Plant response and tolerance mechanism to ionic stress in rhizosphere.

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In the root of wheat subjected to Al stress, the inhibition of cell elongation occurred faster than that of cell division. The inhibition of cell elongation induced the decrease of the length and increase of the diameter of cell. Marked deposition of lignin was observed in the inhibited cell in elongation zone. In tea, Al repressed the Mn toxicity by reducing the transport of Mn. The interelationship between exclusion of organic acids and Al tolerance was investigated. The order of effective repression of Al toxicity by organic acids was citrate > malate > succinate.As to the tolerance mechanism to phosphate starvation, carrot cells selected under phosphate starvation showed a stronger activity of citric acid synthetase than that of wild one. On the other hand, the activity of citrate consuming enzyme, NADP- ICDP was lower in the selected cells.Rupin roots excluded a large amount of acid phosphatase. The molecular analysis of acid phosphatase showed that M.W.was 72 KDa. Furthermore, cDNA encoding the excluded acid phosphatase consisted of 2207 bases.Cucumber plant excreted riboflavin under phosphate starvation. There was positive relaitonship between the amount of riboflavin exclusion and Fe^<3+> reducing activity but its coexistence stimulated the Fe^<3+> reducing activity.