**2.1. Plasma device**

radio-

of radishes (*Raphanus sativus*) and two pea cultivars (*Pisum sativum* cv. "Little Marvel" and *P.* 

in germination [1]. Since then, investigators focused on the following main fields: (1) decontamination of seeds by plasma, (2) breaking of dormancy with plasma, (3) the impact of plasma treatment (PT) on the rate and kinetics of germination, and (4) impact of PT on the root genera-

Decontamination and inactivation of pathogenic microorganisms of seeds by PT have been communicated recently by various groups [2, 3, 5, 6]. Nishioka et al. reported the effectiveness of low-pressure plasma treatment in the inactivation of the seed-borne plant pathogenic bacteria [6]. Researchers reported the impact of PT on germination, sprouting, and dormancy breaking of seeds. Sera et al. investigated the influence of PT on wheat and oat germination. The authors reported that PT did not affect germination of oat seeds, but they did note accelerated root generation in plants grown from plasma-treated seeds [7]. The same group also communicated that PT did change seed germination in Lamb's Quarters seeds [8]. Similar

In contrast, Ji et al. communicated the significant improvement of the germination rate of *Coriander sativum* under nonthermal atmospheric pressure treatment [10]. Dhayal et al. showed about 50% increase in the germination rate, and the activity was increased twice after plasma treatment of safflower [11]. The essential augmentation of the germination rate by low-temperature plasma treatment was registered by Stolárik et al. for pea (*Pisum sativum* L. var. Prophet). Stolárik et al. related the observed effect to the chemical modification of the pea surface by plasma [12]. These results support the observations of the modification of the physical structure of seed coat by the low-pressure argon gas discharge reported

A stimulating effect of cold plasma on both the germination and sprouting of tomato seeds (*Lycopersicon esculentum L. Mill*. cv. "Zhongshu No. 6") has been reported [13]. Similar results were reported for *Pauwlonia tomentosa* seeds [14]. Kitazaki et al. studied growth

frequency plasma irradiation [15]. Dobrin et al. reported that the roots and sprouts of plasma-treated wheat seeds (*T. aestivum*) were longer and heavier than those of the nontreated seeds [9]. The improvement of the germination rate of the seeds of legumes and grain crops (*Lupinus angustifolius* (blue lupine), *Galega virginiana* (catgut), and *Melilotus albus* (honey clover and soy)) by low-pressure (5.28 MHz) plasma was reported by Filatova

The experimental results revealed that oxygen-related radicals strongly enhance growth, whereas ions and photons do not [15]. The positive effect of cold helium plasma treatment on seed germination, growth, and yield was reported recently for wheat [17]. Treatment of spinach seeds by magnetized arc plasma increased the germination rate by 137% [18]. It has been demonstrated that cold atmospheric plasma treatment had little effect on the final germination percentage of radish seeds, but it influenced their early growth [19]. The contradictory data related to the impact of plasmas on the seed germination were summarized in the recent review

enhancement of radish sprouts (*Raphanus sativus* L.) induced by low-pressure O2

results were reported for wheat seeds (*Triticum aestivum*) by Dobrin et al. [9].

and octadecafluorodecalin plasma and observed an essential delay

*sativum* cv. "Alaska") to CF<sup>4</sup>

tion (sprouting).

124 Advances in Seed Biology

by Dhayal et al. [11].

et al. [16].

Plasma treatment (PT) was carried out with the plasma unit EQ-PDC-326 manufactured by MTI Co., USA. The scheme of the experimental unit used for plasma treatment of the seeds is depicted in **Figure 1**. The unit generates the inductive plasma discharge [26].

#### **2.2. Seed materials and plasma gases**

Seeds of tomato (Efrat-70, *Solanum lycopersicum*) and pepper (Roni-272, *Capsicum annuum*) were supplied by Hazera Co. (Israel).

Dry air (99.999%) was supplied by Mifalei Hamzan Co. (Israel).

**Figure 1.** Plasma unit used for treatment of seeds.

#### **2.3. Treatment conditions**

Healthy uniform seeds without visible damages were selected and exposed to the inductive plasma discharge under the following parameters: the plasma frequency was 13.56 MHz (the RF matching is automatic), the pressure was 0.5 Torr, the supplied power of plasma discharge was 18 W, and the volume of the discharge chamber was 45 cm3 .

The parameters of plasma for the used pressure of 0.5 Torr were temperature of electrons (11.76 ± 0.51 eV) and concentration of ions 4.97 ± 1.16 × 10<sup>15</sup>m− <sup>3</sup> (as established with the double Langmuir probe (AlP150, Impedans Ltd. Plasma Measurement, Ireland). The time span of irradiation was varied from 30 to 60 s. During the plasma treatment, the temperature in the discharge chamber was ambient. The seedling measurements and content analyses mentioned in detail below were carried out immediately after the PT of seeds.

#### **2.4. Modeling of water availability conditions**

Water supply to seeds was controlled as follows: the seeds were germinated in 90-mm-diameter Petri dishes. Seedbed was composed in various series of experiments of three filter paper layers (well-watered (WW)), which means nonrestricted water supply); four filter paper layers (medium drought stress (MDS), below in the text); or five filter paper layers (harsh drought stress (HDS), below in the text) of the filter paper (500-H, the thickness was 112 μm, and the maximal pore size was 48 μm).

The stacks were moistened with 4 ml of distilled water (dH2 O) dripped on the stacks by a syringe (see **Figure 2**). The specific conductivity of distilled water was 18MΩ/cm.

Impact of Conditions of Water Supply on the Germination of Tomato and Pepper Seeds http://dx.doi.org/10.5772/intechopen.70386 127

**Figure 2.** Experimental setup for treatment of seeds.

**2.3. Treatment conditions**

**Figure 1.** Plasma unit used for treatment of seeds.

Air

126 Advances in Seed Biology

Healthy uniform seeds without visible damages were selected and exposed to the inductive plasma discharge under the following parameters: the plasma frequency was 13.56 MHz (the RF matching is automatic), the pressure was 0.5 Torr, the supplied power of plasma discharge

plasma

chamber

vacuum pump attachment

The parameters of plasma for the used pressure of 0.5 Torr were temperature of electrons

ble Langmuir probe (AlP150, Impedans Ltd. Plasma Measurement, Ireland). The time span of irradiation was varied from 30 to 60 s. During the plasma treatment, the temperature in the discharge chamber was ambient. The seedling measurements and content analyses men-

Water supply to seeds was controlled as follows: the seeds were germinated in 90-mm-diameter Petri dishes. Seedbed was composed in various series of experiments of three filter paper layers (well-watered (WW)), which means nonrestricted water supply); four filter paper layers (medium drought stress (MDS), below in the text); or five filter paper layers (harsh drought stress (HDS), below in the text) of the filter paper (500-H, the thickness was 112 μm, and the

.

open vessel containing seeds,

the volume is 28 cm3

(as established with the dou-

O) dripped on the stacks by a

was 18 W, and the volume of the discharge chamber was 45 cm3

electrodes

(11.76 ± 0.51 eV) and concentration of ions 4.97 ± 1.16 × 10<sup>15</sup>m− <sup>3</sup>

The stacks were moistened with 4 ml of distilled water (dH2

syringe (see **Figure 2**). The specific conductivity of distilled water was 18MΩ/cm.

**2.4. Modeling of water availability conditions**

maximal pore size was 48 μm).

tioned in detail below were carried out immediately after the PT of seeds.

#### **2.5. Study of the influence of water availability on imbibition**

For the study of the time dependence of seed water absorption (imbibition) by irradiated and nonirradiated tomato and pepper seeds, 100 seeds were placed on humid filter paper stacks in different water conditions (for details see Section 2.4). Seeds were weighed at 1, 3, 6, 9, and 24 hours after plasma treatment with a MRC ASB-220-C2 analytical balance. The relative water imbibition (absorption) was defined as *Δm*(*t*) \_\_\_\_\_ *m*0 100 % = \_\_\_\_\_\_\_ *m*(*t*) − *m*<sup>0</sup> *m*0 100% , where *m*<sup>0</sup> is the total initial mass of seeds and *m*(*t*) is the running total mass of seeds [23]. The comparative study of imbibition was carried out for non-treated pepper/tomato seeds and seeds treated by plasma during 30 and 60s. The experiment was planned with three replications for each treatment.

#### **2.6. Study of influence of water drought and temperature on germination**

For the study of influence of water availability and germination chamber temperature on germination by irradiated and nonirradiated tomato and pepper seeds, 15 pepper/tomato seeds were placed on the upper layer of the filter paper stack and germinated in different water conditions (for details see Section 2.4). The Petri dishes were covered with lids and sealed using a strip of Parafilm in order to prevent water evaporation. Seeds were placed in an incubator at 21 or at 27°C. The incubation cycle included 12 hours of darkness and 12 hours of light per day. The seeds were considered to be germinated when the radicals were half the seed length. The constant conditions of germination were provided by growth chamber model PGI-500H (Illumination 40 W × 5 tubes) (MRC, Israel). The germination percentage was recorded every 24 hours for 12 days in a case of pepper seeds and every 24 hours for 10 days in a case of tomato seeds. The experiment was planned as a completely randomized design with five replications.

The comparative study of germination was carried out for non-treated pepper/tomato seeds and seeds treated by plasma during 30 and 60s.

Germination rate (%) was defined as the number of seeds germinated in 10 or 12 days related to the total number of seeds.
