Peptide hormone required for contiguous Casparian strip diffusion barrier formation in roots via the regulation of CASPs protein expression and distribution in a GSO1-GSO2 signaling pathway. The Casparian strip is required for ion homeostasis (e.g. iron and potassium ions). Interacts with the specific receptor kinases GSO1 and GSO2. Additional isoforms seem to exist. Expressed exclusively in the root stele. Confined to the root stele in the elongation and differentiation zones of both primary and lateral roots. Disappears at the sites of lateral root initiation. In the root tip, present at and above approximately 10 cells after the onset of elongation. Induced by excess iron and further synergistically regulated by lowering the medium pH. Abnormal endodermal barrier formation in cif2-1. The double mutant cif1-1 cif2-1 is defective in ion homeostasis in the xylem due to defect in endodermal barrier formation in the roots. Highly sensitive to excess iron. Retarded growth under low-potassium conditions. Repeatedly interrupted, discontinuous Casparian strip due to patch-like localization of the CASPs proteins. Reduced rosette leaf size.