Limits...
Increased sensitivity to iron deficiency in Arabidopsis thaliana overaccumulating nicotianamine.

Cassin G, Mari S, Curie C, Briat JF, Czernic P - J. Exp. Bot. (2009)

Bottom Line: Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions.However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability.This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron.

View Article: PubMed Central - PubMed

Affiliation: Centre National de la Recherche Scientifique (UMR 5004), Institut National de la Recherche Agronomique, Université Montpellier 2, Ecole Nationale Supérieure d'Agronomie, 2 Place Viala, F-34060 Montpellier cedex 2, France.

ABSTRACT
Nicotianamine (NA) is a non-protein amino acid derivative synthesized from S-adenosyl L-methionine able to bind several metal ions such as iron, copper, manganese, zinc, or nickel. In plants, NA appears to be involved in iron availability and is essential for the plant to complete its biological cycle. In graminaceous plants, NA is also the precursor in the biosynthesis of phytosiderophores. Arabidopsis lines accumulating 4- and 100-fold more NA than wild-type plants were used in order to evaluate the impact of such an NA overaccumulation on iron homeostasis. The expression of iron-regulated genes including the IRT1/FRO2 iron uptake system is highly induced at the transcript level under both iron-sufficient and iron-deficient conditions. Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions. This observation also suggests that the translocation of iron from the root to the shoot is not affected in the NA-overaccumulating line. However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability. This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron. This finding strengthens the notion that extracellular NA in the apoplast could be a major checkpoint to control plant iron homeostasis.

Show MeSH

Related in: MedlinePlus

Decreased water-extractable iron in the NA-overaccumulating line. Col-0 plants and plants overaccumulating NA were sown on half-strength MS medium and were transferred after 5 d to an iron-sufficient [50 μM Fe(III)-EDTA] or iron-deficient medium (no iron added) for an additional 12 d (as indicated below the graph). Soluble iron was extracted in water, then soluble iron (supernatant, grey bars) and the remaining iron (pellet, white bars) were measured by absorbance of Fe2+-o-phenanthroline using thioglycolic acid as the reducing agent. Error bars represent the SE of four repetitions. Differences were found to be highly significant (P <0.01; Student's test) between the soluble pools of Col-0 and the K1 line under iron-sufficient condition as well as between the K1 line soluble pools. Differences between the soluble pools of Col-0 and the K1 line under iron starvation are significant (P <0.05; Student's test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC2657549&req=5

fig5: Decreased water-extractable iron in the NA-overaccumulating line. Col-0 plants and plants overaccumulating NA were sown on half-strength MS medium and were transferred after 5 d to an iron-sufficient [50 μM Fe(III)-EDTA] or iron-deficient medium (no iron added) for an additional 12 d (as indicated below the graph). Soluble iron was extracted in water, then soluble iron (supernatant, grey bars) and the remaining iron (pellet, white bars) were measured by absorbance of Fe2+-o-phenanthroline using thioglycolic acid as the reducing agent. Error bars represent the SE of four repetitions. Differences were found to be highly significant (P <0.01; Student's test) between the soluble pools of Col-0 and the K1 line under iron-sufficient condition as well as between the K1 line soluble pools. Differences between the soluble pools of Col-0 and the K1 line under iron starvation are significant (P <0.05; Student's test).

Mentions: To gain a better insight into the iron phenotype of the K1 NA-overaccumulating line (constitutive induction of the iron uptake mechanisms, enhanced sensitivity to iron starvation despite an increase iron content), the iron availability in this Arabidopsis line was investigated. Fresh leaves of plants grown under control or iron-starved conditions were ground in water. After centrifugation, the pellet was assumed to represent the insoluble fraction whereas the supernatant represented the soluble, available iron. The total iron content related to the fresh weight appeared comparable between the two genetic backgrounds (wild-type versus the K1 line), being slightly higher in the K1 line (Fig. 5), which was consistent with the data presented in Fig. 4A. For the wild-type leaves, however, 30% of the total iron was found in the water-extractable fraction, whereas in the K1 line the soluble iron fraction represented only 6% of the total iron (Fig. 5). Upon iron starvation, although the total iron content decreased in wild-type leaves (as observed in Fig. 4A), the water-extractable iron fraction remained at 30% (Fig. 5), which corresponded to 5 μg of iron (g FW)−1. In the K1 line, the total iron content was still slightly higher than in the wild type (as in Fig. 4A) and the water-extractable iron fraction increased to 12% of this amount (Fig. 5). However, this remained below the value of the wild type and represented 2 μg of iron (g FW)−1, which corresponded to a 2.5-fold decrease of the soluble iron fraction compared with Col-0 plants.


Increased sensitivity to iron deficiency in Arabidopsis thaliana overaccumulating nicotianamine.

Cassin G, Mari S, Curie C, Briat JF, Czernic P - J. Exp. Bot. (2009)

Decreased water-extractable iron in the NA-overaccumulating line. Col-0 plants and plants overaccumulating NA were sown on half-strength MS medium and were transferred after 5 d to an iron-sufficient [50 μM Fe(III)-EDTA] or iron-deficient medium (no iron added) for an additional 12 d (as indicated below the graph). Soluble iron was extracted in water, then soluble iron (supernatant, grey bars) and the remaining iron (pellet, white bars) were measured by absorbance of Fe2+-o-phenanthroline using thioglycolic acid as the reducing agent. Error bars represent the SE of four repetitions. Differences were found to be highly significant (P <0.01; Student's test) between the soluble pools of Col-0 and the K1 line under iron-sufficient condition as well as between the K1 line soluble pools. Differences between the soluble pools of Col-0 and the K1 line under iron starvation are significant (P <0.05; Student's test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2657549&req=5

fig5: Decreased water-extractable iron in the NA-overaccumulating line. Col-0 plants and plants overaccumulating NA were sown on half-strength MS medium and were transferred after 5 d to an iron-sufficient [50 μM Fe(III)-EDTA] or iron-deficient medium (no iron added) for an additional 12 d (as indicated below the graph). Soluble iron was extracted in water, then soluble iron (supernatant, grey bars) and the remaining iron (pellet, white bars) were measured by absorbance of Fe2+-o-phenanthroline using thioglycolic acid as the reducing agent. Error bars represent the SE of four repetitions. Differences were found to be highly significant (P <0.01; Student's test) between the soluble pools of Col-0 and the K1 line under iron-sufficient condition as well as between the K1 line soluble pools. Differences between the soluble pools of Col-0 and the K1 line under iron starvation are significant (P <0.05; Student's test).
Mentions: To gain a better insight into the iron phenotype of the K1 NA-overaccumulating line (constitutive induction of the iron uptake mechanisms, enhanced sensitivity to iron starvation despite an increase iron content), the iron availability in this Arabidopsis line was investigated. Fresh leaves of plants grown under control or iron-starved conditions were ground in water. After centrifugation, the pellet was assumed to represent the insoluble fraction whereas the supernatant represented the soluble, available iron. The total iron content related to the fresh weight appeared comparable between the two genetic backgrounds (wild-type versus the K1 line), being slightly higher in the K1 line (Fig. 5), which was consistent with the data presented in Fig. 4A. For the wild-type leaves, however, 30% of the total iron was found in the water-extractable fraction, whereas in the K1 line the soluble iron fraction represented only 6% of the total iron (Fig. 5). Upon iron starvation, although the total iron content decreased in wild-type leaves (as observed in Fig. 4A), the water-extractable iron fraction remained at 30% (Fig. 5), which corresponded to 5 μg of iron (g FW)−1. In the K1 line, the total iron content was still slightly higher than in the wild type (as in Fig. 4A) and the water-extractable iron fraction increased to 12% of this amount (Fig. 5). However, this remained below the value of the wild type and represented 2 μg of iron (g FW)−1, which corresponded to a 2.5-fold decrease of the soluble iron fraction compared with Col-0 plants.

Bottom Line: Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions.However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability.This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron.

View Article: PubMed Central - PubMed

Affiliation: Centre National de la Recherche Scientifique (UMR 5004), Institut National de la Recherche Agronomique, Université Montpellier 2, Ecole Nationale Supérieure d'Agronomie, 2 Place Viala, F-34060 Montpellier cedex 2, France.

ABSTRACT
Nicotianamine (NA) is a non-protein amino acid derivative synthesized from S-adenosyl L-methionine able to bind several metal ions such as iron, copper, manganese, zinc, or nickel. In plants, NA appears to be involved in iron availability and is essential for the plant to complete its biological cycle. In graminaceous plants, NA is also the precursor in the biosynthesis of phytosiderophores. Arabidopsis lines accumulating 4- and 100-fold more NA than wild-type plants were used in order to evaluate the impact of such an NA overaccumulation on iron homeostasis. The expression of iron-regulated genes including the IRT1/FRO2 iron uptake system is highly induced at the transcript level under both iron-sufficient and iron-deficient conditions. Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions. This observation also suggests that the translocation of iron from the root to the shoot is not affected in the NA-overaccumulating line. However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability. This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron. This finding strengthens the notion that extracellular NA in the apoplast could be a major checkpoint to control plant iron homeostasis.

Show MeSH
Related in: MedlinePlus