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

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Abstract
The synergistic stimulation of ethylene production by kinetin and Ca(2+) in hypocotyl segments of mung bean (Phaseolus aureus Roxb.) seedling was further studied. The requirement for Ca(2+) in this system was specific. Except for Sr(2+), which mimicked the effect of Ca(2+), none of the following divalent cations, including Ba(2+), Mg(6+), Cu(2+), Hg(2+), Co(2+), Ni(2+), Sn(2+), and Zn(2+), showed synergism with kinetin on ethylene production. Fe(2+), however, showed a slight synergism with kinetin. Some of them (Hg(2+), Co(2+), and Ni(2+)) had a strong inhibitory effect, while others (Zn(2+), Mg(2+), Sn(2+), and Ba(2+)) had a slight or no inhibitory effect on ethylene production in the absence or presence of kinetin.Cu(2+) 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 Cu(2+) was applied with Ca(2+), a remarkable synergistic stimulation of ethylene production was observed. Tracer experiments indicated that Cu(2+) enhanced the uptake of (45)Ca(2+) into the tissues during the first few hours of incubation, and this increase of (45)Ca(2+) uptake paralleled the enhancement of ethylene production. When Ca(2+) was applied together with kinetin plus Cu(2+), both the ethylene production and the (45)Ca(2+) uptake were greatly increased over those from the segments treated with Cu(2+) or kinetin alone. The increase in ethylene production as a result of kinetin plus Ca(2+) plus Cu(2+) treatment is equal to the combined increases caused by kinetin plus Ca(2+) and Cu(2+) plus Ca(2+). A possible mechanism accounting for such cooperative effects of Cu(2+), Ca(2+), and kinetin on ethylene production is discussed.