Respiratory Oxygen Response and Respiratory Quotient of Apple Stem Sections during Chilling

Abstract

During natural leaf abscission, 2-year-old potted apple trees (Malus domestica Borkh. cv. MM.111 EMLA) were placed in a room at 6C for chilling [0,600, 900, or 1400 chilling units (CU)]. After each chilling treatment, respiration of shoot segments was measured as CO 2 evolved and O 2 consumed at 22C in several O 2 concentrations. Respiration increased with oxygen concentration after all CU treatments. Carbon dioxide evolved at the several O 2 levels did not show a pattern related to CU, but O 2 consumed decreased at a decreasing rate with additional CU. Respiratory quotient was <1 at 0 and 600 CU and equal to 1 at 900 and 1400 CU, indicating a possible shift in respiratory substrate with chilling.