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United States Department of Agriculture

Agricultural Research Service

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Research Project: GENETIC IMPROVEMENT OF FREEZING TOLERANCE IN WINTER WHEAT

Location: Wheat Genetics, Quality Physiology and Disease Research

2012 Annual Report


1a.Objectives (from AD-416):
Determine the extent of variation in genetic control of freezing tolerance in wheat with the purpose of identifying wheat lines with different and new combinations of genes that confer freezing tolerance. Define the role of phospholipid-related genes in cold acclimation and freezing tolerance.


1b.Approach (from AD-416):
The overall approach is to use artificial freezing of cold-acclimated winter wheat plants, with temperature measurements taken every two minutes in the crown zone of the plants, to precisely describe the components of the freezing process that are injurious to the plants. Pharmacological agents that enhance or inhibit phospholipase enzyme activity will be used in whole-plant assays to assess their impact on cold acclimation and freezing tolerance; concomitant microarray analysis will be used to define the genes involved.


3.Progress Report:
Winter wheat is exposed to a variety of freezing conditions as the seasons progress from the fall through the winter. The ability to respond to these changing conditions contributes to winter survival. Very little is known about the mechanisms involved in this dynamic response. We previously demonstrated that exposure to a mild freeze-thaw cycle results in significantly improved freezing tolerance. The concentrations of chloride, potassium, nitrate, calcium, and phosphorus ions were measured in the sap of cold-acclimated wheat plants as they were exposed to a mild freeze-thaw cycle. Concentrations of chloride and calcium ions increased during the freeze and continue to increase during the thaw, while the concentrations of the other ions decreased throughout the freeze-thaw cycle. The correlation of increased freezing tolerance with increased chloride and calcium ion concentrations suggest that these ions play a role in the freeze-thaw induced freezing tolerance. Similarly, increases in the concentration of fructans, polymers of the simple sugar fructose, have long been associated with increased cold acclimation of winter wheat. To determine whether fructan concentration in the sap is involved in freeze-thaw induced freezing tolerance, the concentrations of fructans were measured in sap from plants frozen to -3C for 24h., and plants that had been similarly frozen and allowed to thaw at +3C for 24h. The level of fructan decreased at both time points relative to the control, suggesting that the mechanisms responsible for freeze-thaw induced freezing tolerance may involve mobilizing simple sugars from carbohydrate polymers in the sap. This information provides a previously unknown response that may be exploited in plant improvement efforts.


4.Accomplishments
1. New role for ions in freezing tolerance of winter wheat. Winter wheat is exposed to a variety of freezing conditions through fall and winter. The ability to respond to these changes contributes to winter survival. Very little is known about the mechanisms involved in this dynamic response. ARS scientists in Pullman, WA, previously demonstrated that exposure to mild freeze-thaw cycles results in significantly improved ability to withstand subsequent exposure to potentially damaging subfreezing temperatures. The concentrations of chloride, potassium, nitrate, calcium, and phosphorus ions were measured in the sap of cold-acclimated wheat plants as they were exposed to a mild freeze-thaw cycle. Concentrations of chloride and calcium ions increased during the freeze and continue to increase during the thaw, while the concentrations of the other ions decreased throughout the freeze-thaw cycle. The correlation of increased freezing tolerance with increased chloride and calcium ion concentrations suggest that these ions enhance the freeze-thaw induced freezing tolerance and could lead to winter wheat with increased tolerance to abiotic stresses.

2. A possible role for carbohydrate polymers in freeze-thaw enhanced freezing tolerance of winter wheat. Increases in the concentration of fructans, polymers of the simple sugar fructose, in plant tissue have long been associated with increased cold acclimation of winter wheat. Exposure of cold acclimated plants to mild-thaw cycles results in increased tolerance of subsequent exposure to potentially damaging subfreezing temperatures. To determine whether fructan concentration in the sap is involved in this freeze-thaw induced freezing tolerance, ARS scientists at Pullman, WA, measured the concentrations of fructans in sap from plants frozen to -3C for 24h., and plants that had been similarly frozen and allowed to thaw at +3C for 24h. The level of fructan decreased at both time points relative to the control, suggesting that the mechanisms responsible for freeze-thaw induced freezing tolerance may involve mobilizing simple sugars from carbohydrate polymers. This information provides a previously unknown response that may be exploited in plant improvement efforts.


Review Publications
Skinner, D.Z. 2012. Genetics of winter wheat response to two freezing treatments. Crop Science. 131(3):380-384.

Last Modified: 7/23/2014
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