Nucleic Acid, Protein, and Starch Synthesis in Developing Cotyledons of Pisum arvense L.

During the cell-division period of cotyledon development inPisum arvense L. cell volume increases slightly but nuclearvolume shows little variation and the DNA content remains atthe 2C to 4C level. During the main period of cell expansionthere is a close correlation between cell volume, nuclear volume,and nuclear DNA content, the nuclei of the largest storage cellsfinally attaining the 64C level. The rate of RNA synthesis increasesseveral days after the increase in DNA has begun and at thesame time accumulation of reserve protein and starch begins.RNA and starch synthesis apparently cease some time before maturationbut protein synthesis continues until the seeds are ripe. Cotyledondevelopment was found to comprise two distinct phases: an initialphase of cell division and differentiation during which DNA,RNA, and protein per unit volume of cell decline; and a phaseof reserve accumulation in which DNA per unit volume of cellremains constant but RNA and protein per unit volume increase,starch synthesis is initiated, and all the cotyledon cells assumethe properties of storage cells.