Expression of ascorbate oxidase in cultured green zucchini cells. Effect of copper and abscisic acid

Cell cultures have been developed from green zucchini (Cucurbita pepo medullosa) and used as a model system for studying the expression of ascorbate oxidase (AO). Addition of copper, the enzyme cofactor, to the culture medium increased the ascorbate oxidase activity, without changes in the specific mRNA and protein level. Therefore, copper presumably activates the apo AO present in the cell. Addition of the phytohormone abscisic acid (ABA) to the medium led to a decrease of both AO activity and content, paralleled by a decrease of the specific mRNA. Thus, it is assumed that ABA modifies the AO protein net synthesis, possibly acting at the transcriptional level