Suppression of the expression of genes encoding ethylene biosynthetic enzymes in harvested broccoli with high temperature treatment

Broccoli (Brassica oleracea L. var. Italica) senesces very rapidly at room temperature after harvest. Postharvest high temperature treatment reduced ethylene production and delayed yellowing of florets during storage. High temperature treatment suppressed 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) activity and the accumulation of ACS transcripts (BO-ACS1). Increase in activity was correlated with that of ethylene production. Changes in ACC synthase activity seemed to reflect the expression of the BO-ACS1 gene with a 1 day lag. High temperature treatment also suppressed ACC oxidase (ACO) activity. However, the changes did not seem to be related to those in ethylene production. High temperature treatment seemed to affect the accumulation of ACO transcripts (BO-ACO1 and BO-ACO2) differently; the accumulation of BO-ACO1 transcripts was delayed and that of BO-ACO2 decreased. These results suggest that inhibition of ethylene production with high temperature treatment could be due to suppression of BO-ACS1 gene expression.