EFFECT OF CALCIUM AND CALMODULIN ANTAGONISTS ON ETHYLENE BIOSYNTHESISIN TOMATO FRUITS

The aim of this work was to elucidate the mode of action of calcium in calcium-inhibited ethylene biosynthesis. In one experiment, mature gr een tomatoes were treated with 1.5% (w/v) CaCl2 + 60 mu M N-6(aminohex yl)-1-naphthalene-sulphonamide (W5). 1.5% (w/v) CaCl2 + 60 mu M N-6(am inohexyl)-5-chloro-1-naphthalenesulphonamide (W7), 1.5% (w/v) CaCl2 al one or distilled water (control). The control and the W7 treatment had much higher ethylene production than either the CaCl2 treatment alone or the CaCl2 + W5 treatment. In another experiment, similar tomatoes were treated with 1.5% (w/v) CaCl2 + 15 mu M trifluoperazine (TFP). 1. 5% (w/v) CaCl2 only, or distilled water (control). The treatment with 1.5% CaCl2 + 15 mu M TFP gave higher ethylene production than 1.5% (w/ v) CaCl2 without TFP, and nearly the same level as the control towards the end of the experimental period. For enzyme and intermediate metab olite assays, mature green tomatoes were treated with 1.5% (w/v) CaCl2 plus either W5 or W7. W5 treatment had a lower ethylene forming enzym e (EFE) activity, higher 1-aminocyclopropane-1-carboxylic acid (ACC) c oncentration, similar levels of ACC synthase activity and 1-(malonylam ino)-cyclopropane-1-carboxylic acid concentration, compared to the con trol and W7 treatment. As W7 is a more potent calmodulin antagonist th an W5, these results suggest a calcium-calmodulin inactivation of EFE activity. (C) 1998 SCI.