Postharvest Biology and Technology, 3 (1993) 235-247 235 © 1993 Elsevier Science Publishers B.V. All rights reserved 0925-5214/93/$06.00 POSTEC 01058 Carbon dioxide action on metabolism of organic and amino acids in crisphead lettuce * Dangyang Ke, Mila Mateos * *, Jingtair Siriphanich, Chingying Li and Adel A. Kader Department of Pomology, University of California, Davis, CA, USA (Accepted 7 May 1993) ABSTRACT Tissue of crisphead lettuce (Lactuca sativa L.) was kept in air or air enriched with 5% to 20% CO 2 at 0°C for 2 to 9 days followed by transfer to air or the CO2-enriched atmosphere at 20°C for 1 day to study the mode of CO 2 action on metabolism of organic and amino acids. Exposure to 20% CO 2 reduced the extractable activity of succinate dehydrogenase. The 20% CO 2 treatment caused a decrease in pH, which partially inhibited the catalytic activity of succinate dehydrogenase and substan- tially activated glutamate decarboxylase. As a result, succinate and y-aminobutyrate accumulated and concentrations of malate and glutamate decreased. Such effects on the organic and amino acids were more pronounced with higher temperature, higher CO 2 concentrations, and longer exposure to CO 2. The accumulation of succinate and y-aminobutyrate was induced by 15% or 20% CO 2 in all the three tested cultivars ('Climax', 'Salinas', and 'Winter Haven') and in both green and white tissues of lettuce, regardless of variation in their susceptibilities to CO 2 injury. Key words: Lettuce; Lactuca satica; Organic acid; Amino acid; Controlled atmosphere; Physiological disorder INTRODUCTION Crisphead lettuce is very sensitive to CO 2 injury (Stewart and Uota, 1971; Brecht et al, 1973; Kader and Morris, 1977). Responses of lettuce to elevated CO 2 atmospheres included a decrease in titratable acidity, induction of phenylalanine ammonia-lyase (PAL), accumulation and oxidation of soluble phenolic compounds, Correspondence to: Adel A. Kader, Department of Pomology, University of California, Davis, CA 95616-8683, USA. * Research supported, in part, by a BARD grant no. U.S.-1746-89. * * The work of M. Mateos was supported by a grant from the Direccion General de Investigation Cientifica y Tecnica (Ministerio de Educacion y Ciencia), Spain.