Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?

Why is that in certain plants deficiency symptoms appear first in youn

1.	Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?
Answer» Appearance of deficiency also depends on the mobility of the element in the plant. Some elements are actively mobilized in plants and are exported to young developing tissues. Deficiency of such elements first appears in the older tissues. For example; the deficiency symptoms of nitrogen, potassium and magnesium are first seen in the senescent leaves. This happens because these elements are mobilized to younger leaves.