CYANIDE SENSITIVITY OF RESPIRATION DURING AGEING OF ARUM SPADIX SLICES

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Summary

Slices of the sterile spadix of Arum may show variable responses ranging from inhibition to stimulation of respiration when exposed to cyanide. Some of the factors responsible for this variation in response were determined to be: (1) age of the spadix-more mature spadices tend to be unaffected or stimulated by cyanide as opposed to very young spadices, which are inhibited; (2) thickness of the slice made from the spadix-thin (c. 60 μm) slices are stimulated by 2.5 mM KCN while thick (>200 μm) slices are inhibited; (3) ageing of slices in aerated water-this response is complex, with slices c. 100 μm thick freshly cut from spadices of intermediate maturity being stimulated by cyanide initially. During the following 24 hours, however, the respiration of the slices is inhibited by cyanide, but from 2–5 days after slicing the spadix slices reach a plateau of stimulation where rates may be almost doubled by cyanide. This is followed by a decline after 8 days' ageing to a situation in which respiration is unaffected by cyanide.

An inhibitor of cyanide-resistant respiration, m-chlorobenzhydroxamic acid, strongly inhibits spadix respiration, with a Kl similar to that of KCN. The effect of this inhibitor is additive to that of cyanide and in appropriate conditions, the two inhibitors together will completely inhibit Arum spadix respiration.

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