Fig. 1: Oral secretions (OS) of Manduca sexta catalyze the conversion of Z-3-hexenal to E-2-hexenal.

a Part of the biosynthetic pathway of green leaf volatiles (GLVs). The re-arrangement of Z-3-hexenal (Z3AL (1)) to E-2-hexenal (E2AL (2)) can either occur spontaneously or enzymatically by a (3Z):(2E)-hexenal isomerase. The (Z-3)/(E-2)-aldehydes can be further converted to their corresponding alcohols and esters. ADH, alcohol dehydrogenase; AKR, aldo-keto reductase; ADR, aldehyde reductase; AAT, alcohol acetyl transferase. b Representative chromatograms of headspace samples from Z-3-GLVs (Z3AL (1), Z-3-hexenol (Z3OL (3)) or Z-3-hexenyl acetate (Z3oAc (5)) and E2AL (2) that were either incubated with M. sexta OS from 5th instar larvae (with OS) or with a buffer as a control (w/o OS). Volatiles were identified using standard compounds. For simplification, the chromatograms of the standard solutions E-2-hexenol (E2OL (4)) and E-2-hexenyl acetate (E2oAc (6)), indicated by a grey, dotted line, are overlaid with the chromatograms in which Z3OL or Z3oAc were used as substrates. Ion 69 was used as qualifier ion for Z3AL and E2AL. Ion 67 was used as qualifier ion for Z3OL, Z3oAc and E2oAc and ion 57 was used as qualifier ion for E2OL. Headspace analysis for all samples and treatments was done in triplicates. a, b Volatile compounds in Fig. 1a are numbered and correspond to those shown in the chromatograms.