Biochemical responses to direct or bicarbonate-induced iron (Fe) deficiency were compared in two Tunisian native grapevine varieties, Khamri (tolerant) and Balta4 (sensitive), and a tolerant rootstock, 140Ru.
Morpho-physiological and biochemical responses of Arabidopsis thaliana (accession N1438) to bicarbonate-induced iron deficiency were investigated. Plants were grown in cabinet under controlled conditions, in a nutrient solution containing 5 lM Fe, added or not with 10 mM NaHCO 3 . After 30 days, bicarbonate-treated plants displayed significantly lower biomass, leaf number and leaf surface area as compared to control plants, and slight yellowing of their younger leaves was observed. Potassium (K ? ) content was not modified by bicarbonate treatment in roots, whereas it was significantly diminished in shoots. Their content in ferrous iron (Fe 2? ) and in leaf total chlorophylls was noticeably lower than in control plants. Root Fe(III)-chelate reductase and phosphoenolpyruvate carboxylase (PEPC) activities were significantly enhanced, but leaf ribulose 1.5-bisphosphate carboxylase (Rubisco) activity was decreased.
Marjoram oil is a rich source of many compounds such as essential oils and fatty acids, but the distribution of these compounds differed significantly between the two varieties studied.
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.
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