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Plant growth promoting bacteria enhance water stress resistance in green gram plants Article in Acta Physiologiae Plantarum · June 2011 DOI: 10.1007/s11738-010-0539-1

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Acta Physiol Plant (2011) 33:203–209 DOI 10.1007/s11738-010-0539-1

ORIGINAL PAPER

Plant growth promoting bacteria enhance water stress resistance in green gram plants D. Saravanakumar • M. Kavino • T. Raguchander P. Subbian • R. Samiyappan

•

Received: 29 August 2009 / Revised: 6 April 2010 / Accepted: 24 May 2010 / Published online: 6 June 2010 Ó Franciszek Go´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako´w 2010

Abstract Plant growth promoting bacterial (PGPB) strains Pseudomonas fluorescens Pf1 and endophytic Bacillus subtilis EPB5, EPB22, EPB 31 were tested for their capacity to induce water stress related proteins and enzymes in green gram (Vigna radiata) plants. Among the different bacteria used, P. fluorescens Pf1 increased the vigour index, fresh weight and dry weight of green gram seedlings in vitro. Quantitative and qualitative analyses of stress-related enzymes indicated the greater activity of catalase and peroxidase in green gram plants bacterized with P. fluorescens Pf1 against water stress when compared to untreated plants. The greater accumulation of proline was recorded in Pf1 treated plants compared to untreated plants. The pot culture study revealed the greater resistance to water stress by green gram plants treated with P. fluorescens Pf1 compared to untreated plants. The greater activity of stress-related enzymes in green gram plants mediated by PGPB could pave the way for developing drought management strategies.

Communicated by B. Barna. D. Saravanakumar (&) T. Raguchander R. Samiyappan Department of Plant Pathology, Tamil Nadu Agricultural University, Coimbatore 641003, India e-mail: [email protected] M. Kavino Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore 641003, India P. Subbian Department of Agronomy, Tamil Nadu Agricultural University, Coimbatore 641003, India

Keywords Bacillus subtilis Endophytes Plant growth promoting bacteria Pseudomonas fluorescens Water stress

Introduction Plants are constantly exposed to a wide range of environmental stresses which limit plant productivity. Over several centuries, breeding programmes have focused on generating crop species with enhanced productivity under suboptimal environmental conditions. Much work has been carried out in understanding the mechanisms behind plant responses to various biotic and abiotic stresses (Staskawicz et al. 1995; Quartacci et al. 2000; Sgherri et al. 2000). Though many genes are induced by these stresses, the control mechanisms for abiotic stress tolerance are based on activation and regulation of specific set of stress-related genes which are involved in signalling, transcriptional control, and protection of membranes and proteins. Over expression of these genes helps the plant system to escape from the drought and other abiotic stresses (Gaff 1997). In this context, the induction and expression of proteins that may confer improved drought resistance and enzymes by beneficial microbes could result in improved means of drought resistance. In a country like India where large population depend on agriculture for their livelihoods, growth of agriculture assumes greater importance. The agriculture in India mainly relies on two monsoon rains namely South West Monsoon and North East Monsoon. The recent failure in monsoon rain leaves 45% of the cropping area under drought (Indian Meteorological Department 2009). Thus, the identification of beneficial microorganisms which mediate drought resistance in crop plants assumes greater importance. In the

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current study, the plant growth-promoting bacteria (PGPB) were tested to enhance drought resistance in green gram (Vigna radiata), the cheap and best source of protein in India, contributing 20% to the overall world pulse production. PGPB are free-living soil bacteria that can either directly or indirectly facilitate the growth of plants (Glick et al. 1995). Of these, the Pseudomonas fluorescens and endophytic Bacillus subtilis have received particular attention throughout the global science because of their catabolic versatility, excellent root colonizing ability and their capacity to produce a wide range of enzymes and metabolites that favour the plant withstand under varied biotic and abiotic stress conditions (Ramamoorthy et al. 2001; Vivekananthan et al. 2004; Mayak et al. 2004; Saravanakumar and Samiyappan 2007). Though there are several reports on the management of plant diseases (Wang et al. 2000; Saravanakumar et al. 2009) and pests (Saravanakumar et al. 2007a) using PGPB, very little is known about the role of PGPB in mediating drought resistance in field crops. Therefore, the objective was fixed: (a) to evaluate the promising strains of P. fluorescens and B. subtilis to enhance drought resistance on green gram plants and (b) to study the differential enzymatic and protein activity during water stress conditions.

Materials and methods Bacterial strains Plant growth promoting bacteria P. fluorescens Pf1 (Nandakumar et al. 2001; Saravanakumar et al. 2007b), and endophytic B. subtilis strains EPB5, EPB 22, and EPB 31 were obtained from the Culture Collection Section, Department of Plant Pathology, Tamil Nadu Agricultural University, India. Plant growth promotion The P. fluorescens and B. subtilis strains were grown in 100 ml King’s B (KB) and Nutrient broth (NB), respectively, in 250 ml conical flasks on a rotary shaker (150 rev min-1) for 48 h at room temperature (28 ± 2°C). The bacterial cells were harvested and centrifuged at 4,000g for 15 min and resuspended in sterile water. The concentration was adjusted using a spectrophotometer to approximately 108 CFU ml-1 and used as bacterial inoculum (Thompson 1996). The bacterial suspensions were prepared and tested for their plant growth-promoting activity using modified standard roll towel method (ISTA 1993). Green gram seeds (var. CO6) were used for testing the efficacy of plant growth promotion by PGPB in vitro. Green gram seeds soaked in 10 ml of the bacterial suspension

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Acta Physiol Plant (2011) 33:203–209

(108 CFU ml-1) for 2 h were blot dried, placed in wet blotters and two-third of the blotter was immersed in water and incubated in growth chamber for 15 days. The germination percentage of seeds was recorded and vigour index was calculated at 10 days after bacterization using the following formula: vigour index = percent germination 9 (shoot length ? root length) (Baki and Anderson 1973). Five seedlings were taken randomly from each bacterial treatment and their fresh weight was recorded. The seedlings were kept in the hot air oven for 7 days at 60°C for complete desiccation, and the dry weight of the seedlings was recorded. Later, individual seedling’s fresh weight and dry weight were calculated. Pot study on water stress The green gram seeds (var. CO6) soaked in 10 ml of the bacterial suspension (108 CFU ml-1) were sown in 20 cm diameter plastic pots (45 9 20 cm) containing potting soil (redsoil:sand:cowdung manure at 1:1:1 w/w/w sterilized at 121°C, 101 kPa for 2 h in two consecutive days). Seeds treated with different bacterial strains P. fluorescens Pf1, and B. subtilis strains EPB5, EPB 22, EPB 31 were sown at 20 seeds per pot separately and grown at 35 and 20°C during day and night, respectively. Till 30 days of sowing, watering (500 ml each pot) was done at 4-day interval. After 30 days of sowing, watering was stopped and observations on water stress were made at consecutive days and scoring was done. An irrigated control (500 ml each pot at 2 days interval) was maintained for comparative studies. Five replica were maintained for each treatment. The experiment was repeated once more. Sample collection After imposing water stress, the plant samples were collected at 24-h interval up to 144 h. One gram of the leaf sample homogenized with 1 ml of sodium phosphate buffer (0.1 M) (pH 7.0) was used for the estimation of catalase (CAT) and peroxidase (PO). Protein content in the extracts was determined by the method of Bradford (1976). Catalase The reaction mixture consisted of 3 ml phosphate buffer (0.1 M, pH 7.0), 2 ml H2O2 (2.5 mM) and 1 ml enzyme extract. The reaction mixture was incubated for 1 min and the reaction was stopped by adding 10 ml 0.7 N sulphuric acid. Then, the reaction mixture was titrated against 0.01 N KMnO4 until a faint purple colour persists for at least 15 s. Activity was expressed as lmol min-1 mg-1 of protein (Barber 1980).

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Peroxidase Assay of PO activity was carried out as per the procedure described by Hammerschmidt et al. (1982). The reaction mixture consisted of 2.5 ml of a mixture containing 0.25% (v/v) guaiacol in 0.01 M sodium phosphate buffer (pH 6.0), and 0.1 M hydrogen peroxide. Enzyme extract (0.1 ml) was added to initiate the reaction which was followed colorimetrically at 470 nm. Crude enzyme preparations were diluted to give changes in absorbance at 470 nm of 0.1–0.2 absorbance units per minute. The boiled enzyme preparation served as blank. Activity was expressed as the increase in absorbance at 470 nm min-1 mg-1 of protein. Proline The leaf tissues (250 mg) were homogenized with 10 ml of 3% aqueous sulphosalicylic acid and centrifuged at 3,000 rpm for 10 min. Two millilitres of the supernatant was taken and to this, 2 ml glacial acetic acid and 2 ml acid ninhydrin mixture were added. The contents were allowed to react at 100°C for 1 h and the reaction was terminated by keeping it on ice bath for 10 min. The reaction mixture was mixed vigourously with 4 ml toluene using vortex mixer for 15–20 s. The chromophore containing toluene was aspirated from the aqueous phase, warmed to room temperature and the optical density was read at 520 nm. The proline is determined from a standard curve (20–100 lg of proline). Toluene served as blank (Bates et al. 1973). Native PAGE analysis of water stress related enzymes Sample preparation The leaf tissues were collected at 120 h of water stress from bacterized (P. fluorescens Pf1, B. subtilis EPB 22, EPB 5, EPB 31) and untreated control green gram plants and homogenized with liquid nitrogen. One gram of powdered sample was extracted with 1 ml of 0.1 M sodium phosphate buffer (pH 7.0) at 4°C. The homogenate was centrifuged for 20 min at 10,000 rpm. Protein extracts prepared from green gram tissues were used for the estimation of defense enzymes. Protein content in the extracts was determined by the method of Bradford (1976) and used in gel assays. Peroxidase To study the expression pattern of different isoforms of peroxidases in different treatments, activity gel electrophoresis was carried out for native anionic polyacrylamide gel electrophoresis. After electrophoresis on resolving gel

of 8% and stacking gel of 4% acrylamide, the gels were incubated in the solution containing 0.15% benzidine in 6% NH4Cl for 30 min in dark. Then few drops of 30% H2O2 were added with constant shaking till the bands appear. After staining, the gel was washed with distilled water and photographed (Sindhu et al. 1984). Catalase Catalase activity was assayed in native PAGE gels as described by Woodbury et al. (1971). Gels were incubated in 0.003% H2O2 for 10 min and developed in a 1% (w/v) ferric chloride (FeCl3) and potassium ferricyanide (K3Fe(CN6)) solution for 10 min. After staining, the gel was washed with distilled water and photographed. Statistical analysis The data were analysed using the IRRISTAT version 92-1 programme developed by the biometrics unit, International Rice Research Institute, Philippines. The treatment means were compared by Duncan’s Multiple Range test (DMRT) (Gomez and Gomez 1984).

Results Plant growth promotion Green gram seeds treated with different bacterial strains (P. fluorescens Pf1, B. subtilis strains EPB5, EPB 22, EPB 31) revealed the significant improvement in plant growth characters over untreated seeds. Among the different bacterial strains used, P. fluorescens Pf1 was found to increase the vigour index of the green gram seedlings. The increase in mean root (16.5 cm) and shoot length (19.0 cm) was greater in P. fluorescens Pf1 treated seedlings compared to untreated control. The higher vigour index (3372) was observed in P. fluorescens strain Pf1 treatment followed by EPB 22 (3125) when compared to untreated control (vigour index of 2272). Similarly, P. fluorescens strain Pf1 treated green gram seedlings recorded significantly higher fresh and dry weight compared to all other treatments (Table 1). Pot study on water stress The results of pot study demonstrated that the plants treated with P. fluorescens Pf1 exhibited greater resistance to water stress compared to all other treatments. After 4 days of water stress, the plants started wilting in untreated control. In contrast, the plants bacterized with P. fluorescens Pf1 showed slight wilting symptoms only after 8 days

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Table 1 Plant growth promoting bacteria on growth attributes of green gram Treatments

Germination (%)

Mean root length (cm)

Mean shoot length (cm)

Vigour index

Fresh weight (mg)

Dry weight (mg)

P. fluorescens Pf1

95

16.5b

19.0c

3372e

542e

251d

90

14.6

a

16.0

b

2754

b

b

152b

16.7

b

16.2

b

3125

d

d

196c

16.6

b

15.7

b

2907

c

c

162b

14.5

a

13.9

a

2272

a

a

114a

EPB 5 EPB 22

95

EPB 31

90

Control

80

365 452 401 305

Vigour index = Percent germination 9 (shoot length ? root length) Values are mean of five replications. In a column, mean values followed by a common superscript letter are not significantly different (P = 0.05) by DMRT

Table 2 Water stress index in green gram plants mediated by plant growth promoting bacteria against water stress under green house conditions Treatments

24 h

48 h

72 h

96 h

120 h

144 h

168 h

192 h

216 h

240 h

P. fluorescens Pf1

1

1

1

1

1

1

1

3

3

5

EPB 5

1

1

1

3

3

5

5

7

7

7

EPB 22

1

1

1

1

1

3

3

5

5

7

EPB 31

1

1

1

1

3

3

5

5

7

7

Control

1

1

1

3

3

5

5

7

7

7

Irrigated control

1

1

1

1

1

1

1

1

1

1

Water stress scoring: 1 Normal looking plant; 3 Slightly showing wilting; 5 Drooping of leaves, wilting, recovery after watering; 7 Severe wilting, drying of leaves, no recovery after watering. All the replicated plants were observed for water stress scoring

of water stress (Table 2). In case of EPB 22 treatment, the plants showed the wilting symptoms after 6 days of water stress when other bacterial strains (EPB5, EPB 31) did not show any significant deviation from the untreated control plants. Activity of water stress related enzymes and proline accumulation The activity of peroxidase and catalase in green gram plants treated with PGPB was observed at different time intervals after imposing water stress. The plants treated with P. fluorescens Pf1 showed the greater activity of catalase (Fig. 1) and peroxidase (Fig. 2) against water stress. These enzymes tend to detoxify the toxic H2O2 accumulated during the water stress conditions. The enzyme activity in P. fluorescens Pf1 and B. subtilis EPB 22 treated plants increased up to 120 h against water stress. The greater enzyme activity was noticed in P. fluorescens Pf1 treated plants even after 144 h of water stress. In case of untreated plants, the enzyme activity started to decline from 72 h of water stress. Proline accumulation was found to be higher in Pf1 treated plants against water stress followed by EPB 22 treatment. In contrast, the proline accumulation in untreated plants was observed only up to 72 h of water stress and later it started to decline (Fig. 3).

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Fig. 1 Catalase activity in green gram plants against water stress mediated by plant growth promoting bacteria. Three samples were analysed for each replication and each treatment consisted of three replications

Separation of stress related enzymes An isozyme study indicated the differential activity of enzymes such as peroxidase and catalase in PGPB-treated plants when they were exposed to water stress. Green gram plants treated with Pf1 and EPB 22 induced more accumulation of catalase enzyme (CAT 1) under water stress


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Fig. 4 Native PAGE analysis of catalase activity in green gram plants treated with plant growth promoting bacteria

Fig. 2 Peroxidase activity in green gram plants against water stress mediated by plant growth promoting bacteria. Three samples were analysed for each replication and each treatment consisted of three replications

Fig. 5 Native PAGE analysis of peroxidase activity in green gram plants treated with plant growth promoting bacteria

Fig. 3 Proline accumulation in green gram plants against water stress mediated by plant growth promoting bacteria. Three samples were analysed for each replication and each treatment consisted of three replications

conditions. In case of untreated plants, the isoform was not observed (Fig. 4). The extra induction of peroxidase isoforms (PO3 and PO6) was noticed in Pf1-treated plants when they were exposed to water stress. On the other hand, less induction was noticed in untreated and regularly irrigated plants (Fig. 5).

Discussion Plant response to water stress is a complex phenomenon that appears to involve the synthesis of polyamines and a new set of proteins whose function is largely unknown.

Drought reduces the availability of CO2 for photosynthesis, which can lead to the formation of reactive oxygen species from misdirecting electrons in the photo systems. In addition, free radicals are produced during abiotic stresses. Reactive oxygen species (ROS) such as superoxide radical (O2-), hydrogen peroxide and hydroxyl radicals (OH) cause lipid peroxidation of membranes (Sgherri et al. 2000). Active oxygen species can act on unsaturated fatty acids and loosen the membranes and finally affect the DNA. The scavenging enzymes are known as antioxidant enzymes and includes peroxidase and catalase (Scandalios 1994). The antioxidant enzymes have the ability to remove free radicals and prevent damage to the membranes and DNA. An earlier study demonstrated that mechanisms that reduce oxidative stress indirectly play an important role in drought tolerance (Bowler et al. 1992). Recently, Kohler et al. (2008) demonstrated the greater activity of antioxidant catalase in lettuce plants under severe drought conditions when inoculated with PGPR, Pseudomonas mendocina and arbuscular mycorrhizal fungi (Glomus intraradices or G. mosseae). The same authors have suggested that they can be used in inoculants to alleviate the oxidative damage elicited by drought. It is interesting to note in the current study that PGPB strain P. fluorescens Pf1 increased the accumulation of catalase and peroxidase

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when green gram plants were exposed to water stress. Similarly, the concept of PGPR elicited ‘induced systemic tolerance’ to salt and drought was proposed recently by Yang et al. (2009). The authors have suggested that PGPR might increase nutrient uptake from soils, thus reducing the need for fertilizers and preventing the accumulation of nitrates and phosphates in agricultural soils. A reduction in fertilizer use would lessen the effects of water contamination from fertilizer run-off and lead to savings for farmers. Thus it is assumed in the present study that the greater accumulation of antioxidant enzymes in green gram plants treated with P. fluorescens Pf1 could also be involved in reduction of oxidative stress generated during water stress. This in turn indicated an enhanced drought resistance in green gram plants bacterized with P. fluorescens Pf1 followed by B. subtilis EPB 22. Further, the accumulation of proline in plants acts as an osmoticum and helps to maintain the water potential of plants under stress which in turn facilitate the plant to extract water from soil (Hanson et al. 1979). It also acts as a storage compound for protein synthesis. Whenever a plant experiences a stress, inhibition of starch biosynthesis takes place and proline accumulation will be used as a source of carbon and nitrogen for the survival of plant (Schellenbaum et al. 1998). Recently, Kohler et al. (2008) reported the highest accumulation of proline in the plants inoculated with P. mendocina, alone or in combination with either of the selected AM fungi under severe drought conditions. Thus, it is also assumed in the current study that accumulation of proline in green gram plants might attribute to the bacterization of P. fluorescens Pf1 followed by B. subtilis EPB 22. Further, it is inferred in the current study that growth promoting activity of beneficial microbes could actively be involved in drought resistance mechanisms. P. fluorescens Pf1 was also found to produce catalase enzyme during stress conditions and this was confirmed by native PAGE analysis (data not shown). This feature helps PGPB to detoxify the compounds accumulated in plant system during adverse conditions (data not shown) besides benefitting the survival of microbes. The results of the current study serve as base for the mediation of PGPB in enhancing water stress resistance in crop plants and aid in developing various strategies including the development of microbial consortia (P. fluorescens and B. subtilis strains) for the management of drought conditions. The efficacy of PGPB should also be evaluated at various locations under field conditions receiving low average rainfall. Further research on the differential expression of various proteins and genes involved in PGPB mediated water stress resistance is required to identify the PGPBs that are suitable for crop plants. In addition, the characterization of beneficial microbes, and suitable formulations for mediating biotic

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and abiotic stress in crop plants will be more advantageous in sustainable agriculture.

References Baki AAA, Anderson JD (1973) Vigour determination in soybean seed by multiple criteria. Crop Sci 13:630–633 Barber JM (1980) Catalase and peroxidase in primary leaves during development and senescence. Z Pflanzenphysiol 97:135–144 Bates L, Waldren RP, Teare ID (1973) Rapid determination of free proline for water-stress studies. Plant Soil 39:205–207 Bowler C, van Montagu M, Inze D (1992) Superoxide dismutase and stress tolerance. Annu Rev Plant Physiol Plant Mol Biol 43:83– 116 Bradford MM (1976) A rapid and sensitive method for quantification of microgram quantities of protein utilizing the principle of protein–dye binding. Anal Biochem 72:248–254 Gaff DF (1997) Mechanisms of desiccation tolerance in resurrection vascular plants. In: Basra AS, Bastra RK (eds) Mechanisms of environmental stress resistance in plants. Harwood Academic Publishers, London, pp 43–58 Glick BR, Karaturovic DM, Newell PC (1995) A novel procedure for rapid isolation of plant growth-promoting pseudomonads. Can J Microbiol 41:533–536 Gomez KA, Gomez AA (1984) Statistical procedure for agricultural research. Wiley, New York Hammerschmidt R, Nuckles EM, Kuc J (1982) Association of enhanced peroxidase activity with induced systemic resistance of cucumber to Colletotrichum lagenarium. Physiol Plant Pathol 20:73–82 Hanson AD, Nelsen CE, Pedersen AR, Everson EH (1979) Capacity for proline accumulation during water stress in barley and its implications for breeding for drought resistance. Crop Sci 19:489–493 Indian Meteorological Department (2009) Present status of drought. Drought Bull 1:3–26 ISTA (1993) Proceedings of the International Seed Testing Association, international rules for seed testing. Seed Sci Technol 21:25–30 Kohler J, Herna`ndez JA, Caravaca F, Rolda`n A (2008) Plant-growthpromoting rhizobacteria and arbuscular mycorrhizal fungi modify alleviation biochemical mechanisms in water-stressed plants. Fun Plant Biol 35:141–151 Mayak S, Tirosh T, Glick BR (2004) Plant growth promoting bacteria that confer resistance to water stress in tomato and pepper. Plant Sci 166:525–530 Nandakumar R, Babu S, Viswanathan R, Raguchander T, Samiyappan R (2001) Induction of systemic resistance in rice against sheath blight disease by Pseudomonas fluorescens. Soil Biol Biochem 33:603–612 Quartacci MF, Pinzino C, Sgherri CLM, Dalla Vecchia F, Navari-Izzo F (2000) Growth in excess copper induces changes in the lipid composition and fluidity of PSII-enriched membranes in wheat. Physiol Plant 108:87–93 Ramamoorthy V, Viswanathan R, Raguchander T, Prakasam V, Samiyappan R (2001) Induction of systemic resistance by plant growth promoting rhizobacteria in crop plants against pest and diseases. Crop Protect 20:1–11 Saravanakumar D, Samiyappan R (2007) ACC deaminase from Pseudomonas fluorescens mediated saline resistance in groundnut (Arachis hypogea) plants. J Appl Microbiol 102:1283–1292


Saravanakumar D, Muthumeena B, Lavanya N, Suresh S, Rajendran L, Raguchander T, Samiyappan R (2007a) Pseudomonas induced defense molecules in rice against leaffolder (Cnephalocrocis medinalis) pest. Pest Manag Sci 63:714–721 Saravanakumar D, Vijayakumar C, Kumar N, Samiyappan R (2007b) PGPR induced defense responses in tea plants against blister blight disease. Crop Protect 26:556–565 Saravanakumar D, Lavanya N, Muthumeena K, Raguchander T, Samiyappan R (2009) Fluorescent pseudomonad mixtures mediate disease resistance in rice plants against sheath rot (Sarocladium oryzae) disease. Biocontrol 54:273–286 Scandalios JG (1994) Regulation and properties of plant catalases. In: Foyer CH, Mullineaux PM (eds) Causes of photo-oxidative stress and amelioration of defense systems in plants. CRC Press, Boca Raton, pp 275–316 Schellenbaum L, Mu`ller J, Boller T, Wienken A, Schu`epp H (1998) Effects of drought on non-mycorrhizal and mycorrhizal maize: changes in the pools of non-structural carbohydrates, in the activities of invertase and trehalose, and in the pools of amino acids and imino acids. New Phytol 138:59–66 Sgherri CLM, Maffei M, Navari-Izzo F (2000) Antioxidative enzymes in wheat subjected to increasing water deficit and rewatering. J Plant Physiol 157:273–279

209

Sindhu JS, Ravi S, Minocha JL (1984) Peroxidases isozyme patterns in primary trisomics of pearl millet. Theor Appl Genet 68:179– 182 Staskawicz BJ, Ausubel FM, Baker BJ, Ellis JG, Jones JD (1995) Molecular genetics of plant disease resistance. Science 268:661– 667 Thompson DC (1996) Evaluation of bacterial antagonist for reduction of summer patch symptoms in Kentucky blue grass. Plant Dis 80:856–862 Vivekananthan R, Ravi M, Ramanathan A, Samiyappan R (2004) Lytic enzymes induced by Pseudomonas fluorescens and other biocontrol organisms mediate defence against the anthracnose pathogen in mango. World J Microbiol Biotechnol 20:235–244 Wang C, Knill E, Glick BR, De’fago G (2000) Effect of transferring 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase genes into Pseudomonas fluorescens strain CHA0 and its gacA derivative CHA96 on their growth-promoting and diseasesuppressive capacities. Can J Microbiol 46:898–907 Woodbury W, Spencer AK, Stahmann MA (1971) An improved procedure using ferricyanide for detecting catalase isozyme. Anal Biochem 44:301–305 Yang J, Kloepper JA, Ryu C (2009) Rhizosphere bacteria help plants tolerate abiotic stress. Trends Plant Sci 14:1–4

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