Nuclear Replication Activity During Seed Development, Dormancy Breakage and Germination in Three Tree Species: Norway Maple (Acer platanoidesL.), Sycamore (Acer pseudoplatanusL.) and Cherry (Prunus aviumL.)

Abstract

Flow cytometric analyses of nuclear DNA levels were carried out during development, stratification and germination of dormant seeds from three tree species with contrasting characteristics. Norway maple (Acer platanoides) and sycamore (Acer pseudoplatanus) have orthodox (desiccation-tolerant) and recalcitrant (desiccation-sensitive) storage behaviours, respectively, and require only a period of cold to break dormancy, whereas, orthodox cherry (Prunus avium) seeds require an initial warm period before cold stratification to fully stimulate germination. Whole embryos and radicle tips of both Norway maple and sycamore were found to have stable high levels of 4C DNA during the latter stages of development and both contained nuclei arrested at the 2C and 4C levels at maturity. Mature cherry embryos had nuclei predominantly arrested at the 2C level. This suggests that the acquisition of desiccation tolerance is not correlated with the arrest of the cell cycle at any particular nuclear DNA level. Neither DNA replication in radicle cells nor germination occurred when seeds were maintained moist at a constant 20 °C. However, in the late stages of cold treatment during stratification, nuclear DNA levels in radicle cells changed in advance of radicle emergence in the orthodox Norway maple and cherry, whereas in the recalcitrant sycamore, change was not recorded until after radicle emergence. These results show that DNA replication has potential use as an indicator of the progress of tree seeds through stratification treatments used to break some types of dormancy. The ways in which this indicator could be exploited for seed quality and performance testing are discussed.