Heavy Metals in Crop Plants: Transport and Redistribution Processes on the Whole Plant Level

Summary

This narrative review synthesises current understanding of how heavy metals are transported and redistributed within crop plants at the whole-plant level. The authors distinguish between essential micronutrients (which damage plants or product quality when excessive) and non-essential pollutants, and explain how xylem and phloem transport systems interact to determine metal accumulation in harvestable organs. Metal-specific mobility patterns are identified—notably that nickel and zinc are highly phloem-mobile and accumulate in growing tissues, whilst iron and manganese are poorly mobile in the phloem and retained in mature leaves.

Regional applicability

The physiological mechanisms reviewed are universal to higher plants and applicable to UK cropping systems. Understanding heavy metal transport is directly relevant to UK agricultural practice given soil contamination from legacy industrial activity and atmospheric deposition, particularly for cereal production and food safety considerations.

Key measures

Heavy metal mobility classification (phloem-mobile vs. xylem-retained); accumulation patterns in roots, shoots, leaves, meristems, fruits and seeds; transport mechanisms via xylem transpiration stream and phloem redistribution

Outcomes reported

The paper reviews the mechanisms and pathways of heavy metal uptake, long-distance transport, and redistribution within crop plants, with emphasis on xylem and phloem transport systems and their interactions. It describes differential mobility and accumulation patterns for essential micronutrients (copper, zinc, manganese, iron, nickel, molybdenum) and non-essential pollutants (cadmium, lead, mercury) in various plant tissues.

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