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Regulation of Expression and Activity of Sorbitol Dehydrogenase in Apple
Department of Horticulture
Sorbitol is the major photoassimilate in apple, and it is primarily converted to fructose by sorbitol dehydrogenase. Slow rates and/or inefficient utilization of sorbitol by apple fruit, as determined by patterns of sorbitol dehydrogenase expression and activity, can adversely affect yield, quality, and economic return. By understanding the mechanisms regulating expression and activity of sorbitol dehydrogenase in apple fruit, new horticultural and/or biochemical or genetic strategies could optimize the competitive position and resulting quality and yield of the fruit.
2010 Project Description
Arabidopsis thaliana was studied as a possible model system for determining regulation of apple sorbitol dehydrogenase (SDH) expression and activity, as Arabidopsis has only one SDH gene and apple SDH genes can be inserted into Arabidopsis. As a first step, SDH expression and activity in wild-type and 2 SDH mutant lines of Arabidopsis were studied. As a result, new fundamental information on plant polyol metabolism in response to drought stress was discovered. The results were presented in a regular seminar series on campus, and have been written and submitted for peer review to an international plant science journal.
SDH was found to play a primary role in sorbitol metabolism in Arabidopsis, but an unexpected role was discovered of ribitol metabolism that is crucial for recovery from drought stress. Sorbitol content increased 2-fold in wild-type and mutant plants during stress but mutants showed a dramatically different phenotype, dying after re-watering. We discovered that the lack of functional SDH in mutant plants led to the accumulation of up to a 15-fold greater ribitol than sorbitol concentration, values that did not decrease in mutant plants after re-watering. The specific, toxic role of ribitol was further demonstrated by a concentration-dependent inhibition of seed germination and seedling development of SDH mutants but not WT plants grown on ribitol-containing media.
Wu, B-H., S-H. Li, M. Nosarzewski, and D. D. Archbold. 2010. Sorbitol dehydrogenase gene expression and enzyme activity in apple: Tissue specificity during bud development and response to rootstock vigor and growth manipulation. Journal of the American Society for Horticultural Science 135: 379-387.