Effects of PGPR (Pseudomonas sp.) and Ag-nanoparticles on enzymatic activity and physiology of cucumber.

The present investigation was aimed to evaluate the role of plant growth promoting rhizobacteria (PGPR) and Ag-nanoparticles on two varieties (American variety, Poinsett 76 and Desi variety, Sialkot selection) of cucumber plants. Cucumber seeds were inoculated prior to sowing with two strains of PGPR, Pseudomonas putida (KX574857) and Pseudomonas stutzeri (KX574858) at the rate of 106cells/ml. Ag-nanoparticles (5ppm) were sprayed on plant at early vegetative phase, 27 d after sowing. The proline, sugar, protein, phenolics, flavonoids, chlorophyll and carotenoids contents and the activities of phenylalanine ammonia-lyase (PAL), superoxide dismutase (SOD) and catalase (CAT) were determined from leaves of plants at early vegetative phase. Ag-nanoparticles enhanced the length of root but decreased the length of shoot and fresh weight of root and shoot as compared to control whereas, the leaf protein, proline, phenolics, flavonoids, chlorophyll b, total chlorophyll, sugar contents and the activity of phenylalanine ammonia-lyase (PAL) were increased significantly over control. Ag-nanoparticles also suppressed the effect of PGPR on root and shoot length but augmented the protein and phenolics contents of leaves of both the varieties. The combined treatment of Ag-nanoparticles and PGPR enhanced flavonoids content and the activities of defense related enzyme PAL and the antioxidant enzymes, superoxide dismutase (SOD) and catalase(CAT) in leaves of plants over control. Ag-nanoparticles was also stimulatory when applied alone. Pseudomonas putida may be used either alone or in combination with Ag-nanoparticles to enhance the antioxidant and defense enzyme activities to enable the plant to tolerate stresses in much better way.