How do auxins cause hydrotropism?

Answer 1

Roots show positive hydrotropism and grow in the direction of water. This tropism causes problems in many cities where tree roots grow toward the drain pipes, and grow into the cracks, and plug up the drains. Hydrotropism causes plants to bend or turn toward water.

Answer 2

Auxins promote cell elongation on the side of the root facing the greater water concentration, which results in bending towards the water source. This bending response occurs due to the differential growth on either side of the root caused by the redistribution of auxins.