Seasonal Fluctuations in Cold Hardiness and Protein Profiles of Five Rhododendron Cultivars

Abstract

A time-course study was conducted to characterize seasonal patterns of cold hardiness (CH) and protein profiles in the leaf tissue of five Rhododendron cultivars (`Grumpy Yellow', `Vulcan's Flame', `Autumn Gold', `Chionoides', and `Roseum Elegans'). Leaf samples were collected monthly (starting in mid September) and leaf discs were subjected to controlled freezing and thawing regimes. CH (LT50 defined as temperature causing 50% injury) was assessed by electrolyte leakage and visual observations. Data indicate that cultivars varied in their CH in nonacclimated state and in their ability to cold acclimate. Results obtained in September showed `Grumpy Yellow' to be least hardy (about –3°C) and `Roseum Elegans' to be most hardy (about –7°C). All cultivars exhibited successive increases in CH during fall and winter. Maximum CH in all cultivars occurred by December/January with `Chionoides' being most hardy (about –31°C) while `Grumpy Yellow' was least hardy (about –20°C). LT50 based on electrolyte leakage was highly correlated with visual rating. Seasonal changes of protein profiles and relationship of specific stress proteins to cultivars' CH and cold acclimation ability are discussed.