Chemical reduction at the root surface

Abstract

A “sandwich” of moist filter paper impregnated with an insoluble hydrous Fe(III)oxide (or an insoluble Mn oxide) was used to investigate chemical reduction taking place near root surfaces. It was felt that these systems were more similar to soil conditions than solution cultures, particularly because root hairs developed. After sterile roots of sunflower seedlings had brown across the filter paper impregnated with an Fe(III) oxide, the paper was sprayed with an alcoholic solution of 2,2'‐bipyridine to detect Fe(II). A positive reaction (pink) was obtained and reflected the pattern of the root system, Non‐sterile roots of seedlings of alfalfa, oats, soybeans and sunflowers were also tested and gave a similar result; sunflowers gave the most striking result. Similar “root prints” were obtained when roots reduced an insoluble Mn oxide under the same conditions. The positive test for ferrous was not instantaneous and a much poorer or negative test was obtained when the paper was allowed to dry before spraying. There are a number of possible explanations for the observations and it is concluded that the use of a strong chelator to detect Fe(II) may give a false impression of the reducing capacity of roots towards Fe(III). Also, in conjunction with the observations made on the direct reduction of an Mn oxide, the results are discussed in relation to iron supply in soils.

Key words:

• Chemical reduction
• root surface
• Fe(III)
• Mn oxides