Regulation of Ethylene Biosynthesis in Broccoli Flower Buds in Controlled Atmospheres

The effect of controlled atmospheres on the regulation of ethylene biosynthesis during the senescence of broccoli flower buds ( Brassica oleracea , L. Italica group cv. Green Valiant) was assessed. The broccoli buds wee stored in the dark at 25C under a continuous stream of nitrogen containing the following percentages of CO 2 -O 2 : 0-20 (air), 0-2.5, 6-20, and 10-20. Generally, respiration, ethylene production, and ethylene-forming enzyme (EFE) activity followed a climacteric like pattern in all atmospheres. The ACC content changed little during the “climacteric”, but increased dramatically during the “post-climacteric” period, when ethylene production and EFE activity decreased. Under high CO 2 , respiration was reduced, but ethylene production and EFE activity were temporarily stimulated early during treatment. Under low O 2 , respiration, ethylene production, EFE activity, and ACC content were reduced, and the “climacteric” and chlorophyll losses were delayed to a greater extent than under high CO 2 . Whatever the treatment, ACC level was not the limiting factor in ethylene biosynthesis in broccoli; the reduction in ethylene production during senescence resulted from the degradation of the system that converts ACC to ethylene. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).