INHIBITION OF SOFTENING BY POLYAMINE APPLICATION IN GOLDEN DELICIOUS AND MCINTOSH APPLES

Pressure infiltration of 'Golden Delicious' and 'McIntosh' apples (Malus domestica Borkh.) with polyamines resulted in an immediate increase in firmness. 'Golden Delicious' apples were 2.7 N (0.25 mM spermidine) to 6.7 N (1.0 mM spermine) firmer, while 'McIntosh' apples were 2.2 N (0.25 mM spermidine) to 5.3 N (1.0 mM spermine) firmer than the water-treated control. During 28 weeks of storage at 0C, the differences between the polyamine-treated and water-treated apples were even larger. Similar results were observed with a 3% Ca treatment, but the Ca treatment reduced the rate of softening to a greater extent than did the polyamine treatments in 'Golden Delicious'. Polyamines increased the endogenous levels of the polyamines infiltrated; however, the levels declined rapidly with time in storage. Both polyamine and Ca inhibited the development of chilling injury symptoms (brown core) in 'McIntosh'. The influence of polyamines on ethylene production was negligible in both cultivars. The Ca treatment, however, inhibited ethylene evolution in 'Golden Delicious'. Polyamines, thus, may affect apple softening through rigidification of cell walls rather than through interactions with ethylene metabolism.