All the chemicals and solvents used in this study were of analytical grade and obtained from HiMedia Chemicals Mumbai, India.
Plant material
The whole plants of S. pauciflorum were collected from the fields locally during July-October, 2008. The botanical identity was confirmed by Herbarium, Department of Botany, University of Rajasthan, Jaipur. (Voucher specimen NO. 110). The plant has been deposited at the Herbarium and Laboratory for further reference.
Establishment of cell cultures
S. pauciflorum was collected from the wild regions of Jaipur. Stem explants were excised from the young plant, washed in running tap water for 30 min, dissected into small pieces and then washed with 2% commercial grade detergent for 5 min. Surface disinfection was done by mercuric chloride (0.1% for 4 min) and thoroughly washed with sterile distilled water, 5 min for each wash. Sterilized stem cuttings were cultured on MS (
8) medium consisting of basal salts and vitamins with 3% w/v sucrose and 0.8% agar supplemented with different growth regulators. Indole-3-acetic acid (IAA), Indole-3-butyric acid (IBA) and Kinetin (kn) at various concentrations (0.5, 1, 1.5 and 2 mg/L) were used. The pH of the medium was adjusted to 5.8 and autoclaved at 15 psi for 15 min. Cultures were maintained at 26 ± 2ºC under 16 h photoperiod illuminated by fluorescent light (2000-3000 lux) and 55 ± 5% relative humidity. Regenerated callus were sub-cultured after 6 weeks on the respective medium. Their growth indices and moisture contents were calculated. Callus of 6 weeks age was harvested and used for further study.
Extract preparation
Callus on different growth hormones was harvested (20 mg dry weight in each case) as the whole plant (including root, shoot and leaf), extracted successively in petroleum ether (pet. ether), methanol and water (60 ºC, 24 h). These extracts were filtered through Whatman filter NO. 1, dried, weighed and stored at 4ºC for further experiment.
Phytochemical analysis
Total phenolics were measured by following the method using Folin-Ciocalteu reagent (
9). A stock solution of the standard phenol (gallic acid) was prepared in ethanol, out of which 0.1 to 0.9 mL was taken into separate test tube and raised to 1 mL of ethanol. To each tube, 2.5 mL of deionized water and 0.1 mL (2N) Folin-Ciocalteu reagent was added and allowed to stand for 6 min. Later, 0.5 mL of 20% sodium carbonate solution was added, incubated for 30 min and the absorbance was taken at 750 nm using UV- Vis spectrophotometer. Total phenolics were expressed as mg gallic acid equivalents (GAE/g dry weight).
Total flavonoids content was measured by the aluminum chloride colorimetric assay (
10). A stock solution of standard quercetin was prepared in ethanol, out of which 0.1 to 0.9 mL was taken, raised to 1 mL with ethanol and added to 10 mL volumetric flask containing 4 mL of distilled water. To this, were added 0.3 mL 5% NaNO2, 0.3 mL 10% AlCl3 (after 5 min) and 2 mL of 1 M NaOH (after 1 min) in sequence. Total volume was made up to 10 mL with distilled water. The solution was mixed well and the absorbance was measured against the prepared blank reagent at 510 nm.
The extracts were applied on Thin Layer Chromatography (TLC; silica gel G coated plates) along with the standard reference compounds in air-tight chamber containing benzene : heptane : alcohol (100 : 100 : 1) for triterpenoids (pet. ether extract) and n-butanol : acetic acid : water (4 : 1 : 5; upper phase) for phenolics (methanolic extract). Identification of compounds was carried out by exposing the plates with I2 vapors, NH3 vapors and UV light chambers. Spraying of terpenoids was done with 20% H2SO4 and 10% SbCl3 separately, whereas spraying of phenolic compounds was through 1% methanolic AlCl3 and Folin-Ciocalteu reagent. Rf values of standard and samples were also calculated. The spots coincided to reference markers were scrapped from unsprayed plates, eluted with methanol, filtered, evoparated to dryness, reconstituted and also crystallized in methanol. The melting point of the isolated compounds was determined in capillary tubes (Toshniwal Melting point apparatus) and subjected to ir spectrum (Perkin Elmer 337, Grating Infrared spectrophotometer).
Quantification of the compounds
Quantification was carried out using PTLC. The levels of terpenoids were estimated colorimetrically by Das and Benergee (
11) method. Optical density (OD) was measured at 540 nm against the blank. Standard curves of the identified compounds were prepared using 0.01-0.1 mg/mL concentration. Total levels of caffeic acid were determined using Folin-Ciocalteu colorimetric reagent (
9). OD was taken at 760 nm using UV-visible spectrophotometer. Standard curve of caffeic acid was prepared using 0.01 to 0.01 mg/mL concentration using similar procedure.
Antibacterial efficacy
For antibacterial screening, pure cultures of test bacteria were used. Antimicrobial assay was performed by agar well diffusion method (
12). Inoculum was prepared by suspending bacteria in Nutrient broth medium and fungus in Sabouraud dextrose broth medium overnight at 37ºC (106-107 CFU/mL concentration). Bacterial and fungal suspensions were inoculated in Nutrient agar and Sabouraud dextrose agar plates, respectively. Plates were then incubated at 37 °C for bacteria and 25ºC in case of fungi for appropriate time periods under aerobic conditions. The diameter of the inhibition zone around each well was measured and recorded by Inhibition Zone Recorder (HiMedia, India). Gentamycin (10 mcg/disc) and Ketonocozole (10 mcg/disc) were used as positive controls for bacteria and fungi, respectively.
1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity
The effect on DPPH radical was determined using the method by Fogliano
et al. (
13). Different concentrations of extract (0.8, 0.6, 0.4, 0.2, 0.1 mg/mL) were prepared in methanol and mixed with 2.5 mL of DPPH (2 mg/10 mL methanol). After 30 min of incubation time, OD was measured at 517 nm. Quercetin was used as standard. OD was measured at 517 nm using UV-Vis spectrophotometer. Negative control (methanol) and positive control (quercetin) were also used. Capability to scavenge the DPPH radical was calculated using the following equation:
DPPH scavenging effect (%) = [(A0 - A1 / A0) × 100]
Here, A0 was the absorbance of the control reaction and A1 was the absorbance in presence of the sample of given extract.
Ferric ion reducing antioxidant potentials (FRAP)
Total reducing power of extracts was determined according to FRAP (Ferric ion reducing antioxidant potentials) method (
14). Specific concentration of standard (ascorbic acid) and extract (62.5-1000 μg/mL) was prepared in 1 mL ethanol followed by the addition of 2.5 mL phosphate buffer (0.2 M, pH = 6.6) and potassium ferricyanide (1%). After 20 min of incubation (50ºC), 10% of trichloroacetic acid (2.5 mL) was added and the solution was centrifuged (1000×g) for 10 min. A volume of 2.5 mL of upper layer was taken and mixed with equal amount of distilled water followed by the addition of ferric chloride (0.5 mL; 1%), incubated for 30 min and OD was measured at 700 nm. A standard calibration curve of ascorbic acid (10-500 mg/mL) was prepared and the antioxidant activity was expressed in mg ascorbic acid equivalents (mg AAE/g) of the extract.
Statistical analysis
All the experiments were performed in triplicate, statistically analyzed and expressed as mean ± standard error (SE).