**3. Results**

#### **3.1. Seed water imbibition**

The previous findings suggest acceleration in the water uptake of PT tomato seeds, under MDS and HDS water conditions compared to non-treated seeds [22, 23]. It is distinctly seen that the fastest water imbibition was observed for 30s plasma-treated seeds (see **Figure 3**). In the case of pepper seeds, the rate of water imbibition is almost the same in plasma-treated and non-treated samples (see **Figure 4**). Under free water supply conditions (WW), the imbibition of PT seeds and non-treated seeds is almost the same for both cultivars.

In addition, it is distinctly seen that the fastest water imbibition was observed under free water supply conditions (WW), and the slowest water absorption was registered under HDS conditions for both cultivars in non-treated and plasma-treated seeds (see **Figures 3** and **4**). The water availability is an important factor influencing the rate of water imbibition.

#### **3.2. Seed germination**

Positive influence of the cold plasma treatment on the germination rate and on the kinetics of germination was recorded for the pepper and tomato seeds under the conditions of medium and harsh drought stress (see **Figures 5** and **6**; **Table 1**) at temperature of 21°C. The change in the germination rate (denoted by *Vi* (viability) in **Table 1**) was much more pronounced for tomato seeds when compared to the pepper ones. Under MDS and HDS water conditions, the germination rate of non-treated seeds was significantly reduced by 8 and 11%, respectively, for tomato seeds and by 1 and 13% for pepper seeds, compared to the well-watered

**Figure 3.** Comparative study of water imbibition by non-treated and 30s plasma-treated tomato seeds under WW, MDS, and HDS conditions.

**3. Results**

128 Advances in Seed Biology

**3.1. Seed water imbibition**

**3.2. Seed germination**

**0**

and HDS conditions.

**20**

**40**

**60**

**Dm/m·100,** 

**%**

**80**

**100**

**120**

The previous findings suggest acceleration in the water uptake of PT tomato seeds, under MDS and HDS water conditions compared to non-treated seeds [22, 23]. It is distinctly seen that the fastest water imbibition was observed for 30s plasma-treated seeds (see **Figure 3**). In the case of pepper seeds, the rate of water imbibition is almost the same in plasma-treated and non-treated samples (see **Figure 4**). Under free water supply conditions (WW), the imbibition

In addition, it is distinctly seen that the fastest water imbibition was observed under free water supply conditions (WW), and the slowest water absorption was registered under HDS conditions for both cultivars in non-treated and plasma-treated seeds (see **Figures 3** and **4**).

Positive influence of the cold plasma treatment on the germination rate and on the kinetics of germination was recorded for the pepper and tomato seeds under the conditions of medium and harsh drought stress (see **Figures 5** and **6**; **Table 1**) at temperature of 21°C. The change in the germination rate (denoted by *Vi* (viability) in **Table 1**) was much more pronounced for tomato seeds when compared to the pepper ones. Under MDS and HDS water conditions, the germination rate of non-treated seeds was significantly reduced by 8 and 11%, respectively, for tomato seeds and by 1 and 13% for pepper seeds, compared to the well-watered

**0 246 8 10 12 14 16 18 20 22 24**

non-treated (WW) 30 s plasma treated (WW) non-treated (MDS) 30 s plasma treated (MDS) non-treated (HDS) 30 s plasma treated (HDS)

**time, h**

**Figure 3.** Comparative study of water imbibition by non-treated and 30s plasma-treated tomato seeds under WW, MDS,

The water availability is an important factor influencing the rate of water imbibition.

of PT seeds and non-treated seeds is almost the same for both cultivars.

**Figure 4.** Comparative study of water imbibition by non-treated and 60s plasma-treated pepper seeds under WW, MDS, and HDS conditions.

**Figure 5.** Germination curves calculated using Richards' fitting function [25] for tomato seeds (at 21°C). (a) WW, (b) WW + 30 s plasma, (c) WW + 60 s plasma, (d) MDS, (e) MDS + 30 s plasma, (f) MDS + 60 s plasma, (g) HDS, (h) HDS + 30 s plasma, and (i) HDS + 60 plasma.

**Figure 6.** Germination curves calculated using Richards' fitting function [25] for pepper seeds (at 21°C). (a) WW, (b) WW + 30 s plasma, (c) WW + 60 s plasma, (d) MDS, (e) MDS + 30 s plasma, (f) MDS + 60 s plasma, (g) HDS, (h) HDS + 30 s plasma, and (i) HDS + 60 plasma.

seeds (see **Table 1**). PT significantly increased the germination rate (*Vi*) of tomato seeds. It increased by 11% for 30 s PT and by 7% for 60 s compared to the medium drought-stressed non-treated seeds, and it increased by 16% for 30 s PT and 11% for 60 s PT compared to the harsh drought-stressed non-treated seeds.

For pepper seeds in HDS, the cold plasma treatment increased the germination rate by 4% for 30 s PT and 10% for 60 s PT seeds when compared to harsh drought-stressed non-treated seeds. However, in the case of medium drought stress, the final percentage of germination rate was almost the same in 60 s plasma-treated and non-treated samples (see **Table 1**).

Impact of Conditions of Water Supply on the Germination of Tomato and Pepper Seeds http://dx.doi.org/10.5772/intechopen.70386 131


Note: WW, well-watered; WW + plasma, well-watered + plasma; MDS, medium drought stress; MDS + plasma, medium drought stress + plasma; HDS, harsh drought stress; HDS + plasma, harsh drought stress + plasma

*Vi* is the viability, *Me*is the time, *Qu* is the dispersion, and *Sk* is the skewness, details in text.

seeds (see **Table 1**). PT significantly increased the germination rate (*Vi*) of tomato seeds. It increased by 11% for 30 s PT and by 7% for 60 s compared to the medium drought-stressed non-treated seeds, and it increased by 16% for 30 s PT and 11% for 60 s PT compared to the

**Figure 6.** Germination curves calculated using Richards' fitting function [25] for pepper seeds (at 21°C). (a) WW, (b) WW + 30 s plasma, (c) WW + 60 s plasma, (d) MDS, (e) MDS + 30 s plasma, (f) MDS + 60 s plasma, (g) HDS, (h) HDS + 30 s

For pepper seeds in HDS, the cold plasma treatment increased the germination rate by 4% for 30 s PT and 10% for 60 s PT seeds when compared to harsh drought-stressed non-treated seeds. However, in the case of medium drought stress, the final percentage of germination rate was almost the same in 60 s plasma-treated and non-treated samples (see **Table 1**).

harsh drought-stressed non-treated seeds.

plasma, and (i) HDS + 60 plasma.

130 Advances in Seed Biology

The values of each experiment (bold line in the table) were significantly marked by different statistical letters at P ≤ 0.05 according to Student's t-test.

**Table 1.** Effect of water availability conditions, temperature (21°C), and cold plasma treatment on seed germination in tomato and pepper seeds.

Under free water supply conditions (WW), the germination percentage of PT seeds is slightly and insignificantly decreased in both cultivars.

The positive influence of plasma treatment on germination of tomato seeds at 27°C temperature was also shown (see **Table 2**). The cold plasma treatment significantly increased germination rate (*Vi*) under MDS conditions by 8% for 30 s PT and by 12% for 60 s PT compared to the MDS non-treated seeds. In HDS conditions, germination increased by 6% for 30 s PT and by 11% for 60 s PT when compared to the HDS non-treated seeds. In the case of pepper seeds, the 27°C temperature significantly decreased the germination percentage in all water regimes (see **Table 2**). Interestingly, at 27°C, while in WW conditions, germination rates of non-PT pepper seeds were much higher than the rates of treated seeds, when grown under MDS and HDS, the rates of germination of PT seeds were higher than those of WW-grown pepper seeds.

In order to elucidate the data describing the kinetics of germination, Richards' curves were fitted to a number of experiments [23, 27, 28]. Fitting experimental data by Richards' curves is shown in **Figures 5** and **6**. The solution of Richards' differential equation worked out for the growth of modeling results in Richards' curve, which is an extension of the logistic or sigmoid functions, which are the *S*-shaped curves describing the kinetics of germination. The Richards' function *Yt* demonstrating a variable inflection point was calculated according to Eq. (1): *Yt* <sup>=</sup> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *<sup>a</sup>* [<sup>1</sup> <sup>+</sup> *<sup>b</sup>* <sup>⋅</sup> *<sup>d</sup>* <sup>⋅</sup> exp(−*<sup>c</sup>* <sup>⋅</sup> *<sup>t</sup>*))]

$$Y\_r = \frac{a}{\left[1 + b \cdot d \cdot \exp(-c \cdot t)\right]^{\frac{1}{d}}} \tag{1}$$

where *Yt* is the germination percentage; *a*, *b*, *c* and *d* are the fitting parameters; and *t* is the time.

Fitting of experimental data by Eq. (1) supplied the best values of the fitting parameters summarized in **Table 1**, in which *Me* (median) denotes the time of 50% germination and characterizes the rate of this process. The quartile deviation of germination time *Qu* describes the deviation range of Richards' curve relative to *Me*, and *Sk* (skewness) represents the asymmetry of Richards' curve relative to the inflection point (mode) (see **Figure 7**). For calculation of these quantities, the useful formulae developed by Hara were implemented [28].


Note: WW, well-watered; WW + plasma, well-watered + plasma; MDS, medium drought stress; MDS + plasma, medium drought stress+ plasma; HDS, harsh drought stress; HDS + plasma, harsh drought stress + plasma. The values of each experiment (bold line in the table) were significantly marked by different statistical letters at P ≤ 0.05 according to Student's t-test.

**Table 2.** Effect of water availability conditions, temperature (27°C), and cold plasma treatment on seed germination on tomato and pepper seeds.

**Figure 7.** Richards' germination curve (see Eq. (1)). The quantitative parameters of germination are shown.

As it is recognized from the data supplied in **Table 1** for tomato seeds, the value of *Me* is distinctly lower (by *ca*. 5–15 and 5–10 hours) after 30 and 60 s of plasma treatment in the cases of MDS and HRS, respectively. Consider that germination is accelerated as *Me* decreases [28].

As it is seen from **Table 1**, for pepper seeds the value of *Me* is distinctly lower (by *ca*. 10–15 and 8–12 hours) after 30 and 60 s of PT in the cases of MDS and HRS, respectively. Parameters *Qu* and *Sk* were not affected markedly by the cold plasma treatment, as is seen from **Table 1**.

#### **4. Discussion**

functions, which are the *S*-shaped curves describing the kinetics of germination. The Richards'

Fitting of experimental data by Eq. (1) supplied the best values of the fitting parameters summarized in **Table 1**, in which *Me* (median) denotes the time of 50% germination and characterizes the rate of this process. The quartile deviation of germination time *Qu* describes the deviation range of Richards' curve relative to *Me*, and *Sk* (skewness) represents the asymmetry of Richards' curve relative to the inflection point (mode) (see **Figure 7**). For calculation of

these quantities, the useful formulae developed by Hara were implemented [28].

**Cultivar Treatment** *Vi* **(%) at 27°C**

Tomato WW 84±3b

Pepper WW 64±7a

*Yt* <sup>=</sup> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *<sup>a</sup>* [<sup>1</sup> <sup>+</sup> *<sup>b</sup>* <sup>⋅</sup> *<sup>d</sup>* <sup>⋅</sup> exp(−*<sup>c</sup>* <sup>⋅</sup> *<sup>t</sup>*))]

demonstrating a variable inflection point was calculated according to Eq. (1):

is the germination percentage; *a*, *b*, *c* and *d* are the fitting parameters; and *t* is the

WW + 30 s PT 83±5b WW + 60 s PT 97±2a MDS 81±2b MDS + 30 s PT 89±3ab MDS + 60 s PT 93±4a HDS 85±3b HDS + 30 s PT 91±2ab HDS + 60 s PT 96±2a

WW + 30 s PT 20±4b WW + 60 s PT 28±6b MDS 53±19a MDS + 30 s PT 59±11a MDS + 60 s PT 61±11a HDS 31±12a HDS + 30 s PT 44±11a HDS + 60 s PT 45±9a

Note: WW, well-watered; WW + plasma, well-watered + plasma; MDS, medium drought stress; MDS + plasma, medium

The values of each experiment (bold line in the table) were significantly marked by different statistical letters at P ≤ 0.05

**Table 2.** Effect of water availability conditions, temperature (27°C), and cold plasma treatment on seed germination on

drought stress+ plasma; HDS, harsh drought stress; HDS + plasma, harsh drought stress + plasma.

according to Student's t-test.

tomato and pepper seeds.

\_\_1 *d* (1)

function *Yt*

132 Advances in Seed Biology

where *Yt*

time.

In the present study, we demonstrated that the cold radiofrequency air plasma treatment has a crucial impact on the water imbibition and seed germination of pepper and tomato seeds. This effect is reasonably attributed to the hydrophilization of the surface of seeds by the plasma treatment [22, 23, 29]. The imbibition and germination in turn were adversely affected by water availability conditions of the seedbed. This effect was well expected, and it was already addressed by investigators [30–32]. However, at the conditions of the lower water availability, both the germination rate and the kinetics of germination were essentially positively affected by the cold radiofrequency air plasma treatment. The MDS conditions used in our work represent the naturally occurring conditions typical for seedbeds, where no free water is usually present, but water is given abundantly and then drained. HDS conditions represent lower water availability, causing water stress during germination. It should be emphasized that seed germination and early seedling growth are critical stages for plant establishment, and plants are more sensitive to drought stress during these stages [33]. Our results support the findings reported recently by investigators, which studied the influence of the cold plasma treatment on the oilseed rape (*Brassica napus* L.) seed germination under drought stress [31]. Ling et al. reported that, under drought stress, cold plasma treatment significantly improved the germination rate by 4.4–6.25% for various species of the oilseed rape [34]. Seedling growth characteristics, including shoot and root dry weights, shoot and root lengths, and lateral root number, were significantly improved after the cold plasma treatment. It is noteworthy that in our experiments the similar improvement of the germination rate was obtained and confined in the range of 1–12% for pepper and tomato seeds at 21°C, under various conditions of restricted water availability. Indeed, for tomato seeds it was shown that there is a direct relationship between uptake of water and germination rate (this conclusion is supported by recent results reported by other groups [35]), while for pepper seeds, no such correlation was found. This means that other possible effects of PT are responsible for the improvements in germination rates of pepper under plasma treatment (such as the regulation of energy metabolism [36]).

In addition, it was also shown that temperature plays a key role in the effect of plasma on seed germination of pepper. Our experiment demonstrates that at a high temperature of 27°C, in WW conditions, germination rates of non-PT pepper seeds were much higher than the rates of treated seeds, grown under MDS and HDS. The rates of germination of PT seeds were higher than those of WW-grown pepper seeds but considerably lower than those at 21°C. The reason for the drastic decrease in germination rates of PT seeds under WW conditions at higher temperatures remains unclear and would be further investigated. For tomato seeds the differences between germination rates at 27°C and those at 21°C were not so dramatic. These preliminary results demonstrate the importance of determining the right combination of germination temperature and PT duration for each cultivar tested. They may explain some of contradictory effects in investigations of the impact of plasma treatment on germination rates and germination speeds found reported by other researchers.
