Iron chlorosis, a world wide problem, the relation of chlorophyll biosynthesis to iron

Abstract

Iron‐Chlorosis is a world‐wide problem, particularly in semi‐arid regions containing calcareous soils. Although most soils contain adequate total iron, the amount available to the plant is dependent on factors such as iron species and plant genotype.

Iron is reduced to ferrous form at the root surface if necessary and transported to the leaf through the xylem in a combined form. In the leaf it is used for chlorophyll (Chl) formation as well as for the functioning of various iron‐containing enzymes.

Chlorophyll is formed in higher plants from the precursor δ‐amino‐levulinic acid (ALA). This intermediate, ALA, functions for both heme and chlorophyll formation and may be formed through a primary biosynthesis pathway in higher plants requiring a 5‐carbon substrate, such as a ketoglutarate or glutamate. This pathway may be activated by iron, related to aconitase ativity and/or the formation of ferredoxin (Fd). Ferredoxin could be necessary to activate the ALA‐synthesizing enzyme. With plants that are iron‐stressed, Fd would be limiting and directly affect Chi biosynthesis.