Inhibition of Ethylene Production by Cobaltous Ion

Abstract

The effect of Co2+ on ethylene production by mung bean (Phaseolus aureus Roxb.) and by apple tissues was studied. Co2+, depending on concentrations applied, effectively inhibited ethylene production by both tissues. It also strongly inhibited the ethylene production induced by IAA, kinetin, IAA plus kinetin, Ca2+, kinetin plus Ca22, or Cu2+ treatments in mung bean hypocotyl segments. While Co2+ greatly inhibited ethylene production, it had little effect on the respiration of apple tissue, indicating that Co2+ does not exert its inhibitory effect as a general metabolic inhibitor. Ni2+, which belongs to the same group as Co2+ in the periodic table, also markedly curtailed both the basal and the induced ethylene production by apple and mung bean hypocotyl tissues.In a system in which kinetin and Ca2+ were applied together, kinetin greatly enhanced Ca2+ uptake, thus enhancing ethylene production. Co2+, however, slightly inhibited the uptake of Ca2+ but appreciably inhibited ethylene production, either in the presence or in the absence of kinetin. Tracer experiments using apple tissue indicated that Co2+ strongly inhibited the in vivo conversion of L-IU_'4Clmethionine to 14C_ ethylene. These data suggest that Co2+ inhibited ethylene production by inhibiting the conversion of methionine to ethylene, a common step which is required for ethylene formation by higher plants.Co2+ is known to promote elongation, leaf expansion, and hook opening in excised plant parts in response to applied auxins or cytokinins. Since ethylene is known to inhibit these growth phenomena, it is suggested that Co2+ exerts its promotive effect, at least in part, by inhibiting ethylene formation.We have previously reported that Ca2+ or Sr2+ synergistically stimulated ethylene production in the presence of kinetin, whereas Co2+ or Ni2+, in contrast, greatly inhibited ethylene production in the presence or in the absence of kinetin (16, 18). As ethylene is endogenously produced by ripening fruit tissues (1, 3, 4, 5) and as its production in vegetative tissues can be regulated by the application of auxin (1,7,11,14,19,20), kinetin (1,15,16,19), auxin plus kinetin (1,15,19), Ca2+ (16,17), kinetin plus Ca2+ (16, 17), or Cu2+ (1,2,18), it is important to determine whether Co2+ also inhibits these ethyleneproducing systems. Evidence from tracer studies has established methionine as the in vivo precursor of ethylene in fruit and vegetative tissues (1,3,4,22,24,29). This paper describes the inhibitory effect of Co2+ on ethylene production by treated ness at 24 C. Segments 2 cm long were cut from hypocotyls at a point 1 cm below the hook, as previously described (16). Lots of 20 segments were incubated in 5 ml of a medium consisting of 50 mm potassium phosphate buffer (pH 6), 2% sucrose, various concentrations of Co2+, Ni2+, Ca2+, Cu2+, IAA, or kinetin as indicated, in a 50-ml Erlenmeyer flask. A plastic center well containing 0.2 ml of 40% KOH was hung in the flask to absorb CO2 evolved. The flasks were sealed with rubber serum-caps, and incubated...

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Induction of in vitro flowering in Capsicum frutescens under the influence of silver nitrate and cobalt chloride and pollen transformation

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Several aspects on the plant growth and development in space environment. Trace gases generated in closed plant cultivation systems and their effects on plant growth.

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