Thermogenic Respiration in Aroids

Abstract

For reasons which will SOon become obvious, this review-at first glance polemic and too inclusive-pays more than the customary attention to biological matters. It deals with thermogenicity in plants, a property which, according to the available evidence, is connected with cyanide-resistant respiration, a type of cellular respi­ ration insensitive to inhibition by terminal inhibitors such as cyanide, azide, and carbon monoxide (CO), and by inhibitors such as antimycin A and HOQNO, which act between band c-type cytochromes (18,62,63,73,80; cf 105, 106). The definition is not absolute, since degrees of cyanide resistance varying from 0 to 100%, and even stimulation by cyanide (100), have been found in plant tissues, pollen grains, and mitochondria (18, 19, 23, 25,46,70, 82, 86, 145, 146,201), often as a function of plant or organ development (131, 2(0). The insensitivity resides in the mitochondria (19,64,65, 150, 188,205,206). When isolated from resistant tissues, they turn out to contain a dual for respiratory electron transfer: the classical, cyanide­ sensitive electron transport system which is coupled to phosphorylation, and a cyanide-insensitive pathway which branches from the classical one on the substrate side of cytochrome c and is phosphorylative to a much lesser extent (19,64,65, 150, 188, 205, 206). The alternate pathway is specifically inhibited by iron-complexing agents such as hydroxamic acids, a, a'-dipyridyl, K-thiocyanate, and 8-hydroxyquinoline (19,25, 46, 170). A ferrosulfoprotein with an apparent Km for O2 lower than that of a flavoprotein oxidase is probably (but not certainly) involved (83). Temporary re-