Outline
Comptes Rendus

Pharmacology, toxicology / Pharmacologie, toxicologie
Responses of antioxidant potentials in Dioscorea rotundata Poir. following paclobutrazol drenching
Comptes Rendus. Biologies, Volume 330 (2007) no. 11, pp. 798-805.

Abstract

The effect of paclobutrazol (PBZ) treatments on the antioxidant metabolism of white yam (Dioscorea rotundata Poir.) was investigated in the present study. PBZ @ 15 mg l−1 plant−1 was given to plants by soil drenching, 30, 60, and 90 days after planting (DAP). The non-enzymatic antioxidant contents like ascorbic acid (AA), reduced glutathione (GSH) and α-tocopherol (α-toc), activities of antioxidant enzymes like superoxide dismutase (SOD), ascorbate peroxidase (APX), polyphenol oxidase (PPO) and catalase (CAT) were extracted and assayed on 100 DAP from leaf, stem and tubers of both control and PBZ treated plants. It was found that PBZ has a profound effect on the antioxidant metabolism and caused an enhancement in both non-enzymatic and enzymatic antioxidant potentials under treatments in white yam. Our results have good significance, as this increase the innate antioxidant potential of this food crop, which is helpful to satisfy the needs of antioxidants in diet and thereby make it an economically important food crop.

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DOI: 10.1016/j.crvi.2007.08.010
Keywords: Dioscorea rotundata, Paclobutrazol, Antioxidants, Antioxidant enzymes

Cheruth Abdul Jaleel 1; Paramasivam Manivannan 1; Muthiah Gomathinayagam 1; Ramalingam Sridharan 1; Rajaram Panneerselvam 1

1 Stress Physiology Lab, Department of Botany, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India
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     author = {Cheruth Abdul Jaleel and Paramasivam Manivannan and Muthiah Gomathinayagam and Ramalingam Sridharan and Rajaram Panneerselvam},
     title = {Responses of antioxidant potentials in {\protect\emph{Dioscorea} rotundata} {Poir.} following paclobutrazol drenching},
     journal = {Comptes Rendus. Biologies},
     pages = {798--805},
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Cheruth Abdul Jaleel; Paramasivam Manivannan; Muthiah Gomathinayagam; Ramalingam Sridharan; Rajaram Panneerselvam. Responses of antioxidant potentials in Dioscorea rotundata Poir. following paclobutrazol drenching. Comptes Rendus. Biologies, Volume 330 (2007) no. 11, pp. 798-805. doi : 10.1016/j.crvi.2007.08.010. https://comptes-rendus.academie-sciences.fr/biologies/articles/10.1016/j.crvi.2007.08.010/

Version originale du texte intégral

1 Introduction

Cellular damage or oxidative injury arising from free radicals or reactive oxygen species (ROS) now appears the fundamental mechanism underlying a number of human diseases [1]. Antioxidants are radical scavengers, which protect the human body against free radicals that may cause pathological conditions such as anaemia, asthma, arthrists, inflammation, neurodegeneration, Parkinson's diseases, mongolism, ageing process, and perhaps dementias [2]. Free radicals can be scavenged through chemoprevention utilizing natural antioxidant compounds present in foods [3] and medicinal plants [4]. Some medicinal plants have been shown to have both chemopreventive and/or therapeutic effects on human diseases [5].

A pathway for ascorbic acid (AA) biosynthesis featuring GDP-mannose and l-galactose has recently been proposed for plants. AA is a very important reducing substrate for H2O2 detoxification in photosynthetic organisms [6]. AA participates in the removal of H2O2 as a substrate of ascorbate peroxidase (APX). Reduced glutathione (GSH) is another most important non-enzymatic antioxidant molecule, which functions as an effective ROS detoxifier [7]. α-Tocopherol (α-toc) was consumed predominantly as a radical scavenging antioxidant against lipid peroxidation [8].

The enzymatic antioxidant defence system includes superoxide dismutase (SOD), ascorbate peroxidase (APX), polyphenol oxidase (PPO), catalase (CAT) and glutathione reductase (GR) [9]. SOD is a major scavenger of superoxide anion radical (O2) that catalyses the dismutations of O2 with great efficiency, resulting in the production of H2O2 and O2 [10]. The H2O2 scavenging system represented by APX and CAT are more important in imparting tolerance than SOD, as reported in plants subjected to oxidative sreesses [11]. PPO is believed to be ubiquitous in the plant kingdom and they are primarily associated with the enzymatic browning and off-flavour generation [12].

White yam (Dioscorea rotundata Poir.) is one of the important edible tuber crops cultivated in India and many other tropical countries, including Africa [13]. Yams are valuable sources of carbohydrate, fibres, and low-level fats, which makes them a good dietary nutrient, and also processed into various staple, intermediate, and end-product forms [14]. Yams also have medicinal properties. Several species of Dioscorea are amongst the principle sources of diosgenin, which can be converted into medicinally important steroids [15]. Diosgenin is transferred to serum dehydroepiandrosterone in human intestine and is associated with reduced lipid peroxidation and lowered serum triglycerides [16]. A lot of works have already covered the food value [17], nutritional aspects [18], cultivation [19], processing technologies [20], medicinal aspects [21,22], growth-regulator effects [14,23,24], tissue culture, and genetic stability studies [25] of yam plants. But only little attention has been drawn to the antioxidant properties of this food plant. Although there are reports on effects of temperature on antioxidative status of yams [26] and antioxidant variations in different physiological regions of yam tubes [12], the literature regarding antioxidant properties and methods to enhance the antioxidant potentials in white yam is scarce. It therefore seems important to test the methods to increase the innate antioxidant potential of this food crop, in order to satisfy the needs for antioxidants in diet and thereby make it an economically important food crop.

Triazoles are a group of compounds, which have both fungitoxic and plant growth-regulating properties [27]. In addition, they can also protect plants against various environmental stresses [28]. Triazoles affect the isoprenoid pathway, and alter the levels of certain plant hormones by inhibiting gibberellin synthesis, reducing ethylene evolution, and increasing cytokinin levels [29]. Some of the previous works carried out in our lab revealed the morphological and physiological changes associated with triazole treatment in various plants, including inhibition of plant growth, decreased internodal elongation, increased chlorophyll levels, enlarged chloroplasts, thicker leaf tissue, increased root-to-shoot ratio, alkaloid production and enhancement in carbohydrate metabolism [14,24,30–38]. Paclobutrazol (PBZ) [(2RS; 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-12,4-triazol-1-yl)-pentan-3-ol], a triazole, fungicide, having plant-growth regulator (PGR) properties, is reported to inhibit gibberellic acid (GA) biosynthesis and increase abscisic acid (ABA) and cytokinin contents [27]. Therefore, there is a need to investigate the efficacy of this compound in the enhancement of antioxidant potentials in white yam plants in order to increase their medicinal properties, thereby making them an economically valuable crop plant. Hence, this study aims to evaluate the ability of PBZ to enhance the antioxidative potentials, with special emphasis to both non-enzymatic and enzymatic antioxidant constituents.

2 Materials and methods

2.1 Plant materials and PBZ treatment

Tubers of Dioscorea rotundata cv. Sree Priya were obtained from the Central Tuber Crop Research Institute (CTCRI), Kerala, India, and planted at the Botanical Garden of the Annamalai University. PBZ was obtained as CULTAR 25% w/v. In the preliminary experiments, four concentrations (10, 15, 20, and 25 mg l−1 plant−1) of PBZ were prepared and used for tuber treatment, in order to determine the optimum concentration at which maximum sprouting occurred. Among these concentrations, 15 mg l−1 plant−1 was found to enhance the antioxidant potentials; at lower (10 mg l−1 plant−1) and higher (20 and 25 mg l−1 plant−1) concentrations, there was no significant effect. Hence, 15 mg l−1 plant−1 were used for this study. The treatment was given by soil drenching on three vegetative growth periods, i.e., 30, 60, and 90 DAP. For each treatment, one litre of the solution was used. The control plants were given tap water. The plants were uprooted on 100 DAP washed and separated into leaf stem and tubers for extraction and assay of antioxidant potentials.

2.2 Non-enzymatic antioxidant estimations

2.2.1 Ascorbic acid content

Ascorbic acid (AA) content was assayed as described by Omay et al. [39]. The extract was prepared by grinding 1 g of fresh material with 5 ml of 10% TCA, centrifuged at 3500 rpm for 20 min, and re-extracted twice; the supernatant was made up to 10 ml and used for assay. To 0.5 ml of extract, 1 ml of DTC reagent (2,4-dinitrophenyl hydrazine-thiourea-CuSO4 reagent) was added, incubated at 37 °C for 3 h and 0.75 ml of ice-cold 65% H2SO4 was added, allowed to stand at 30 °C for 30 min; the resulting colour was read at 520 nm in a spectrophotometer (U-2001-Hitachi). The AA content was determined using a standard curve prepared with AA.

2.2.2 Reduced glutathione

The reduced glutathione (GSH) content was assayed as described by Griffith and Meister [40]. 200 mg of fresh material was ground with 2 ml of 2% metaphosphoric acid, and centrifuged at 17,000 rpm for 10 min. The supernatant was neutralized by adding 0.6 ml of 10% sodium citrate. 1 ml of assay mixture was prepared by adding 100 μl of extract, 100 μl of distilled water, 100 μl of 5,5-dithio-bis-(2-nitrobenzoic acid), and 700 μl of NADPH. The mixture was stabilized at 25 °C for 3–4 min. Then 10 μl of glutathione reductase were added, and the absorbance was read at 412 nm in a spectrophotometer.

2.2.3 α-Tocopherol content

α-Tocopherol (α-toc) activity was assayed as described by Backer et al. [41]. 500 mg of fresh tissue were homogenized with 10 ml of a mixture of petroleum ether and ethanol (2:1.6 v/v), and the extract was centrifuged at 10,000 rpm for 20 min, whereas the supernatant was used for estimation of α-toc. To 1 ml of extract, 0.2 ml of 2% 2,2-dipyridyl in ethanol was added and mixed thoroughly and kept in dark for 5 min. The resulting red colour was diluted with 4 ml of distilled water and mixed well. The resulting colour in the aqueous layer was measured at 520 nm. The α-toc content was calculated using a standard graph made with known amount of this species.

2.3 Antioxidant enzyme extractions and assays

2.3.1 Superoxide dismutase (SOD, EC 1.15.1.1)

The activity of SOD was assayed as described by Beauchamp and Fridovich [42]. The reaction mixture contained 1.17×10−6 M of riboflavin, 0.1 M of methionine, 2×10−5 M of KCN, and 5.6×10−5 M of nitroblue tetrazolium (NBT) salt dissolved in 3 ml of 0.05 M sodium phosphate buffer (pH 7.8). Three millilitres of the reaction medium were added to 1 ml of enzyme extract. The mixtures were illuminated in glass test tubes by two sets of Philips 40-W fluorescent tubes in a single row. Illumination was started to initiate the reaction at 30 °C for 1 h. Identical solutions that were kept under dark served as blanks. The absorbance was read at 560 nm in the spectrophotometer against the blank. The SOD activity is expressed in U mg−1 protein (U = change in 0.1 absorbance h−1 mg−1 protein).

2.3.2 Ascorbate peroxidase (APX, EC 1.11.1.1)

The activity of APX was determined by the method of Asada and Takahashi [43]. The reaction mixture (1 ml) contained 50 mM of potassium phosphate buffer (pH 7.0), 0.5 mM of ascorbic acid, 0.1 mM H2O2, and 200 μl of enzyme extract. The absorbance was read as decrease at 290 nm against the blank, correction was done for the low, non-enzymatic oxidation of ascorbic acid by H2O2 (extinction coefficient 2.9 mM−1 cm−1). The enzyme activity was expressed in units mg−1 protein (U = change in 0.1 absorbance min−1 mg−1 protein).

2.3.3 Polyphenol oxidase (PPO, EC 1.10.3.1)

The assay of PPO was carried out by the method of Kumar and Khan [44]. Assay mixture for PPO contained 2 ml of 0.1 M phosphate buffer (pH 6.0), 1 ml of 0.1 M catechol, and 0.5 ml of enzyme extract. This was incubated for 5 min at 25 °C, after which the reaction was stopped by adding 1 ml of 2.5 N H2SO4. The absorbance of the purpurogallin formed was read at 495 nm. 2.5 N H2SO4 was added at the zero time to the blank of the same assay mixture. PPO activity is expressed in U mg−1 protein (U = change in 0.1 absorbance min−1 mg−1 protein).

2.3.4 Catalase (CAT, 1.11.1.6)

The activity of CAT was measured according the method of Chandlee and Scandalios [45] with small modifications. The assay mixture contained 2.6 ml of 50 mM potassium phosphate buffer (pH 7.0), 0.4 ml of 15 mM H2O2, and 0.04 ml of enzyme extract. The decomposition of H2O2 was followed by the decline in absorbance at 240 nm. The enzyme activity was expressed in units mg−1 protein (U = 1 mM of H2O2 reduction min−1 mg−1 protein). The enzyme protein was estimated by the method of Bradford [46] for all the enzymes.

2.4 Statistical analysis

Statistical analysis was performed using the one-way analysis of variance (ANOVA) followed by the Duncan's Multiple Range Test (DMRT). The values are mean ± SD for six samples in each group. p values ⩽0.05 were considered as significant.

3 Results and discussion

The effect of PBZ treatments on antioxidant potentials was previously checked after seven days of each treatment (data not shown) and it was shown that 90 DAP treatment and 100 DAP sampling were sufficient to indicate, in a reliable way, the new activity levels of the antioxidative status.

The non-enzymatic antioxidant, AA, content varied with the application of PBZ @ 15 mg l−1 plant−1 in D. rotundata plants when compared to control. Fig. 1a shows the changes in AA content of white yam on 100 DAP due to PBZ treatment. The AA content in leaf, stem, and tuber increased largely in PBZ-treated plants when compared to control. GSH content was highly influenced in all parts of the plants due to PBZ treatment (Fig. 1b). α-Toc content also increased under PBZ treatment in white yam when compared to control plants (Fig. 1c). The increase extent was larger in the tubers compared to other parts of the plant.

Fig. 1

Effect of PBZ (15 mg l−1 plant−1) on AA (a), GSH (b) and α-toc (c) contents of leaf, stem, and tubers of Dioscorea rotundata plants. Values are given as mean ± SD of six samples in each group. Bar values are not sharing a common superscript (a, b) differ significantly at p⩽0.05 (DMRT).

The non-enzymatic antioxidant contents play major roles in maintaining the balance between free-radical production and elimination [47]. Jaleel et al. [48] have shown that plant-growth regulator treatments in Catharanthus roseus induced several changes in the antioxidative system profiles. In plants, the AA-glutathione cycle has been shown to be of great importance in free-radical scavenging and in multiple-stress reactions [49]. The enhancement of antioxidant defence mechanism under triazole treatment can be correlated with the ability of triazoles in protecting plants from abiotic stresses [33–35,37]. PBZ-treated plants have a more efficient free-radical scavenging system that enables them to detoxify active oxygen species [50]. The application of this triazole compound, being a fungicide that can alter the metabolic equilibrium, can exhibit stress-like symptoms in plants [51], but simultaneously it can protect plants from apparently unrelated abiotic stresses, like the NaCl one [34].

The increase in non-enzymatic antioxidants can be correlated with plants' native protective mechanism against oxidative stress arisen from fungicide application [36]. Being the major antioxidant species in plants, the contents in AA, GSH, and α-toc vary in different subcellular compartments, according to the intensity of the stress [52]. The GSH content was found increased under pesticide and herbicide application [53], as well as in drought-stressed Catharanthus roseus [47]. The increase in GSH can be correlated with its ability to scavenge single oxygen, peroxides, and hydroxyl radicals and is involved in recycling of AA in the ascorbate-glutathione pathway in chloroplasts [54]. An increase in the AA content was reported in Catharanthus plants under salinity [34,55]. AA being a triazole compound, our results are also in agreement with this. AA can function as the ‘terminal antioxidant’ on plants because the redox potential of ascorbate/monodehydro ascorbate pair (+280 nm) is lower than that of most of the bioradicals [56]. From out results, it can be concluded that the PBZ application can enhance largely the non-enzymatic antioxidants' quantity, which is of great importance in imparting economic values to the plant.

Fig. 2a represents the comparison of the effects of PBZ-treatment on SOD activity in leaf, stem, and tubers of white yam on 100 DAP with untreated control plants. In case of non-PBZ plants, the SOD-activity remains low, whereas the addition of PBZ enhanced the SOD-activity; this was highly marked over the control plants. Fig. 2b illustrates the APX activity in the yam plants under cultivation with or without PBZ-treatment on 100 DAP. From the figure, it is clear that the APX activity was increased due to PBZ treatment in all parts of the plant. In different parts (leaf, stem, and tuber), the PPO activity varied considerably. PPO activity increased due to PBZ treatment when compared to control on 100 DAP (Fig. 2c). The CAT activity was comparatively low in white yam plants. There was only a slight increase in the activity of this antioxidant enzyme upon treatment with PBZ (Fig. 2d).

Fig. 2

Effect of PBZ (15 mg l−1 plant−1) on SOD (a), APX (b), PPO (c) and CAT (d) activities of leaf, stem, and tubers of Dioscorea rotundata plants. Values are given as mean ± SD of six samples in each group. Bar values are not sharing a common superscript (a, b) differ significantly at p⩽0.05 (DMRT).

Plants receiving PBZ have significantly higher antioxidative system levels when compared to plants under non-PBZ normal conditions [57]. The involvement of the antioxidative system in the regulation of free-radical metabolism was followed by measuring changes in the antioxidant enzyme activities when plants experience stress from an abiotic factor like a fungicide (PBZ); there should be an enhancement in the production of toxic free-radicals of H2O2, O2, O2 or OH, which should be detoxified in terms of increased antioxidant enzyme activities. Enhancement of SOD activity under PBZ treatment may be an indicator of superoxide production. High levels of SOD should be followed by scavenging of H2O2 catalysed by APX and CAT [47]. The APX found in organelles is believed to scavenge H2O2 produced from the organelles, whereas the function of cytosolic APX is probably to eliminate H2O2 that is produced in the cytosol or apoplast and that has diffused from organelles [58]. Increased APX, SOD, and CAT activities were reported in propiconazole-treated Vigna plants [33] and in Catharanthus roseus under drought stress [47]. The increase in CAT found under PBZ treatment was of great importance in plants' protective mechanisms under abiotic stress. The H2O2 scavenging system represented by CAT is more important in imparting tolerance than SOD, as reported in oxidative-stressed Catharanthus plants [59]. The changes in CAT may vary according to the intensity of stress, time of assay after stress and induction of new isozyme(s) [60]. The level of antioxidative response depends on species, the development, and the metabolic state of the plant, as well as on the duration and intensity of the stress [61]. In conclusion, our results indicated that the PBZ application at low concentration could be used as a potential tool to increase non-enzymatic and enzymatic antioxidant potentials in food plants like D. rotundata.


References

[1] M.G. Repetto; S.F. Llesuy Antioxidant properties of natural compounds used in popular medicine for gastric-ulcers, Braz. J. Med. Biol. Res., Volume 35 (2002), pp. 523-534

[2] O. Polterait Antioxidants and free radical scavengers of natural origin, Curr. Org. Chem., Volume 1 (1997), pp. 415-440

[3] F. Borelli; A.A. Izzo The plant kingdom as a source of anti-ulcer remedies, Phytother. Res., Volume 14 (2000), pp. 581-591

[4] M.C. Sabu; R. Kuttan Antidiabetic activity of medicinal plants and its relationship with their antioxidant property, J. Ethnopharmacol., Volume 81 (2002), pp. 155-160

[5] S. F'guyer; F. Afaq; H. Mukhtar Photoprevention of skin cancer by botanical agents, Photodermatol. Photoimmunol. Photomed., Volume 19 (2003), pp. 56-72

[6] S.E. Lee; H.J. Hwang; J.S. Ha; H.S. Jeong; J.H. Kim Screening of medicinal extracts for antioxidant activity, Life Sci., Volume 73 (2003), pp. 167-179

[7] N. Chaparzadeh; M.L. Amico; R.K. Nejad; R. Izzo; F.N. Izzo Antioxidative responses of Calendula officinalis under salinity conditions, Plant Physiol. Biochem., Volume 42 (2004), pp. 695-701

[8] M.G. Bartoli; M. Simontacchi; E. Tambussi; J. Beltrano; J. Montaldi; S. Puntarulo Drought and watering-dependent oxidative stress: Effect of antioxidant content in Triticum aestivum L. leaves, J. Exp. Bot., Volume 50 (1999), pp. 375-383

[9] D. Prochazkova; R.K. Sairam; G.C. Srivastava; D.V. Singh Oxidative stress and antioxidant activity as the basis of senescence in maize leaves, Plant Sci., Volume 161 (2001), pp. 765-771

[10] N. Smirnoff; G.L. Wheeler Ascorbic acid in plants: Biosynthesis and function, Crit. Rev. Plant Sci., Volume 19 (2000), pp. 267-290

[11] S. Elkahoui; J.A. Hernandes; C. Abdelly; R. Ghrir; F. Limam Effects of salt on lipid peroxidation and antioxidant enzyme activities of Catharanthus roseus suspension cells, Plant Sci., Volume 168 (2005), pp. 607-613

[12] G.K. Isamah; S.O. Asagba; A.E. Thomas Lipid peroxidation o-diphenolase, superoxide dismutase and catalase profile along the three physiological regions of Dioscorea rotundata Poir. cv. Omi., Food Chem., Volume 69 (2000), pp. 1-4

[13] R. Panneerselvam; C.A. Jaleel; R. Somasundaram; R. Sridharan; M. Gomathinayagam Carbohydrate metabolism in Dioscorea esculenta (Lour.) Burk. tubers and Curcuma longa L. rhizomes during two phases of dormancy, Colloids Surf. B: Biointerfaces, Volume 59 (2007), pp. 59-66

[14] C.A. Jaleel; R. Gopi; P. Manivannan; A. Kishorekumar; M. Gomathinayagam; R. Panneerselvam Changes in biochemical constituents and induction of early sprouting by triadimefon treatment in white yam (Dioscorea rotundata Poir.) tubers during storage, J. Zhejiang Univ. Sci.: B, Volume 8 (2007), pp. 283-288

[15] J. Van Staden; D.L. Fowlds Micropropagation of medicinal Dioscorea species (Y.P.S. Bajaj, ed.), High-Tech and Micropropagation III, Biotechnology in Agriculture and Forestry, vol. 19, Springer-Verlag, Berlin, Heidelberg, 1992, pp. 425-442

[16] B. Chapagain; Z. Wiesman Variation in diosgenin level in seed kernels among different provenances of Balanites aegyptiaca Del (Zygophyllaceae) and its correlation with oil content, Afr. J. Biotechnol., Volume 4 (2005), pp. 1209-1213

[17] I.O. Fasidi; N.O. Bakare Distribution of food reserves in Dioscorea dumetorum (Kunth) Pax tubers during sprouting, Food Chem., Volume 52 (1995), pp. 423-426

[18] P.B.A. Grindley; F. Omoruyi; H.N. Asemota; E.Y.A. Morrison Carbohydrate digestion and intestinal ATPases in streptozotocin induced diabetic rats fed extract of yam (Dioscorea cayenensis) or dasheen (Colocasia esculenta), Nutr. Res., Volume 22 (2002), pp. 333-341

[19] F.O. Olasantan Effect of time of mulching on soil temperature and moisture regime and emergence, growth and yield of white yam in Western Nigeria, Soil Tillage Res., Volume 50 (1999), pp. 215-221

[20] S.E. Omonigho; S.E. Ikenebomeh Effects of different preservative treatments on the chemical changes of pounded white yam (Dioscorea rotundata) in storage at 28±2°C, Food Chem., Volume 68 (2000), pp. 201-209

[21] J.E. Kelmanson; A.K. Jager; J. Van Staden Zulu medicinal plants with antibacterial activity, J. Ethnopharmacol., Volume 69 (2000), pp. 241-246

[22] M.G. Kulkarni; R.A. Street; J. Van Staden Germination and seedling growth requirements for propagation of Dioscorea dregeana (Kunth) Dur. and Schinz – A tuberous medicinal plant, South Afr. J. Bot., Volume 73 (2007), pp. 131-137

[23] S.K. Kim; J.T. Kim; S.W. Jang; S.C. Lee; B.H. Lee; J.J. Lee Exogenous effect of gibberellins and jasmonate on tuber enlargement of Dioscorea opposita, Agron. Res., Volume 3 (2005), pp. 39-44

[24] C.A. Jaleel; A. Kishorekumar; P. Manivannan; B. Sankar; M. Gomathinayagam; R. Gopi; R. Somasundaram; R. Panneerselvam Alterations in carbohydrate metabolism and enhancement in tuber production in white yam (Dioscorea rotundata Poir.) under triadimefon and hexaconazole applications, Plant Growth Regul., Volume 53 (2007), pp. 7-16

[25] S. Ahuja; B.B. Mandal; S. Dixit; P.S. Srivastava Molecular, phenotypic and biosynthetic stability in Dioscorea floribunda plants derived from cryopreserved shoot tips, Plant Sci., Volume 163 (2002), pp. 971-977

[26] Y.T. Chen; K.W. Lin Effects of heating temperature on the total phenolic compound, antioxidative ability and the stability of dioscorin of various yam cultivars, Food Chem., Volume 101 (2007), pp. 955-963

[27] R.A. Fletcher; A. Gilley; T.D. Davis; N. Sankhla Triazoles as plant growth regulators and stress protectants, Hort. Rev., Volume 24 (2000), pp. 55-138

[28] L.A.C.I. Voesenek; J.J. Benschop; J. Bou; M.C.H. Cox; R.A.M. Vreeburg; A.J.M. Peeters Interactions between plant hormones regulate submergence-induced shoot elongation in the flooding-tolerant dicot Rumex palustris, Ann. Bot., Volume 91 (2003), pp. 205-211

[29] A.P. Kamountsis; A.G. Chronopoulon-Sereli Paclobutrazol affects growth and flower bud production in gardenia under different light regimes, Hort. Sci., Volume 34 (1999), pp. 674-675

[30] C.A. Jaleel; R. Gopi; P. Manivannan; A. Kishorekumar; B. Sankar; R. Panneerselvam Paclobutrazol influences on vegetative growth and floral characteristics of Catharanthus roseus (L.) G. Don., Indian J. Appl. Pure Biol., Volume 21 (2006), pp. 369-372

[31] A. Kishorekumar; C.A. Jaleel; P. Manivannan; B. Sankar; R. Sridharan; R. Somasundaram; R. Panneerselvam Differential effects of hexaconazole and paclobutrazol on the foliage characteristics of Chinese potato (Solenostemon rotundifolius Poir., J.K. Morton), Acta Biol. Szegediensis, Volume 50 (2006), pp. 127-129

[32] A. Kishorekumar; C.A. Jaleel; P. Manivannan; B. Sankar; R. Sridharan; R. Panneerselvam Comparative effects of different triazole compounds on growth, photosynthetic pigments and carbohydrate metabolism of Solenostemon rotundifolius, Colloids Surf. B: Biointerfaces (2007) | DOI

[33] P. Manivannan; C.A. Jaleel; A. Kishorekumar; B. Sankar; R. Somasundaram; R. Sridharan; R. Panneerselvam Propiconazole induced changes in antioxidant metabolism and drought stress amelioration in Vigna unguiculata (L.) Walp., Colloids Surf. B: Biointerfaces, Volume 57 (2007), pp. 69-74

[34] C.A. Jaleel; R. Gopi; P. Manivannan; R. Panneerselvam Responses of antioxidant defense system of Catharanthus roseus (L.) G. Don. to paclobutrazol treatment under salinity, Acta Physiol. Plant., Volume 29 (2007), pp. 205-209

[35] C.A. Jaleel; P. Manivannan; B. Sankar; A. Kishorekumar; R. Gopi; R. Somasundaram; R. Panneerselvam Induction of drought stress tolerance by ketoconazole in Catharanthus roseus is mediated by enhanced antioxidant potentials and secondary metabolite accumulation, Colloids Surf. B: Biointerfaces (2007) | DOI

[36] C.A. Jaleel; R. Gopi; G.M. Alagu Lakshmanan; R. Panneerselvam Triadimefon induced changes in the antioxidant metabolism and ajmalicine production in Catharanthus roseus (L.) G. Don., Plant Sci., Volume 171 (2006), pp. 271-276

[37] B. Sankar; C.A. Jaleel; P. Manivannan; A. Kishorekumar; R. Somasundaram; R. Panneerselvam Effect of paclobutrazol on water stress amelioration through antioxidants and free radical scavenging enzymes in Arachis hypogaea L., Colloids Surf. B: Biointerfaces (2007) | DOI

[38] M. Gomathinayagam; C.A. Jaleel; G.M.A. Lakshmanan; R. Panneerselvam Changes in carbohydrate metabolism by triazole growth regulators in cassava (Manihot esculenta Crantz); effects on tuber production and quality, Comptes Rendus Biologies, Volume 330 (2007), pp. 644-655

[39] S.T. Omaye; J.D. Turnbull; H.E. Sauberilich Selected methods for the determination of ascorbic acid in animal cells, tissues and fluids, Methods in Enzymology, Academic Press, New York, 1979, pp. 3-11

[40] O.W. Griffith; A. Meister Potent and specific inhibition of glutathione synthesis by buthionine sulfoximine (S-n-butylhomocysteine sulfoximine), J. Biol. Chem., Volume 254 (1979), pp. 7558-7560

[41] H. Backer; O. Frank; B. De Angells; S. Feingold Plasma tocopherol in man at various times after ingesting free or ocetylaned tocopherol, Nutr. Rep. Int., Volume 21 (1980), pp. 531-536

[42] C. Beauchamp; I. Fridovich Superoxide dismutase: Improve assays and an essay applicable to acrylamide gels, Ann. Biochem., Volume 44 (1971), pp. 276-287

[43] K. Asada; M. Takahashi Production and scavenging of active oxygen in photosynthesis (D.J. Kyle; B. Osmond; C.J. Arntzen, eds.), Photoinhibition, Elsevier, Amsterdam, 1987, pp. 227-287

[44] K.B. Kumar; P.A. Khan Peroxidase and polyphenol oxidase in excised ragi (Eleusine coracana cv. PR 202) leaves during senescence, Indian J. Exp. Bot., Volume 20 (1982), pp. 412-416

[45] J.M. Chandlee; J.G. Scandalios Analysis of variants affecting the catalase development program in maize scutellum, Theor. Appl. Gen., Volume 69 (1984), pp. 71-77

[46] M.M. Bradford A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein dye binding, Ann. Biochem., Volume 72 (1976), pp. 248-253

[47] C.A. Jaleel; P. Manivannan; B. Sankar; A. Kishorekumar; R. Gopi; R. Somasundaram; R. Panneerselvam Water deficit stress mitigation by calcium chloride in Catharanthus roseus; effects on oxidative stress, proline metabolism and indole alkaloid accumulation, Colloids Surf. B: Biointerfaces, Volume 60 (2007), pp. 110-116

[48] C.A. Jaleel; R. Gopi; P. Manivannan; B. Sankar; A. Kishorekumar; R. Panneerselvam Antioxidant potentials and ajmalicine accumulation in Catharanthus roseus after treatment with giberellic acid, Colloids Surf. B: Biointerfaces (2007) | DOI

[49] M. Drazkiewicz; E.S. Polit; Z. Krupa Response of ascorbate-glutathione cycle to excess copper in Arabidopsis thaliana (L.), Plant Sci., Volume 164 (2003), pp. 195-202

[50] M. Kopyra; E.A. Gwozdz Antioxidant enzymes in paraquat and cadmium resistant cell lines of horseradish, Biol. Lett., Volume 40 (2003), pp. 61-69

[51] E. Nilsen; D.M. Orcutt The Physiology of Plants Under Stress-Abiotic Factors, John Wiley and Sons, Inc., New York, 1996 (p. 689)

[52] T. Gaspar; T. Frank; B. Bisbis; C. Kevers; L. Jouve; J.F. Hausman; J. Dommes Concepts in plant stress physiology, application to plant tissue cultures, Plant Growth Regul., Volume 37 (2002), pp. 263-285

[53] D.G. Davis; H.R. Swanson Activity of stress-related enzymes in the perennial weed Leafy spurge (Euphorbia esula L.), Environ. Exp. Bot., Volume 46 (2001), pp. 95-108

[54] C.H. Foyer Prospects for enhancement of the soluble antioxidants, ascorbate and glutathione, BioFac., Volume 15 (2001), pp. 75-78

[55] C.A. Jaleel; R. Gopi; P. Manivannan; R. Panneerselvam Antioxidative potentials as a protective mechanism in Catharanthus roseus (L.) G. Don. plants under salinity stress, Turk. J. Bot., Volume 31 (2007), pp. 245-251

[56] J.G. Scandalios; L. Guan; A.N. Polidoros Catalases in plants: gene structure, properties, regulation and expression (J.G. Scandalios, ed.), Oxidative Stress and the Molecular Biology of Antioxidant Defenses, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, USA, 1997, pp. 343-406

[57] S. Lurie; R.Z. Lipsker; B. Aloni Effects of paclobutrazol and chilling temperatures on lipids, antioxidants and ATPase activity of plasma membrane isolated from green bell pepper fruits, Physiol. Plant., Volume 91 (1994), pp. 593-598

[58] K. Asada Ascorbate peroxidase a hydrogen-scavenging enzyme in plants, Physiol. Plant., Volume 85 (1992), pp. 235-241

[59] C.A. Jaleel; P. Manivannan; A. Kishorekumar; B. Sankar; R. Panneerselvam Calcium chloride effects on salinity induced oxidative stress, proline metabolism and indole alkaloid accumulation in Catharanthus roseus, C. R. Biologies, Volume 330 (2007) no. 9, pp. 674-683

[60] C.A. Jaleel; P. Manivannan; A. Kishorekumar; B. Sankar; R. Gopi; R. Somasundaram; R. Panneerselvam Alterations in osmoregulation, antioxidant enzymes and indole alkaloid levels in Catharanthus roseus exposed to water deficit, Colloids Surf. B: Biointerfaces, Volume 59 (2007), pp. 150-157

[61] B. Karthikeyan; C.A. Jaleel; R. Gopi; M. Deiveekasundaram Alterations in seedling vigour and antioxidant enzyme activities in Catharanthus roseus under seed priming with native diazotrophs, J. Zhejiang Univ. Sci. B, Volume 8 (2007), pp. 453-457


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