Mn plays a crucial role in photosynthesis and is an essential component of many enzyme systems specifically associated with photosynthesis.

Mn deficiency produces an interveinal chlorosis of young, recently unfolded leaves. The boundary between the green and chlorotic area tends to be rather diffuse, the veins being surrounded by a definite zone of non chlorotic interveinal tissue. Symptoms are usually seen on the fully expanded leaves and not on the youngest leaves. The affected leaves may become completely chlorotic.