Anomalous Growth Response of Bean Plants in Iron-deficient Media to Cyanide

Abstract

IRON is an essential element for the growth of plants. It is a component of several enzymes, chiefly in the form of iron porphyrins, and probably undergoes reduction and oxidation during the course of electron transport¹. These metal enzymes, in particular cytochrome oxidase, are severely inhibited, at least in vitro, by cyanide². Inhibition of plant respiration by cyanide is possibly caused in part by interference with cytochrome oxidase³ as well as other enzymes, which suggests a relationship between cyanide inhibition and iron. It might therefore be expected that the growth of plants grown in an iron deficient medium would be more severely inhibited by cyanide than plants grown in a medium containing sufficient iron. Indeed, Tissières⁴ showed that cyanide strongly inhibited the respiration of Aerobacter aerogenes grown in the absence of iron, whereas cells grown in the presence of iron were relatively insensitive. MacDonald and DeKock⁵ have also indicated that iron-deficient leaves are more sensitive to cyanide than normal leaves. There seems to be little information on the effects of cyanide on higher plants grown with and without iron. Because of the apparent connexion between this element and cyanide inhibition, I decided to investigate this relationship. I expected to obtain results on growth similar to those of Tissierès on the respiration of bacteria and so it was somewhat surprising to discover that this was not the case.