PH
Many plants adjust their growth according to the direction of light, a response called phototropism.
Light-sensitive proteins help trigger changes in the distribution of growth hormones within the plant. Cells on one side of a young stem can elongate more than those on the other, gradually bending the stem toward the light.
This is why a houseplant placed beside a window may slowly lean in that direction and change orientation after its pot is rotated.
© Royal Horticultural Society