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The activity of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO; EC 1.4.3.3) in germinating seeds of  Callistephus chinensis  was studied. For maximum recovery of ACO activity  in vitro , the presence of 10% (w/v) insoluble polyvinylpolypyrrolidone (PVPP) and 30% of glycerol in the extraction medium was necessary. The optimum pH for this activity was 7.0. Ethylene production by whole achenes or enzymatic extract increased due to increasing 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations. Saturation level of ACC for  in vivo  ACO activity was 10 −1  M and V max  was 10.89 nL C 2 H 4 ·mg protein −1 ·h −1 . For  in vitro  ACO activity, the saturation level of ACC was 10 −3  M and V max  was 2.299 nL C 2 H 4 ·mg protein −1 ·h −1 . Both,  in vivo  and  in vitro  ACO activities did not follow Michaelis-Menten kinetics. The Hill coefficients ( h ) were estimated on the basis of non-linear estimation. Their values were 0.63 for  in vivo  ACO activity and 1.73 for  in vitro  ACO activity. The experimental data show that ACO from  C. chinensis  seeds is an oligomeric enzyme with at least two active sites. During seed germination,  in vitro  ACO activity was detectable after 12 hours of imbibition, while  in vivo  ACC conversion to ethylene was observed after 24 h, i.e. – after radicle protrusion. The activity of ACO in  C. chinensis  seeds is associated with germination  sensu stricto , and might be a good marker of this process.

journal of horticultural research

In vivo and in vitro Activity of 1-aminocyclopropane-1-carboxylic Acid Oxidase in Germinating Seeds of China Aster (Callistephus chinensis Nees)