Research Article

Effects of UV Radiation on Germination, Growth, Chlorophyll Content, and Fresh and Dry Weights of Brassica rapa L. and Eruca sativa L.

Hussan Ara Begum1, Muhammad Hamayun1, Noor Shad1, Waqar Khan3, Jawad Ahmad1, Muhammad Ezaz Hasan Khan2, David Aaron Jones2 and Kishwar Ali2*

1Department of Botany, Abdul Wali Khan University Mardan, Khyber Pakhtunkhwa, Pakistan; 2School of General Education, College of the North Atlantic Qatar, Doha, Qatar; 3School of Plant Sciences, Nanjing Agriculture University, Nanjing, 210095, P.R. China.

Received | January 20, 2020; Accepted | May 28, 2021; Published | July 15, 2021

*Correspondence | Kishwar Ali, School of General Education, College of the North Atlantic Qatar, Doha, Qatar; Email: kishwar.ali@cna-qatar.edu.qa

Citation | Begum, H.A., M. Hamayun, N. Shad, W. Khan, J. Ahmad, M.E.H. Khan, D.A. Jones and K. Ali. 2021. Effects of UV radiation on germination, growth, chlorophyll content, and fresh and dry weights of Brassica rapa L. and Eruca sativa L. Sarhad Journal of Agriculture, 37(3): 1016-1024.

DOI | https://dx.doi.org/10.17582/journal.sja/2021/37.3.1016.1024

Keywords | Brassica rapa L., Eruca sativa L., UV radiation, Germination, Chlorophyll content, Ozone depletion

Introduction

The growth and development of plants depend upon energy obtained from the sunlight. A slight change in the wave length of light can alter the whole plant physiology and biochemistry (Schmitt and Wulff, 1993). Light waves of 400-700 nm wavelengths have greater effect on a plant’s responses which cause alteration within the magnitude relation of UV light to influence the biomass allocation (Maliakal et al., 1999). Around the earth, the presence of the ozone layer at about 10-30 km above the earth surface is protecting us from harmful UV lights (Maliakal et al., 1999). One of the biggest threats to life is from the diluted stratospheric layer and the global weather alteration. Reduction in the ozone layer can cause UV light of 280-320 nm wave length to reach the earth surface. Due to thinning of ozone layer around the earth, adverse effects of UV light also increase and its intensity is multiplied by a number of topographic factors (Reddy et al., 2004). Hartley firs noted the adverse effects of UV light in 1881(Hartley, 1881; Tevini and Teramura, 1989).

Effect of UV light is high at high altitude as compared to low lying areas and it almost effect all functions of the plant starting from germination. Depletion in the ozone layer lead to enhanced the penetration of solar UV radiation to earth surface. The UV radiation reaching earth surface can affect the growth of plant. The daily UV shocks also affect the plumule and radicle length of newly growing plant (Flint and Caldwell, 2003). High intensities of UV light are destructive to all organisms including microbes (Zaman et al., 2018; Barnes et al., 1993). Paul (2001) studied species and found that UV contacts can cause alterations physiologically, morphologically, and chemically and affect it molecularly. High levels of UV light reduce chlorophyll production, soluble proteins and Rubisco in C3 plants (Nasser, 2001). As a stress factor UV light reduces growth, damages photosynthetic pigments, reduces carbon intake, and affects many other functional and hormonal systems (Fukushima and Saito, 2000; Hollosy, 2002). Due to UV light, intraspecific variations also occur in plants regarding biochemicals, wet or dry mass etc. (Kolb et al., 2001). Most plant species are very responsive to UV light while fewer are not affected by it (Teramur, 1983). UV light badly affects physiological and biochemical processes. UV treated seeds get disturbance in their protein production, exchange of gases, water distribution, hormonal and enzymatic activities (Khan et al., 2020; Hieng et al., 2004). UV treatment is harmful to plants either directly or indirectly (Horneck et al., 1995; Joshi et al., 2007). It is reported that treatment with UV causes the reduced activity of photosystem II in photosynthesis. UV exposure disturbs the stomatal opening and closing, reduces gaseous exchange lowering transpiration rate (Day and Vogelmann, 1995; Dube and Bornman, 1992).

UV light also brings alteration in cell division, hormonal imbalances with distressed nucleic acid (Mpoloka, 2008). UV light also causes a reduction in plants size, leaf size and low biomass with curled leaves (Furness et al., 1999). Members of family brassicaceae are used as pot-herb and are very important worldwide for their chemical constituents (Gomes and Rose, 2001), flavonoids and mineral nutrients (Hanaka et al., 2016; Moreno et al., 2006). Mahdavian et al. (2008) reported that UV light caused reduction in chlorophyll, anthocyanin and proline content of vegetable plants.

The present study’s objective was to evaluate how UV light affects seed germination. specifically, in plants acclimatizing to cool habitat that are said to be vulnerable to high temperatures and to record changes in plants treated with UV light. In the present study seeds of some brassica species were used to screen for UV sensitivity.

Materials and Methods

Brassica rapa L. and Eruca sativa L. seeds were used in the experiment due to the importance of these plants as pot-herbs. Healthy seeds of these species were collected. Clean seeds of Brassica rapaL. and Eruca sativa L. were first sterilized with 0.5% sodium hypochlorite for two minutes, washed and soaked in distilled water for 2 hrs. Petri plates with two disks of Whatman no.1 filter paper was used, the soaked 20 seeds were placed in the Petri plates. Seeds were placed in 7groups of petri plates for treatment, each group with three replicates. The 1 group was of control, 2 groups were of 30mins, 2 groups were for 60 mins and 2 group were of 120mins.The 6 groups were exposed for 30, 60 and 120 minutes to UV radiation daily.

There were 6 treatments with 1 control (30, 60 and 120 min) each having three replicates. For germination study, petri plates were kept at room temperature. Observations on germination were recorded daily. Small amounts of distilled water were added periodically to keep the petri plates moist. Germination was recorded daily up to 15 days. On 12th day chlorophyll pigments were determined. At the end of experiment, radicle and plumule lengths of the seedlings and their fresh and dry weights were recorded. Plumule and radical lengths were recorded on 14th day of the experiment.

Fresh and dry weights

On 16th day of seed germination, the fresh weight of each plate was find out, after finding fresh weight, then the plants were kept in oven for 48 hours to dry. On next day the dry weight was determined.

Estimation of chlorophyll content

The Two-hours soaked seeds are exposed to UV radiation for 0 (control), 30, 60 and 120 min daily till 15 days, subsequently at 12th day chlorophyll in the leaf was determined through chlorophyll meter.

Results and Discussion

Studies demonstrated that high intensities of UV light bring several changes not only externally and internally but also disturb it chemically (Shaukat et al., 2013). The overall germination rate was significantly reduced, compared to the control group, with greater exposure to ultraviolet radiation. In Eruca sativa, the irradiation rate of ultraviolet radiation reduces significantly by 30 and 120 minutes while 60 minutes irradiation increases the germination percentage, and in Brassica rapa, the 60 and 120 minutes treatment, the germination is increased compare to 30 minutes (Table 1) but is still less than the control treatment. The results obtained in the present study showed that UV irradiation prominently affected the seed germination and chlorophyll contents of the selected plants. Brassica rapa L. and Eruca sativa L. were treated with UV light for 30, 60 and 120 mins. Germination percentage was reduced in both plants at 30 and 120 mins while at 60 mins there was little increase as compared to the 30 and 120 mins but was less than the control set.

 

Table 1: Percent seed germination of Brassica rapa L. and Eruca sativa L. exposed to UV light.

Treatment UV-B exposure	% seed germination of Brassica Rapa	% seed germination of Eruca Sativa
Control	19.33 ± 0.33	18.77 ± 0.33
30 min	18.77 ± 0.33	17.00 ± 0.58
60 min	19.00 ± 0.67	19.77 ± 0.33
120 min	19.00 ± 0.67	17.00 ± 0.58

 

Sugimoto (2013) reported that UV light suppresses the gibberellin in lettuce seeds which hindered the germination. These results were in agreement with the previous available literature (Kakani et al., 2003; Shetta, 2008; Liu and Zhong, 2009; Shetta and Areaf, 2009). Seeds radiated with UV light at germination of seed and appearance of seedling stage have more affect than other stage (Saile-Mark and Tenivi, 1997; Li et al., 2009).

Radicle and plumule lengths

The growth of the radicles in both plants (Brassica rapa L. and Eruca sativa L.) was greater in the 60 and 120 minutes treatment as compared to control and 30 min treated with ultraviolet radiation, (Table 2). In contrast, shoot growth was increased in 30 min in Brassica rapa while a decreased in 60 and 120 min exposure treatment, compared to control. Similarly decrease in shoot length was recorded Eruca sativa as compared to control set (Figure 3 and 4). The early growth stages of seeds and seedlings are very sensitive to any environmental effect including UV light (Sultan, 2000; Pliura et al., 2008). Germination of seeds irradiated with UV light and its chlorophyll content is also subjected to the plant growth stage and environmental factors (Ali et al., 2018; Kuhlmann and Muller, 2009). Previous record also showed that not only germination percentage is affected but shoot length is also decrease in some plants (Peykarestan and Seify, 2012). Plants showing less UV affect have high concentrations of Flavonoids and phenols in them (Close and McAthur, 2002; Kolb et al., 2001). Phenols are induced to accumulate in plants upon exposure to UV light as stress indicator (Kozlowska et al., 2007; Ravindran et al., 2008) and protect plants against stresses (Abreu and Mazzafera, 2005; Olenchenko and Zagoskina, 2005; Ganeva and Zozikova, 2007).

 

Table 2: Shoot and root length of Brassica rapa L.

Treatment UV-B exposure	Shoot length	Root length
Control	2.33 ± 0.14	1.19 ± 0.047
30 min	2.71 ± 0.028	1.16 ± 0.036
60 min	1.56 ± 0.060	1.54 ± 0.056
120 min	1.74 ± 0.043	1.52 ± 0.029

 

 

 

Fresh and dry weight estimation

The fresh and dry weight determines the effects of UV radiation on germination and growth. On the 16th day of germination the fresh weight was find out. Both the Fresh and Dry weight were decreased as compared to Control. In both species (Brassica rapa L. and Eruca sativa L.) the Fresh and dry weight in control is more as compare to the replicates treated with UV light (30, 60 and 120min) (Table 4 and 5). Seeds are protected by flavonoids present in their seed coats (Tepfer et al., 2003). The current study showed that in all treatments the shoot and root length in both plants were affected after irradiated with UV light. Root and shoot lengths of the germinating seedlings were affected by UV light in the present study. Shaukat et al. (2011) reported that growth of root and shoot was stifled by exposing to UV light. Likewise, the fresh and dry weight of the seedling which shows the growth of the seedlings also decreases. Mladin et al. (2014) reported that UV light impaired the photosystem II which results in low or even no photosynthesis that results in low biomass. UV light effect the plants but the plant’s defense systems try to lessen this impact by activating its antioxidant system (Horva’th et al., 2007). UV light enhances the activity of antioxidant enzyme (Nita et al., 1996). Kondo and Kawashima (2000) also reported that UV light enhances the activity of enzymes related to antioxidants.

 

Table 3: Shoot and root length of Brassica rapa L. and Eurca sativa L.

Treatment UV-B exposure	Shoot length	Root length
Control	2.35 ± 0.012	1.39 ± 0.012
30 min	1.93 ± 0.018	0.913 ± 0.023
60 min	1.51 ± 0.015	1.010 ± 0.030
120 min	1.78 ± 0.018	1.127 ± 0.012

 

 

Table 4: Effects of ultraviolet radiation on fresh and dry weight of Brassica rapa L.

Treatment UV-B exposure	Fresh weight	Dry weight
Control	0.823 ± 0.023	0.700 ± 0.032
30 min	0.680 ± 0.023	0.590 ± 0.032
60 min	0.850 ± 0.023	0.613 ± 0.032
120 min	0.623 ± 0.023	0.513 ± 0.032

 

Table 5: Effect of ultraviolet radiation on Fresh and Dry weight of Eruca sativa L.

Treatment UV-B exposure	Fresh weight	Dry weight
Control	0.287 ± 0.098	0.220 ± 0.017
30 min	0.197 ± 0.026	0.143 ± 0.098
60 min	0.292 ± 0.048	0.220 ± 0.023
120 min	0.216 ± 0.003	0.177 ± 0.003

 

 

 

Chlorophyll contents

Irradiation of Brassica rapa L. and Eruca sativa L. seeds to UV light, the effect of chlorophyll was comparative to the control group. The total chlorophyll pigments increased significantly as compare to the control group. The chlorophyll contents ratio increases in all treatment (30, 60, and 120min) exposed to ultraviolet radiation, as compared to control (Table 6). The increase in chlorophyll content was dependent on exposure to time duration. The present study showed that the chlorophyll b content was increased after treatment with UV light in both plants (Figure 7 and 8). This is supported by Shaukat et al. (2011) who recorded that UV light decreased chlorophyll a content but no reduction occurs in chlorophyll b content. The differences in effect on chlorophyll a and b contents also recorded by Gitz et al. (2004) and reported that it might be due to dissimilar pathways of both a and b chlorophyll contents (Figure 9-12). The chlorophyll a pathway either sensitive to UV shocks more than that of chlorophyll b or chlorophyll a pathway ruined prior to chlorophyll b pathway. The intensity and time duration also greatly affect the chlorophyll contents of the plant (Ranjbarfordoei et al., 2009). Many of the previous research support that UV light reduces the total chlorophyll content of the plant (Day and Vogelmann, 1995; Ambasht and Agarwall, 1998; Skorska, 2000; Ravindran et al., 2008).

 

Table 6: Effect on chlorophyll pigments exposed to UV radiation.

Treatment UV exposure	Brassica rapa L.	Eruca sativa L.
C0ntrol	9.44 ± 0.014	7.33 ± 0.082
30 min	11.48 ± 0.020	9.41 ± 0.014
60 min	7.63 ± 0.014	8.50 ± 0.023
120 min	14.56 ± 0.020	10.32 ± 0.097

 

 

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Conclusions and Recommendations

Exposure of seeds to UV light significantly reduced germination percentage with decrease in speed of germination. UV exposure affected the radicle and plumule length. The shoot length decreased in all UV exposure as compared to control, the result is same in root length. UV radiation also caused curling and twisting of seedling. UV radiation suppressed the fresh and dry weight of plant, due to ultraviolet radiation the fresh and dry weight is reduced significantly in UV exposure, compare to control. Exposure to UV light can also increased the chlorophyll pigments in UV exposure as compared to control. The ultraviolet radiation reduced the plant growth, seedling and germination, but it increased the chlorophyll contents.

Novelty Statement

The current study concludes that the ultraviolet (UV) radiations decrease crop productivity. The UV radiation reduces the overall plant growth, damages seedling and inhibits germination, but at the same time, it can increase the chlorophyll content of plants.

Author’s Contribution

Hussan Ara Begum and Muhammad Hamayun: Designed the study.

Noor Shad, Waqar Khan and Jawad Ahmad: Performed the experimental work.

Muhammad Ezaz Hasan Khan, David Aaron Jones and Kishwar Ali: Wrote the manuscript.

All authors contributed to the present research equally.

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