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Regulation of Sorbitol Dehydrogenase Activity During Apple Fruit Development: Genotypic Differences and the Impact of Cultural Practices
D. D. Archbold
Department of Horticulture
Project Description
The earliest stage of apple fruit development, termed fruit set, is the most critical for defining crop yield and quality. A key event during apple fruit set is a natural fruit drop phase that is often chemically manipulated to reduce total yield in order to optimize fruit quality; the fruit drop may be due to a poor ability to utilize inported assimilate or low levels of assimilate.
We have discovered that activity of sorbitol dehydrogenase (SDH) which converts sorbitol, the main photosynthetic product in apple, to fructose increased in seeds but was lower and nearly constant in fruit cortex. We identified 9 SDH gene isomers in apple, created gene-specific primers to monitor expression of each, and developed an antibody to detect SDH protein. Five of the nine SDH genes present in the apple genome were expressed in apple fruit, two in both seed and cortex, one was limited to cortex, and 2 were only in seed tissues. SDH isomeric proteins of different pi values were detected in apple fruit, 4 in seeds and 4 in cortex. The present work is the first to show that SDH is highly active in apple seed and that SDH genes are differentially expressed in seed and cortex during early development.
Impact
The results of this work will now allow the determination of the role of both sorbitol utilization and availability in natural and chemically induced fruit drop in apple. Once a clear cause-effect relationship has been determined, current horticultural practices can be modified and new techniques can be developed to achieve optimum thinning response.
Publications
Nosarzewski, M. and D.D. Archbold. 2007. Tissue-specific expression of sorbitol dehydrogenase in apple fruit during early development. J. Exp. Bot. 58:1863-1872.
Nosarzewski, M., A.M. Clements, A.B. Downie, and D.D. Archbold. 2004. Sorbitol dehydrogenase expression and activity during apple fruit set and early development. Physiol. Plant. 121:391-398.
Archbold, D.D., M. Nosarzewski, A.M. Clements, and A.B. Downie. 2004. Early apple fruit development and sorbitol dehydrogenase. Acta Hort. 636:443-436.