Chilling tolerance of cucumber (Cucumis sativus) seedling radicles is affected by radicle length, seedling vigor, and induced osmotic‐ and heat‐shock proteins

Abstract

Cucumber seedling radicles decrease in chilling tolerance as they increase in length or decrease in vigor. The protein content of the apical 5 mm of the radicle decreased with decreases in chilling tolerance (R2 = 0.92). This general reduction in protein content was reflected in a decrease of six dehydrin‐like proteins with apparent molecular weights of 13.0, 15.0, 16.8, 23.0, 26.8, and 33.5 kDa. The disappearance of naturally occurring dehydrin‐like proteins in cucumber seedling radicles as they elongate or lose vigor was correlated with a loss of chilling tolerance. Exposure to an osmotic (0.6 M mannitol) or heat (2 min at 45°C) stress enhanced chilling tolerance. The osmotic‐shock treatment induced both chilling tolerance and the appearance or strengthening of dehydrin‐like proteins previously present in radicles. The heat‐shock treatment also induced high levels of chilling tolerance and protein(s) that reacted with a 23 and 70 kDa antibody. However, these heat‐shock protein (HSPs) did not cross react with the probe for dehydrin‐like proteins. When organized into high, medium, and low chilling tolerance groups, radicle that were chilling tolerant contained either the 13.0 and 16.8 kDa dehydrin‐like proteins, or the 15.0 and 23.0 kDa dehydrin‐like proteins, or the 23 or 70 kDa HSP.