Plants require a variety of mineral elements from the soil or from another medium in which they grow. If a plant's growth medium lacks an essential mineral element, the plant will display a characteristic set of symptoms before it dies. Nitrogen and iron are essential mineral elements for plants. Plants deficient in these elements are stunted in growth and show yellowing symptoms in their leaves. In the accompanying animation, we describe the yellowing symptoms of nitrogen and iron deficiencies.
Nitrogen and iron are essential elements for the growth of a plant. The molecule chlorophyll contains nitrogen, and thus the plant requires nitrogen to produce this green pigment. Without nitrogen, the plant becomes yellow, or chlorotic, as the yellow pigments that are present in the plant become unmasked by the disappearing chlorophyll.
If a plant has been grown with adequate nitrogen, its leaves will grow in deep green. If such a plant is transferred to a nitrogen-deficient medium, as in the accompanying animation, the plant will begin to display deficiency symptoms. In this case, the nitrogen in the mature leaves is transported out of these leaves and donated to the developing leaves of the plant. These new leaves grow in green, but the older leaves, which donated the nitrogen, undergo chlorosis.
In the iron deficiency, there is a different symptom. Iron remains sequestered in the mature leaves and is not transported to new leaves as they develop. Therefore, if a plant is transferred to an iron-deficient medium, its mature leaves remain green, but its new leaves grow in yellow. Although iron is not a component of the chlorophyll molecule, it is required in the production of chlorophyll. Therefore, without iron, the new plant tissue cannot make chlorophyll and undergoes chlorosis.
As depicted in the iron and nitrogen deficiencies, a plant's symptoms depend on how the plant normally uses an essential element, as well as whether the plant can transfer that element through its vascular system from mature tissue to developing tissue.