A tomato antisense 1-aminocyclopropane-1-carboxylic acid oxidase gene causes reduced ethylene production in transgenic broccoli

In this paper 11 transgenic broccoli (Brassica oleracea L. var. italica) lines containing a tomato antisense 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene from pTOM13 were evaluated. Changes in respiration, ethylene production and ACC oxidase activity were studied in mature flowers. Averaged across all ACC oxidase transgenic lines, there was an initial increase followed by a substantial decrease in ethylene production compared with the controls. Of the 11 transgenic lines, 10 lines showed a significant reduction in fethylene production relative to the controls from 50 h after harvest. Green Beauty flowers showed a significant reduction in respiration between the transgenics and control and demonstrated how ethylene levels could control the stable, or climacteric-like increase in respiration. ACC oxidase activity was higher in transgenic plants, consistent with the initially higher ethylene production. ACC oxidase activity did not, however, reflect the increase in ethylene production found after 50 h for the controls. These results suggest that two ethylene production systems may operate with only the second being inhibited by the antisense ACC oxidase used and that the later system was not detected by the ACC oxidase assay used. The results do show that post-harvest ethylene synthesis and therefore possibly broccoli senescence can be regulated by using an antisense ACC oxidase gene.