If the functioning of stomata in leaves of plants is stopped, it would:
Inhibit transpiration and photosynthesis.
Stomata are tiny pores in leaves and some other parts of plants like stems, roots, etc., which help in massive exchange of gases between plants and surroundings. It also helps in control of transpiration in plants. If their functioning is hampered, there would be no intake of carbon dioxide which would affect photosynthesis process and also hamper the transpiration process.