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Iron Coatings on Rice Roots: Morphology and Models of Development¹

ABSTRACT

Scanning electron microscopy and X-ray microanalysis were employed to characterize the morphological properties of iron coatings on rice roots at different growth stages. This information is needed for further understanding of the influence of Fe coatings on rice plant development. Rice root coatings are visible about 1 week after flooding as a brownish discoloration which thickens with age of the root. No coating was found on younger parts of major roots near their tips or on young secondary roots which are critical regions of nutrient uptake. Roots of ‘Brazos’ cultivar rice (Oryza sativa L.) plants grown in Beaumont clay soil had a relatively thin coating of FeOOH mixed with soil particles before panicle differentiation. As a rice plant approached maturity and the outermost cell wall of the root decomposed, a mixture of FeOOH and soil particles began to fill the rectangular spaces that had once been occupied by epidermal cells. Casts in open cell cavities are porous and rough on the exterior side of the root. There were many shapes of casts and they generally matched the varied shapes of the outer layer of epidermal cells of rice roots. Roots of Brazos cultivar rice grown to maturity in Katy fine sandy loam soil have completely developed polyhedral casts. Precipitation of relatively pure FeOOH on cell walls formed hollow casts with the shapes of the original cells. The models presented describe hypothetical steps in the formation of the two types of casts observed by the oxidation of Fe²⁺ by O₂ and precipitating of iron on the walls of closed and open cell cavities.

¹ Contribution no. TA 15658, Texas Agric. Exp. Stn.

² Formerly Graduate Student, currently Technician, Texas Agric. Exp. Stn., Rt. 7, Box 999, Beaumont, TX 77706; Professor, Dep. of Soil & Crop Sciences, Texas A&M University, College Station, TX 77843; and Associate Professor, Texas Agric. Exp. Stn., Beaumont, respectively.

Received for publication November 19, 1979. Accepted for publication June 12, 1980.