acclimation changes of flavonoids in needles of conifers during heat and drought stress 2015

The long-term harsh climate conditions in 2015 distorted already from June up to November in all study trees of Tsuga and Taxus the intracellular organization of the needles. Intimately involved in these repressive processes were the flavanols, a small subgroup of the flavonoids. They were not only deposited in vacuoles of conifer needles but also in the nuclei and chromosomes. Among the many flavonoids the small group of catechin derivatives and polymers named flavanols can exclusively be stained blue with DMACA (dimethylaminocinnamaldehyde). From mid-July onward, the vacuolar flavanols of the epidermal cell layers were gradually diminished as evidenced by decreasing blue staining of nuclei and vacuoles. Subsequently, in August also the large spongy mesophyll cells showed the flavanols decreasing progressively. Apparently, the antioxidant flavanols operate as oxygen radical scavengers. (ROS) were used up during the harsh environmental stress conditions. Both, Tsuga and Taxus reacted in this way. However, it is quite surprising that in all study trees the palisade cells did not contain such vacuolar flavanols. Only these cells were in June the first to show a loss of chlorophyll from chloroplasts as well as an efflux of flavanols from the nuclei. Conversely, from September onward another group of phenols, the yellow-staining flavanols were newly formed in the palisade cells and later on also in the mesophyll cells. Obviously, they were assembled finally to stabilize finally the fragile cell sites. Summing up, the present study shows by cytological studies that the climatic conditions in 2015 produced the worst disturbance of subcellular structures observed since 2000 when our studies on nuclear phenols in needles of conifers were initiated.