Cultivated Rice Varieties viewed from Root Characters : (V) Phosphorus compounds in roots and varietal resistabilities against soil reduction

Abstract

As already reported by many researchers, varietal differences of the resistability against soil reduction are mainly caused by the oxidizing power of roots, that is, by the energy releasing power for the maintenance of metabolic activities. Under the reductive soil conditions, it was also pointed out that the fall of the root respiration occured, accompanying with the degradation in the phosphorylation processes of sugars in roots. Therefore it is assumed that the more resistant, varieties may produce the organic phosphates much more in contrast to the inorganic ones, under both natural and abnormal conditions. From these viewpoints, the authors determined varital differences of organic and inorganic phosphorus compounds in roots, both quantitatively and qualitatively, in order to show the relationship between their conetnts and the varietal resistabilities. The experiments composing the studies and the main results obtained were as follows: 1) The absorption of 32p measured by the counting method (Tab. 1): The more resistant variety (Norin 69) absorbed the radioactive element much more in roots than the less resistant one (Norin 36), at both the 6 th an 9 th leaf stages. It was also ascertained under abnormal conditions. The abnormal condition means the plots which were treated whith hydroquinon in order to deprive the plants and the medium of oxygen. 2) Phosphate contents in roots determined by chemical analyses (Tab. 2 & Fig. 1): Contents of both organic and inorganic phosphates were more or less larger in the roots of the more resistant variety (Norin 37), as compared with the less resistant one (Norin 41), under both conditions mentioned above. It was almost always assured at every growth stages selected. Besides the ratios of the organic phosphates to the inorganic ones because higher in the normal plants than in those injured by the chemical. It was especially true in the more resistant variety (Fig. 2). 3) Organic phosphates found by the qualitative analysis (Fig. 3): The paper chromatographic method applied to the acid soluble organic phosphates in roots showed that 3-phosphoglyceric acid was never recognizable in both varieties treated. From this fact, it was inferred that some of organic phosphates to be translocated migth be vanished or not synthesized when the root respiration was checked. 4) Anatomical observations of roots treated with hydroquinon (Fig. 4): Epidermis and its neighbouring tissues wer discolored yellow or brown. It was also alike in stele, of which strands seemed to be stoppered. These phenomena suggest that nutrients migration from root to top may be largely disturbed.