Effect of calcium and calmodulin antagonists on ethylene biosynthesis in tomato fruits

Abstract

The aim of this work was to elucidate the mode of action of calcium in calcium-inhibited ethylene biosynthesis. In one experiment, mature green tomatoes were treated with 1.5% (w/v) CaCl 2 + 60 μM N-6(aminohexyl)-1-naphthalene-sulphonamide (W5). 1.5% (w/v) CaCl 2 + 60 μM N-6(aminohexyl)-5-chloro-1-naphthalenesulphonamide (W7), 1.5% (w/v) CaCl 2 alone or distilled water (control). The control and the W7 treatment had much higher ethylene production than either the CaCl 2 treatment alone or the CaCl 2 + W5 treatment. In another experiment, similar tomatoes were treated with 1.5% (w/v) CaCl 2 + 15 μM trifluoperazine (TFP), 1.5% (w/v) CaCl 2 only, or distilled water (control). The treatment with 1.5% CaCl 2 + 15 μM TFP gave higher ethylene production than 1.5% (w/v) CaCl 2 without TFP, and nearly the same level as the control towards the end of the experimental period. For enzyme and intermediate metabolite assays, mature green tomatoes were treated with 1.5% (w/v) CaCl 2 plus either W5 or W7. W5 treatment had a lower ethylene forming enzyme (EFE) activity, higher 1-aminocyclopropane-l-carboxylic acid (ACC) concentration, similar levels of ACC synthase activity and 1-(malonylamino)-cyclopropane-1-carboxylic acid concentration, compared to the control and W7 treatment. As W7 is a more potent calmodulin antagonist than W5, these results suggest a calcium-calmodulin inactivation of EFE activity.