Uptake of glycine betaine and its analogues by bacteroids of Rhizobium meliloti.
Bacteroids isolated from alfalfa nodules induced by Rhizobium meliloti 102F34 transported glycine betaine at a constant rate for up to 30 min. Addition of sodium salts greatly increased the uptake activity, whereas other salts or non-electrolytes had less effect. The apparent Km for glycine betaine uptake was 8.3 microM and V was about 0.84 nmol min-1 (mg protein)-1 in the presence of 200 mM-NaCl which gave maximum stimulation of the transport. Supplementing bacteroid suspensions with various energy-yielding substrates, or ATP, did not increase glycine betaine uptake rates. The uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), and the respiratory inhibitor potassium cyanide strongly inhibited glycine betaine uptake, but arsenate was totally inactive. Glycine betaine transport showed considerable structural specificity: choline, proline betaine, gamma-butyrobetaine and trigonelline did not competitively inhibit the system, although choline and proline betaine were transported by bacteroids. Both a high-affinity activity and a low-affinity activity were found for choline uptake. These osmoprotective compounds might have a significant role in the maintenance of nitrogenase activity in bacteroids subjected to salt stress.
Fougère
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Laboratoire de Biologie végétale et Microbiologie, URA CNRS 79, Faculté des Sciences et des Techniques, Université de Nice, Parc Valrose, France.
Le Rudulier
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D001622:Betaine / Q000378:metabolism* / Q000494:pharmacology; D001692:Biological Transport / Q000502:physiology; D002794:Choline / Q000378:metabolism; D000455:Medicago sativa / Q000382:microbiology*; D009994:Osmolar Concentration; D010101:Oxygen Consumption / Q000187:drug effects; D011392:Proline / Q000031:analogs & derivatives / Q000378:metabolism; D012231:Rhizobium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology
D001622:Betaine; D012965:Sodium Chloride; D011392:Proline; D002794:Choline; C003342:stachydrine