Differences in Freeze Tolerance of Zoysiagrasses: I. Role of Proteins

Genotypic variation in winter injury exists among zoysiagrasses (Zoysia spp.), but the physiological basis for these differences is not understood. Our objective was to determine the relationships between protein accumulation, polypeptide composition, and freeze tolerance of zoysiagrass. Thirteen genotypes of zoysiagrass with contrasting cold hardiness were identified. Cold acclimation was induced with 4 wk of 8/2°C day/night cycles and a 10-h photoperiod of 300 micromol m-2 s-1. Rhizomes and stolons of zoysiagrass were harvested from nonacclimated and cold-acclimated plants and used for protein analysis. Protein composition was analyzed using sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting with an antidehydrin polyclonal antibody. Buffer-soluble protein concentrations were higher among cold-acclimated (7.3 g kg-1 dry wt.) than nonacclimated (5.1 g kg-1 dry wt.) plants. The SDS-PAGE analysis indicated few differences in polypeptide composition among genotypes irrespective of cold acclimation. Immunoblotting indicated that dehydrin polypeptides (23 and 25 kDa) increased during cold acclimation. Abundance of the 23-kDa dehydrin polypeptide was positively associated (r2 = 0.41) with genetic variation in freezing tolerance. Our results suggest that dehydrins are associated with zoysiagrass cold acclimation, but that only the 23-kDa dehydrin plays a role in improving freeze tolerance.