Nicotianamine and related phytosiderophores: Their physiological significance and advantages for plant metabolism

Abstract

Recently, several unusual organic acids, with similar carbon and nitrogen structure, have been implicated in iron (Fe) metabolism in higher plants.

These compounds (e.g. nicotianamine, mugineic acid, and avenic acid), which can form stable complexes with various metal ions, have been isolated and identified in various plant species representing several higher plant families. Studies concerning their chemical properties and possible physiological functions have led scientists to reconsider some hypothetical models concerning the basic biochemical processes of Fe metabolism in soil‐plant systems. These models include mechanisms of Fe transport across root‐cell membranes, compartmentation and Intracellular Fe movement and storage processes, and processes involved in competition between microorganisms and higher plant‐roots for available iron stores in the rhizosphere.

Clearly, Fe presents specific problems to plant metabolism. These problems are associated with its reactivity and ability to catalyze many reactions of a potentially destructive nature, particularly those reactions associated with oxygen.

The nicotianamine group of phytosiderophores may have several advantages for plant metabolism. These relate not only to the acquisition and movement of Fe via simple complexation mechanisms, but also to providing a means of controlling the extent and variety of its potentially damaging biochemical reactions. This paper outlines the physiological significance and possible advantages that nicotianamine and related phytosiderophores may provide plants in controlling metabolic reactions involving the potentially metabolically ‘dangerous’ but essential micronutrient‐Fe.

Key words:

• Iron transport mechanism
• Iron physiology
• Iron biochemistry