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Plasma Chemistry and Plasma Processing

, Volume 37, Issue 6, pp 1621–1634 | Cite as

Air Atmospheric Dielectric Barrier Discharge Plasma Induced Germination and Growth Enhancement of Wheat Seed

Original Paper
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Abstract

Air atmospheric dielectric barrier discharge plasma (DBD) was attempted to pretreat wheat seed to improve its germination and growth in this study. The effects of the DBD plasma treatment on the wheat seed germination, seedling growth, osmotic-adjustment products, lipid peroxidation level, and antioxidant enzymes activity were investigated. The experimental results showed that the DBD plasma treatment with an appropriate time scale could promote the wheat seed germination and seedling growth. The germination potential, germination rate, germination index, and vigor index increased by 26.7, 9.1, 16.9, and 46.9% after 7 min’s DBD plasma treatment, respectively; the root length, shoot length, fresh weight, and dry weight of the seedlings also increased after the DBD plasma treatment. The osmotic-adjustment products, proline and soluble sugar contents, in the wheat seedlings were significantly enhanced after the DBD plasma treatment with an appropriate time scale, while the malondialdehyde content decreased. Moreover, the activities of superoxide dismutase and peroxidase also increased after the DBD plasma treatment. The DBD plasma treatment led to etching effect on the wheat seed coat, resulting in the improvement of its water absorption capacity.

Keywords

Dielectric barrier discharge plasma Germination Seedling growth Seed treatment Wheat 

Introduction

Plant seeds were the most important factors influencing crop yield in the agricultural production, the seeds with good quality were generally characterized as high seed vigor, which would germinate rapidly and then grew to uniformity and robust seedlings in fields [1, 2]. The germination and growth states, such as germination rate, emergence rate, full stand, and robust seedlings, were vital to crop yield [3, 4, 5]. Therefore, it is quite important to improve seed vigor and quality in the agricultural production.

Lots of methods have been used to improve the seed vigor, such as chemicals treatment [6, 7], ultrasonic scratching [8], electric field treatment [9], magnetic treatment [10], and ion beam scratching [11]. The chemicals treatments in seeds might bring environmental pollution due to chemical residues, and they were usually time-consuming, labor-intensive, and expensive because of the utilization of lots of chemicals. Therefore, more attention has been paid to the physical treatments recently. The physical treatment could enhance the seed vigor via influencing the biochemical processes, such as proteins and enzymes activity [12]. However, the physical treatments had also some limitations; for instance, strong ultrasonic oscillation or ion beam collision might injure seed cell, increasing the number of destroyed seeds, and it would also result in a relatively higher possibility of non-uniform treatment [8, 9, 10, 11].

Cold plasma was one of the physical methods for seed treatment, composed of ionized gases, radicals, excited atoms, molecules, electrons, and strong electric field. Previous researches have demonstrated that cold plasma treatment could improve seed germination and seedling growth, including Carthamus tinctorium L., wheat, tomato, and soybean [13, 14, 15]. As one kind of the cold plasma, dielectric barrier discharge (DBD) plasma could be easily triggered at a normal pressure and room temperature, and it could generate strong electric field, electrons, and various active species [16]. Previous researches have showed that DBD plasma at a high frequency of approximately 8.0–15.4 kHz could enhance seed germination [17, 18, 19]. In our previous research, DBD plasma with a power–frequency of 50 Hz was attempted to treat wheat seed, and the wheat seed germination and seedling growth were improved [20]; however, the effects of the DBD plasma treatment on the physiological and biochemical processes of the wheat seedling were still unknown.

Therefore, the aim of this study was to explore the influence of DBD plasma treatment with a power–frequency of 50 Hz on the physiological and biochemical processes of the wheat seedling. The germination and growth characteristics, osmotic adjustment ability, membrane lipid peroxidation (MDA), and enzyme activities of the wheat seedlings were evaluated after the DBD plasma treatment. In addition, the effects of the DBD plasma on the wheat seed coat and water absorbing capacity were also evaluated. It was expected to provide an alternative option for seed treatment using DBD plasma.

Materials and Methods

Wheat Seed Sample

The wheat seeds (Xiaoyan 22) were obtained from the Seed Research Institute of Northwest A&F University, China. The wheat seeds were cleaned and air dried, and then stored at 0–5 °C in a refrigerator prior to use.

DBD Plasma Apparatus for Seed Treatment

The DBD plasma apparatus for the wheat seed treatment was illustrated in Fig. 1, which was similar with our previous research [20]. Specially, the reactor vessel was made of a Plexiglas™ cylinder with an inner diameter of 100 mm and height of 8 mm, and the reactor volume was about 62.8 mL. A stainless-steel plate with a diameter of 120 mm and thickness of 2 mm was selected as the high voltage electrode, and a metal net with 40 mesh was selected as the ground electrode. A quartz glass piece with a diameter of 180 mm and thickness of 1.5 mm was selected as the dielectric barrier, which was under the high voltage electrode and contacted with it tightly. For each treatment, 50 wheat seeds were put on the ground electrode and treated by DBD plasma. The power supply was an alternating current with a discharge voltage range of 0–50 kV and a frequency of 50 Hz; the discharge voltage for the seed treatment was 13.0 kV in this study, which was measured across the electrodes; and air was injected into the reactor vessel as the carrier gas with a gas-flow rate of 1.5 L min−1. The DBD plasma treatment time was 0, 1, 4, 7, 10, and 13 min, which was marked as CK, T1, T4, T7, T10, and T13 treatment, respectively. Each treatment was repeated three times. The typical voltage and current waveforms obtained in the DBD plasma system was shown in Fig. 2, and the discharge power at the discharge voltage of 13.0 kV was 1.50 W.
Fig. 1

Schematic diagram of the DBD plasma system for seed treatment

Fig. 2

Typical voltage and current waveforms obtained in the DBD plasma system

Seed Germination Tests

The wheat seeds were soaked in deionized water for 5 h, disinfected for 2 min using 70% alcohol, followed by rinsing in autoclaved distilled water, and then prepared for germination. Seed germination tests were conducted in each petri dish (9 cm) containing two layers of filter paper and 10 mL of deionised water. The seeds from each treatment were tested on three petri dishes with 50 seeds per dish. During germination, autoclaved distilled water was added every other day to maintain constant moisture. The seeds were incubated in a germination incubator at 20 °C, 12 h light/12 h dark photoperiod with a photo flux density of 120 µmol m−2 s−1, and 70% air humidity. The radicle protrusion at 1 mm was recorded as the criterion for germination. The seeds were incubated in the germination incubator for 4 d, and the germination potential was calculated on the 1st day of plant (24 h after plant), and germination rate was calculated on the 4th day of plant. Germination characteristics were calculated using the following equations [21]:
$$ {\text{Germination}}\,{\text{potential}}\, ( {\text{\% )}}\text{ = }\frac{{{\text{number}}\,{\text{of}}\,{\text{seeds}}\,{\text{germinated}}\,{\text{in}}\, 1\,{\text{d}}}}{{{\text{total}}\,{\text{number}}\,{\text{of}}\,{\text{seeds}}}} \times 100\% $$
(1)
$$ {\text{Germination}}\,{\text{rate}}\, ( {\text{\% )}}\text{ = }\frac{{{\text{number}}\,{\text{of}}\,{\text{seeds}}\,{\text{germinated}}\,{\text{in}}\, 4\,{\text{d}}}}{{{\text{total}}\,{\text{number}}\,{\text{of}}\,{\text{seeds}}}} \times 100\% $$
(2)
$$ {\text{Germination}}\,{\text{index}}\text{ = }\sum \left( {{{{\text{G}}_{\text{t}} } \mathord{\left/ {\vphantom {{{\text{G}}_{\text{t}} } {{\text{D}}_{\text{t}} }}} \right. \kern-0pt} {{\text{D}}_{\text{t}} }}} \right) $$
(3)
$$ {\text{Vigor}}\,{\text{index}}\text{ = }{\text{Root}}\,{\text{length}}\,({\text{cm}}) \times \text{Germination index } $$
(4)
where Gt represented number of germinated seeds on the t day, and Dt represented germination days.

Analytical Methods

15 seedlings from each petri dish were randomly taken to measure the total root and shoot length, fresh weight, soluble sugar, proline, MDA, and enzyme activity on the 4th day of plant; subsequently, they were dried overnight in an oven at 80 °C and the dry weight was measured. Proline was measured using ninhydrin spectrophotometry as given by Bates et al. [22], and its concentration was expressed as μmol g−1 fresh weight of the coleoptiles. Soluble sugar was measured using anthrone colorimetry as reported by Ci et al. [23], and its content was expressed as mg g−1 fresh weight of the coleoptiles. MDA was measured using trichloroacetic acid–thiobarbituric acid spectrophotometry as reported by Liu et al. [24], and its content was expressed as μmol g−1 fresh weight of the coleoptiles. For enzymatic activity measurement, the frozen coleoptiles were homogenized with 5% (w/v) polyvinylpyrrolidone, 1.2 mL of 100 mmol L−1 potassium phosphate buffer (pH = 7.0) containing 1 mmol L−1 EDTA, and 1% Triton X-100, and the homogenates were centrifuged at 10,000 rpm for 20 min at 4 °C, and then the supernatant (recorded as crude enzymes) was used for enzymatic activity measurement. Superoxide dismutase (SOD) activity was measured using the method given by Liu et al. [25], and peroxidase (POD) activity was measured using the method given by Chance and Maehly [26]. Scanning electron microscopy (SEM, S-4800, Hitachi) was used to characterize the morphology of the wheat seed coat. The changes of the water absorbing capacity of the wheat seed were calculated as the method given by Yang and Shen [27].

Statistical Analysis

All treatments were conducted at least three replicates. The data in this study were recorded as the mean value ± standard deviation. The SPSS statistical software (Version 16.0) and one-way analysis of variance (ANOVA) were used to confirm the variability of the data and the validity of the results. Differences among treatments were compared using Duncan’s multiple range tests at 0.05 probability level.

Results and Discussion

Effect of the DBD Plasma Treatment on the Wheat Seed Germination

The results of the wheat seed germination potential, germination rate, germination index, and vigor index after the DBD plasma treatment were illustrated in Table 1. The germination potential was 62.5% in the CK treatment, and it significantly increased to 77.5% in the T4 treatment; while there was no significant difference among the T4, T7, T10, and T13 treatments. Similar with the germination potential, an appropriate DBD plasma treatment could improve the germination rate of the wheat seed; approximately 88.0% of the germination rate was obtained in the CK treatment, and it was enhanced to 95.3% in the T4 treatment; however, further increasing the treatment time did not improve the germination rate, and the difference among the T4, T7, T10, and T13 treatments was not significant. On the other hand, the germination index increased from 36.7 in the CK treatment to 41.0 in the T4 treatment, and further increasing the treatment time did not improve the germination index because the difference among the T4, T7, T10, and T13 treatments was not significant. The vigor index increased by 17.5, 28.1, and 46.9% after the T1, T4, and T7 treatments, respectively, compared with the CK treatment; however, the vigor index was about 464.8 in the T13 treatment, and there was a 17.9% decline as compared with that in the T7 treatment.
Table 1

Effect of DBD plasma treatment time on the wheat seed germination

Treatment time (min)

Germination characteristics

Germination potential (%)

Germination rate (%)

Germination index

Vigor index

0 (CK)

62.5 ± 6.1c

88.0 ± 3.5b

36.7 ± 1.0c

385.2 ± 15.4c

1 (T1)

69.8 ± 3.3bc

91.9 ± 1.7ab

39.1 ± 0.7bc

452.6 ± 28.7b

4 (T4)

77.5 ± 4.3ab

95.3 ± 3.2a

41.0 ± 3.5a

493.3 ± 64.8b

7 (T7)

79.2 ± 1.1a

96.0 ± 2.0a

42.9 ± 1.6a

565.8 ± 23.9a

10 (T10)

77.3 ± 5.0ab

94.0 ± 2.0a

41.6 ± 1.7ab

486.9 ± 23.1b

13 (T13)

75.2 ± 3.4ab

90.7 ± 2.3ab

41.4 ± 0.9ab

464.8 ± 51.7b

Lowercase letters a–c in the same column represent significance analysis; the different letters mean significant difference among various treatments at P ≤ 0.05 level

The changes in the wheat seed germination characteristics suggested that there existed an appropriate DBD plasma treatment dose to promote the wheat seed germination. Similar phenomenon was observed by Li et al. [15], in whose research the cold plasma treatment with much lower or higher energy levels did not improve soybean germination, and only appropriate cold plasma dose promoted seed germination. Tong et al. [21] also reported that Andrographis paniculata germination potential was enhanced by a DBD plasma treatment with an appropriate dose or intensity.

A brief comparison on seeds treatment by the cold plasmas has been summarized in Table 2. The germination potentials of the wheat seed and oilseed rape seed were enhanced by 6 and 6.7% after 15 s’ radio frequency plasma treatment, respectively [29, 30], while it took 30 min to improve the germination potential of the Carthamus tinctorium L. seed by 6% [28]. The germination potentials of chenopodium album seed and oat seed were also different after the microwave plasma treatment [14, 31]. The germination potential of tomato seed increased by 28% after 10 s’ magnetized plasma [32]. The germination potential of the wheat seed in this study was comparable with that of pea seed, while their discharge powers were quite different [33]. These different results suggested that the enhancement effect in seed germination was dependent on seed species to a certain extent. Previous research has reported that active particles generated by the cold plasma could penetrate through the seed coat and directly influenced cells inside the seeds; while the seed coat operated like a partially permeable membrane, which only allowed passage of certain small ions or particles [14]. The thickness of the seed coat was quite different among seed species, which showed different barrier effects for active particles penetration, and thus affecting their germination. Hence, it is necessary to optimize the operation conditions for seed treatment by the cold plasma.
Table 2

A brief comparison on seeds treatment by cold plasmas

Plasma types

Seed species

Treatment time

Improvement in germination potential (%)

Frequency

References

Radiofrequency plasma

Carthamus tinctorium L.

30 min

6

13.56 MHz

[28]

Radiofrequency plasma

Wheat

15 s

6

3 × 109 MHz

[29]

Radiofrequency plasma

Oilseed rape

15 s

6.7

13.56 MHz

[30]

Microwave plasma

Chenopodium album

30–48 min

40

2.45 MHz

[31]

Microwave plasma

Oat

20 min

22.2

2.45 MHz

[14]

Magnetized plasma

Tomato

10 s

28

–

[32]

DBD

Pea

2 min

17.5

14 kHz

[33]

DBD

Wheat

7 min

16.7

50 Hz

This study

Effect of DBD Plasma Treatment on the Wheat Seedling Growth

Root length, shoot length, fresh weight, and dry weight of seedlings were important indexes to characterize the seedling growth. The results of the wheat seedling growth characteristics were illustrated in Table 3. The root length was 1573.7 mm in the CK treatment, and it significantly increased to 1979.7 mm in the T7 treatment, while it further decreased to 1685.3 mm in the T13 treatment; that is, there existed an appropriate plasma dose to promote the root growth. Similarly, the shoot length was approximately 468.8 mm in the CK treatment, and it was significantly enhanced to 490.9 mm in the T4 treatment; while further increasing the treatment time did not improve the shoot length, and the difference among the T4, T7, T10, and T13 treatments was not significant. On the other hand, the fresh weight of the seedlings increased from 1.9375 g in the CK treatment to 2.2049 g in the T4 treatment, and further increasing the treatment time did not improve the fresh weight because the difference among the T4, T7, T10, and T13 treatments was not significant. Similar with the changes of the fresh weight, the highest dry weight was also obtained in the T4 treatment, as shown in Table 3. These results suggested that an appropriate DBD plasma treatment dose was necessary to promote the wheat seedling growth.
Table 3

Effect of DBD plasma treatment time on the wheat seedling growth

Treatment time (min)

Growth characteristics

Root length (mm)

Shoot length (mm)

Fresh weight (g)

Dry weight (g)

0 (CK)

1573.7 ± 79.8c

468.8 ± 5.6b

1.9375 ± 0.0566b

0.6778 ± 0.0058c

1 (T1)

1737.0 ± 58.9b

481.6 ± 3.0ab

2.1299 ± 0.0903ab

0.7063 ± 0.0424abc

4 (T4)

1759.3 ± 46.4b

490.9 ± 5.1a

2.2049 ± 0.1487a

0.7223 ± 0.0093ab

7 (T7)

1979.7 ± 68.4a

478.9 ± 14.6ab

2.0960 ± 0.0641ab

0.6979 ± 0.0085abc

10 (T10)

1754.3 ± 55.2b

486.7 ± 25.5a

2.1091 ± 0.0705ab

0.6790 ± 0.0241bc

13 (T13)

1685.3 ± 30.4b

485.6 ± 9.5a

2.0474 ± 0.1772ab

0.7288 ± 0.0341a

Lowercase letters a–c in the same column represent significance analysis; the different letters mean significant difference among various treatments at P ≤ 0.05 level

Lots of researches have demonstrated that the cold plasma treatment could promote seedling growth of plants; Dhayal et al. [28] reported that the seedling growth of Carthamus tinctorius L. was significantly enhanced by a cold plasma treatment; Zhou et al. [34] observed that the tomato seedling growth was improved by an atmospheric pressure plasma treatment; Sera et al. [14] also found that wheat and oat seedling growth was enhanced by a cold plasma treatment. Moreover, Li et al. reported that a cold plasma treatment with an appropriate energy level promoted the soybean seedling growth, while much lower or higher energy levels did not show any promoting effects [15].

Effects of DBD Plasma Treatment on Proline and Soluble Sugar Levels in the Wheat Seedlings

Proline and soluble sugar were two important components participating in osmotic protection for plants; lots of plants could alter their osmotic adjustment abilities by accumulating proline and soluble sugar levels when the outside environment changed [24, 35]. To study the effects of DBD plasma treatment on osmotic adjustment abilities of the wheat seed, the evolutions of proline and soluble sugar levels in the wheat seedling were evaluated, and the results were illustrated in Fig. 3. On the one hand, DBD plasma treatment with an appropriate time scale could promote the generation of proline; the proline content was about 0.115 μmol g−1 FW in the CK treatment, and it significantly increased to 0.400 μmol g−1 FW in the T4 treatment; however, further increasing the treatment dose could not improve the proline formation, and the difference among the T4, T7, T10, and T13 treatments was not significant. On the other hand, the soluble sugar level also significantly increased to 5.40 mg g−1 FW in the T4 treatment, compared with that in the CK treatment (approximately 3.42 mg g−1 FW); whereas the changes of the soluble sugar levels among the T4, T7, T10, and T13 treatments were not significant.
Fig. 3

Evolution of proline and soluble sugar level with DBD plasma treatment time (lowercase letters a–b in the same column represent significance analysis; the different letters mean significant difference among various treatments at P ≤ 0.05 level)

The evolutions of proline and soluble sugar levels in the wheat seedling after the DBD plasma treatments suggested that the DBD plasma treatment with an appropriate time scale was able to promote the osmotic adjustment abilities of the wheat seedling. Previous research has demonstrated that physical treatment on seeds was able to improve the proline content in the maize seedlings [36]. Chen et al. [37] found that the soluble sugar level in brown rice was enhanced after a cold plasma treatment. Li et al. [30] also observed that the soluble sugar level in oilseed rape significantly increased after a cold plasma treatment.

Effect of DBD Plasma Treatment on MDA Level in the Wheat Seedlings

The changes of outside environment could affect enzymatic and non-enzymatic anti-oxidative reaction systems; in certain conditions, lots of reactive oxygen species would generate via auto-oxidation reactions of lipids, resulting in damage to the membrane lipids [35, 38]. MDA was generally measured as an indicator of the membrane lipid peroxidation and membrane damage [30]. To study the effect of DBD plasma treatment on membrane damage of the wheat seed, the evolution of MDA level in the wheat seedling was evaluated, and the result was illustrated in Fig. 4. As could be seen, the MDA level was significantly reduced after the DBD plasma treatment with an appropriate time scale; the MDA content was approximately 0.817 μmol g−1 FW in the CK treatment, and there were approximately 15.3% and 26.1% declines in the T4 and T10 treatments, respectively. These results indicated that the DBD plasma treatment with an appropriate time scale could promote the wheat seed germination and seedling growth by reducing the membrane damage derived from the membrane lipid peroxidation. Similar phenomenon was observed by Yin et al. [32], in whose research the MDA level in tomato seedlings decreased after a cold plasma treatment. Tong et al. [21] also reported that the MDA level in Andrographis paniculata seedlings significantly decreased after an air plasma treatment. In addition, Li et al. [30] reported that the MDA level in oilseed rape seedlings increased under drought stress, but it was significantly reduced after a cold plasma treatment.
Fig. 4

Evolution of MDA content with DBD plasma treatment time (lowercase letters a–d in the same column represent significance analysis; the different letters mean significant difference among various treatments at P ≤ 0.05 level)

Effects of DBD Plasma Treatment on Antioxidant Enzymes Levels in Seedlings

Plants could adjust the activities of the antioxidant systems to improve their adaptation to the changes of the outside environment; in this case, several antioxidant enzymes, such as SOD and POD, would increase [32, 35]. The SOD could convert the reactive oxygen species O2·− to H2O2, and H2O2 would be further converted to O2 and H2O molecules by POD; and thus the damage of the reactive oxygen species to the membrane lipids would reduce [30, 32, 35, 36]. To study the effects of DBD plasma treatment on antioxidant enzymes levels in the wheat seedlings, the evolutions of SOD and POD in the wheat seedlings were evaluated, and the results were illustrated in Fig. 5. On the one hand, the SOD level in the wheat seedlings firstly increased to a certain extent and then decreased with the increase of DBD plasma treatment dose; for instance, the SOD content was about 125.4 U g−1 FW in the CK treatment, and it significantly increased to 151.5 U g−1 FW in the T4 treatment; whereas the difference among the T4, T7, and T10 treatments was not significant; however, there was approximately 11.0% decline in the SOD content in the T13 treatment, compared with that in the T4 treatment. On the other hand, there existed an appropriate DBD plasma treatment dose to improve the POD level in the wheat seedlings; the POD content was about 5.5 U g−1 FW min−1 in the CK treatment, and it significantly increased to 10.2 U g−1 FW min−1 in the T4 treatment; however, there was approximately 17.6% decline in the POD content in the T13 treatment, compared with that in the T4 treatment.
Fig. 5

Evolution of SOD and POD activities with DBD plasma treatment time (lowercase letters a–d in the same column represent significance analysis; the different letters mean significant difference among various treatments at P ≤ 0.05 level)

These results indicated that the DBD plasma treatment with an appropriate time scale could promote the activities of the antioxidant systems in the wheat seedlings, improved their adaptation to the changes of the outside environment, reduced oxidative damage and helped to maintain normal physiological metabolic activities. Similar phenomena were observed by Henselova et al. [19], in whose research the SOD activity in maize seedlings was enhanced after a low-temperature plasma treatment. Li et al. [30] also reported that cold plasma treatment could enhance the SOD activity in oilseed rape seedlings. In addition, Yin et al. [32] found that the POD activity in tomato seedlings was improved after a magnetized plasma treatment.

Analysis on the DBD Plasma Roles

Previous researches have demonstrated that cold plasma-induced reactions on seed coat could lead to etching effect on the seed coat, and then some active species would penetrate into the seeds, which might benefit physiological reactions [14, 39, 40]. To explore the effect of DBD plasma treatment on the morphology of the wheat seed coat, SEM was used to examine the changes of the morphology of the wheat seed coat, and the results were illustrated in Fig. 6. Some square mesh structures were clearly observed on the seed coat before the DBD plasma treatment (Fig. 6a), while these square mesh structures were destroyed gradually with the DBD plasma treatment time continued, and the boundary layer was difficult to identify after 10 min of treatment (Fig. 6e). Furthermore, cracks were obviously observed on the seed coat after the DBD plasma treatment, as shown in Fig. 6f.
Fig. 6

SEM photographs of the wheat seed coat

These results suggested that etching effect on the seed coat occurred during the DBD plasma treatment in this study, which might benefit the seed germination. Filatova et al. [41] reported that etching effect derived from discharge plasma such as ionized molecular nitrogen N2 + and ionized O2 + played important roles in stimulating the biochemical processes of seeds and influencing seed germination. Similar phenomena were also observed by Tong et al. [21], who reported that relative electroconductivity of seeds was improved after an air plasma treatment due to the etching effect of the air plasma.

The seed coat of plants may impede their capacity for water absorption, affecting seed germination [33]. To explore the effect of DBD plasma treatment on the water uptake of the wheat seed, the evolution of the water uptake with the DBD plasma treatment dose was illustrated in Fig. 7. The water uptake firstly increased to a certain extent and then decreased with the increase of the DBD plasma treatment dose; for instance, the water uptake was approximately 41.2% in the CK treatment, and it significantly increased to 61.6% in the T7 treatment; however, it decreased to 55.4% in the T13 treatment. These results suggested that DBD plasma treatment with an appropriate time scale could promote the water absorption capacity of the wheat seeds, and thus benefited seed germination and seedlings growth. Filatova et al. found that cold plasma treatment could improve the water absorption of grains and legumes seeds [41].
Fig. 7

Evolution of water uptake of the wheat seeds with DBD plasma treatment time (lowercase letters a–d in the same column represent significance analysis; the different letters mean significant difference among various treatments at P ≤ 0.05 level)

Some O-containing species and N-containing species would generate in the discharge plasma system [42], which probably affect the wheat seed germination and seedling growth. Previous researches have demonstrated that some active ions and radicals in the discharge plasma process penetrated into the seed coat, and then influenced several physiological actions in plants [39, 40]. Sera et al. [14] found that the phenolic compounds contents in the wheat and oat seeds were changed after a discharge plasma treatment, and they attributed these changes to the reactions of active species. Bormashenko et al. [43] reported that the germination rate of the oat seed was improved after the radiofrequency plasma treatment, and they attributed the improvement to the active species oxidation derived from the discharge plasma. Ji et al. [17] reported that the plasma-generated nitric oxide was a crucial regulator for cellular activation, which could improve the coriandum sativum seed germination.

In this study, we measured the ozone concentration at the outlet of the reactor, it was approximately 0.12 g m−3 at the discharge voltage of 13.0 kV, and it did not increase in the T1-T13 treatments; therefore, the differences in the germination characteristics among the T1-T13 treatments could not be attributed to ozone concentration although the ozone could participate in the oxidation processes. It must be noted that NOx generated in the discharge plasma process probably affect seed germination. Kitazaki et al. [18] measured the ozone and NOx concentrations in the discharge plasma process, and reported that there was a little direct correlation between these species concentration and the growth enhancement; however, it was difficult to distinguish them; and they attributed the enhancement to the synergetic effects of plasma particles.

Therefore, due to the etching and oxidation effects derived from the electrons and reactive species, the water absorption capacity, osmotic adjustment substances, and antioxidant enzymes activities of the wheat seed were improved after the DBD plasma treatment, and then its germination and seedling growth were promoted.

Conclusions

Air atmospheric dielectric barrier discharge plasma induced germination and growth of wheat seeds was investigated in this study. The germination potential, germination rate, germination index, and vigor index were all improved after the DBD plasma treatment with an appropriate time scale, as well as the seedlings length and weight. The DBD plasma treatment resulted in etching and oxidation effects on the wheat seed coat, improved its water absorption capacity, increased the proline and soluble sugar generation, promoted the antioxidant enzymes activities, and reduced MDA accumulation. These findings suggested that the DBD plasma affected not only the wheat seed coat, but was also involved in some physiological reactions inside the seed. Therefore, the DBD plasma might be an alternative option for wheat seed improvement.

Notes

Acknowledgements

The authors thank the Projects funded by State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau (A314021402-1520), Institute of Soil and Water Conservation (A315021525), the National Natural Science Foundation, P.R. China (51608448), and Fundamental Research Fund for the Central Universities (Z109021617) for the financial supports to this research.

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Copyright information

© Springer Science+Business Media, LLC 2017

Authors and Affiliations

  • Yujuan Li
    • 1
    • 2
  • Tiecheng Wang
    • 1
    • 2
    • 3
  • Yiran Meng
    • 1
    • 2
  • Guangzhou Qu
    • 1
    • 2
  • Qiuhong Sun
    • 3
  • Dongli Liang
    • 1
    • 2
  • Shibin Hu
    • 1
    • 2
  1. 1.College of Natural Resources and EnvironmentNorthwest A&F UniversityYanglingPeople’s Republic of China
  2. 2.Key Laboratory of Plant Nutrition and the Agri-environment in Northwest ChinaMinistry of AgricultureYanglingPeople’s Republic of China
  3. 3.State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water ConservationNorthwest A&F UniversityYanglingPeople’s Republic of China

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