Membrane Lipid Breakdown in Relation to the Wound-induced and Cyanide-resistant Respiration in Tissue Slices

Abstract

A study of a variety of bulky storage organs and fruits [potato tubers (Solanum tuberosum cv. Russet and cv. Desiree), avocado fruit (Persea americana cv. Hass), banana fruit (Musa cavendishii cv. Valery), sweet potato (Ipomoea batatas), parsnip (Pastinaca sativa), carrot (Daucus carota), rutabaga (Brassica napobrassica), turnip (B. rapa), radish (Rhaphanus sativus), Jerusalem artichoke (Helianthus tuberosus), red beet (Beta vulgaris), jicama (Pachyrrhizus erosus), horseradish (Rorippa armoracia), Daikon radish (Rhaphanus sativus) and ginger (Zingiber)] reveals that fresh slices fall into 2 categories with respect to their sensitivity to CN. Fresh slices in the first class are CN-sensitive, whereas slices of the second class are resistant to, and often stimulated by, CN. In tissue slices which are initially CN-sensitive, cutting initiates a burst of lipolytic activity. In CN-resistant fresh slices, there is no measurable lipid breakdown. Slicing evokes the wound-respiration which is 5- to 10-fold that of the parent organ. Slice aging, in turn, evokes a further 2- to 3-fold respiratory increase, the wound-induced respiration, whether fresh slice respiration is CN-sensitive or -resistant. Estimation of the contribution by the cytochrome and alternative paths shows that the wound respiration in both groups is mediated by the cytochrome path. The wound-induced respiration in the 1st class is cytochrome path mediated, whereas, in some members of the 2nd group, both pathways are utilized. Uncouplers of oxidative phosphorylation elicit a CN-sensitive increment in fresh slices as great or greater than the wound-induced respiration. Accordingly, de novo synthesis of mitochondria is ruled out as an explanation of the latter. The integrity of endomembranes, perhaps including mitochondrial membranes, is seemingly a prerequisite for the operation of the alternative path, i.e., alternative path activity is lost concomitantly with membrane lipid breakdown. The development of the wound-induced respiration is not coextensive with the development of the CN-resistant path in all tissue slices. The fundamental process of aging appears to involve activation of preexisting respiratory capacity. Fresh slices from whatever source fail to utilize exogenous 14C-labeled glucose, whereas aged slices do so readily. A transport lesion is indicated, the healing of which does not depend on the development of the wound-induced respiration, but does depend on fatty acid, and presumably membrane lipid, biosynthesis.