Effects of ethylene and hydrogen cyanide on β-cyanoalanine synthase activity in satsuma mandarin ( Citrus unshiu Marc.) fruit

Abstract

Exogenous ethylene increased β-cyanoalanine synthase activity in satsuma mandarin fruit. An inward decreasing gradient in the activity was found in ethylene-treated fruit; the highest activity was in the flavedo and the lowest in the juice sacs. β-Cyanoalanine synthase activity in the peel (flavedo and albedo) increased in parallel with increasing ethylene concentrations up to 500 ppm and then leveled off. Green mature fruit were less responsive to ethylene in the induction of β-cyanoalanine synthase activity than more mature fruit. Regardless of ripening stage, the latter group of fruit responded to ethylene to reach similar maximum enzyme activities, which were approximately two-fold greater than those of green mature fruit. 2,5-Norbornadiene, a specific inhibitor of ethylene action, repressed the ethylene-induced increase in β-cyanoalanine synthase activity. Hydrogen cyanide did not induce β-cyanoalanine synthase but rather reduced the activity at high concentrations.