Ca2+ effects on ethylene, carbon dioxide and 1‐aminocyclopropane‐1‐carboxylic acid synthase activity

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Abstract
The response of pericarp disks from ripening tomato (Lycopersicon esculentum Mill. cv. Traveler‘76) to CaCl2, additions was studied to determine the effect of Ca2+ on ethylene and CO2 production. Application of 5 mM CaCl2 resulted in a 2, 20, 33, 39, and 50% increase in ethylene production in disks obtained from preclimacteric minimum, climacteric rise, climacteric peak, one, and two days postclimacteric fruit, respectively. CaCl2 concentrations of 10 and 50 mM gave no additional stimulation of ethylene production; CO2 production at 5 mM CaCl2 was not different from controls, but is increased at 10 and 50mM CaCl2. CaCl2 also increased ethylene production in disks treated with 1‐aminocyclopropane‐1‐carboxylic acid (ACC) or aminoethoxy‐vinylglycine. Chloride salts of K+, Na+, Mg2+, Sr2+ and La3+ did not stimulate ethylene production. SrCl2 stimulated ethylene production to a lesser degree than CaCl2. Disks from potato (Solanum tuberosum L. cv. Katahdin) tubers produced greater quantities of ethylene and ACC when 5 mM CaCl2 was included in the incubation medium (K. B. Evensen, 1983. Physiol. Plant. 60:125–128). Ca2+‐treated disks had more than three times as much ACC synthase activity as control disks after 18 to 24 h incubation, when ethylene and ACC were maximal. The apparent Km for S‐adenosylmethionine was 13 μM at 29°C, pH 8.0 in extracts from both Ca2+‐treated and control disks. Inclusion of 1 to 50 mM CaCl2 in the assay medium did not significantly affect enzyme activity. ACC synthase extracted from control and Ca2+‐treated disks had a pH optimum of 8.5 and an apparent molecular weight of 72 kdalton, estimated by gel filtration. It is likely that the presence of Ca2+ in the buffer allows greater synthesis of ACC synthase as part of the wound‐healing response in potato, while in tomato the predominant effect is on membrane stabilization.