Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

Summary

This in vitro study demonstrates that bicarbonate ions inhibit iron mobilisation from cotyledons in citrus seedlings, reducing iron availability in shoots and roots. The blockade of translocation triggers upregulation of Strategy I iron acquisition genes and enhanced root enzymatic activities, representing a compensatory stress response that persists even when iron is later resupplied in bicarbonate-containing media. These findings suggest that bicarbonate-induced chlorosis in citrus may operate through disrupted remobilisation of seed iron reserves rather than simply limiting soil iron uptake.

Regional applicability

The study was conducted in vitro under controlled laboratory conditions and does not specify geographic origin or field applicability. Findings are relevant to understanding citrus iron nutrition physiology globally, including in the United Kingdom where citrus is grown under protected cultivation. Transferability to field conditions would depend on whether bicarbonate accumulation mimics actual soil/water conditions affecting UK citrus production.

Key measures

Iron concentration in shoots, roots and cotyledons; gene expression (NRAMP3, FRO1, FRO2, HA1, IRT1, PEPC1); enzymatic activities (H+-ATPase, PEPCase, ferric chelate reductase); seedling growth over 21 days culture with 15-day iron resupply phase

Outcomes reported

The study measured iron concentration in seedling organs, gene expression of iron acquisition genes (NRAMP3, FRO1, FRO2, HA1, IRT1), and enzymatic activities (H+-ATPase, PEPCase) in citrus seedlings grown under iron-deprived conditions with or without bicarbonate supplementation. Bicarbonate was shown to inhibit iron translocation from cotyledons to shoots and roots, triggering compensatory iron-stress responses in root tissues.

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