Studies on the Ferreous Coating Formation in Roots of Rice Plants : IV. Oxidation of ferrous ions and ferreous coating formation

[摘要] The authors reported in the previous paper (1961) that the ferreous coating formation (F. C. F) in rice roots should be closely tied up with metabolic activities of plants, because of the experimental confirmation of the parallelisms among F. C. F., nutrients uptake and the growth. This paper dealt with both of the repetition of the assay and the clarification of the mechanism of F. C. F., whether coating formation must be directly related with the oxidation of ferrous ions by roots in media or not. Fundamental methods of the experiment were as follows: the plot with plants, of which roots were immersed in the FeSO4 solution (its concentration, 8 ppm) and that without plants were set, of which roots were excluded from light. After placing them f or definite hours, the amounts of Fe++ and Fe+++ ions in the solution were determined colorimetrically by the o-phenanthroline method. Moreover by the same method, the ferreous coatings were also measured after the coatings were washed away by 0.5 N-HCl solution. Those values mentioned below were then calculated: (A) Amounts of Fe sorbed by roots=(Total Fe ions in plots without plants)-(the same in those with plants) (B) Amounts of Fe++ ions oxidized by roots=(Amounts sorbed by roots)+(Fe++ ions oxidized by rootts, remaining in the solution) (C) Amounts of ferreous coating in roots=(HCl-soluble Fe in roots immersed in th Fe++ solution)-(the same in roots solution-cultured as usual) Rates of those values were also calculated with respect to root dry weight and hours treated. Main results obtained were as follows: (1) The rates of Fe++ sorption and F. C. F. declined gradually, and both of them went hand in hand as the growth advanced (Fig. 1). (2) These rates were positively correlated, when they were estimated at the same stage of the growth (8th leaf stage) (Fig. 2). (3) Changes of Fe++ oxidation, sorption by roots and relative growth rates of roots were parallely declined with the growth (Fig. 3). (4) In the younger and more vigorous stages of the growth, Fe++ sorption by roots took precedence of that of Fe+++ (Fig. 4). (5) When Fe++ concentrations in media became higher, the rate of Fe++ sorption and F. C. F. rose parallely (Fig. 5). From these results, the authors concluded that F. C. F. in rice roots must be closely tied up with root oxidation. F. C. F. must therefore occur according to following processes, that is, Fe++ ions in media should be oxidized and sorbed by roots, so as to make ferreous coatings on root surface. In this case, the process must be predominant when rather large but not injurious amounts of Fe++ ions are present in media, that happens usually under the water logged condition. Now the authors propose that the estimations of plant activity and soil conditions will be possible by means of F. C. F. determination.

[学科分类] 农业科学（综合）