Abstract
Severe over-stresses of climate caused dramatic changes in the intracellular distribution of the flavonoids. This was studied in needles from the current year’s growth of the following species and varieties: Tsuga canadensis, Taxus baccata, T. aurea, T. repens, T. nana, and T. compacta. The mode of steady changes in flavonoids was evaluated by microscopic techniques. Most of the flavonoids stain visibly yellow by themselves. The colorless flavanol subgroup can be stained blue by the DMACA reagent. In mid-summer 2013, outstanding high temperatures and intense photo-oxidative irradiation caused in a free-standing tree of Taxus baccata dramatic heat damage in a limited number of cells of the palisade layers. In these cells, the cytoplasm was burned brown. However, the nucleus maintained its healthy “blue” colored appearance which apparently was a result of antioxidant barrier effects by these flavanols. In late May 2014, excessive rainfall greatly affected all study trees. Collectively, in all study trees, a limited number of the mesophyll nuclei from the needless grown in 2013 and 2014 became overly turgid, enlarged in size and the flavanols leached outward through the damaged nuclear membranes. This diffusive stress event was followed one to three days later by a similar efflux of DNA. Such a complete dissolution of the nuclei in young tissues was the most spectacular phenomenon of the present study. As a common feature, leaching of both flavanols and DNA was markedly enhanced with increasing size and age of the cells. There is evidence that signalling flavonoids are sensitized to provide in nuclei and cytoplasm multiple mutual protective mechanisms. However, this well-orchestrated flavonoid system is broken down by extreme climate events.
Highlights
Histological and kinetic research with conifer species showed flavanols to be associated with nuclear histones [1,2]
The question whether flavonoids are more important as antioxidants or as signalling compounds was discussed in the scientific literature
The crowns of the Taxus bushes decreased from 3 m to 0.5 m in the following order: Taxus baccata, with the varieties repens, aurea, compacta, and diamond nana
Summary
Histological and kinetic research with conifer species showed flavanols to be associated with nuclear histones [1,2]. The structurally diverse proteins interact with variable physico-chemical properties of flavonoids to yield distinct binding types with different affinities. In this context, the question whether flavonoids are more important as antioxidants or as signalling compounds was discussed in the scientific literature. If concerning the variable expression of flavonoids even inside of plant nuclei, signalling functions altering DNA-protein complexes should be of basic importance [9]. In contrast to the leaves of deciduous trees, the evergreen conifers have long-lived needles which are exposed over four or more years to environmental stresses. The present paper tries to broaden our knowledge by describing dislocation of flavonoids within distinct cells of needles as a response to climate events 2013–2014
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