Final answer:
IAA moves from growing regions to other plant tissues through a process called polar transport, which is essential for plant responses like phototropism and gravitropism, and plays a critical role in plant growth and development.
Step-by-step explanation:
The process by which the plant hormone IAA (Indole-3-Acetic Acid) moves from the growing regions of a plant shoot to other tissues is known as polar transport. This movement is guided by the concentration gradient of IAA in plant cells. In shoots, a higher concentration on the lower side stimulates cell expansion, causing the shoot to grow upwards. This process is integral to plant growth responses, including phototropism and gravitropism. During gravitropism, IAA is directed to the bottom side of the plant, causing differential growth that changes the direction of plant growth. With roots, IAA inhibits elongation on the lower side, allowing the upper side to grow normally, anchoring the plant more deeply into the soil.
Conversely, in shoots, IAA promotes growth on the lower side, causing the shoot to curve upward. Other important roles of IAA include its involvement in apical dominance, flowering, fruit setting, and various other developmental processes such as vascular tissue differentiation and leaf development.