Fig. 8.

Hypothetical model for Al-induced citrate secretion from roots of a typical pattern II-type rice bean plant. At least four steps are involved in the process. Step 1: Al³⁺ interacts with a receptor (R) on the plasma membrane to initiate a signal transduction pathway, which triggers the de novo biosynthesis of an unidentified transcription factor (TF). Step 2: reversible protein phosphorylation is required for the TF to interact with sequences in the promoter of VuMATE1 and induce its expression. Step 3: translation of Vu-MATE1 mRNA into protein. Step 4: a K252a-sensitive protein kinase is involved in the phosphorylation of VuMATE1 for activation of VuMATE1 to transport citrate out of the cell through the plasma membrane. (This figure is available in colour at JXB online.)