Too hot and plants can't properly regulate water loss, shrivel, and die. Too cold, even well above freezing, and they can have problems moving their liquids due

Too hot and plants can't properly regulate water loss, shrivel, and die. Too cold, even well above freezing, and they can have problems moving their liquids due to increased viscosity. In both extremes you can have temps too far from optimal that inhibit enzyme reactions, killing the plants.