Variation in Nuclear DNA Content in Pinus taeda L. Tissue Cultures of Diploid Origin

Abstract

Summary Despite prolonged efforts to obtain plant regeneration from pine callus cultures, little attention has been given to the genetic condition of callus cultures. We measured nuclear DNA content in loblolly pine (Pinus taeda L.) callus during six months of continuous culture. Absolute DNA content was measured quantitatively using microspectrophotometry in conjunction with an internal standard. Twenty to thirty percent of the cells in the cultures contained nuclear DNA contents in excess of the 4C amount with the remainder having the 2C-4C amount, equivalent to cells in a diploid cell cycle. Cells with increased DNA contents arose early and were present throughout the culture period. Examination of occasional shoot meristems that formed on «callus-induction» medium revealed that shoots formed which contained cells with abnormal nuclear DNA content as compared with controls. Because polyploidy is deleterious to pines, these results demonstrate the importance of screening tissue cultures for genetic stability in an in vitro propagation program.