Abstract
Bicarbonate-induced iron (Fe) deficiency (+Bic) is frequently observed in kiwifruit orchards, but more research attention has been paid to direct Fe deficiency (-Fe) in plants, including kiwifruit. Here we compared the differences of kiwifruit plants between -Fe and +Bic in: (1) the traits of 57Fe uptake and translocation within plants, (2) Fe forms in roots, and (3) some acidic ions and metabolites in roots. The concentration of 57Fe derived from nutrient solution (57Fedfs) in roots was less reduced in +Bic than -Fe treatment, despite similar decrease in shoots of both treatments. +Bic treatment increased 57Fedfs distribution in fine roots but decreased it in new leaves and stem, thereby displaying the inhibition of 57Fedfs translocation from roots to shoots and from fine roots to xylem of coarse roots. Moreover, +Bic imposition induced the accumulation of water-soluble Fe and apoplastic Fe in roots. However, the opposite was observed in -Fe-treated plants. Additionally, the cell wall Fe and hemicellulose Fe in roots were less reduced by +Bic than -Fe treatment. +Bic treatment also triggered the reduction in H+ extrusion and the accumulation of NH4+, succinic acid, and some amino acids in roots. These results suggest that, contrary to -Fe, +Bic treatment inhibits Fe translocation to shoots by accumulating water-soluble and apoplastic Fe and slowing down the release of hemicellulose Fe in the cell wall in kiwifruit roots, which may be related to the decreased H+ extrusion and the imbalance between C and N metabolisms.
Highlights
Kiwifruit (Actinidia Lindl.) is highly susceptible to iron (Fe) deficiency [1], in calcareous soils that comprise approximately 30% of arable land area worldwide [2] and generally contain bicarbonate concentrations in a range of 0.3–4 mM [3,4]
Both -Fe and +Bic treatments decreased the concentration of 57 Fe derived from nutrient solution (57 Fedfs) in shoots, and the Fe-decreasing effect was further enhanced by combined Fe deficiency (-Fe+Bic) treatment (Table 1)
52.4%, respectively, when compared with the control (Table 1). These results indicate that the 57 Fedfs concentration in roots was less reduced in +Bic than -Fe treatment, despite similar decrease in shoots of both treatments
Summary
Kiwifruit (Actinidia Lindl.) is highly susceptible to iron (Fe) deficiency [1], in calcareous soils that comprise approximately 30% of arable land area worldwide [2] and generally contain bicarbonate concentrations in a range of 0.3–4 mM [3,4]. More than 30% of global kiwifruit yield is from Shaanxi and Sichuan provinces in China where the orchard soils are characterized by high bicarbonate concentration [6,7]. Under direct Fe deficiency (-Fe) conditions, the enhancement of Fe uptake and translocation within plants have been well demonstrated by isotope labeling experiment [8] and analysis of gene expression [9]. Under +Bic conditions, on the contrary, Fe uptake and translocation in plants seems to be blocked. 1997 [3] reported that Fe uptake and translocation declined with
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