Severely distorted Feulgen-DNA amounts in Pinus (Coniferophytina) after nonadditive fixations as a result of meristematic self-tanning with vacuole contents

Abstract

Highly divergent nuclear DNA amounts were obtained in Pinus mugo and Pinus cembra when meristematic tissue from root tips was fixed either with neutral formaldehyde or various nonadditive agents as methanol – acetic acid, ethanol – acetic acid, alcohols alone, Carnoy's fluid, acetone, or was directly hydrolyzed with 5 M HCl. After formaldehyde fixation, the 1C values in P. mugo and P. cembra amount to 20.16 and 24.16 pg, respectively, when calibrated against Allium cepa as internal standard, but 1C values after application of nonadditive fixatives are strongly reduced to 25–41% of the former values. This phenomenon is explained by the observation that in Pinus a large fraction of the meristematic cells contains a considerably large vacuome, whose content (probably condensed tannins) becomes immobilized after formaldehyde fixation and further on does not interfere with the Feulgen reaction, whereas after nonadditive fixations the vacuole contents extravasate and strongly tan the whole meristem and especially the nuclei. The Feulgen reaction is impaired. The tint and absorbance spectra are different in pine and Allium cepa nuclei. Pinus Feulgen-DNA values obtained after fixations other than formaldehyde must be regarded as highly distorted from the true genomic DNA content. Self-tanning as a source of methodical error in DNA content determinations by cytochemical techniques may be widespread because of the frequent occurrence of tannins in the plant kingdom.Key words: Feulgen reaction, DNA contents, tannins, Pinus, conifers.