Variations in Adenylates and Adenylate Energy Charge During Phosphate-mediated Inhibition of Ethylene Biosynthesis in Penicillium digitatum

Abstract

Summary Changes in adenine nucleotides and adenylate energy charge in shake cultures of Penicillium digitatum were determined under conditions when ethylene biosynthesis was either activated or inhibited. Activation of ethylene biosynthesis under phosphate-limiting growth conditions was accompanied by a 28% decrease in the ATP level of the mycelia. Under these growth conditions, changes in the adenylate energy charge were inversely related to the concentration of AMP but did not correlate with changes in the rate of ethylene biosynthesis or in total adenylate nucleotides. Adenine and AMP, when added individually, partially prevented the inhibitory effect of 0.01 mM orthophosphate on ethylene biosynthesis. On addition of orthophosphate, orthophosphate and adenine, or orthophosphate and AMP a rapid decrease within 2 hours in ethylene biosynthesis occurred without a striking increase in the ATP level of the cultures. In non-growing mycelia of P. digitatum , there was considerable modulation in the concentration of individual adenine nucleotides but only small changes in the adenylate energy charge were observed. The data indicated that levels of adenylates, glutamate, or the adenylate energy charge do not mediate or limit phosphate inhibition of ethylene biosynthesis. However, it is suggested that an orthophosphate-repressible phosphatase and/or a protein kinase may be involved in this process.