Phospholipase A2 Activity during Cold Acclimation of Wheat

The temperature lethal to 50% of the plants (LT50) and phospholipase A(2) (PLA(2)) activity levels were investigated in three wheat (Triticum aestivum L.) lines that had been cold acclimated 0 to 5 wks at 3 degrees C. In the cold-tolerant winter wheat 'Eltan', the level of PLA(2) activity increased significantly during the first week of cold acclimation, but activity did not increase until the second week of acclimation in cold-sensitive winter wheat Oregon Feed Wheat #5 and spring wheat 'Louise'. The PLA(2) activity declined in all lines by the end of 4 wks of acclimation. The LT50 decreased (greater freezing tolerance) during the time that PLA, levels were elevated and then increased concomitant with decreased PLA(2) activity. A chilling treatment of -5 degrees C for 45 min resulted in elevated PLA(2) activity in nonacclimated Eltan, as well as in all three wheat lines that had been acclimated for 1 wk, but not in plants that had been acclimated for more than 1 wk. These results suggest that PLA(2) activity is involved in response to cold temperature in wheat, but the intrinsic level of freezing tolerance and the level of acclimation reached by the plants mediates its activity.