Pyridine nucleotide levels in potato tuber tissue and its mitochondrial fraction after wounding

Abstract

Summary After mechanical injury of potato tubers (Solanum tuberosum L. var. Bintje) the levels of NAD+, NADH, NADP+ and NADPH were determined in extracts of the tuber tissue and its mitochondrial fraction. The incubation periods after wounding varied from five hours to three days. The levels of all forms of coenzymes, except the mitochondrial NADH level, increased after wounding. The relative increase of (NADP+ + NADPH) was much greater than that of (NAD+ + NADH) resulting in maximally a 3-4 times higher (NADP+ + NADPH)/ (NAD+ + NADH) ratio. The first changes could be detected five hours after wounding both in the tissue as a whole and in the mitochondrial fraction. In intact as well as in wounded tissue most of the NAD content was present in the oxidized form while NADP was largely reduced. In the isolated mitochondria both coenzymes were present in the oxidized form. The NAD+/NADH ratio in the tissue was lowered in the first day after wounding to a value which was stable during the next two days. The NADP+/NADPH ratio decreased not before two days after wounding. The mitochondrial oxidation/reduction ratios did not change significantly. Later in the storage period the levels of NAD+ and NADP+ in the mitochondria increased to a lesser extent during the first day of woundreaction. A correlative behaviour of coenzymes and apoenzymes after wounding is discussed.