Time and rate of synthesis of phytin in corn grain during the reproductive period

The progress of phytin synthesis in developing corn grain was followed during 10 weeks from just prior to pollination to complete maturity of the grain, at first at short intervals and at weekly intervals after the second week. The time of initiation of phytin synthesis in the developing corn grain was not definitely established by this investigation. It was shown, however, that phytin was present in the pistillate structure prior to fertilization, although the concentration was only 0.013%, or 2.1% of the total phosphorus. Phytin remained at this low level for 2 weeks after pollination in agreement with the previous findings of DeTurk, et al.. The weekly gain in percentage of phytin phosphorus in the developing grain increased from the second to the fourth week, diminished somewhat during the fifth, and all but ceased during the sixth week. The synthesis then increased rapidly during the seventh week after which there was no further formation of phytin in the grain. The maximum rate of synthesis occurred during the seventh week following pollination. During this period 25.3 mgm of phytin phosphorus were formed daily per ear. Formation of phytin during the first 4 weeks did not occur at the expense of nonphytin phosphorus stored in the immature fruits. This is indicated by the fact that translocation from the stalks and leaves or in part, from the soil supplied as much as was needed for phytin formation. During the fifth, sixth, and seventh weeks nonphytin phosphorus already in the developing grain contributed part of that used in phytin synthesis. The amount was greatest in the seventh week when it provided 71 of the 177 mgms converted into phytin, leaving 106 mgm, or 60% of the total so used, to be supplied from leaves, stalk, and soil. The evidence secured indicated that the cellular structure of the ovule is largely laid down during the first 4 weeks after pollination, with its full complement of nonlabile phosphorus. Active phytin synthesis accompanies this reaction during the third and fourth weeks and then becomes the dominant phosphorus reaction through the seventh week, at which time it is essentially completed. At full maturity, 10 weeks after pollination, phytin phosphorus amounted to 0.271%, or 88% of the total phosphorus. In addition to finding phytin in unfertilized corn ovaries, it was also found to be present in corn pollen and silks. The percentage of phytin phosphorus in these materials was 0.043 and 0.057, respectively.