The Developmental Biochemistry of Cottonseed Embryogenesis and Germination

Cotton cotyledons have been found to synthesize de novo during germination two enzymes, a carboxypeptidase and isocitratase. The mRNA for this synthesis is transcribed in embryogenesis at a point when the embryos have reached two-thirds of their final size. The translation of the mRNA is prevented during the completion of embryogenesis by the plant hormone abscisic acid, which is produced by the tissues surrounding the embryo and absorbed by the embryo. The inhibition of the translation of the mRNA appears to require the concomitant synthesis of nonribosomal RNA. The mRNA for the two enzymes can be prematurely induced in younger cotyledons by excision of the embryo from the mother plant. This also stops DNA synthesis and cell division in this tissue. The synthesis of the mRNA and the cessation of DNA synthesis and cell division normally occur at the time in embryogenesis when the vascular connection between the mother plant and the incipient seed degenerates. It is postulated that these events are the result of a loss of vascular factors supplied by the mother plant. The synthesis of the two enzymes appears to be identically regulated, and they may represent a body of enzymes that are required for germination and whose synthesis is under the same coordinated regulation.