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:
This is the final report for this project, which has been replaced by new project 5348-21000-030-00D, "Genetic Improvement of Wheat and Barley for Resistance to Biotic and Abiotic Stresses". For additional information, see the new project 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. We previously demonstrated that exposure to mild (-3C/+3C) freeze-thaw cycles results in significantly improved freezing tolerance. The compositions of the phospholipid components of the cell membranes were monitored in plant crowns (actively growing regions) at several time points during two freeze-thaw cycles. The composition changed in consistent ways, showing evidence of changing during the thaw and partially reverting to the prior state during the thaw. These results demonstrate that the plants are physiologically active at -3C, and restructure phospholipids in characteristic ways, concomitant with enhanced freezing tolerance. This information provides a previously unknown response that may be exploited in plant improvement efforts. Winter wheat plants respond to cold temperature in many ways; we have generated segregating populations from crosses of wheat plant lines that differ in their ability to tolerate different aspects of freezing stress, measured as cooling rate, minimum temperature, time maintained at minimum temperature, warming rate as the freezing episode ends, total time frozen, and degree-minutes, a combined measure of temperature and time. This year, we produced seed of over 800 progeny from crosses of parents with disparate abilities to withstand these components of the freezing process. Analysis of the ability of these lines to withstand freezing process components is expected to identify lines with combined abilities to tolerate different aspects of freezing stress, resulting in improved winterhardiness.
1. Evidence of a subfreezing response mechanism in winter wheat. Exposure of cold-acclimated winter wheat plants to 24 hr. freeze-thaw cycles at -3C and +3C results in significantly improved ability to survive subsequent freezing to potentially damaging temperatures. Little is known of the mechanisms involved in this response to subzero temperature. ARS scientists at Pullman, Washington, monitored the composition of phospholipids (components of the cell membranes) in the actively growing regions of the plants at several time points during two freeze-thaw cycles. Phospholipids changed in consistent ways, such that they were very different after two freeze-thaw cycles that initially. This altered phospholipid composition may be related to the enhanced freezing tolerance, providing a means of evaluating plants for winterhardiness.
Kwang-Hyun, B., Skinner, D.Z. 2012. Production of reactive oxygen species by freezing stress and the protective roles of antioxidant enzymes in plants. Journal of Agricultural Chemistry and Environment. 1:34-40. doi:10.4236/jacen.2012.11006.