大麦根のカチオン特にマグネシウムの吸収に関する基礎的研究
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Magnesium uptake by plants, as one of the five major nutrients for growth, has generally been considered to be due to an inactive absorption by roots as in the case of calcium. However, little information has been obtained, which affords us the actual evidences. On the other hand, the magnesium deficiency of crops recently observed over this country has been attributed primarily to the unbalanced fertilization of potassium against magnesium. This seems to require an analytical knowledge of cationic interactions in the nutrient uptake. From the above point of view, the investigations were performed on the absorption of magnesium comparing with those of potassium and calcium. The present paper outlines the results obtained in a period 1956-1961. Plant material and nutrient medium used in many cases were excised roots of barley seedlings and chloride solutions, and the absorption tests for them were carried out under controlled conditions. Pot experiments for intact plants were also applied. I On the mechanism of magnesium absorption, especially in relation to root metabolism. I. 1: Culturing method of barley seedlings and general technique of absorption tests using their excised roots were described, and the adoptability of the material and the method was discussed. In preliminary experiments, the order of amounts of cations absorbed by this material was potassium>magnesium>calcium. (fig. 1-3) I. 2: The relation between cation absorption and root respiration were studied. Magnesium absorbed was composed of two parts, one being able to be retained in tissue even under anaerobic condition and the other depending apparently on aerobic metabolism. Magnesium and potassium showed similar increasing effects on the respiration of roots in spite of that a considerable difference in their amount absorbed was found, (fig. 4, 5; table 1-3) I. 3: When the metabolic activities of roots were varied by changing temperature and adding glucose or some organic acids, there were certain responses in the absorption of potassium and magnesium. In the latter absorption, the addition of members of Kreb's cycle into salt solution showed distinctly a promotive effects, (fig. 6, 7; table 4-6) I. 4: By the addition of several inhibitory substances of respiration, negative absorption of potassium was observed, whereas the magnesium-absorbing ability remained to a certain extent. The effects of addition of organic acids on magnesium absorption were not obtained in the case of inhibition of iron-containing enzyme in respiratory system, (fig. 8; table 7) I. 5: The nature of the "initial absorption" of cations was investigated. There was no participation of root metabolism in this absorption of magnesium. It may be noticed that this non-metabolic absorption of magnesium corresponds to the anaerobic absorption (I. 2) and to the uninhibited absorption (I. 4) in their nature and amounts. (fig. 9, 10; table 8, 9) I. 6: A large portion of magnesium absorbed by root tissiue was lost when it was immersed in some chloride solutions. The effect of anaerobisis or respiratory inhibition on the loss of magnesium absorbed into external water was much less than that in the case of potassium. These findings support the view that in considerable extent magnesium is absorbed metabolically and retained non-metabolically by roots, (fig. 11-15) I. 7: The influence of simultaneous anion absorption on cation absorption was studied, using various salt solutions. It appeared that the potassium absorption is related to the physiological activity of the anion accompanied, whereas in the case of magnesium the feasibility of absorption of the anion possibly acts as a restricting factor. The relationships among the amounts of cations, anions and oxygen absorbed by roots were discussed, and the effects of respiratory inhibitors on them were also examined. In the soil culture experiment for intact plants where magnesium and potassium were added equivalently as the four kinds of nutrient salts, the effect of phosphates on the absorption of magnesium or potassium was emphasized, compared with the results of the excised root test. (fig. 16-20; table 10-12) I. 8: The general process of cation absorption was discussed based on the above obtained results, and the absorption mechanisms of magnesium, potassium and calcium were considered respectively. II On the complementary ion effects between magnesium and other cations in the ionic environment of plant roots. II. 1: As to the availability of nutrients on clays, the release of exchangeable cations adsorbed on bentonite or kaolinite into the solutions containing the minute amount of hydrogen chloride was examined. Potassium and sodium adsorbed on the clays as a complementary ion markedly reduced the releasability of magnesium, while calcium slightly increased it. The releasability of potassium, in reverse case, was increased as the exchangeable magnesium increased. II. 2: The interactions of nutrient cations in their absorption from chloride solutions were investigated, using the excised roots of barley seedlings. The presence of potassium or calcium in solutions caused a considerable decrease of magnesium absorption, the latter being more effective. Reciprocally, magnesium increased the absorption of potassium and decreased that of calcium. The order of relative repressing effects of several cations on magnesium absorption was monovalent>divalent cations, and followed the lyotropic series. II. 3; The process of cation adsorption by roots from bicarbonate solutions was taken as the third phase. Adsorbing materials used were the excised roots and the fine pieces of air-dried roots of barley, and also cation exchange resins for comparison. Except a resin with a strong acidic nature, the adsorption rate of magnesium was apparently increased by the presence of monovalent cations but decreased by that of divalents. But conversely the potassium absorption was decreased by the addition of magnesium. II. 4: The next step in the analysis was the estimation of the effects in the "contact uptake". Medium prepared in this case was suspensions of the clay saturated with adsorbed cations in various ratios. The absorption of magnesium by the excised roots from the above medium was reduced by the presence of either potassium or calcium on the clay, especially the effect of increased amount of potassium being much greater. The order of relative repressing effects of cations on magnesium absorption was contrary to that observed in the absorption from chloride solutions (II. 2). The contact exchange adsorption of cations by the resin from clay suspensions was also examined. II. 5: The soil and solution culture experiments for intact plants were carried out in a similar design, in order to observe the integrated result of the cationic interactions described in the above sections. Magnesium uptake in both tops and roots was reduced whenever the increments of potassium were added to soil, whereas when those of calcium were added it was increased in soil culture but reduced in solution culture. Potassium uptake was not notably affected by the added amounts of other cations. Similarly to magnesium, calcium uptake was reduced by the addition of potassium, but the influence of the fertilizer treatments on calcium content was found more remarkably in tops than in roots. II. 6: Comparing the foregoing results, the relations among them and the locality of the cationic interaction most effective on the net results were discussed. The general conclusion to be drawn from the results of these studies is as follows. The behavior of cations in the absorption by barley roots is largely different according to the ionic species. The absorption of magnesium may be considered to be operative mainly through the ion exchange which takes place due to the electrostatic binding of cations with protoplasmic proteins, and it has a absorption mechanism accelerated by the activation of Kreb's cycle-electron transporting system in respiration. Besides, there is a possibility that the absorption involves a somewhat passive process caused by the cation-anion balance in tissue. On the other hand, it is suggested that the absorption of potassium proceeds through a labile combining participated by some product of glycolysis and it has an active mechanism connecting with energy metabolism and material synthesis. On the absorption of calcium, from its relatively small amount absorbed by the excised roots and the results of pot experiments, it is supposed that its transporting process to tops takes part in the absorption. The cationic interactions observed in the various systems of soil-plant root environment have appeared reflecting the characteristics of those phase. It is indicated that the repressing effects of other cations on magnesium absorption operate principally on the absorption-surface of roots and that the physico-chemical nature is predominant over the effects. When soil is applied as a medium, the cationic interaction which regurates ion activities in the medium have a powerful influence on the integrated result.
- 大阪府立大学の論文
- 1963-03-31