Which of the following explains the rapid growth of a seedling shaded by a neighboring plant?
1) Far-red light activates Pr to induce phototropism
2) Phytochrome responds to blue light to induce phototropism
3) The seedling is exposed to more far-red than red light, therefore Pfr becomes Pr
4) Phytochrome responds to far-red light to induce thigmotropism