]. In
contrast, with a mixture of free radicals, negative and positive ions, molecules, reactive
species (RS), and electrons, atmospheric nonthermal plasma—ANTP—technologies have
been developed as an alternative nonthermal emerging technology for food and agricultural
applications. ANTP technology is capable of inactivating or decontamination of microor-
ganisms without inducing thermal damage and produces no hazardous residues [5, 1618].
Initially, low-pressure plasma was used to treat biomaterials, including seeds, because
it produces homogeneously distributed plasma in an entire operating area [17, 19, 20].
However, the low-pressure plasma requires a vacuum system to generate and control the
plasma phase, this is considerably expensive and complex [16, 19]. Additionally, certain
biomaterials are unable to withstand low-pressure settings without deteriorating [21, 22].
Subsequently, the advent of ANTP has attracted substantial attention due to its ability to
treat biological and agricultural materials in an ambient environment. As a result, ANTP,
also known as ‘cold plasma’, has been utilized for many agricultural purposes, from seeds
to harvest [5, 15, 21, 2325], particularly in rice production [17, 2628]. Several reports
demonstrate that ANTP treatment can enhance seed imbibition and germination [21, 25,
27, 29]. Seed germination requires a complicated network of hormones, metabolism, and
developmental changes that do not occur if the seed is not in the ideal levels of moisture,
oxygen, temperature, and light [21, 30]. Our previous report showed the sterilization capa-
bility of streamer plasma [27] however, there is no report on the subsequent effect on rice
seed vigor or the underlying mechanism behind the phenomena. Only a few ANTP struc-
tures can be practically used in large-scale applications that can treat more than 10,000
seeds for each operation, especially in agriculture. Generally, scaling up an atmospheric
cold plasma system is challenging due to the difficulty in controlling the plasma state
which involves several reactor designs and process parameters, such as a high electric field,
high discharge voltage, and a high gas flow rate, all of which require a large power source
[19, 31, 32]. All previous research has been conducted at the laboratory stage and scale,
with ~ 20g of rice seed/grain being the maximum treated capacity [17, 27, 33]. However,
nutrition and field tests require at least 0.3–1kg to meet the standardized experimental
parameters and volume. Therefore, scaling up the ANTP area is currently the primary chal-
lenge that needs attention. Recently, electrical discharge phenomena such as corona dis-
charge and dielectric barrier discharge (DBD) have become a promising approach for pro-
ducing ANTP systems because they can take place at atmospheric pressure. Electrical gas
discharge mainly relies on the electric field distribution between the electrode geometrical
configurations and dielectric permittivity [32, 34, 35]. Generated by highly localized elec-
tric fields associated with sharp electrodes, corona discharge requires relatively low power
and appears in several forms, such as streamer corona, glow corona, and spark discharge
[16, 31, 36, 37]. However, corona discharge plasma is extremely difficult to control because
it can quickly spark (arc) [31, 36]. In contrast, the DBD structure typically consists of two
parallel electrode plates with dielectric layers placed between the electrodes which provide
micro discharge filaments of nanosecond duration with more stability and homogeneity
[16, 37, 38]. However, with the proper electrode and power source design, both electrical
discharge plasma can be obtained with low operational power.
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Here, we present two types of large-scale electrical discharge plasma systems, streamer
corona plasma (SCP) and DBD plasma, used for treating 1kg of rice seeds each. We stud-
ied and compared the effects of the SCP and DBD plasma on rice seed enhancement,
germination, and radicle emergence—RE—speed under the same power source. Optical
emission spectroscopy was performed to elucidate the underlying mechanism and essential
reactive species that affect seed quality during treatment. A scanning electron microscope
was employed to understand the plasma-induced physiochemical response of the seed sur-
face after SCP and DBD plasma applications. The primary nutritional value of rice seeds
was defined to substantiate whether the application of plasma degrades physical and physi-
ological seed quality. This overall investigation is helpful not only for future ANTP design
parameters but also for improving the efficiency and effectiveness of cold plasma for seed
enhancement.
Materials andMethods
Experimental Setup
Two large-scale ANTPs, SCP and DBD plasma, were designed and fabrication. Then, the
developed ANTPs were validated using optical emission spectroscopy (OES) and apparent
contact angle (ACA) measurement.
Atmospheric Nonthermal Plasma Design andFabrication
Figure 1a demonstrates the atmospheric nonthermal SCP treatment of rice seeds. The
SCP is generated by using a hybrid structure, combining the corona discharge plasma and
DBD plasma [16, 27, 32]. Rice seeds were placed on a dielectric layer laid on top of the
grounded electrode. There are approximately 20.3 seeds per 1g, so an electronic balance
was used to count the rice seeds before treatment. Through this way, we treated approxi-
mately 19,500 seeds. The top electrode was the sharp tip array connected to a high voltage
alternating current (AC) power supply (7kV with a repetition rate of 1kHz). The gap dis-
tance between the top and bottom electrodes was set to 0.7cm, and the operational gas was
air mixed with Ar (Ar-air) by flowing argon to mix with the surrounding air at a flow rate
of 2L/min. The SCP was generated and directly radiated to the seed under ambient atmos-
pheric conditions (Fig.1a-bottom). Although the SCP method applies plasma dispropor-
tionally to the top of the seed surface, our recent work shows that due to the combination
of corona and the DBD structure the whole seed surface (top and bottom) is exposed to
plasma and is consequently modified [28, 32, 39]. Figure1b demonstrates the DBD plasma
structure employing the same plasma source as the SCP. The DBD structure comprises
of two metal plate (top and bottom) electrodes, and glass containers which serve as two
dielectric layers covering the top and bottom planar electrodes with a gap of approximately
0.7cm. In the DBD process, the working gases are also a mixture of Ar and air. The Ar
with a flow rate of 0.5L/min is injected into the plasma active area which is controlled but
a flow meter. Thus, DBD provides the microscale filament discharge plasma entirely inside
a closed container and covers all seed surfaces (Fig.1b-bottom). However, both electri-
cal discharge plasma structures have fundamental differences in electric field distribution,
electrode structures, and cold plasma generation [16, 31]. For example, the SCP employed
a sharp tip electrode to induce a highly localized electric field (105 V/cm) to generate
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corona discharge plasma [16, 31, 32]. In contrast, DBD employs two dielectric layers to
induce a large electric field in the airgap and is significantly low in the dielectric layer itself
(103V/cm) [39]. As a result, the ANTPs will have different amounts of plasma components
and interaction rates on the rice seeds. After treatments, the plasma-treated seed was thor-
oughly mixed and drawn randomly for validating the plasma treatments and evaluate their
effects on seed quality.
Validation oftheAtmospheric Nonthermal Plasma
To elucidate and compare the rice seed enhancement after surface modification and func-
tionalization via SCP and DBD plasma, rice seeds were treated via each plasma process
until the seed surface became modified entirely, defined by the ACA measurement. Optical
emission spectroscopy (Thorlabs CCS200, wavelength 200−1000nm) coupled with fiber
optics was employed to acquire the optical emission spectrum of reactive species generated
during plasma treatment. For apparent contact angle measurement, the ACA of a 0.25µl
water droplet from a well-controlled micropipette (0.1–2µl, Bravo, CAPP, Denmark) was
measured under an optical microscope in conjunction with computer-aided measurement.
Typically, non-treated rice seed surfaces are highly hydrophobic, having ACA 120°
after an 0.25µL water droplet application (Fig.2a-top). Therefore, each plasma process
was performed on rice seeds until the seed surface was transformed entirely to a super-
hydrophilic state (ACA 0°) (Fig.2a middle and bottom). The result shows that the SCP
requires considerably less treatment time (2min) to complete hydrophilic surface transfor-
mation when compared to the DBD plasma (10min). The high efficiency of the modified
surface via SCP is probably due to the energy requirement for producing SCP being much
less than that of DBD at the same power source and electrode distance [31, 39], resulting in
Fig. 1 Electrical discharge plasma on rice seed. a Schematic diagram of streamer corona plasma (SCP)
treatment of rice seeds (top) and the optical image (bottom, scale bar = 7mm; Ar and HV denote argon and
high voltage, respectively). b Schematic diagram of dielectric barrier discharge (DBD) plasma treatment of
rice seeds (top) and the optical image (bottom, scale bar = 7mm)
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a stronger impact ionization and consequently a higher physical–chemical reaction on the
seed surface. To verify this hypothesis, we performed optical emission spectroscopy during
DBD (Fig.2b-top) and SCP (Fig.2b-bottom) because the change in ACA is attributed to
the physical, by etching process via energetic particles, and chemical reaction of reactive
oxygen and nitrogen species (RONS) on the seed surface during plasma treatment, turning
hydrophobic to hydrophilic [27, 40]. The OES shows that the RONS generated in the range
of ultraviolet spectra (250–450nm) [18, 37], ·OH (309nm), N2+ (391nm), N2, or NO lines
(316, 337, 358, 427.5nm) in the DBD structure (Fig.2b top-inset) is significantly lower
than those presented in the SCP structure (Fig.2b-bottom). As a result, the SCP requires
a shorter treatment time for surface activation. RONS are recognized as the most active
plasma components for seed treatment due to their ability to initiate oxidation processes
critical for the degradation of organic compounds [41, 42], inactivate microorganisms [27,
28, 37], and enhance surface wettability [23, 43].
Application oftheSCP andDBD Plasma forRice Seed Enhancement
Seed Germination andVigor Test
Seeds (Oryza sativa var. Indica cv. KDML105) were obtained from the Rice Department.
Before the experiment, the samples were stored at 5°C and 12% relative humidity (RH).
Germination tests were conducted immediately after plasma treatment following ISTA
guidelines [9], using four replicates of 100 seeds each. The seeds were placed on moistened
blotter paper and stored in a transparent box in a plant-growth chamber (Daihan Labtech,
Model LGC-5201) that was set to 20°C in the dark for 16h. and 30°C under cool white
lamps (~ 1200lx) for 8h. at 85% RH.
Fig. 2 Electrical discharge plasma on rice seed. a The apparent contact angle—ACA—of water droplets on
(top) non-treated, (middle) after 2min streamer corona plasma—SCP—treatment and (bottom) after 10min
dielectric barrier discharge—DBD—seed (scale bar 3.5mm). b Optical emission spectra (OES) of DBD
plasma (top) and SCP (bottom) during treatment from the same plasmasource and electrode distance
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Seed vigor was verified using the RE test [9]. According to the International Seed Test-
ing Association (ISTA), seed vigor is “the sum of those properties that determine the activ-
ity and performance of seed lots of acceptable germination in a wide range of environ-
ments” [9]. Currently, [8] propose that the extent of previous deterioration and the repair
period can determine the length of the lag period and therefore the percentage germination
in rice. After seed imbibition, cellular repair activities promoted recovery from damage
incurred during quiescence, and the speed and efficacy of repair were closely linked to RE
and germination performance [44, 45]. As a result, the RE test was designed to evaluate
rice seed vigor after plasma treatment in this study. Seed RE was evaluated using tech-
niques similar to those expressed for the germination test, but the RE was counted at 4h.
intervals up to 104h. after the start time. Calculation of the RE time (tRE), the mean RE
time (MRET) and the time required for 50% of viable seeds to emerge (t50RE), were con-
ducted using GERMINATOR software [46]. The software was used in combination with
the least sum of squares method to find the right parameters to fit the cumulative RE curves
to the four-parameter Hill function.
where y is the cumulative RE percentage at time x (hr.), y0 is the intercept on the y axis
(≥ 0), a is the maximum cumulative RE percentage (≤ 100), b is controlling the shape and
steepness of the curve and c is the t50RE. The MRET describes the average time for a seed
to RE, or the delay (lag period) from the start of imbibition to RE. In Fig.4a, seed lot has
the longest average delay (high MRET), is the latest to start to germinate and has the great-
est spread of RE over time. Following the seed ageing/repair hypothesis [6], the lower the
values of MRET and t50RE are the better the seed quality (high seed vigor).
Scanning Electron Microscopy (SEM)
Plasma-treated and non-treated rice seeds with a moisture content of 5 8% were attached
to aluminum stubs, sputtered with platinum in a vacuum evaporator, and visualized with a
scanning electron microscope (S-4800, HITACHI, Japan).
Nutrient Contents
Seed moisture content was evaluated from three hundred grams of rice seed samples using
the analytical methods adopted by the Association of Official Analytical Chemists [47].
The major nutrients, carbohydrate, fat, and protein, were analyzed according to the in-
house method TE-CH-042 based on AOAC [48].
Statistical Analysis
The data reported in this article are the means of quadruplicate analyses, along with their
standard errors. To determine the significance of the differences between the means, one-
way ANOVA and Tukey’s HSD post hoc tests were performed for analytical analysis. The
threshold for a substantial difference was set at 5%. The applications of these statistical
analyses were carried out using the R software package [49].
y
=y0+ax
b
c
b
+x
b
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Results andDiscussion
Application oftheSCP andDBD Plasma forRice Seed Enhancement
Responses of rice seed quality to large-scale SCP and DBD plasma were determined by
following the sequence in the methodology. Figure3a shows the effects of plasma on the
RE percentage of rice seeds after DBD and SCP treatments. The 100 rice seeds were sepa-
rately exposed to DBD and SCP plasma for 10 and 2min, respectively. Then, the RE test
was performed immediately after the plasma treatments in accordance with ISTA guide-
lines [9], with four replicates of each treatment (see also Materials and Methods). RE was
counted after producing a 2 mm radicle (Fig.3d and e). GERMINATOR software [46]
was utilized to calculate the tRE, t50RE, and MRET, indicating the seed vigor level (Fig.4a
and b). The results showed that plasma-treated seeds require less tRE than non-treated
seeds (Fig.3a). For example, at 55h., after the set time the percentage of RE of DBD- and
Fig. 3 Seed vigor and quality enhancement via electrical discharge plasma. a Single counts of radicle emer-
gence in rice seed (Oryza sativa L.) after cold plasma process. b Radicle emergence time (t50RE) and mean
radicle emergence time (MRET) of treated rice seeds. c Germination percentage and seedling length of rice
seeds after cold plasma treatment. d, e Representative picture of radicle emergence at 55h and 77 h after
beginning to germinate of DBD-treated seeds, respectively (scale bar 3.5cm). f Representative pictures of
seedlings following the control, DBD treatment and SPC treatment; from left to right (scale bar 3.5cm).
The error bar denotes the standard error (n = 4). Means within a column of each bar with the same lower-
case letters are not significant at p ≤ 0.05 based on Tukey’s honest significant difference test
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SCP-treated seeds was 18.5% and 24.5%, respectively, while that of non-treated seeds was
only 8.25%. From seed aging/repair hypothesis, the RE speed would imply the vigor and
field emergence of indica rice seed [8, 50]. DNA repair mechanisms can reverse damage
to cellular components, restoring cellular function prior to the initiation of RE and growth
post-germination [44]. DNA repair is linked to the cell expansion in RE in the many spe-
cies including rice seeds [44]. This can delay RE and field establishment of grain crops
[6, 45]. Based on this hypothesis, the results suggested that both SCP and DBD provide
higher seed vigor than non-treated seeds. Figure3b. shows the effect of plasma treatment
on RE time. The results showed that the SCP-treated rice seeds had the lowest t50RE, ~ 62h.
(Fig.3b left, blue). However, there was no significant difference in t50RE between DBD-
treated seeds (red color) and non-treated seeds (black color), at approximately 70h. The
MRET of all conditions was similar to the t50RE, indicating no significant deviation of RE
between seed lots. Thus, the overall result confirms that the SCP strongly impacts rice seed
functionalization and modification, resulting in higher seed vigor enhancement. Interest-
ingly, the germination percentage after DBD and SCP treatments was not different from
non-treated seeds (control) (Fig.3c-left). The germination percentage was approximately
92%, which is the typical percentage of good seed quality [6, 27]. On average, 14-day seed-
lings of plasma-treated seeds showed longer shoot lengths than the control group. Statisti-
cally significant increases in shoot length were observed in response to the DBD plasma
treatment (Fig.3c). The large-scale SCP and DBD plasma had no effect on root and shoot
growth of rice seeds. Seedlings showed all their essential structures that well developed
and healthy (Fig.3f). Thus, the results indicated that neither plasma treatment harmed the
seeds but improved the characteristics of seedling growth. Seed vigor enhancement via
plasma treatments demonstrates its ability to yield vigorous seedlings that become robust
and uniform plants.
Evaluation ofthePost‑discharge Reaction onRice Seed Surface Morphology
andPhysicochemical Alteration
The overall result suggests that both electrical discharge plasma, SCP and DBD, can
enhance rice seed vigor via surface modification and functionalization. Thus, to gain
Fig. 4 Rice seed vigor test using GERMINATOR software via cumulative radicle emergence curves. a
Cumulative radicle emergence data is used as input for the curve fitting module. Multiple radicle emergence
parameters are automatically extracted. Gmax indicates the maximum germination capacity of a seed lot.
The time required for 50% of viable seeds to germinate and mean radicle emergence time are the t50RE
and MRET, respectively. b Cumulative radicle emergence curves of (red) non-treated, (blue) after 2 min
streamer corona plasma treatment and (green) after 10 min dielectric barrier discharge seed. Error bars
denote the confidence intervals error bars (n = 4; p < 0.05); missing error bars indicate that they are smaller
than the symbols
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deeper insight into their interactions and mechanisms on the seed surface, SEM was
employed to examine rice seed morphology after plasma applications. Figure5a demon-
strates the natural rice seed morphology (before the plasma process), showing small nee-
dle-like features on the entire seed surface with a thin seed coat covering the seed (Fig.5b).
It was observed that after plasma treatments, some needle-like structures were damaged
or broken (Fig.5c and e) during the nanoscale plasma etching process [32]. Furthermore,
both plasma-treated seeds had smoother surfaces (Fig.5d and f) than the non-treated seeds
(Fig.5b) and had a cleaner surface without epicuticular wax that decrease surface wetting
and moisture loss of rice seeds. Seed surface erosion presented in the SEM image indicates
that the seeds interacted with active plasma species, the electric field, oxygen radicals and,
bombarded ions during treatment, resulting in modifications of the seed coat. Figure5g
demonstrates the overall physicochemical interaction of plasma on the seed surface, which
increases hydrophilicity and water permeability, both of which are crucial factors for seed
germination [51]. Electrical discharge plasma-induced seed surface modification involves
several physical and chemical processes. For example, a built-in high electric field, 105V/
cm in the electrical charge plasma system [31], can enhance the high energy electron injec-
tion and consequently impact the ionization process [16, 31], leading to several RONS and
ion generation depending upon the operational gas ambient conditions [5, 21, 37]. Fur-
thermore, the bombardment of highly energetic ions and particles plays an essential role
in morphological alterations via surface etching [37] which causes ruptures of the surface
membrane, potentially facilitating water absorption. Several RONS and active ions, such
as NO, N2O, ·OH, O3 and H2O2, are responsible for surface functionalization, for example,
by increasing polar groups such as carbonyl, carboxyl, hydroxyl, and amino groups on the
seed surface [21, 52]. Furthermore, it has been shown that lipid peroxidation following
Fig. 5 Rice seed surface morphology and physicochemical interaction of plasma. SEM images of the rice
seed surface a, b before plasma treatment, c, d after DBD plasma treatment and e, f after SCP plasma treat-
ment. The scale bars on the left and right images represent 500µm and 100μm, respectively. g The overall
physicochemical interaction of plasma on the seed surface increases the hydrophilicity and water perme-
ability, which are essential factors for seed germination. h The primary nutritional content in the seeds after
plasma processes. The vertical bars represent the standard error of the means
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plasma therapy might cause oxidative damage to the membrane bilayer [53, 54] resulting in
enhanced water permeability and thus enhanced imbibition.
In terms of seed vigor enhancement, RONS can infiltrate seeds, which promotes physi-
ological responses [18, 55]. Typically, the seed coat characteristics and its permeability
to water and oxygen are involved in the germination process [56]. Thus, enhanced seed
imbibition can resume the metabolism of quiescent seeds and stimulate embryo rehydra-
tion and metabolism activation [18, 51]. Furthermore, the germination of a seed involves
a complex network of plant hormones such as abscisic acid (ABA), gibberellic acid (GA),
brassinosteroids, ethylene, and auxin [21, 57]. Specifically, ABA and GA play an important
role in the process, ABA inhibits seed germination during embryo maturation, while GA
enhances the germination process [21, 57]. Direct plasma treatment of seeds in ambient air
allows the seed to be exposed to ions and the electric field and a mixture of short-lived and
long-lived RONS (e.g., NO, NO2, NO3, O, OH, O3, H2O2) (Fig.5g). Therefore, by modi-
fying cell wall polysaccharides, RONS can increase germination by weakening the seed
coat. H2O2 and NOx may affect ABA levels, limiting dormancy while promoting GA bio-
synthesis for germination. [21, 37, 57, 58]. Additionally, by modulating NO levels through
NO2, NO3 in seeds ABA levels are reduced while GA levels are increased [21, 58]. As
a result, seed vigor and germination processes are improved, even in a large-scale SCP
system that simultaneously rendered 10,000–20,000 rice seeds. Although plasma treatment
can enhance seed vigor and surface modification, it raises an obvious concern about the
primary nutritional content in the seeds. Thus, seed nutritional contents were investigated
after plasma treatments. Figure5h shows that the carbohydrate, fat, and protein contents of
plasma-treated seeds, as well as the seed moisture content, were not significantly different
from those of non-treated seeds. The results suggest that plasma can improve seed vigor
primarily through surface functionalization but has no adverse effects on seed nutrition.
Conclusions
In conclusion, this research has shown that large-scale electrical discharge plasma treat-
ments (SCP and DBD) can significantly enhance the vigor of rice seeds and the growth
parameters of seedlings compared with untreated seeds. The morphological change of the
rice seed surface demonstrated the effectiveness of plasma interaction on the seed surface,
resulting in improved water uptake and the permeability of the seeds and thus triggering
the initiation of germination and eventually becoming an essential factor affecting fast radi-
cle emergence (RE) and germination parameters. Plasma-treated seeds required ~ 13% less
RE time than non-treated seeds at 55h. after the set time, while the final germination per-
centage of plasma-treated and non-treated seeds was not significantly different. The overall
results indicate that both electrical discharge plasma treatments do not harm seeds and have
become potential alternative seed enhancement methods in seed technology.
Acknowledgements The Rice Department, Ministry of Agriculture and Cooperatives (Thailand) kindly
provided the rice seed samples used in this research.
Author Contributions TR and SS were involved in the conceptualization, methodology, investigation, and
writing of the original draft. DO was involved in the conceptualization, methodology, review, writing and
editing. TR and SS contributed equally to this work.
Funding This project is funded by National Research Council of Thailand (NRCT) and Kasetsart Univer-
sity: N42A650281and partially supported by the Kasetsart University Research and Development Institute
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
1138
Plasma Chemistry and Plasma Processing (2022) 42:1127–1141
1 3
(KURDI). S. Srisonphan acknowledges the funding support from the NSRF via the Program Manage-
ment Unit for Human Resources & Institutional Development, Research and Innovation [grant number
B05F640160].
Data Availability The data that support the findings of this study are available from the corresponding
author upon reasonable request.
Declarations
Conflict of interest The authors declare that they have no known competing financial interests or personal
relationships that may have appeared to influence the work reported in this paper.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Com-
mons licence, and indicate if changes were made. The images or other third party material in this article
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material. If material is not included in the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly
from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.
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... Molina et al. [41] proved that during plasma exposure of wheat seeds, dissociation of water molecules is predominating over processes involving air impurities, resulting in higher intensities of OH bands. The fingerprints of NO•, OH and O• were also detected by Nishime et al. [42] using a coaxial dielectric barrier discharge reactor used for treatment of winter wheat seeds, Rahman et al. [43] using a low pressure dielectric barrier discharge in Ar/O 2 and Ar/Air to treat wheat seeds, Rongsangchaicharean et al. [44] using a streamer corona plasma (SCP) and dielectric barrier discharge (DBD) to treat rice seeds, Adhikari et al. [45] using a cold plasma air-jet instrument to prime tomato seedlings, Sarinont et al. [46] using a scalable dielectric barrier discharge device to treat seeds of radish sprouts, Gao et al. [47] using a dielectric barrier discharge plasma reactor to treat pea seed or tap water, Guragain et al. [48] using a gliding arc discharge reactor used to treat water, and Billah et al. [49] using a dielectric barrier discharge air plasma. ...
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