Effect of titanium dioxide nano particles on seed

03

PLANT SCIENCES FEED ORIGINAL ARTICLE

2013

ISSN : 2231 - 1971 http://psf.lifescifeed.com

EFFECT OF TITANIUM DIOXIDE NANO PARTICLES GERMINATION AND GERMINATION INDICES IN ONION

ON

SEED

RASKAR S AND LAWARE SL Titanium dioxide (TiO2) nanoparticles (NPs) are known for photo-catalytic activity, high stability and low costs. They are environmental friendly and found to be safe for human. The hydrophilic conversion and photocatalytic properties of TiO2 NPs have commercial applications in sustainable agriculture. These particles have been used in pathogen treatments as well as decomposition of phytotoxic compounds. In present investigation, different concentration (10 to 50µg mL-1) of TiO2 NPs were prepared in distilled water and used for the treatment in onion seeds to study their effect on seed germination and early seedling growth. Results indicate that TiO2 NPs at lower concentration enhances seed germination, promptness index and seedling growth. These results point out the possible use of TiO2 NPs in onion to promote seed germination and early seedling growth to have healthy and sturdy seedling stock for plantation in the field. KEYWORDS: Titanium dioxide, nanoparticles, onion, seed germination.

Cite this article as: Raskar S and LawareSL. Effect of titanium dioxide nano particles on seed germination and germination indices in onion. Plant Sciences Feed, 2013; 3 (9): 103-107. AUTHOR AFFILIATIONS: EMAIL :

1Department of Botany, Periyar University, Salem - 636 011.

2 Department of Biotechnology, Dr. N. G. P. Arts and Science College, Coimbatore - 641 048 [email protected]

The researchers are having many questions in their mind and debate about the risks and benefits of the many manufactured nanomaterials into the environment. Many of biological scientists are working on NPs to evaluate their potential adverse effects on the ecosystems and on human health. The literature on the ecotoxicity of nanoparticles and nanomaterials as well as the chemistry of both manufactured and natural NSPs are well documented in some reports [5, 6, 7].

Considering the wide uses of these particles it is projected that these NSPs will enter into various ecosystems, where their actions are not known. Therefore, organisms which will interact with NPs are expected to have beneficial or adverse effects. The interactions between microorganisms and metals have been well documented and ability of microorganisms to extract and/or accumulate metals is already employed in biotechnological processes such as bioleaching and bioremediation [8]. The biocidal properties (antifungal and antibacterial) of the NPs have significant practical relevance and can be tapped to control of bacterial and fungal organisms responsible for crop losses. However, it must be very clear that these NPs should not have adverse effects in plant systems. Hence, in present investigation it was planned to study the influence of TiO2 nanoparticles on seed germination and seedling growth in onion. 2. METHODOLOGY

Titanium dioxide (TiO2) P25 powder of particle size 21 nm and purity > 99.5% was obtained from the researchers in the field of nanomaterial synthesis. These were made of 80% anatase and 20% rutile. Seed of local onion variety was procured from NRC (National Research centre for onion and garlic), Rajgurunagar. (i) Effect of nanoparticles on seed germination.

The graded concentrations (00, 10, 20, 30, 40 and 50 g mL-1) of TiO2 nanoparticles prepared in distilled water were added aseptically to sterilized petriplates

Plant Sciences Feed Vol. 3 Issue 9

(ii) Seed germination Indices Parameters like Promptness index (PI), Germination stress tolerance index (GSI), SLSI (shoot length stress tolerance index), Root length stress tolerance index (RLSI), Dry matter stress tolerance index (DMSI) were calculated by using following formulae [9]. (a) Promptness index (PI) = nd2(1.0) + nd4(0.75)+ nd6(0.5) + nd8(0.25) Where n is the no. of seed germinated at day "d" (b) Germination stress tolerance index (GSI) = PI of treated seeds / PI of control seeds x 100. (c) Seedling vigour was computed according to following formulae [10].

Vigour index-I= Germination% × Seedling length (cm). Vigour Index-II=Germination% × Seedling dry weight (g).

(iii)Seedling growth stress Indices.

Shoot length stress tolerance index (SLSI) = Shoot length of treated seedling / shoot length of control seedling x 100.

(a) Root length stress tolerance index (RLSI) =Root length of treated seedling / Root length of control seedling x 100. (b) Dry matter stress tolerance index (DMSI) = Dry matter of stressed plant / Dry matter of control plant x 100. 3. RESULTS

Results pertaining to seed germination and early seedling growth clearly indicate that TiO2 NPs promote seed germination and seedling growth linearly from 10µg mL-1 upto 40µg mL-1 concentration; however at 50µg mL-1 concentration of TiO2 NPs a significant decrease in seed germination was observed (Table-1). All the concentrations of TiO2 NPs showed increase in shoot length and total seedling height, however significant increase in total seedling length over control was observed in 20, 30 and 40 µg mL-1 concentrations of TiO2 NPs. The root length increased in all the concentration of TiO2 NPs except 50µg mL-1, nevertheless significant increase in root length over control was observed in 20 and 30 µg mL-1 concentrations of TiO2 NPs. On the other hand significant decrease in root length over control was observed in 50µg mL-1 concentrations of TiO2 NPs. The root-shoot ratio decreased concomitantly from lower to

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Nanoparticles are microscopic particles with at least one dimension less than 1000 nm. For this, these NPs are very attractive materials to handle in biological system. Nanoparticles are found to be very suitable in sensing and detection of biological structures and systems [1]. Metal NPs appear in different shapes such as nanopowder or nano-cluster or nano-crystal and different sizes ranging from 2 nm to 1000 nm. Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and atomic or molecular structures [2]. Engineered nanomaterials are gaining popularity because of their positive impact on economic sectors; hence these are being produced for various applications within industry [3, 4].

lined with Whatman no. 1 filter paper. Surface sterilized seed of onion were germinated (25 seed per plate) in each concentration of nanoparticles. Similar experiment without nanoparticles was conducted as control. After 10 days of treatment, seedlings were selected randomly and separated into shoots and roots. Seedling growth in terms of root length, shoot length, fresh weight and dry weight were recorded and result were compared to see effect of nanoparticles on seed germination and early seedling growth.

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1. INTRODUCTION

tolerance index (SHSI) values showed increase in all the treatments of TiO2 NPs over control; however, highest value (106.92) was observed in 40 g mL-1 and 50 g mL-1 concentrations of TiO2 NPs showed significantly lower SHSI value i.e. 101.65 but it was slightly more when compared to control. Root length stress tolerance index (RLSI) values showed increase in lower concentrations (i.e. from 10 to 30g mL-1) of TiO2 NPs over control and significant decrease in RLSI value (92.48) was observed in 50 g mL-1 concentrations of TiO2NPs. Dry matter stress tolerance index (DMSI) values showed significant increase in all the treatment except 50g mL-1 over control with maximum increase (111.36 and 112.12) in 30 and 40 g mL-1 treatments of NPS respectively (Table 2).

Table 1: Effect of TiO2 NPs on seed germination of Allium cepa Concentration of TiO2 NPs (g mL-1)

Germination %

Shoot Length (cm)

Root length (cm)

Seedlings Height (cm)

Root-Shoot Ratio

Control 10g mL-1 20µg mL-1

94.68 95.25 96.32

7.62 7.84 8.12

4.52 4.58 4.62

12.14 12.42 12.74

0.59 0.58 0.57

Fresh Weight (mg) 414.16 422.12 436.28

98.12

8.46

4.52

12.98

0.53

462.92

30µg mL-1 40µg mL-1 mL-1

50g CD 5%

97.68

8.38

92.02 1.72

4.56

8.16 0.22

4.18 0.16

12.94 12.34 0.48

Table 2: Effect of TiO2 on PI, GSI, PHSI, RLSI, and DMSI of Allium cepa Concentration of Tio2 NPs (g mL-1) Control 10g mL-1 20µg mL-1 30µg mL-1 40µg mL-1 50g mL-1 CD 5%

4. DISSCUSSION

0.54 0.51 0.26

Dry Weight (mg) 5.28 5.44 5.52

458.92

5.88 5.92

422.08 12.08

5.34 0.14

PI

GSI

SHSI

RLSI

DMSI

82.73 84.92 86.71 86.99

100.00 102.64 104.81 105.15

100.00 102.31 104.94 106.59

100.00 101.33 102.21 100.88

100.00 103.03 104.55 111.36

83.95 2.64

101.47 1.46

101.65 1.64

92.48 1.92

101.14 1.32

88.10

106.49

Seed germination results indicate that TiO2 NPs at their lower concentrations promoted seed germination and early seedling growth in onion, however at higher concentration showed slight adverse effects. Similar results were reported in wheat seed germination, where highest percent seed germination was observed at 2 ppm concentration of TiO2 NPs [11] and in Foeniculum vulgare with 60 ppm TiO2 nanoparticles [12]. According to authors, these results might be due to types of nanoparticles and difference in plant species; they further concluded that nanosized TiO2 presents the possibility to overcome problems associated with seed germination in plant species which have low seed germination. The main reason for this increased percent seed germination could be the generation of superoxide and hydroxide anions by nano-TiO2 that might have encouraged intake of water and oxygen needed for quick germination [13]. The experiment conducted in spinach seeds with nanoTiO2 showed enhanced imbibitions and accelerated seed germination Zheng et al. [14]. Authors observed

106.92

100.00

112.12

that the growth of spinach plants was greatly improved at concentrations of 250–4,000 mg L-1 nano TiO2 than concentrations of bulk-TiO2. Clement et al. [15] observed that seed soaked in suspension of TiO2 anatase NPs at concentration 100 mg L-1 positively influenced seed germination and root growth in flax. They attributed these positive effects to antimicrobial properties of anatase crystalline structure of TiO2 that might have increased plant resistance to stress. Based on studies on NPs effect on seed germination mechanism it could be stated that nanoparticles might have helped and promoted the water absorption by the seeds and increased abilities of seed to absorb and utilize water efficiently. It can also be stated that NPs might have promoted seed antioxidant system [16] and reduced the oxidative stress by reducing reactive oxygen species (ROS), malonyldialdehyde content and increasing antioxidant enzymes [17] which could be the reasons for improved seed germination and early seedling growth. In contrast with above observations and findings, Ghosh et al. [18] observed adverse effect of TiO2 nanoparticles in Nicotina tabacum. They attributed such inhibition to DNA injury induced by TiO2 NPs. This evidence supports

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Data with respect to the promptness index (PI) clearly show that PI increased upto 40g mL-1 concentration of TiO2 NPs and decreased significantly in 50 g mL-1 concentration of TiO2 NPs than 40 g mL-1 concentration of TiO2 but was at par with control. Germination stress tolerance index (GSI) indicates speed of seed germination. All the treatments showed increased values for GSI over control. Amongst the treatments 40g ml-1 concentration of TiO2 NPs exhibited higher GSI (106.49) and 50g mL-1 TiO2 NPs exhibited lower value i.e. 101.47. Seedling height stress

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higher concentrations of TiO2 NPs, this indicates that root length promotion is comparatively less, when compared to shoot length (Table 1).


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Results show that TiO2 NPs at lower concentration enhance seed germination, promptness index, and seedling growth. Results indicate that lower concentrations are not harmful to the seed germination and early seedlings growth. However, concentration over and above 50µg mL-1 can be inhibitory for seed germination and seedling growth in onion.

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