title: Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots.
abstract: The effect of bicarbonate ion (HCO3(-)) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated "in vitro" on two iron-deprived media, supplemented or not with 10mM HCO3(-) (-Fe+Bic and -Fe, respectively). After 21d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO3(-) (+Fe+Bic or +Fe, respectively). -Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than -Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO3(-) upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H(+)-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When -Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO3(-) prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.
authors: Department of Citriculture and Vegetal Production, Instituto Valenciano Investigaciones Agrarias, Crta Náquera-Moncada, km 4.5, Valencia 46113, Spain.
authors: Mary-Rus
authors: MR
authors: Martínez-Cuenca
authors: Francisco
authors: F
authors: Legaz
authors: M Ángeles
authors: MÁ
authors: Forner-Giner
authors: Eduardo
authors: E
authors: Primo-Millo
authors: Domingo J
authors: DJ
authors: Iglesias
mesh_terms: D001639:Bicarbonates / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D018533:Biomass; D002957:Citrus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D018548:Cotyledon / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D007501:Iron / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D013312:Stress, Physiological / Q000187:drug effects* / Q000235:genetics
chemical_list: D001639:Bicarbonates; D010940:Plant Proteins; D007501:Iron