CARBON PARTITIONING IN AN APPLE MUTANT DEFICIENT IN MALIC ACID
To elucidate the biochemical background with respect to the different ability of the two apple forms to store malic acid, enzyme activities related to malate metabolism were compared. The activity of phosphoenolpyruvate carboxylase (PEPC) was slightly increased in the-low acid apple and for the activity of phosphoenolpyruvate carboxykinase (PEPCK) a 3-fold activation in the same fruit was found. There was no difference in the activity of NAD-dependent malic acid dehydrogenase (MDH) and NADP-dependent malic enzyme (ME). It is suggested that in the low-acid fruit, in which there was no decrease in the activity of the enzymes involved in malate metabolism, it is an inability to accumulate malate that is responsible for the low-acid content of the apple.