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

Deacclimation of Scots pine (Pinus sylvestris) in northern Finland (65 degr ees N) was studied from the perspective of protein metabolism, which was re lated to nitrogen fertilization. Two-year-old seedlings were fertilized wit h 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 duri ng the natural deacclimation period from mid-March to the beginning of June 1998. Deacclimation was followed by monitoring various physiological varia bles: freezing resistance decreased and osmotic potential increased during the experiment and needle dry weight increased from bud flushing onwards. T he concentration of soluble proteins in needles was higher in fertilized se edlings but decreased transiently in the 884 kg N ha(-1) fertilized seedlin gs 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 5 6-kDa dehydrins, The concentration of these dehydrins decreased during deha rdening more rapidly in fertilized seedlings than in the control plants. Th e fertilized seedlings started to grow earlier than the unfertilized plants . In conclusion, nitrogen fertilization provided good reserves for new grow th but did not affect deacclimation of pine needles.