Abstract
Needle primordia of Tsuga canadensis (hemlock) arising from flank meristems of a shoot apex, form cell lineages consisting of four or eight cells. Within a recently established lineage there is striking uniformity in the pattern of nuclear flavanols. This fact points to an identical transcriptional expression of these flavanols during cell cycling. However two lineages, even if located close together within the same meristem, can be very different in the expression of both cell shape and nuclear flavanol pattern, indicating that epigenetic positional signals are operating in a collective specification of cell lineage development. There is a wide range of nuclear flavanol patterning from a mosaic-like distribution in an activated cell type to a homogenous appearance in silenced cell types. Single cells deriving from lineages are desynchronized because they underlie a signaling network at a higher tissue level which results in stronger epigenetic modifications of their nuclear flavanols. As an extreme case of epigenetic modulation, transient drought conditions caused a drastic reduction of nuclear flavanols. Upon treatment with sucrose or cytokinin, these nuclear flavanols could be fully restored. Analytical determination of the flavanols revealed 3.4 mg/g DW for newly sprouting needles and 19.6 mg/g DW for anthers during meiosis. The roughly 6-fold difference in flavanols is apparently a reflection of the highly diverging organogenetic processes. Collectively, the studies provide strong evidence for combinatorial interplay between cell fate and nuclear flavanols.
Highlights
A first paper indicating that flavanols associate with nuclear chromatin of Tsuga canadensis was published by Feucht et al [1]
The present paper provides new aspects on possible roles of flavanols in Tsuga canadensis regarding genome assembly linked with cell cycling, resting nuclei and cell differentiation
Most lineages of Tsuga canadensis consist of four cells (Figure 1(a–c))
Summary
A first paper indicating that flavanols (catechins) associate with nuclear chromatin of Tsuga canadensis was published by Feucht et al [1]. Low levels of flavanols associated with histone proteins [8] appear to be related to a higher accessible form of euchromatin. Low molecular weight monomeric flavanols as found in the nuclei of conifer species [9] appear to be advantageous in this respect. They associate in a weak and reversible mode with histones. Such a feature allows a highly dynamic and flexible chromatin modification which, according to Kouzarides [10], is of fundamental importance for functional genomes. The present paper provides new aspects on possible roles of flavanols in Tsuga canadensis regarding genome assembly linked with cell cycling, resting nuclei and cell differentiation
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