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Articles

Stimulation of Ethylene Production in the Mung Bean Hypocotyls by Cupric Ion, Calcium Ion, and Kinetin ¹

^a Department of Vegetable Crops, University of California, Davis, California 95616

The synergistic stimulation of ethylene production by kinetin and Ca²⁺ in hypocotyl segments of mung bean (Phaseolus aureus Roxb.) seedling was further studied. The requirement for Ca²⁺ in this system was specific. Except for Sr²⁺, which mimicked the effect of Ca²⁺, none of the following divalent cations, including Ba²⁺, Mg⁶⁺, Cu²⁺, Hg²⁺, Co²⁺, Ni²⁺, Sn²⁺, and Zn²⁺, showed synergism with kinetin on ethylene production. Fe²⁺, however, showed a slight synergism with kinetin. Some of them (Hg²⁺, Co²⁺, and Ni²⁺) had a strong inhibitory effect, while others (Zn²⁺, Mg²⁺, Sn²⁺, and Ba²⁺) had a slight or no inhibitory effect on ethylene production in the absence or presence of kinetin.

Cu²⁺ alone, depending on the concentration applied, stimulated ethylene production with a lag period of about 2 hours and had no synergism with kinetin on ethylene production. When Cu²⁺ was applied with Ca²⁺, a remarkable synergistic stimulation of ethylene production was observed. Tracer experiments indicated that Cu²⁺ enhanced the uptake of ⁴⁵Ca²⁺ into the tissues during the first few hours of incubation, and this increase of ⁴⁵Ca²⁺ uptake paralleled the enhancement of ethylene production. When Ca²⁺ was applied together with kinetin plus Cu²⁺, both the ethylene production and the ⁴⁵Ca²⁺ uptake were greatly increased over those from the segments treated with Cu²⁺ or kinetin alone. The increase in ethylene production as a result of kinetin plus Ca²⁺ plus Cu²⁺ treatment is equal to the combined increases caused by kinetin plus Ca²⁺ and Cu²⁺ plus Ca²⁺. A possible mechanism accounting for such cooperative effects of Cu²⁺, Ca²⁺, and kinetin on ethylene production is discussed.