Amino Acid and Protein Changes during Cold Acclimation of Green‐Type Annual Bluegrass (Poa annua L.) Ecotypes

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Abstract
Cold acclimation is associated with many metabolic changes that lead to increase freezing tolerance. This study was conducted to assess amino acid and protein changes occurring during cold acclimation of green‐type annual bluegrass ecotypes cold hardened under both environmentally controlled and simulated‐winter conditions in an unheated greenhouse. These biochemical changes were monitored in three ecotypes of contrasting freezing tolerance originating from Western Pennsylvania (OK), Coastal Maryland (CO), and central Québec (CR). Cold hardening induced major changes in amino acid levels in overwintering crowns of the three ecotypes and the highest contributions to total amino acid accumulation after acclimation at subfreezing temperatures came from proline, glutamine, and glutamic acid. Higher levels of amino acid and greater differences among ecotypes were observed after acclimation at subzero temperatures. Amino acid levels, including proline, were not related to the differential freezing tolerance among the three annual bluegrass ecotypes tested. Specific soluble polypeptides and thermostable proteins showed cold responsiveness and in some cases, their peak accumulation coincided with maximum freezing tolerance of annual bluegrass. In plants hardened to winter conditions in a unheated greenhouse, there was a distinct accumulation of polypeptides from fall until midwinter with a subsequent decrease in the spring.