C. P. P. Reid

Production of Hydroxamate Siderophore Iron Chelators by Ectomycorrhizal Fungi

Numerous ectomycorrhizal fungi were surveyed for their ability to produce iron-chelating, hydroxamate siderophores (HS). Production of HS was determined by a bioassay based on the stimulation of th...

Hydroxamate siderophores in the iron nutrition of plants

Abstract Most fungi and some bacteria respond to Fe deprivation by producing high affinity, ferric‐specific Fe transport ligands called hydroxamate siderophores (HSs). These secondary hydroxamic acids have molecular weights between 500 and 1200 daltons and typically contain three 6‐N‐hydroxyornithine moieties that combine to form ferric chelates with stability constants of approximately 1030. Higher plants under iron‐stressed conditions have been reported to assimilate Fe supplied as Fe(III)‐HSs. This has been confirmed in our laboratories in preliminary studies which demonstrated the uptake and translocation of 55Fe supplied to monooot seedlings as the HS, ferrichrome. Monocot seedlings were also able to absorb and translocate a mixture of fungal HS ligands. These results suggested that the presence of HSs in the vicinity of the root would enhance Fe availability in soil systems. The presence of HSs in a variety of soils was established. Soils from 49 sites representing 22 different taxonomic subgroups w...

Utilization of iron by oat when supplied as ferrated synthetic chelate or as ferrated hydroxamate siderophore

Abstract Utilization of iron by oat (Avena sativa, var. Victory) when supplied as ferrated ethylenediamine[di(o‐hydroxyphenylacetic) acid] (EDDHA), or the ferrated microbially‐produced hydroxamate siderophore, ferrichrome, was examined. Ten‐day‐old iron‐deficient seedlings, grown in aerated Hoaglands nutrient solution (minus iron) buffered at pH 7.0 with CaCO3, were placed in fresh nutrient solution in which 10‐8M 55FeCl3 (23.7 mCi/mg) was added with excess EDDHA (10‐5M), excess ferrichrome (10‐5M), or without chelate, and grown for 6 days. At 2, 4, and 6 days, 55Fe content of shoots from the ferrichrome treatment was significantly greater than from the EDDHA treatment, and at 6 days was nearly 100X greater (10154 vs. 112 dpm mg‐1 dry wt.). Although oat readily utilized iron from ferrichrome relative to EDDHA when ligand was in excess of total iron, uptake of 55Fe by plants was greater in the no chelate treatment. Reduction of chlorosis was evident in both the ferrichrome and no chelate treatments. Resul...

Comparison of the abilities of hydroxamic and other natural organic acids to chelate iron and other ions in soil

Hydroxamate siderophores (HSs), in the form of desferrioxamine B, desferrichrome A, and an unknown mixture derived from Boletus edulis, formed stable iron (Fe) chelates in both acid and alkaline soils as determined by chelation modeling and laboratory experiments. Desferrioxamine B and the unknown mixture were more strongly adsorbed to soil than desferrichrome A. Data obtained using similar methodology indicated that citrate, oxalate, α-ketoglutarate, malate, malonate, succinate, and pyruvate did not chelate Fe effectively at alkaline soil pH, and only citrate was a reasonably effective Fe-chelating agent at acid soil pH. These data, coupled with previous work demonstrating biologically significant levels of HS in soils, indicate that HS can function as Fe mobilizers in ecosystems.

An Escherichia coli bioassay of individual siderophores in soil

Abstract A bioassay system using mutant strains of Escherichia coli K12 was developed which can detect four different types of siderophores. These types are: ferrichrome and its analogs; enterochelin; coprogen, rhodotorulic acid, and ferrioxamines A, B, D1, and G; and a group of unidentified chelators which forms a part of E. colis high affinity iron transport system. The amount of the four siderophore types in concentrated water extracts of bulk and rhizosphere soil from a field sample was estimated using this bioassay.

Effects of synthetic and microbially produced chelates on the diffusion of iron and phosphorus to a simulated root in soil

SummaryHydroxamate siderophores (HS) are microbially produced, ferric-specific chelates, known to occur in soil, and to be capable of providing iron to higher plants. This study examined the potential for HS to influence the diffusion of both iron and phosphorus to plant roots in soil.The HS desferrioxamine-B (DFOB) and desferriferrichrome (ferrichrome) were compared with the synthetic chelates ethylenediamine [di(o-hydroxyphenylacetic)acid] (EDDHA) and ethylenediamine-tetraacetic acid (EDTA), and citrate, oxalate, and distilled water in their ability to increase diffusion of iron using a simulated root technique. Chelate solutions were pumped through porous fiber bundles imbedded in soil previously labeled with55Fe. In a sandy loam of pH 7.5,55Fe diffusion caused by 10−4M DFOB was twice that of water, but similar to that caused by 10−4M EDDHA. However, 10−3M EDDHA resulted in greater diffusion than 10-3M DFOB. The diffusions resulting from equimolar quantities of citrate, oxalate, and EDTA were similar to that with distilled water. In a clay soil of pH 5.2 previously labeled with55Fe and32P, the response in55Fe diffusion to chelate treatments was: 10−4M EDDHA > 10−4M ferrichrome > 10−3M DFOB > 10−4M DFOB > water. Both ferrichrome and EDDHA caused2P diffusion to increase substantially over that of distilled water. These results suggest that hydroxamate siderophores present in the rhizosphere could effectively increase the level of soluble iron for root uptake and possibly increase phosphorus uptake by solubilization of phosphorus from iron phosphates at acid pH.

Response of grain sorghum to hydroxamate siderophore iron source

Previous work had suggested microbially‐produced chelates as potential sources of plant available iron for crops grown on alkaline‐calcareous soils. A “hot spot”; soil (Pernitas fine sandy loam) which historically produced severe iron stress on field grown grain sorghum (Sorghum bicolor L. Moench) was used in this greenhouse study. Iron utilization by grain sorghum was examined where Fe was supplied as three types of ferrated microbially‐produced hydroxamate siderophores; ferrioxamine B (FOB), rhodotorulic acid (RA) and a mixture of ferrichrome‐ferrichrome A (1: 3; Fc‐FcA). Also included in the experiment were ferrated synthetic chelate ethylenediamine [di(o‐hydroxyphenylacetic)acid] (Fe‐EDDHA) and Amaranthus spp plant complexed iron (Fe‐AR). Soil applications were compared with foliar spray treatments using ferrous sulfate, FOB and the Fc‐FcA mixture. Each siderophore source was applied at rates of 1.1 and 3.3 kg Fe ha‐1 soil. The synthetic chelate and Fe‐AR sources were applied at 3.3 kg Fe ha‐l soil. U...