Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2014
Publication Date: 4/11/2014
Citation: Skinner, D.Z., Bellinger, B.S., Hansen, J.C., Kennedy, A.C. 2014. Carbohydrate and lipid dynamics in wheat crown tissue in response to mild freeze-thaw treatments. Crop Science. 54:1–8. DOI: 10.2135/cropsci2013.09.0604. Interpretive Summary: Describing the changes that happen in a wheat plant as it activates to cold temperature provides a means of identifying plants that are especially good at developing freezing tolerance. This study was undertaken to characterize changes in sugars and in lipids in the rapidly-growing regions of wheat plants when they were exposed to a series of mild freeze/thaw episodes, as might happen in the fall of the year. The lipid composition changed dramatically after each freezing event; the concentrations of simple sugars increased and the concentrations of polymers of sugars first decreased, then increased. These changes are associated with increased cold tolerance, thus, these results provide a means to identify plants that respond more rapidly, and more strongly to the onset of cold temperature, thereby identifying plants with improved freezing tolerance.
Technical Abstract: Freezing tolerance resulting from cold hardening is critical to survival of fall-planted crops such as winter wheat. Exposure of winter wheat plants to cycles of freeze-thaw at temperatures just below, and just above freezing results in incremental improvements of freezing tolerance. Defining the physiological changes that are associated with this acquired freezing tolerance will enable the identification of plant lines that respond efficiently to these freeze/thaw cycles. Changes in the concentrations of carbohydrates in the cellular fluids of wheat crowns, and of lipids extracted from wheat crown tissue, in response to exposure to 24 hour freeze(s) at -3°C, with or without a following thaw of 24 hours at 3°C were quantified. Unique profiles of carbohydrates and lipids were observed after each temperature treatment. Concentrations of simple sugars, and sucrose and related carbohydrates, increased in the first 24 hours of exposure to -3°C, and continued to increase whether the plants were then an exposed to a further 24 hrs. at -3°C or were exposed to 3°C for 24 hrs. The concentration of fructans decreased during the first 24 hrs. of exposure to -3° C, and continued to decrease if the plants were exposed to 3° C for 24 hrs. However, if the plants were exposed to a continuous -3° C for 48 hrs, the concentration of fructans within the cellular fluid increased. Concomitantly, the concentrations of numerous lipid species changed with each 24 hr. temperature treatment. Previous studies have shown these temperature treatments result in improved ability to withstand subsequent exposure to potentially damaging temperature. Results presented here indicate that carbohydrates and lipids in wheat crowns are actively restructured at subzero temperatures, and that the resulting profiles are associated with a greater ability to withstand more severe temperatures. Identifying plant lines especially able to restructure the cellular components at subzero temperatures may enable the development of plant lines with improved freezing tolerance.