ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
A two-week salt treatment (NaCl, 100 mM) induced a 50% inhibition of acetylene reduction activity (ARA) of faba bean (Vicia faba L. var. minor cv. Soravi) nodules, associated with a large increase in the nodule pool of amino acids. The concentration of proline in the different nodule compartments was determined after calculating their respective volumes from their areas on electron micrographs. The proline concentration exhibited a large increase, especially in the cytosol where its amount was 8-fold enhanced under salt stress, whereas the low proline content of bacteroids was less affected. Increase of proline concentration in faba bean nodules subjected to salt stress was correlated with an enhancement of the cytosolic Δ1-pyrroline-5-carboxylate synthetase (EC 2.7.2.11 + EC 1.2.1.41; P5CS) activity. Experiments with purified symbiosome preparations showed that the greatest proline content occurred in the peribacteroid space (PBS), where proline was the most abundant amino acid, with a concentration reaching 15.3 mM under salt stress. Proline accumulation in the PBS resulted both from a diffusive transport from the host cell to the symbiosomes through the peribacteroid membrane (PBM) and from the very low rate of uptake by faba bean bacteroids. This accumulation could be partly responsible for the 1.7-fold enlargement of the symbiosome volume observed in salt-stressed nodules. In incubations of bacteroids, isolated from salt-stressed or unstressed plants and supplied with O2 by purified oxyleghemoglobin, addition of proline stimulated neither O2 consumption nor ARA. These results were consistent with proline playing a role as osmoticum, rather than energy source for bacteroid N2 fixation in amide-exporting legumes such as faba bean.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1034/j.1399-3054.1998.1040106.x
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