CHARACTERIZATION OF MG2+-INDUCED BITTER PIT-LIKE SYMPTOMS ON APPLES - A MODEL SYSTEM TO STUDY BITTER PIT INITIATION AND DEVELOPMENT

Vacuum infiltration of MgCl2 solutions into intact apple fruits induces bitter pit-like symptoms [Mg2+-induced pits(MgIP)]. Including Ca2+ in the infiltration media prevents MgIP.Golden Delicious apple fruit were infiltrated with various concentrations of Ca2+ and Mg2+ with and without Ca2+-affecting reagents or other cations. Including-trifluoperazine with Mg2+ increased pitting over that with Mg2+ alone. Verapamil and nefedipine had no effect on MgIP or its attenuation by Ca2+. Cyclopiazonic acid attenuated MgIP. Ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and 2,3,5-triiodobenzoic acid attenuated MgIP. Cycloheximide and actinomycin D inhibited MgIP, while puromycin had no effect. Heating fruits at 38-degrees-C prior to infiltrating the fruits with MgCl2 attenuated MgIP. Cations Ba2+, La3+, Co2+, and Sr2+ included at 20.0 mM prevented MgIP (induced by 0.18 M Mg2+). Ca2+ (3.0 mM) included with 0.18 M Mg2+ inhibited MgIP 50%. K+ and Na+ partially inhibited MgIP. We have demonstrated that treatments affecting calcium homeostasis or cellular metabolism can alter MgIP development. We conclude that MgIP may be a useful tool to understanding natural bitter pit development.