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?

Explanation

The appearance of the deficiency symptoms depends upon the mobility of the mineral elements in the plant. For instance, the elements such as nitrogen, potassium, magnesium that are actively mobilised within the plant, the deficiency symptoms tend to appear first in the older tissues. On the other hand, the elements like calcium are relatively immobile, the deficiency symptoms tend to appear first in the young tissues