How do plants control the direction of auxin movement?

How do plants control the direction of auxin movement?

Auxin is produced at the top of a plant and moves in one direction because of gravity

Auxin becomes positively charged and bonds to negatively charged sugars in the phloem, travelling with them

Auxin travels in the xylem and is actively transported in the direction the plant needs it to go

Transport proteins for auxin are only located on the basal side of the cell