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Several studies have used A. thaliana as a model to identify the physiological and molecular mechanisms underlying iron deficiency tolerance in plants. Here, Arabidopsis thaliana and Thellungiella salsuginea were used to investigate the differential responses to iron deficiency of these two species. Plants were cultivated in hydroponic medium containing 5 or 0 µM Fe, for 10 days. Results showed that rosette biomass was more reduced in T. salsuginea than in A. thaliana when grown on Fe-deficient medium. As a marker for iron deficiency tolerance, the induction of ferric chelate reductase (FCR) and phosphoenolpyruvate carboxylase (PEPC) activities was observed only in A. thaliana roots. In addition, we found that the accumulation of phenolic acids in roots of N1438 ecotype of A. thaliana was stimulated by Fe deficiency. Furthermore, an increase of flavonoids content in the root and exudates was observed under Fe-deficiency in this ecotype. Unlike other abiotic stresses, it appears that iron deficiency effects were more pronounced in Thellungiella than in Arabidopsis. The higher tolerance of the Arabidopsis plant to iron deficiency may be due to the metabolic changes occurring in the roots. [ABSTRACT FROM AUTHOR]

idopsis thaliana seedlings were grown in hydroponic culture under controlled conditions in mediums with different NO/NH ratios. The mediums were not buffered, against pH change, but their pH was reset at pH 5.5 each 2 days. When ammoniacal N source was predominant, the whole plant biomass deposition was diminished, parallely to several parameters which revealed degraded leaf physiological status, such as leaf chlorosis associated with diminished chlorophyll content, lowered K, Ca, and water content, along with restricted leaf expansion, and apparition of cellular stress symptoms. However, leaf functioning for biomass production did not seem affected, since biomass production rate per unit leaf surface area remained unchanged. Indeed, the main factor of decrease biomass production was leaf elimination and/or repression of leaf initiation. The results are discussed in the context of literature data on the effects of NH on ion fluxes at the root level and properties of K transport systems in Arabidopsis. Disturbance of mineral (cationic) nutrition by NH seemed to be a major cause of the detrimental effect of ammoniacal nutrition. [ABSTRACT FROM AUTHOR]

Abstract: Potassium-sodium interaction was compared in two natural accessions of Arabidopsis thaliana, Columbia-0 and NOK2. Seedlings were grown in the presence of 0 or 50 mM NaCl and 0.1; 0.625 or 2.5 mM K+. At the lowest K+ concentration, salt treatment inhibited both K+ uptake and growth. Increasing the K+ availability did not modified salt response in Columbia-0, but restored nearly normal net K+ uptake in NaCl condition and alleviated NaCl growth reduction in NOK2. The effect of K+ and NaCl on transcript level of several K+ and Na+ transporters in both shoots and roots was assessed using semi-quantitative RT-PCR. The mRNA abundance of the NHX1 and SOS1 Na+/H+ antiporters was significantly increased by 50 mM NaCl in the two accessions. NHX1, which is responsible for Na+ sequestration into vacuoles, was more up-regulated in NOK2 leaves than in Columbia-0''s in NaCl stress condition. AKT1, which is the major channel involved in K+ absorption, was down-regulated in salt stress condition, but was not responding to K+ treatments. Only in NOK2, SKOR and AKT2, which respectively control xylem and phloem K+ transport, were markedly up-regulated by 2.5 mM K+ in both roots and shoots, independently of NaCl. Phenotypic and gene expression analyses suggest that the relative salt tolerance of NOK2 is mainly due to a high ability to sequester Na+ in the vacuole and to take up and transport K+. Up-regulation of SKOR and AKT2 by K+, and of NHX1 by NaCl could participate in determining this phenotype. To cite this article: R. Kaddour et al., C. R. Biologies 332 (2009). [Copyright &y& Elsevier]