The DNA Content of Nuclei in the Embryo of Dry Seeds ofPinus PineaandLactuca Sativa

Abstract

The DNA content of nuclei in the embryo of dry seeds of Pinus pinea and Lactuca sativa was determined by means of a Deeley type cytophotometer. It was found that in the root apex, shoot apex and cotyledon in Pinus and in the root apex and cotyledon in Lactuca all nuclei measured were 2C. Only in the root apex of one embryo (probably an immature seed) of Lactuca were both 2C and 4C nuclei found. The exclusive occurrence of 2C nuclei (G₁ stage of the nuclear cycle for cells of meristematic type) in the embryo of Pinus pinea and Lactuca sativa is discussed. It is suggested that the situation found in the resting embryos of the two species reflects a strict control of the sequence of DNA synthesis and mitosis, probably bound to the genetic make-up of the species.