Foliar fertilization: possible routes of iron transport from leaf surface to cell organelles

ABSTRACT

Iron (Fe) plays a pivotal role in plant nutrition as well as human health. Foliar application is being adopted as an economic, targeted and environment friendly alternative over soil fertilization. However, dependency of foliar fertilization on crop species, environment, Fe compound and Fe status of plant makes it a complex practice. Though a large body of evidence is available on Fe movement from root to shoot, very little is known on its movement from the leaf surface (extracellular) to various organelles (intracellular). This article presents possible pathways of foliar-fed Fe including crossing leaf physical barriers to reach the apoplast, crossing the plasma membrane, moving through plasmodesmata, phloem loading and unloading and storage in intracellular compartments. We have also emphasized on various chelating agents present in intracellular environments along with membrane-bound proteins aiding in Fe movement. Further, genes involved in Fe uptake and transport from leaf surface are discussed. At organelle level, presence of importer/exporter in outer membranes or bound Fe (Fe(II) to Fe(III)) form needs to be identified. The long-distance transport of Fe in phloem supports the existence of unknown oxido-reductases. The understanding of Fe mobilization pathways from foliage to sink tissues might also assist in molecular biofortification.

KEYWORDS:

• Apoplast–symplast
• Fe-chelates
• foliar fertilization
• iron storage
• phloem transport

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Virtual Fertilizer Research Center, USA [Grant No. 02838/14].