Ontogenetic Variation of Nitrogenase, Nitrate Reductase, and Glutamine Synthetase Activities in Oryza sativa

Azotobacter chroococcum and Pseudomonas putida enhance pyrroloquinazoline alkaloids accumulation in Adhatoda vasica hairy roots by biotization

Adhatoda vasica is used in the treatment of cold, cough, chronic bronchitis, asthma, diarrhea, and dysentery. The biological activities of this species are attributed with the presence of alkaloids, triterpenoids, and flavonoids. Agrobacterium rhizogenes-mediated transformation of A. vasica, produces pyrroloquinazoline alkaloids, was achieved by infecting leaf discs with strain ATCC15834. The bacterial strain infected 82.7% leaf discs and 5-7 hairy root initials were developed from the cut edges of leaf discs. In this study, seven strains of Azotobacter chroococcum and five strains of Pseudomonas putida were used for the biotization of hairy roots. Plant growth-promoting rhizobacteria (PGPR) develops symbiotic association with roots of plants and increases the growth parameters of plants. PGPR (A. chroococcum and P. putida) increased the profiles of nitrogenase and acid phosphatase enzymes, biomass, dry matter contents, anthranilate synthase activity and accumulation of pyrroloquizoline alkaloids in the biotized hairy roots. Both enzymes (nitrogenase and acid phosphatase) maintain sufficient supply of nitrogen and dissolved phosphorus to the cells of hairy roots therefore, the levels of anthranilate synthase activity and pyrroloquinazoline alkaloids are increased. Total seven pyrroloquinazoline alkaloids (vasicine, vasicinone, vasicine acetate, 2-acetyl benzyl amine, vasicinolone, deoxyvasicine and vasicol) were identified from the biotized hairy roots of A. vasica. In our study, biotization increased the profiles of pyrroloquinazoline alkaloids therefore, this strategy may be used in increasing the production of medicinally important secondary metabolites in other plant species also. Our hypothetical model demonstrates that P. putida cell surface receptors receive root exudates by attaching on hairy roots. After attachment, the bacterial strain penetrates in the biotized hairy roots. This endophytic interaction stimulates acid phosphatase activity in the cells of biotized hairy roots. The P. putida plasmid gene (ppp1) expression led to the synthesis of acid phosphatase in cytosol. The enzyme enhances phosphorus availability as well as induces the formation of phosphoribosyl diphosphate. Later, phosphoribosyl diphosphate metabolizes to tryptophan and finally tryptophan converts to anthranilic acid. The synthesized anthranilic acid used in the synthesis of alkaloids in A. vasica.

Interaction of Combined Nitrogen with the Expression of Root-Associated Nitrogenase Activity in Grasses and with the Development of N(2) Fixation in Soybean (Glycine max L. Merr.)

Soluble root N concentrations of corn, sorghum, pearl millet, rice, wild rice, and soybeans were determined and related to measurements of nitrogenase activity and changes in availability of combined N to plants. In corn, sorghum, and pearl millet, applications of fertilizer N increased soluble root N concentrations, but root-associated nitrogenase activity was negligible in control and treated plants. Applications of NH(4)NO(3) to rice increased the water soluble root N concentrations and inhibited root-associated nitrogenase activity. In wild rice, root-associated nitrogenase activity was absent during vegetative growth and developed at the reproductive growth stage. The soluble root N concentration decreased progressively as wild rice grew indicating that the availability of combined N in the root environment declined. Therefore, development of nitrogenase activity in wild rice is associated with the change in availability of combined N in the root environment. The development of nitrogenase activity in wild rice was probably not due to colonization of roots by N(2)-fixing bacteria because most probable numbers of recovery did not significantly vary throughout the plants' growth cycle. In field-grown soybeans with or without fertilizer N application, we also observed a relationship between a decrease in soluble root N concentration and the development of nitrogenase activity.

Physiology of Root-Associated Nitrogenase Activity in Oryza sativa

An intact method for measuring immediately linear rates of acetylene reduction was used to investigate the relationship between temperature, pH, O(2) concentration, and light intensity with the rate of root-associated nitrogenase activity in rice (Oryza sativa L.). Nitrogenase activity varied over a temperature range of 10 to 50 degrees C and optimal rates of acetylene reduction were recorded at 35 degrees C. Nitrogenase activity was also influenced by the pH of the liquid surrounding the roots prior to assay. Maximal rates of acetylene reduction were recorded over a pH range from 5.8 to 7.5. Nitrogenase activity was significantly reduced by concentrations of O(2) 0.5% (v/v) or more when the intact plant assay method was used, and no optimum was detected. However, when the plant tops were removed and the cut ends sealed from the atmosphere for 4 hours, acetylene reduction rates were maximal at 0.25% O(2) (v/v). When plants were moved from sunlight (1,400 microeinsteins per square meter per second) to shade (9.6) root-associated nitrogenase activity at 35 degrees C significantly decreased 15 min later to one-fourth the rate and recovered upon return to sunlight. When the light intensity reaching the leaf canopy was progressively reduced from 1,050 to 54 microeinsteins per square meter per second the rate of root-associated nitrogenase activity decreased from 550 +/- 135 to 192 +/- 55 nanomoles ethylene per gram dry root per hour. The study suggests that the rate of root-associated nitrogenase activity in rice at constant temperature may well be mediated by variations in the concentration of O(2) resulting from changes in the rate of photosynthesis as well as variations in the rate of transport of photosynthate.