Effect of ABA and slow drying on DNA replication in carrot (Daucus carota) embryoids

Abstract

Addition of abscisic acid (ABA) at the torpedo‐shaped stage of development and slow dehydration are two parameters necessary to produce completely desiccation‐tolerant carrot (Daucus carota L.) embryoids. The mode of action of these parameters is still largely unidentified. Employing flow cytometry we investigated their effect on DNA replication and cell cycle activity of the developing embryoids. DNA replication was determined as percentage of 4C nuclei. Addition of ABA did not alter DNA replication and cell cycle during embryoid development in vitro, in spite of the putative quiescent state of the torpedo‐shaped embryoids. In contrast, during slow drying the nuclei were preferentially arrested in the presynthesis G0/G1‐phase and the amount of G2 nuclei decreased. Dry zygotic carrot embryos do not contain any G2 nuclei and are completely desiccation tolerant. The decline of G2 nuclei in dry somatic embryoids seems to coincide with the increase in desiccation tolerance, which is incomplete compared to zygotic embryos. Our results suggest that in order to withstand anhydrobiosis, DNA replication may be controlled during the embryoid developmental program and slow dehydration, but not by the plant growth regulator ABA.