The plant will prioritize magnesium supply to young leaves; therefore, signs of deficiency first manifest in older leaves.
The main symptoms are interveinal chlorosis of older leaves, which means that the tissue between the veins turns yellow in color, while the veins remain green. Severe deficiency may cause stunting. Symptoms vary across different crops, but it is common for chlorosis to begin on the tips of older leaves and progress around the leaf margins inwards, towards the petiole.
Magnesium is a macronutrient that is the central molecule in chlorophyll and essential for stabilization of other macromolecule such as nucleic acids. Plants absorb magnesium through their roots in the form of Mg2+. Once inside, magnesium is relatively mobile and translocates from older parts to younger parts of the plant if necessary such as with a deficiency.
Deficiency occur most frequently in acidic soils and soils containing high amounts of potassium fertilizer.