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) li nes containing a tomato antisense 1-aminocyclopropane-1-carboxylic acid (AC C) oxidase gene from pTOM13 were evaluated. Changes in respiration, ethylen e production and ACC oxidase activity were studied in mature flowers. Avera ged 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 reduct ion in fethylene production relative to the controls from 50 h after harves t. Green Beauty flowers showed a significant reduction in respiration betwe en the transgenics and control and demonstrated how ethylene levels could c ontrol the stable, or climacteric-like increase in respiration. ACC oxidase activity was higher in transgenic plants, consistent with the initially hi gher ethylene production. ACC oxidase activity did not, however, reflect th e 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 l ater system was not detected by the ACC oxidase assay used. The results do show that post-harvest ethylene synthesis and therefore possibly broccoli s enescence can be regulated by using an antisense ACC oxidase gene.