Auxin tells the stem cells to stop growing and the gynoecium to start forming in flowers

Source: sciencedaily.com
Farming & Agribusiness

Scientists have found that the plant hormone auxin governs the change from cell division at shoot tips to the development of female parts of a flower. Auxin levels are themselves controlled by the CRABS CLAW protein, which joins forces with another protein to negatively regulate stem cell growth. This highly regulated process is essential for successful plant reproduction and could be manipulated to improve crop production.