Studies on the counteracting function of crop plants against adverse root environment ( with special emphasis on aluminum toxicity)

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1. Several wheat varieties and one variety each of oat and barley were grown in culture solutions without and with Al, and the Al tolerance was compared among these materials. The results demonstrated that the Al tolerance was oat>wheat varieties>barley and there was varietal difference in the Al tolerance among wheat varieties.2. By using hematoxylin staining method, the wheat varieties used in the previous experiment were ranked for the Al tolerance. The ranks well coincided with growth in the culture solution with Al treatment. Thus the method is available for breeding of crop plants to improve the Al tolerance.3. Al tolerance of Haruminori,which was a wheat variety bred in Hokkaido, was equivalent to that of Atlass 66 which was reported as a variety with the strongest Al tolerance. Thus, this variety is usable as a gene source for the improvement of Al tolerance of wheat.4. Toxicity of <AlSO(^+_4)> to plants was considerably weaker than those of <Al^(3+)> and <AlOH^(2+)> . Thus, ap … More plication of sulfate containing fertilizers such as ammonium sulfate, potassium sulfate and superphosphate is more desirable for crop production in acid soils than Cl containing fertilizers.5. Inhibition of root elongation by aluminum was not caused by Ca deficiency induced by Al, but caused by aluminum toxicity itself.6. Process of the Al toxicity in the roots of crop plants was assumed to be as follows. When Al concentration in the growth medium is low, roots exclude Al and the root elongation is not retarded by Al. But when Al concentration becomes high, the cell wall of epidermis in the young root portion is elapsed, thickened and deformed, and the plasmalemma in the same portion is denatured and elapsed. As a result, a large amount of Al intrudes into the root tissues and the root elongation is retarded. The critical Al concentration for the appearance of the toxicity is different among plant species such as from 0.5 to higher than 30 ppm Al. The site of aluminum exclusion contributed to the tolerance is assumed to be at the epidermis. Less