A simple method to study the oxidizing power of rice roots under submerged soil conditions

Abstract

AbstractA method was developed to visualize and to study the oxidizing power of rice roots growing under submerged soil conditions. The experimental set up consisted of a transparent jar with an inner core containing the submerged soil surrounded by a coarse (500 μm) and a fine (30 μm) meshed nylon net and a plastic folio. The space of about 1 cm between the jar wall and the soil column was either filled with water (before removing the plastic folio) or with agar containing the redox indicator. Three‐week‐old rice (Oryza saliva L.) seedlings grown in a sandy soil under controlled growth chamber conditions were transplanted into the jars between the plastic folio and the fine‐meshed (30 μm) nylon net. The agar medium (0.5% agar) containing 10 ppm leuco melhylene blue redox indicator or 5 mM ferrous sulphate or precipitated ferrous sulfide (10 m M ferrous sulphate + 4 m M Na2S) was filled in the transparent jars immediately after sucking out water. Within 4 h the oxidizing power of rice roots became visible by bluish coloration all along of roots and the agar medium around roots due to oxidation of leuco methylene blue. In case of ferrous sulphate reddish brown coloration was observed after one day around the roots and on the surface of roots because of ferrous iron oxidation. When agar medium blackened by precipitated FeS was used the root zone first became transparent because of oxidation of FeS and after few days the roots became reddish brown indicating iron oxyhydroxide deposition. The use of ferrous sulphate and ferrous sulfide enables to study the oxidizing power of rice roots for extended periods, whereas it is not possible to grow rice plants in leuco methylene blue for more than a few hours. However (results not shown), rice cultivars showed differences in oxidizing power of the roots.