EurAsian Journal of BioSciences EurAsia J BioSci 2, 83-90 (2008)

Induction of salt tolerance in pepper (Capsicum annuum) by 24-epibrassinolide Samira Ibn Maaouia Houimli1*, Mounir Denden1, Salem Ben El Hadj2 1Laboratoire D'Agronomie, Institut Supérieur Agronomique de Chott Mariem 4042 Sousse, Tunisie 2Laboratoire de Production Végétale, Institut National Agronomique de Tunisie 43, Avenue Charles Nicolle, 1082 Mahrajène, Tunisie

*Corresponding Author: [email protected] Abstract In order to study the effectiveness of brassinosteroids on the amelioration of the inhibitory effect of salinity on pepper plants, a short-term experiment was conducted in greenhouse to test different concentrations of 24-epibrassinolide (0.0, 0.01, 0.05, 0.1, and 0.5 mg L-1) by foliar application on growth, relative water contents and chlorophyll fluorescence of pepper (Capsicum annuum cv. Beldi) plants irrigated with salt water (0.4 g L-1 NaCl). Salt decreases the different parameters of growth. However, its effects were more pronounced on the shoot than root growth. An exogenous supply of 24-epibrassinolide was found to be successful in alleviating of the inhibitory effects of salt stress on shoot growth parameters and the leaf relative water contents. However, non-significant effect of 24-epibrassinolide was observed on root growth and chlorophyll fluorescence. Out of the five concentrations, the effects of 0.5 mg L-1 proved the best under stress conditions. Keywords: Chlorophyll fluorescence, 24-epibrassinolide, growth, relative water contents, salt stress. Houimli SM, Denden M, El Hadj SB (2008) Induction of salt tolerance in pepper (Capsicum annuum) by 24-epibrassinolide. EurAsia J BioSci 2, 10, 83-90. www.ejobios.com/content/2/10/83-90

INTRODUCTION Salinity is a major environmental stress that adversely affects plant growth and metabolism. Salts inhibit plant growth by osmotic stress, specific ion toxicity, ion imbalance and oxidative stress (Tester and Davenport 2003). Many crop plants including peppers are susceptible and cannot survive under conditions of high salinity or can survive but with decreased yields. To alleviate this problem, a number of studies were conducted with the aim of removing the inhibitory effect of salt stress on plant growth, using different types of phytohormones (Nandini et al. 2002, Chakrabarti et al. 2003, Hussein et al. 2007, Tuna et al. 2008). Among these, brassinosteriods (BRs) have been the main focus of many researches in the last 20-30 years (Rao et al. 2002, Anuradha and Rao 2003). Brassinosteriods (BRs) are steroidal plant ©EurAsian Journal of BioSciences, 2008

hormones, essential for plant growth and development (Sasse 2003). After the discovery and isolation of brassinolide from Brassica napus pollens, a large number of related steroids have been isolated and identified from various plant sources including angiosperms, gymnosperms and alga, and based on this Sasse (2003) suggested that these compounds are probably ubiquitous in the plant kingdom. Research on brassinosteroids, has revealed that they elicit a wide spectrum of morphological and physiological responses in plants including stem elongation, pollen tube growth, leaf bending and epinasty, root inhibition, induction of ethylene biosynthesis, proton pump activation, xylem differentiation and the regulation of gene expression (Li and Received: July, 2008 Accepted: November, 2008 Printed: November, 2008 83

EurAsian Journal of BioSciences Chory 1999, Mussig et al. 2002, Sasse 2003). In addition to stimulating growth, they are effective in reducing abiotic stresses such as moisture, drought, low and high temperature, salinity, and heavy metal (Clouse and Sasse 1998, Rao et al. 2002, Anuradha and Rao 2003; Ozdemir et al. 2004, Ali et al. 2007, Hayat et al. 2007, Hasan et al. 2008) induced inhibitory effects (Rao et al. 2002). The objective of the present study was to observe the effect of the exogenous application of 24epibrassinolide as a foliar spray on the growth and chlorophyll fluorescence of pepper plants under saline and non-saline conditions. MATERIAL AND METHODS A pot experiment was conducted to assess the interactive effect of the foliar application of 24-epibrassinolide (24-epbr) and root zone salinity on the morpho-physiological attributes of the pepper cultivar 'Beldi'. Seeds were obtained from Department of Agronomy, Institut Supérieur Agronomique de Chott Mariem, Sousse (Tunisie). Fifteen seeds were sown in each small plastic pot (10 pots) at 10 mm depth. Pots were filled with commercial peat. They were germinated in a greenhouse under natural light conditions, a daytime temperature of 24-30°C. After the second true leaf appeared, the combine effect of salinity and 24-epibrassinolide was investigated by applying two salinity levels (0 and 4 g L-1 NaCl) and five 24-epibrassinolide levels (0.0, 0.01, 0.05, 0.1, and 0.5 mg L-1). 2 mg of 24-epibrassinolide (Sigma-E 1641) was dissolved in 2 mL of ethanol (stock solution). Different concentrations of 24epibrassinolide were made by dilute a volume of stock solution with distilled water. The treatment was applied once with a manual sprayer, plants from each treatment were sprayed with 150 mL of each solution. Growth measurement After 12 days of treatment application, the data were recorded. Fifteen plants, representing each treatment, were up-rooted carefully and washed properly under tap water. Plant height and roots lengths were recorded. The plants were then separated into 84

Houimli et al. roots and shoots. Leaf area was measured with a LI-3100 leaf meter (LI-COR. Inc., Lincoln, NE, USA). Shoots and roots fresh weights (FW) were determined, and dry weights (DW) were obtained after oven drying the samples at 70°C for 72 h. Leaf relative water contents The relative water contents (RWC) in the leaf samples was estimated using the following equation Turner (1981): RWC (%)= [(FW - DW)/ (TW - DW)] 100 Where, FW is fresh weight, DW is dry weight and TW is turgid weight. Chlorophyll fluorescence Chlorophyll fluorescence was measured using a portable fluorometer F.I.M, 1500, ADC (Fluorescence Induction Monitor 1550, Analytical Development Company Limited). The leaf was dark-adapted for 30 min, then dark fluorescence F0, maximal fluorescence Fm and photochemical yield Fv/Fm (where, Fv= Fm-F0) were recorded. Statistical analysis All analyses were done on a completely randomized. The results were subjected to one-way analysis of variance (ANOVA) and the mean differences were compared by the Duncan test at 5% significance level. RESULTS Growth Salinity decreased the length, leaf area, fresh and dry mass of shoots (Fig. 1). Whereas the 24-epibrassinolide increased the values for both stressed and unstressed plants. Under the control conditions, all 24epibrassinolide treatments had ameliorative effects on the shoot parameters growth. The 0.5 mg L-1 level was the most effective. However, under salt stress conditions, only the treatment with 0.5 mg L-1 of 24epibrassinolide significantly increased the length, leaf area, fresh and dry mass (Fig. 1). Exogenous application of different levels of 24-epibrassinolide to seedling pepper plants did not cause a significant increase or decrease effects on the root growth parameters including the length, fresh and dry mass of pepper plants under control or saline conditions, whereas, salinity had a significant ©EurAsian Journal of BioSciences, 2008

EurAsian Journal of BioSciences

Houimli et al.

Fig 1. Effects of 24-epibrassinolide (EBR) at different concentrations on shoot growth parameters. (A) length (cm), (B) leaf area (cm2), (C) Fresh and (D) dry mass (mg) of pepper plants grown under control (closed circles) and saline conditions (open circles).

Fig 2. Effects of 24-epibrassinolide (EBR) at different concentrations on the relative water content of pepper plants grown under control (closed circles) and saline conditions (open circles).

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