Soluble proteins and dehydrins in nitrogen-fertilized Scots pine seedlings during deacclimation and the onset of growth

Deacclimation of Scots pine (Pinus sylvestris) in northern Finland (65 degrees N) was studied from the perspective of protein metabolism, which was related to nitrogen fertilization. Two-year-old seedlings were fertilized with calcium ammonium nitrate (0, 442 and 884 kg N ha(-1)) in the summer prior to the study, Needles were harvested for analyses at 3-week intervals during the natural deacclimation period from mid-March to the beginning of June 1998. Deacclimation was followed by monitoring various physiological variables: freezing resistance decreased and osmotic potential increased during the experiment and needle dry weight increased from bud flushing onwards. The concentration of soluble proteins in needles was higher in fertilized seedlings but decreased transiently in the 884 kg N ha(-1) fertilized seedlings before budbreak. The abundance of several small polypeptides (17-32 kDa) decreased in the spring, A 60-kDa protein, identified by immunoblotting as a dehydrin, was detected in all treatments, The quantity of this dehydrin decreased with resumption of growth, along with the appearance of 50- and 56-kDa dehydrins, The concentration of these dehydrins decreased during dehardening more rapidly in fertilized seedlings than in the control plants. The fertilized seedlings started to grow earlier than the unfertilized plants. In conclusion, nitrogen fertilization provided good reserves for new growth but did not affect deacclimation of pine needles.