Myosin XI directs the movement of organelles such as plastids and mitochondria in plant cells. It is responsible for the light-directed movement of chloroplasts according to light intensity and the formation of stromules interconnecting different plastids. Myosin XI also plays a key role in polar root tip growth and is necessary for proper root hair elongation. A specific Myosin XI found in "Nicotiana tabacum" was discovered to be the fastest known processive molecular motor, moving at 7μm/s in 35 nm steps along the actin filament.