Changes in Nucleic Acids and Other Phosphorus-Containing Compounds of Developing Wheat Grain

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Abstract
In both the developing endosperm and testa-pericarp there was a relationship between the content of inorganic phosphorus, acid-soluble acid-labile phosphorus, and acid-soluble organic phosphorus ("phytic acid"), and the water content. The times of restriction of supply of water to the endosperm and to the testa-pericarp fairly closely corresponded with the times of initiation of rapid synthesis of phytic acid and of a corresponding rapid decline in content of inorganic phosphorus and reactive phosphoryl groups. The changes in DNA content of the endosperm indicate that rapid cell division occurred in the endosperm until about 14 days after flowering and further increase in size was due to cell expansion. The DNA content of the testa-pericarp indicates that the number of cells present was essentially constant throughout the period of development studied. In the endosperm, RNA increased rapidly during the period of cell division and thereafter the amount remained constant or declined slightly; the RNA content of the testa-pericarp showed little change during development, in agreement with the low rate of protein synthesis in this tissue. The changes in lipid and lipid-phosphorus content probably reflected the expected increase in the amount of intracellular membranes.