Abscisic acid and zygotic embryogenesis in Pinus taeda.

Indirect ELISA was used to quantify (+)-abscisic acid (ABA) in developing zygotic embryo and megagametophyte tissues from two loblolly pine (Pinus taeda L.) mother trees. On a dry weight basis, embryonic and megagametophytic ABA concentrations were highest during early development and decreased steadily to their lowest values at cone ripening. Embryonic ABA concentration was significantly higher than megagametophytic ABA concentration. The ABA content of embryos was lowest during early to mid-development; it increased rapidly during mid-development, subsequently declined, and then either remained constant or declined at cone ripening (late development). Total ABA per embryo increased rapidly just before the rapid increase in embryo dry weight. Total ABA per megagametophyte remained constant throughout development, except during mid-development when it temporarily declined.