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

Abstract

During the cell-division period of cotyledon development in Pisum arvense L. cell volume increases slightly but nuclear volume shows little variation and the DNA content remains at the 2C to 4C level. During the main period of cell expansion there is a close correlation between cell volume, nuclear volume, and nuclear DNA content, the nuclei of the largest storage cells finally attaining the 64C level. The rate of RNA synthesis increases several days after the increase in DNA has begun and at the same time accumulation of reserve protein and starch begins. RNA and starch synthesis apparently cease some time before maturation but protein synthesis continues until the seeds are ripe. Cotyledon development was found to comprise two distinct phases: an initial phase of cell division and differentiation during which DNA, RNA, and protein per unit volume of cell decline; and a phase of reserve accumulation in which DNA per unit volume of cell remains constant but RNA and protein per unit volume increase, starch synthesis is initiated, and all the cotyledon cells assume the properties of storage cells.