THE EFFECT OF PHYTASE ON THE AVAILABILITY OF P FROM MYOINOSITOL HEXAPHOSPHATE (PHYTATE) FOR MAIZE ROOTS

The effect of adding phytase to the root medium of maize plants on the P-availability of added myo-inositol hexaphosphate (phytin) has been studied in pot experiments. When 40 mM phytin-P in nutrient solution w as incubated in quartz-sand for 15 days in the absence of plants, 80% of it could be recovered from the solution as soluble organic P. Maize plants growing on this mixture assimilated P from phytin at rates com parable to those from inorganic phosphate (Pi). At a lower addition ra te (2 mM phytin-P) only 10% was recovered in the soil solution, and pl ant growth was severely limited by P. At this low phytin level, the ad dition of phytase (10 enzyme units per kg sand) increased the plants' dry weight yield by 32%. The relative increases of the Pi concentratio n in the solution and of the amount of P in the plants were even highe r, indicating that the observed growth stimulation was due to an incre ased rate of phytin hydrolysis. The enzyme-induced growth stimulation was also observed with plants growing in pots filled with soil low in P, when phytin was added. However, on three different soils the additi on rates of phytin and phytase necessary for obtaining a significant p hytase effect were both about 10 times higher than those required in q uartzsand. It is concluded that the P-availability from organic source s can be limited by the rate of their hydrolytic cleavage.