Characterization of the Phosphate-mediated Control of Ethylene Production by Penicillium digitatum

Characterization of the phosphate effect on ethylene production by Penicillium digitatum is reported. A low level of phosphate (0.001 millimolar) was about 200 to 500 times as effective as a high phosphate level (100 millimolar) in stimulating ethylene production and the stimulation was readily reversed by addition of phosphate. This phosphate effect did not operate in static cultures. The precursor of ethylene in the stimulated low phosphate system was glutamate but not alpha-ketoglutarate, which is a precursor in static systems. Actinomycin D and cycloheximide effectively inhibited the low phosphate/high ethylene-producing system. Alkaline phosphatase and protein kinase activities were higher in low than in high phosphate systems. We suggest that phosphate level regulates ethylene production by P. digitatum and that the regulation involves a phosphorylation or dephosphorylation reaction of some enzyme system associated with ethylene production. Phosphate-mediated control of ethylene production may also involve the transcriptional and translational machinery of the fungal cell. P. digitatum apparently can produce widely different levels of ethylene by different pathways, depending on culture conditions under which it is grown.