[Show abstract][Hide abstract] ABSTRACT: The role and metabolism of indole-3-acetic acid in gram-negative bacteria is well documented, but little is known about indole-3-acetic acid biosynthesis and regulation in gram-positive bacteria. The phytopathogen Rhodococcus fascians, a gram-positive organism, incites diverse developmental alterations, such as leafy galls, on a wide range of plants. Phenotypic analysis of a leafy gall suggests that auxin may play an important role in the development of the symptoms. We show here for the first time that R. fascians produces and secretes the auxin indole-3-acetic acid. Interestingly, whereas noninfected-tobacco extracts have no effect, indole-3-acetic acid synthesis is highly induced in the presence of infected-tobacco extracts when tryptophan is not limiting. Indole-3-acetic acid production by a plasmid-free strain shows that the biosynthetic genes are located on the bacterial chromosome, although plasmid-encoded genes contribute to the kinetics and regulation of indole-3-acetic acid biosynthesis. The indole-3-acetic acid intermediates present in bacterial cells and secreted into the growth media show that the main biosynthetic route used by R. fascians is the indole-3-pyruvic acid pathway with a possible rate-limiting role for indole-3-ethanol. The relationship between indole-3-acetic acid production and the symptoms induced by R. fascians is discussed.
Applied and Environmental Microbiology 04/2005; 71(3):1169-77. · 3.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The culture of pasture legumes is of special interest for the world's agriculture because it results in the production of high value protein accompanied by improvement of soil fertility, since they undergo symbioses with dinitrogen-fixing bacteria. Alfalfa is the most important forage crop for the arid and semi-arid areas, where increased salinity of irrigated fields is one of the major constraints that limit crop productivity. Recently, using in vitro selection, we obtained alfalfa genotypes with increased tolerance to PEG 6000, an agent that mimics drought. Here, we present studies on salt tolerance with adult plants of these alfalfa genotypes grown either on nitrate or diazotrophically at various non-lethal salt concentrations. Growth parameters and parameters related to nodule physiology and development have been analysed. All R lines had a higher salt tolerance than their explant source genotype (T1) in germination and growth on nitrate-containing medium. Under diazotrophic growth conditions, R1 and R3 were with higher relative salt tolerance than T1. Nodule biomass was depressed at high salt concentrations in all genotypes. This growth decline went in pair with changes in carbohydrate partitioning and in the hormonal balance.
[Show abstract][Hide abstract] ABSTRACT: Plant hormones are present and active in minor concentrations in plant tissue. To allow quantification in a restricted amount
of material, i.e., protoplasts, chloroplasts, seedlings, seeds, buds, or apical root- and stem regions, a sensitive analytical
technique is a prerequisite. During the last two decades, procedures for phytohormone analysis as well as the available hardware
have improved substantially. Fluorimetry is widely used for the analysis of indole-3-acetic acid (IAA) because it is more
specific and therefore more sensitive than ultraviolet detection (for a review see
1). Good detection limits for derivatized IAA are obtained in Electron Impact (EI+) (2,3) or negative ion chemical ionization (NICI) GC-MS* (4,5).