Sensitivity to and requirement for iron in Plantago species

Abstract

The relative importance of some aspects of iron nutrition for the distribution of six Plantago species (P. maritima L., P. coronopus L., P. major ssp. major L., P. serpentina All., P. media L. and P. lanceolata L.) with different habitat requirements for soil pH and moisture was evaluated. Iron efficiency and Fe tolerance of hydroponicallygrown plants were assessed by determining the decrease in relative growth rates caused by suboptimal and supraoptimal external Fe concentrations. Marked interspecific differences were observed in visual symptoms of Fe deficiency and Fe toxicity and in the external Fe concentrations leading to 50 % inhibition of maximal relative growth rates ( &! % ). Whereas P. serpentina displayed a clear preference for low external Fe concentrations, growth rates of P. maritima and P. media were found to be increased at higher concentrations. Severe growth restriction at both low and high Fe concentrations was evident in P. lanceolata and P. major. A broad optimum was observed in P. coronopus exhibiting a low external Fe requirement and a high tolerance to supra-optimal Fe concentrations. Iron efficiency and Fe tolerance differed in a way which was only partly correlated with the expected Fe availability at the natural habitat of the species, suggesting that Fe concentrations are of minor importance for their distribution, or that some of the mechanisms that render Fe oxides available for uptake in situ are masked in solution experiments.To gain insight into the impact of the physiological and morphological characteristics of the species on Fe efficiency, the effect of Fe status on shoot : root ratio, relative root surface area, root Fe(III) reductase and proton extrusion capacity were investigated. Roots of all species showed increased Fe chelate reduction activity upon growth at suboptimal Fe concentrations ; marked differences were observed with respect to the kinetic parameters of the reductase. Maximal velocity of the reduction was positively correlated with relative growth rate and was not related to the Fe efficiency of the species. By contrast, K m corresponded to Fe efficiency ranking and can therefore be regarded as an important parameter for the uptake of Fe at low availability. Enhanced ability to acidify the rhizosphere was only observed in P. major. From the morphological characteristics investigated, root surface area appears to be the most important parameter in the uptake of Fe at suboptimal external concentrations.

Iron Enhances Aluminum-induced Leaf Necrosis and Plant Growth Inhibition in Eucalyptus camaldulensis

“…This suggests that Fe efficiency in E. camaldulensis is comparable with the highly Fe-efficient group of Plantago species, in which growth did not differ between 1 and 10 lM of Fe when plants were raised in hydroponic conditions (Schmidt and Fuhner, 1998). This specific characteristic of E. camaldulensis was also indicated by the minor effect of different Fe treatments had on the chlorophyll content (Table 2) (Abadia et al, 1989;Fordor et al, 1995).…”

Dissecting iron deficiency‐induced proton extrusion in Arabidopsis roots

“…The efficiency of Fe acquisition could be linked either to the ability to mobilize additional sources of Fe or to a higher rate of induction of FRO2 and IRT1 . The maximal velocity of FRO2 activity was found to be positively related to the relative growth rate of the species and was not related to the maintenance of the growth at low Fe concentrations (Schmidt & Fühner, 1998), making the capacity of rhizosphere acidification a likely candidate for a determinant of Fe uptake efficiency. While no clear differences among the weak and strong acidifiers were observable regarding the reduction of chlorophyll concentration or decrease in biomass production, strong acidifiers were generally characterized by a stable shoot–root ratio.…”

Fe homeostasis in plant cells: Does nicotianamine play multiple roles in the regulation of cytoplasmic Fe concentration?

“…Depending on the redox conditions of the soil, external iron levels to which plant roots are exposed may vary considerably, reaching toxic levels in the absence of oxygen. The deleterious eect of Fe toxicity is observed as blackening of root tips, inhibition of root growth and necrotic spots on the leaves (`bronzing'); (Snowdon and Wheeler 1995; Schmidt and FuÈ hner 1998). Several strategies to minimize oxidative stress induced by essential and nonessential heavy metals have been described in higher plants (Howden et al 1995;Murphy et al 1997;Gonza lez et al 1998;van der Zaal et al 1999).…”