Ethylene Suppression Modifies Gene Expression and Activity of Aroma Volatile-Related Enzymes in ‘Delbard Estivale’ Apples J. Harb Birzeit University Birzeit Palestine O. Saleh and B. Khraiwesh University of Freiburg Germany I. Lara Àrea de Post-Collita, UdL-IRTA, XaRTA Lleida Spain J. Streif KOB, Ravensburg Germany Keywords: alcohol dehydrogenase, alcohol o-acyltransferase, AVG, ‘Delbard Estivale’, lipoxygenase, Malus domestica Borkh., 1-MCP, pyruvate decarboxylase Abstract The aim of this study was to assess the effect of AVG- and 1-MCP treatment on the postharvest behaviour of ‘Delbarde Estivale’ apple kept at room temperature, with special emphasis on the biosynthesis of odor volatiles. Fruits were harvested at the proper time, and subjected to AVG (ReTain ® ) treatment 3 weeks before harvest date. Another lot of fruits were treated with 1-MCP. Both treatments had a negative impact on the biosynthesis of odour-volatiles, in particular on ester- type compounds. The activities of lipoxygenase (LOX), alcohol dehydrogenase (ADH), and pyruvate decarboxylase (PDC) were declined by these treatments, whereas the alcohol o-acyltransferase (AAT) activity was higher in 1-MCP treated fruit. Gene expression assessment confirmed these trends. Results confirm the important role of an adequate supply of substrates for the biosynthesis of volatile esters in apple fruit. INTRODUCTION Aroma is a very important attribute for sensory quality of apple (Malus domestica Borkh.) fruit. In spite of this relevance, post-harvest procedures have focused preferentially on other quality aspects such as firmness and visual quality, and aroma has been generally disregarded. Apple fruit produce many aroma-related volatile compounds, but the most important contributors to fruit flavour are esters. Ethylene is required for the biosynthesis of volatile esters in apple, as it is known to modulate the expression of alcohol o-acyltransferase (AAT) (Defilippi et al., 2005), which catalyses the last step in the biochemical pathway, and is thus directly responsible for the generation of this kind of compounds. The relationship between the biosynthesis of odour volatiles and ethylene is important, since the usage of ethylene suppression chemicals, mainly AVG and 1-MCP, is increasing. Mir et al. (1999) found that AVG inhibited volatile production by ‘Jonagored Jonagold’ apple fruit, which appeared to be independent of respiration. Also, Fan et al. (1998) found that the synthesis of certain volatiles was inhibited by AVG treatment of preclimacteric fruits. Concerning 1-MCP, Li et al. (2006) stated that although 1-MCP treatment prolonged post-harvest life of apples, it repressed the regeneration of esters during post-storage ripening. ‘Delbard Estivale’ is an early apple variety with sweet flavour, although a bit more acid than that of ‘Golden Delicious’. The aim of this study was to assess the effect of AVG- and 1-MCP treatment on the generation of volatile compounds during the post- harvest life of ‘Delbard Estivale’ apples kept at room temperature, and to determine which steps in the biochemical pathway are dependent on ethylene regulation. 1093 Proc. 6 th International Postharvest Symposium Eds.: M. Erkan and U. Aksoy Acta Hort. 877, ISHS 2010