Cadmium Toxicity Induced Changes in Nitrogen Management in Lycopersicon esculentum Leading to a Metabolic Safeguard Through an Amino Acid Storage Strategy
Résumé
Tomato (Lycopersicon esculentum) seedlings were grown in the presence of cadmium. After I week of Cd treatment, a sharp decline in biomass accumulation in the leaves and roots was observed, together with a decrease in the rate of photosynthetic activity due to both Rubisco and chlorophyll degradation and stomata closure. Cadmium induced a significant decrease in nitrate content and inhibition of the activities of nitrate reductase, nitrite reductase, glutamine synthetase (GS) and ferredoxin-glutamate synthase. An increase in NADH-glutamate synthase and NADH-glutamate dehydrogenase activity was observed in parallel. The accumulation of ammonium into the tissues of treated plants was accompanied by a loss of total protein and the accumulation of amino acids. GIn represented the major amino acid transported through xylem sap of Cd-treated and control plants. Cadmium treatment increased the total amino acid content in the phloem, maintaining GIn/Glu ratios. Western and Northern blot analysis of Cd-treated plants showed a decrease in chloroplastic GS protein and mRNA and an increase in cytosolic GS and glutamate dehydrogenase transcripts and proteins. An increase in asparagine synthetase mRNA was observed in roots, in parallel with a strong increase in asparagine. Taken together, these results suggest that the plant response to Cd stress involved newly induced enzymes dedicated to coordinated leaf nitrogen remobilization and root nitrogen storage.
Mots clés
Cadmium stress -Lycopersicon esculentum -Nitrogen -Senescence Cd
cadmium Fd-GOGAT
ferredoxin-dependent glutamate synthase GaBa
γ-amino-n-butyric acid GDH
glutamate dehydrogenase GS
glutamine sunthetase
cadmium
Fd-GOGAT
ferredoxin-dependent glutamate synthase
GaBa
γ-amino-n-butyric acid
GDH
glutamate dehydrogenase
GS
Domaines
Sciences du Vivant [q-bio]
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Licence : Domaine public
Licence : Domaine public