Superficial Scald and Bitter Pit Development in Cold-Stored Transgenic Apples Suppressed for Ethylene Biosynthesis

The plant hormone ethylene regulates climacteric fruit ripening and plays a major role in the development of superficial scald in apple fruits during cold storage. The effect of cold storage at 0 °C on development of superficial scald and bitter pit (BP) in transgenic Greensleeves (GS) apples suppressed for ethylene biosynthesis was investigated. Four apple lines were used: untransformed GS; line 68G, suppressed for 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO); and lines 103Yand 130Y, suppressed for ACC synthase (ACS). Fruits from the transformed lines 68G, 103Y, and 130Y produced very little ethylene during 3 months of cold storage at 0 °C and after subsequent transfer to 20 °C, whereas untransformed fruits produced significant ethylene during cold storage, which increased dramatically at 20 °C. Respiration, expressed as CO2 production, was similar in all four apple lines. After 2 months at 0 °C, all apple lines showed some BP symptoms, but lines 68G and 103Y were more affected than untransf...