The balance of malate synthesis and metabolism in response to ion uptake in excised wheat roots

Abstract

Malic acid in wheat roots was labeled by incubation in KH 14CO 3 for 1 h and then transferred to unlabeled salt solutions. The amount of 14CO 2 released from labeled roots was greatest in CaCl 2 solutions, which resulted in the largest net decrease in malic acid concentration and least in KHCO 3 in which malic acid continued to accumulate. Similar results were obtained from short-term (10 min) labeling when KH 14CO 3 was added to roots in different salt solutions and the subsequent release of 14CO 2 was monitored. Calculations suggest that the regulation of malic acid uptake to the vacuole in response to ionic balance determines whether or not newly synthesized malic acid is decarboxylated. Decarboxylation, rather than reduction of synthesis, was the principal means of regulating malic acid concentration. However, in CaCl 2 solutions inhibition of synthesis also contributed to the net reduction in malic acid concentrations.