Biology – 6.2 Plant nutrition – mineral requirements | e-Consult

A plant deficient in magnesium ion will display distinct symptoms, primarily affecting the older leaves first. The most characteristic symptom is interveinal chlorosis. This means the areas between the veins of the leaves will turn yellow, while the veins themselves remain green. This is because magnesium is a central atom in the chlorophyll molecule. A lack of magnesium prevents the formation of functional chlorophyll in the affected areas.

As the deficiency progresses, the yellowing will spread, eventually affecting the entire leaf, leading to necrosis (tissue death) in the affected areas. The leaf margins may also become distorted or curled. Growth will be stunted, and the plant may appear generally weak and pale. The deficiency typically affects the lower leaves first due to the mobility of magnesium within the plant.

Underlying Reason: Magnesium is a key component of the chlorophyll molecule. Without sufficient magnesium, chlorophyll synthesis is impaired, leading to interveinal chlorosis and ultimately necrosis. Magnesium is also involved in the activation of enzymes required for photosynthesis, further contributing to the reduced photosynthetic capacity of the plant.