EFFECT OF FLUORIDE AND SALICYLIC ACID ON ... - Semantic Scholar

49 Research report

Fluoride 47(1)49–55 January-March 2014

Effect of fluoride and salicylic acid on seedlings of watermelon Ram, Verma, Gadi

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EFFECT OF FLUORIDE AND SALICYLIC ACID ON SEEDLING GROWTH AND BIOCHEMICAL PARAMETERS OF WATERMELON (CITRULLUS LANATUS) Amra Ram,a Pooja Verma,a BR Gadib Jodhpur, India

SUMMARY: The effect of sodium fluoride (NaF) on seed germination and biochemical parameters were studied in in vitro grown seedlings of watermelon (Citrullus lanatus) under salicylic acid (SA) treatment. After seven days of NaF treatment, reductions were observed in percentage of seed germination, root and shoot length, vigor index, pigment content, chlorophyll stability index (CSI), and membrane stability index (MSI) with increasing concentrations of NaF (1 and 10 mM). Seedlings treated with SA, both alone and in with combination of NaF, showed an increase in seed germination as well as other growth parameters. NaF-treated seedlings were found to accumulate more soluble sugars and phenolics, which were further increased by SA treatment thereby indicating a synergistic effect of SA and NaF on the accumulation of sugars and phenols. Therefore, these parameters are not directly related to a higher vigor index, membrane stability, and seedling growth. Treatment with SA reduced the adverse effects of NaF by increasing seed germination, root and shoot length, vigor index, pigment content, CSI, and MSI by some mechanism other than the accumulation of sugars and phenols. The possible reasons for the ameliorative effects of SA in seedlings of watermelon growing under F stress are discussed. Keywords: Biochemical parameters; Chlorophyll a and b; Chlorophyll stability index. Fluoride toxicity in plants; Membrane stability index; Phenols; Pigments; Salicylic acid; Seedling growth; Sugars; Watermelon (Citrullus lanatus). INTRODUCTION

Chronic fluoride (F) exposure causes diverse toxic effects in both humans1 and animals.2 F is not an essential element for the normal growth of plants and in higher concentration it is toxic for plants, especially for early seedling growth.3 Seed germination and early seedling growth are important phases for the successful growth and survival of plants and these physiological parameters of plants are greatly affected by NaF at different concentrations due to its inhibitory activities.3,4 Several physiological and biochemical processes are known to be markedly affected by F such as chlorosis and necrosis of leaf, inhibition of the nutrient uptake, reduction of plant growth, and enzyme activities.4-7 In India, several states are F endemic8 including Rajasthan where ground water contains a high amount F in all the 33 districts.9 In Rajasthan, due to irregular and low rainfall and recurrent drought, ground water is the main water source for irrigation for agricultural purposes. In addition, the soil of northwest Rajasthan contains elevated F due to the excessive use of diammonium phosphate fertilizers.10 Salicylic acid (SA) is a phenolic compound which plays an important role as a signaling molecule for the regulation of several physiobiochemical processes in plants.11,12 Through changes in hormonal levels, it plays protective roles in plants aDepartment

of Botany, Jai Narain Vyas University, Jodhpur 342005, India; bFor correspondence: Dr BR Gadi, Associate Professor, Department of Botany, Jai Narain Vyas University, Jodhpur 342005, India; E-mail:[email protected]

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against pathogens and many abiotic stresses including drought, salt, and heavy metals.12,13 Watermelon (Citrullus lanatus) is a fruit crop in the arid region of Rajasthan.14 It is used to flavor summer drinks and smoothies in the region, where the temperature may rise up to 50ºC during the summer season. Seeds of watermelon are demulcent, diuretic, tonic, and seen as helpful for lowering blood pressure and improving cardiovascular function. Immature fruits are used as vegetables and both the fresh and dry rinds are important as cattle feed. Several studies have been conducted on the effects of F stress on seed germination, early seedling growth, and biochemical content.4-6 However, no study has been done on reducing plant F toxicity by the application of plant growth regulators such as salicylic acid. Therefore, the present investigation was undertaken to ascertain the influence of salicylic acid on NaF-induced stress on early seedling growth and certain biochemical parameters viz. pigments, sugars, phenols, chlorophyll stability index (CSI), and membrane stability index (MSI). MATERIAL AND METHODS

Sterilized seeds of C. lanatus were germinated in individual petri dishes and labeled as control (distilled water) and respective treatment solutions (1 and 10 mM NaF, 1 and 10 mM NaF+0.25 mM SA, and 0.25 mM SA). Petri dishes were kept at 28±2ºC in a Biochemical Oxygen Demand (BOD) incubator. The germination percentage was recorded on the third day after seed sowing. After seven days of treatment, the root length, shoot length, and vigor index15 were measured and whole seedlings were used for estimation of the photosynthetic pigments content,16 chlorophyll stability index,17 membrane stability index,18 total soluble sugars,19 and phenolics content.20 For the statistical analysis, three replicates were maintained for each treatment and each experiment was repeated twice. All data were subjected to one-way ANOVA test and means were compared by Student’s t-test. RESULTS AND DISCUSSION

Percentage of seed germination: The present study revealed that the increasing concentration of NaF decreased the percentage of seed germination in C. lanatus (Table 1). The higher concentration of NaF (10 mM) reduced the germination percentage by 23% as compared to the control. F-induced inhibition of germination may be due to a reduction of amylase activity which is essential for seed germination.21 SA treatment increased the seed germination, both when used alone (8% increase compared to seed germination in the control group) and in combination of NaF (22% increase when compared to seed germination with NaF 10 mM). SA stimulates the seed germination via bio-synthesis of gibberellic acid (GA) which induces the amylase synthesis.22 Root and shoot length: As shown in Table 1, the average root and shoot length decreased with increasing NaF concentration. Shoot growth in the seedlings was more affected than root growth. F-induced reduction in root and shoot length may be due to an unbalanced nutrient uptake by seedlings.23 SA increased the root and

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shoot length relative to the respective control groups. In consonance to our study, SA enhances shoot and root growth in many plants possibly by regulating cell elongation and cell division and by the prevention of auxins oxidation.13 Table 1. Effect of sodium fluoride (NaF) on seed germination, root and shoot length, and vigor index in C. lanatus seedlings under s alicylic acid (SA) treat ment. Values are mean±SE, n=3 Group

Seed G ermination (% )

Root Length (cm)

Shoot Lengt h (cm)

Vigor Index

Cont rol

90.81±1.28

7.46±0. 002

5.36±0.050

1065.04±25.16

NaF 1 mM

78.30±1.02*

5.83±0. 18*

3.66±0.031*

743.81±11. 21*

NaF 10 mM

70.40±1.13

4.16±0. 009*

2.96±0.021*

502.53±30. 55*

SA 0.25 mM

97.83±1.11*

8.66±0. 003*

6.63±0.052

1496.87±10.00

NaF 1 mM + SA 0.25mM

90.59±1.19

6.83±0. 012

4.66±0.011*

1042.00±13.09

NaF 10 mM + SA 0.25mM

85.65±1.02*

5.33±0. 011

4.20±0.019

816.66±6.89

0.0276

0.021

0.011

1.102.00

CD at 5% level

†

†

*p≤0.05, Pesaran’s cross -s ectional dependence (CD) t est .

Vigor index: In the study, the seed vigor index was also reduced by increasing the concentration of NaF since it is determined by the multiplication of seed germination and seedling growth (root and shoot length) which were reduced by NaF. However, seedlings treated with SA alone and with combination of NaF showed the higher seed vigor index as compared to their respective controls. Pigment content: Chlorophyll-a (Chl-a), chlorophyll-b (Chl-b), total chlorophyll, and carotenoids content were found to be decreased with increasing of NaF concentration as compared to control (Figure 1). Carotenoids

Figure 1. Effect of sodium fluoride (NaF) on pigment content, chlorophyll-a (Chl-a), chlorophyllb (Chl-b), total chlorophyll (Total chl), and carotenoids, in in-vitro grown seedlings of C. lanatus under salicylic acid (SA) treatment. Bar represents standard error of mean (n=3). *significantly different at p