iron chlorosisdevelops only between veins of young leaves while chlorosis occurs in older leaves.why?

Answer 1

Iron isn't a terribly mobile nutrient, and so when an iron shortage occurs, it occurs in the new leaves, as the plant can't move iron from the older leaves to the newer leaves. Other more mobile nutrients, such as nitrogen, will move from older leaves to newer leaves, so chlorosis will occur in the older leaves. Iron is used in the formation of chlorphyll, so no chlorophyll = no green.

I'm not exactly sure why it only occurs between the veins, but I imagine it has something to do with the mobility (or lack of) of iron in the plant. Hope that helps....