Hormone and Dehydrin Expression Responses to Cold Acclimation in Two Zoysiagrass Cultivars with Contrasting Freezing Tolerance

Zoysiagrass (Zoysia spp.), a warm-season turfgrass genus, is subjected to freezing damage in the US transition zone and other similar climate regions. This study was designed to investigate changes in hormones and dehydrin expression in responses to cold acclimation (CA) in two zoysiagrass cultivars. Two zoysiagrass cultivars (‘Meyer’, cold tolerant; ‘Cavalier’, relatively cold sensitive) were subjected to either CA (8/4°C day/night and a photosynthetically active radiation of 250 mmol m⁻² s⁻¹ over a 10-h photoperiod) or no CA in growth chambers for 28 d. Cold-acclimated Meyer had greater overall freezing tolerance (stolon temperature resulting in 50% survival [LT₅₀] = −15.4°C) than cold-acclimated Cavalier (stolon LT₅₀ = −8.2°C). Leaf abscisic acid (ABA) content increased and cytokinins (trans-zeatin riboside and isopentenyl adenosine) declined during CA. Cold-acclimated Meyer accumulated higher levels of ABA but less cytokinins relative to cold-acclimated Cavalier. Leaf ABA content was 37% higher in cold-acclimated Meyer than in cold-acclimated Cavalier at 28 d. Meyer had higher levels of indole-3-acetic acid than Cavalier. Cold acclimation induced dehydrin (12, 23, and 65 kDa) expression in leaf tissues of both cultivars. Cold-acclimated Meyer had greater abundance of the dehydrins (12, 23, 30, and 35 kDa) in stolon tissues and in leaf tissues (12, 30, and 65 kDa) than cold-acclimated Cavalier. The results of this study suggest that higher levels of ABA and certain dehydrin expression and lower levels of cytokinins during CA may be associated with freezing tolerance in zoysiagrass.