Iron resupply-mediated deactivation of Fe-deficiency stress responses in roots of sugar beet

Abstract

Different root zones with or without increased Fe-reducing activities have been studied in Fe-deficient sugar beet (Beta vulgaris L.) plants after Fe resupply to the nutrient solution. The subapical regions of roots from Fe-deficient plants decreased by 19 and 88% their capacity to reduce ferric chelates after 24 and 96 h of Fe resupply, respectively. Iron resupply caused 52 and 96% decreases in phosphoenolpyruvate carboxylase activity in root extracts after 24 and 96 h, respectively, and also caused general decreases in other enzyme activities involved in carboxylic acid metabolism. The large pools of carboxylic acids in Fe-deficient roots decreased by 9 and 48% after 24 and 96 h of Fe resupply, respectively. The activities of pyruvate decarboxylase and lactate dehydrogenase, enzymes related to anaerobic metabolism, decreased by 88% after 24 h of Fe resupply. The mitochondrial quinone and pyridine nucleotide pools became more oxidised in the Fe-deficient root tips after Fe resupply. Iron resupply caused a 70% decrease in root oxygen consumption rates 96 h after Fe resupply. Results indicate that deactivation of the Fe deficiency stress responses of sugar beet roots upon Fe resupply occurs in a progressive manner in a time scale of several days.

Changes in iron and organic acid concentrations in xylem sap and apoplastic fluid of iron-deficient Beta vulgaris plants in response to iron resupply

“…One day after Fe resupply, organic acid concentrations had decreased in apoplastic fluid (this study) and whole leaves (Ló pezMillá n et al, 2001a), but did not change markedly in xylem sap (this study) and whole roots (Ló pez-Millá n et al, 2001c). This suggests that, at this short Fe resupply time, leaf organic acids are actively consumed (depleting apoplastic and symplastic pools), while the transport of organic acids from the roots to the shoots via xylem (i.e., anaplerotic, non-autotrophic C export) is still similar to that occurring in Fe-deficient plants.…”

“…6). The decrease in xylem C transport at these longer Fe resupply times (2-4 d) is likely to be associated with the progressive decreases in root enzymatic activities involved in organic acid metabolism triggered by Fe resupply (Ló pez-Millá n et al, 2001c). The gradual improvement of leaf photosynthetic rates with re-greening after Fe resupply would make non-autotrophic C export from roots to leaves unnecessary.…”

“…Iron resupply to Fe-deficient plants also decreases organic acid concentrations, mainly Cit and malate, in roots, xylem sap and whole leaves (Ló pez-Millá n et al, 2001a, 2001c. In the short term, the effects of Fe resupply have been less studied, although there is a lag-phase of 1-2 d in which leaf Fe concentrations increase rapidly (Thoiron et al, 1997;Ló pez-Millá n et al, 2001a), whereas Chl concentrations increase much more slowly (Nishio and Terry, 1983;Larbi et al, 2004).…”

Physiological responses and differential gene expression in Prunus rootstocks under iron deficiency conditions

“…The response found in the P 2175 genotype under iron deficiency was atypical for FC-R activity and the proton release never detected before in our hydroponic conditions. However, the rhizosphere acidification, as a part of the response mechanism for the Strategy I plants against lack of iron, has been reported in other plum genotypes under different growing conditions (Romera et al, 1991), and in other woody plants such as pear (Donnini et al, 2009), peach-almond hybrids (Molassiotis et al, 2006), cork oak , grapevine (Jiménez et al, 2007) and herbaceous species (López-Millán et al, 2001;Santi et al, 2005).…”

Root-zone temperature affects the phytoextraction of iron in contaminated soil

“…In the root-cell plasma membrane, the activity of Fe(III)-chelate reductase is induced or stimulated by iron deficiency conditions (López-Millán et al, 2001). This activity depends on active proton exturtion and is conceivably related to the presence of a transmembrane electron-transport system located in the plasma membrane and reponsible for generating Fe(II) prior to uptake by dicotyledonous and non-graminaceous monocotolydenous plants (Mori, 1999;Vizzotto et al, 1999).…”