The C₆-aldehyde-forming system in Agropyron repens

A vigorous formation of the volatile C₆ compounds typical of plant lipoxygenase/hydroperoxide lyase systems (n-hexanal and hexenals) was observed in mechanically disrupted tissue of quick grass (Agropyron repens). Evidence for the precursor properties of linolenic acid and for the primary main cleavage product (Z)-3-hexenal was obtained from time-course studies. Both the lipoxygenase and the hydroperoxide lyase activities occur in a pellet sedimenting at 15 000 × g. The relative proportions of 13- to 9-hydroperoxi-(E,Z)-10,12-octadecadienoic acids were 81 to 19 under the conditions used. The enantiomeric composition of the 13-hydroperoxide, the sole substrate for the lyase, was approx. 74 to 26 (13S to 13R) and remained unchanged during prolonged incubation. The contribution of lytic activities to the formation of 1-penten-3-ol is suggested. The limited activity of the hexenal-forming system was neither caused by the carbonyls themselves nor by a hydroperoxide deficiency, and the inactivation followed third-order reaction kinetics.