Accumulation of γ-Aminobutyric Acid in Apple, Strawberry and Tomato Fruit in Response to Postharvest Treatments R. Deewatthanawong and C.B. Watkins Department of Horticulture, Cornell University Ithaca NY 14853 USA Keywords: Malus × domestica Borkh., Fragaria × ananassa Duch., Solanum pennelli, Solanum lycopersicum, chilling injury, CO 2 injury, stress, 1-methylcyclopropene Abstract γ-Aminobutyric acid (GABA) concentrations have been investigated in apple and strawberry fruit exposed to elevated CO 2 levels, and in tomato fruit of S. pennellii introgression lines in cultivated tomato (S. lycopersicum) stored at 3°C. In apple fruit, external CO 2 injury was much greater in fruit exposed to 2.5 and 5% CO 2 than at 1% CO 2 , and injury was enhanced by 1-methylcyclopropene (1-MCP) and inhibited by diphenylamine (DPA) treatment before exposure to 5% CO 2 . GABA accumulated in fruit skin to a greater extent when exposed to 2.5 and 5% CO 2 than to 1% CO 2 , while 1-MCP treated fruit had enhanced GABA accumulation and DPA treated fruit less GABA accumulation compared with 5% CO 2 alone. Strawberries contained undetectable amounts of GABA at harvest, but its concentration increased markedly during storage in 20% CO 2 . Tomato fruits of L. pennellii introgression lines stored at 3°C for 3 weeks showed elevated GABA concentrations, and the % increase over GABA concentrations at harvest was greater in fruit of introgression lines with higher susceptibility to chilling injury. Overall, the results suggest that GABA accumulations may be related to postharvest stresses in fruit, but further research is required to understand the relationships. INTRODUCTION γ-Aminobutyric acid or 4-aminobutyric acid (GABA) is a four-carbon non-protein amino acid that has long been of interest to plant physiologists because it accumulates in response to stress conditions such as salinity, anoxia, hypoxia, drought, heat, and chilling in a number of plant systems (Aurisano et al., 1995; Mayer et al., 1990; Wallace et al., 1984; Zushi and Matsuzoe, 2007). GABA has also been increasingly recognized as an important contributor to the C:N balance, and may be an integral part of the tricarboxylic acid cycle under both stress and non-stress conditions (Bouche and Fromm, 2004; Fait et al., 2007). In addition it may have roles as a regulator of cytosolic pH, protection against oxidative stress, defense against insects, as an osmoregulator and as a signaling molecule (Bouche and Fromm, 2004). Compared with other plant systems, less is known about GABA metabolism in fruit and vegetables in response to postharvest stresses during storage. GABA concentrations decreased during early storage of cold stored cherimoya fruits, but then increased (Escribano and Merodio, 2001). GABA accumulated in cherimoya fruits stored at 20% CO 2 , but then decreased after fruits were transferred to air (Merodio et al., 1998). Makino et al. (2008) found that GABA concentrations increased in tomato fruits stored in modified atmospheres, while a metabolic profiling study showed increasing GABA concentrations in controlled atmosphere-stored pear fruit that developed flesh browning (Franck et al., 2007). The objective of the current study was to screen a number of fruit types under controlled atmosphere and cold conditions as part of an initial study on GABA metabolism in harvested products. We tested apple and strawberry fruit under elevated CO 2 concentrations, and tomato fruit under chilling injury (CI)-inducing conditions. The ‘Empire’ apple in elevated CO 2 was chosen because of the sensitivity of the fruit to external CO 2 injury (Fawbush et al., 2008), the strawberry because of its tolerance to 947 Proc. 6 th International Postharvest Symposium Eds.: M. Erkan and U. Aksoy Acta Hort. 877, ISHS 2010