THE BINDING OF ZINC IN ROOT-CELLS OF CROP PLANTS BY PHYTIC ACID

Appreciable quantities of Zn are bound as Zn phytate (myo-inositol kis -hexaphosphate) within small vacuoles of cortical cells in the elongat ion zone of root tips of zinc tolerant Deschampsia caespitosa. These Z n/P-containing globular deposits have now been shown to occur in the r oots of soybean, lucerne, lupins, tomato, rapeseed, cabbage, radish, w heat and maize. The globules are most frequent in the endodermis and p ericycle but may also occur in the stele and inner cortex. The X-ray d ata again confirmed the presence of phytate with a relatively stable p roportion of Zn and a species-dependent, variable, proportion of K, Mg and Ca to P. Analysis of soybean plants by atomic absorption spectros copy showed that the Zn concentration in the shoots doubled in respons e to an increase in Zn supply from 1 to 100 mu M while the concentrati on of Zn in the root symplast was approximately 22 times greater than in the shoot, suggesting restricted transport to the shoot. It is sugg ested that the genetic expression of the capacity to bind heavy metals by means of phytate in endodermal cells may provide a strategy for ke eping the above-ground content of heavy metals low. It may be possible to incorporate the trait into transformed roots that can be utilized for the treatment of industrial wastes.