Induction of pre-chorismate, jasmonate and salicylate pathways by Burkholderia sp. RR18 in peanut seedlings.

AIMS: To characterize the mechanisms by which bacteria in the peanut rhizosphere promote plant growth and suppress Aspergillus niger, the fungus that causes collar rot of peanut. METHODS AND RESULTS: In all, 131 isolates cultured from the peanut rhizosphere were assayed for growth promotion in a seedling germination assay. The most effective isolate, RR18, was identified as Burkholderia sp. by 16S sequencing analysis. RR18 reduced collar rot disease incidence and increased the germination rate and biomass of peanut seeds, and had broad-spectrum antifungal activity. Quantitative analyses showed that RR18 induced long-lasting accumulation of jasmonic acid, salicylic acid and phenols, and triggered the activity of six defence enzymes related to these changes. Comparative proteomic analysis of treated and untreated seedlings revealed a clear induction of four abundant proteins, including a member of the pre-chorismate pathway, a regulator of clathrin-coated vesicles, a transcription factor and a hypothetical protein. CONCLUSION: Burkholderia sp. RR18 promotes peanut growth and disease resistance, and stably induces two distinct defence pathways associated with systemic resistance. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates that a strain of the Burkholderia cepacia complex can elicit both salicylic- and jasmonic-acid-mediated defences, in addition to having numerous other beneficial properties.

Purification, characterization and application of lipoxygenase isoenzymes from Lasiodiplodia theobromae.

Lipoxygenase oxidizes linoleic acid into hydroperoxy octadecadienoic acid (HPOD), which is important in food and flavour industries for production of bread and flavouring compounds. As Lasiodiplodia theobromae is an unexplored, good source of lipoxygenase, it was purified from it by size-exclusion (Sephadex G100) and ion-exchange (DEAE-cellulose) chromatography and characterized. Upon purification, L. theobromae was found to contain two different lipoxygenases, one of 93 kDa (LOX1) and another of 45 kDa (LOX2). Both the isoenzymes were having optimum pH 6.0 and optimum temperatures 50 and 40 °C, respectively. The catalytic efficiency of LOX1 and LOX2 was found to be 1300 and 1.67 × 10(9), respectively. The catalytic efficiency of LOX2 is higher than the catalytic efficiency of soya bean LOX1 that is 10.9 × 10(6). Both the isoenzymes of LOX oxidized linoleic acid to produce 9-HPOD and 13-HPOD both; however, LOX1 produced more of 9-HPOD and LOX2 produced more of 13-HPOD. Both the LOXes were not inhibited by jasmonic acid. Addition of LOX1 and LOX2 altered the elasticity as well as viscosity of dough prepared from bleached wheat flour.