In order to analyze the responses of dark respiration to non-lethal freezing stress, frosthardened shoots of winter rape (Brassica napus var. oleifera) and ivy (I-ledera helix) were exposed to -9~ overnight. After thawing the 02 uptake of leaf slices was measured at 20~ with an oxygen electrode and the cytochrome and alternative pathways were estimated poisoning the respective pathways with CN and SHAM. Following freezing the total 02 uptake was increased 1,5 times in rape and 1.8 times in ivy and the dark C02 evolution of intact ivy leaves exhibited a similar rise. The alternative pathway was more increased (3.8 x in rape and 2.6 x in ivy) than the cytochrome pathway (1.3 and 1.6 x) now coming to about 20 % of the total respiration. There was no evidence of uncoupling of respiration after freezing. However, an enhanced supply of substrate may also contribute to the respiratory rise after freezing since the saccharose content of rape leaves was 2.9 times higher than before freezing.
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