Changes in Leaf and Crown Hormones Triggered By Cold Acclimation and Deacclimation in Two Cool-Season Turfgrasses.

The objective of this study was to quantify changes in major hormones in leaf and crown tissues during cold acclimation and deacclimation of annual bluegrass (Poa annua) (AB) and creeping bentgrass (Agrostis stolonifera) (CB), two cool-season grasses with significant variability in winter survival. Plants were established in greenhouse and then moved to a growth chamber for cold acclimation and deacclimation treatments, consisting of a non-acclimated control at 20 °C; cold acclimation at 2 °C; cold acclimation at -2 °C; deacclimation at 8 °C for 1 and 5 d. Following each treatment, freezing tolerance was calculated based on lethal temperature resulting in 50% kill (LT₅₀).  Crown tissues were harvested for hormone analyses, including indole-3-acetic acid (IAA), zeatin, abscisic acid (ABA), gibberellic acid (GA), salicylic acid (SA) and jasmonic acid (JA). Overall, CB exhibited higher freezing tolerance (lower LT₅₀) in response to cold acclimation and deacclimation treatments.  Increases in ABA, IAA, and zeatin contents of crowns were observed in response to prolonged cold acclimation, and to a greater extent for AB compared to CB. During deaclimation, AB also exhibited higher GA levels. Differences in hormone accumulation among the two species in relation to freezing tolerance will be discussed.