Impact-induced blackspots and membrane deterioration in potato (Solanum tuberosum L) tubers

Abstract

Tubers of the potato cultivar Maris Piper (MP) were grown in 1996 and stored for 8 months, whereas tubers of the cultivar Colmo (CM) were grown in 1997 and harvested immature. In a timecourse study the two cultivars, which had two distinct physiological ages, were investigated for blackspot susceptibility in relation to cellular integrity. Tubers were equilibrated at 5 °C and struck by a falling bolt. The site of impact was analysed for cation efflux from tuber half-discs and enzymatic activity of polyphenoloxidase (PPO), lipoxygenase (LOX), ascorbate peroxidase (APX) and catalase after 0, 1, 2, 4, 8, 16 and 32 h of tuber incubation. Tubers of MP were 10 times more blackspot-susceptible than those of CM. The membranes of MP leaked more K+, Mg2+ and Ca2+ than those of CM. Both cultivars showed a very fast increase in K+ leakage immediately after impact. Thereafter, CM seemed to reconstitute the membranes, while high efflux of K+ from MP continued for up to 32 h of incubation. Mg2+ efflux from MP increased and peaked 8 h after impact, but no effect was found on CM. Ca2+ and Na+ effluxes were not influenced by the impact. More than twice the activity of LOX and more than three times the activity of PPO were found in CM compared to MP, but little effect of impact was registered. The activity of APX was higher in MP than in CM, and again little effect of impact was found. Little effect of impact on catalase activity was found and the level of catalase activity was similar in both cultivars. © 2000 Society of Chemical Industry