Abstract
Both mannitol and sucrose (Suc) are primary photosynthetic products in celery (Apium graveolens L.). In other biological systems mannitol has been shown to serve as a compatible solute or osmoprotectant involved in stress tolerance. Although mannitol, like Suc, is translocated and serves as a reserve carbohydrate in celery, its role in stress tolerance has yet to be resolved. Mature celery plants exposed to low (25 mM NaCl), intermediate (100 mM NaCl), and high (300 mM NaCl) salinities displayed substantial salt tolerance. Shoot fresh weight was increased at low NaCl concentrations when compared with controls, and growth continued, although at slower rates, even after prolonged exposure to high salinities. Gas-exchange analyses showed that low NaCl levels had little or no effect on photosynthetic carbon assimilation (A), but at intermediate levels decreases in stomatal conductance limited A, and at the highest NaCl levels carboxylation capacity (as measured by analyses of the CO2 assimilation response to changing internal CO2 partial pressures) and electron transport (as indicated by fluorescence measurements) were the apparent prevailing limits to A. Increasing salinities up to 300 mM, however, increased mannitol accumulation and decreased Suc and starch pools in leaf tissues, e.g. the ratio of mannitol to Suc increased almost 10-fold. These changes were due in part to shifts in photosynthetic carbon partitioning (as measured by 14C labeling) from Suc into mannitol. Salt treatments increased the activity of mannose-6-phosphate reductase (M6PR), a key enzyme in mannitol biosynthesis, 6-fold in young leaves and 2-fold in fully expanded, mature leaves, but increases in M6PR protein were not apparent in the older leaves. Mannitol biosynthetic capacity (as measured by labeling rates) was maintained despite salt treatment, and relative partitioning into mannitol consequently increased despite decreased photosynthetic capacity. The results support a suggested role for mannitol accumulation in adaptation to and tolerance of salinity stress.
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Selected References
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- Bagnasco S., Balaban R., Fales H. M., Yang Y. M., Burg M. Predominant osmotically active organic solutes in rat and rabbit renal medullas. J Biol Chem. 1986 May 5;261(13):5872–5877. [PubMed] [Google Scholar]
- Bental M., Pick U., Avron M., Degani H. The role of intracellular orthophosphate in triggering osmoregulation in the alga Dunaliella salina. Eur J Biochem. 1990 Feb 22;188(1):117–122. doi: 10.1111/j.1432-1033.1990.tb15378.x. [DOI] [PubMed] [Google Scholar]
- Bongi G., Loreto F. Gas-Exchange Properties of Salt-Stressed Olive (Olea europea L.) Leaves. Plant Physiol. 1989 Aug;90(4):1408–1416. doi: 10.1104/pp.90.4.1408. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bradford M. M. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976 May 7;72:248–254. doi: 10.1016/0003-2697(76)90527-3. [DOI] [PubMed] [Google Scholar]
- Davis J. M., Fellman J. K., Loescher W. H. Biosynthesis of Sucrose and Mannitol as a Function of Leaf Age in Celery (Apium graveolens L.). Plant Physiol. 1988 Jan;86(1):129–133. doi: 10.1104/pp.86.1.129. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Downton W. J., Grant W. J., Robinson S. P. Photosynthetic and stomatal responses of spinach leaves to salt stress. Plant Physiol. 1985 May;78(1):85–88. doi: 10.1104/pp.78.1.85. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gee R., Goyal A., Byerrum R. U., Tolbert N. E. Two Isoforms of Dihydroxyacetone Phosphate Reductase from the Chloroplasts of Dunaliella tertiolecta. Plant Physiol. 1993 Sep;103(1):243–249. doi: 10.1104/pp.103.1.243. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Loescher W. H., Tyson R. H., Everard J. D., Redgwell R. J., Bieleski R. L. Mannitol Synthesis in Higher Plants : Evidence for the Role and Characterization of a NADPH-Dependent Mannose 6-Phosphate Reductase. Plant Physiol. 1992 Apr;98(4):1396–1402. doi: 10.1104/pp.98.4.1396. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Longstreth D. J., Nobel P. S. Salinity effects on leaf anatomy: consequences for photosynthesis. Plant Physiol. 1979 Apr;63(4):700–703. doi: 10.1104/pp.63.4.700. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Rumpho M. E., Edwards G. E., Loescher W. H. A pathway for photosynthetic carbon flow to mannitol in celery leaves : activity and localization of key enzymes. Plant Physiol. 1983 Dec;73(4):869–873. doi: 10.1104/pp.73.4.869. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Storey K. B., Storey J. M. Freeze tolerance in animals. Physiol Rev. 1988 Jan;68(1):27–84. doi: 10.1152/physrev.1988.68.1.27. [DOI] [PubMed] [Google Scholar]
- Tarczynski M. C., Jensen R. G., Bohnert H. J. Stress protection of transgenic tobacco by production of the osmolyte mannitol. Science. 1993 Jan 22;259(5094):508–510. doi: 10.1126/science.259.5094.508. [DOI] [PubMed] [Google Scholar]
- Wintermans J. F., de Mots A. Spectrophotometric characteristics of chlorophylls a and b and their pheophytins in ethanol. Biochim Biophys Acta. 1965 Nov 29;109(2):448–453. doi: 10.1016/0926-6585(65)90170-6. [DOI] [PubMed] [Google Scholar]