SEASONAL-VARIATION OF WESTERN WHITE-PINE (PINUS MONTICOLA DON,D.) FOLIAGE PROTEINS

Recently, a western white pine protein, Pin m III, was shown to be ass ociated with overwintering and frost hardiness of western white pine f oliage. To examine whether Pin m III is directly involved in frost har diness by functioning as an antifreeze protein, work is underway to cl one the gene encoding this protein and to assess the function of this gene in freezing tolerance by incorporating the gene in a test plant, such as tobacco. Here, we examined in more detail, by SDS-PAGE and als o by two dimensional gel electrophoresis, the seasonal variation of ad ditional proteins in western pine foliage. SDS-PAGE analysis of three seedlots showed that different proteins reached a maximum level in dif ferent months, although most proteins (5 to 11) reached a maximum leve l in winter months (December, January and February), The 2-D gel analy sis of foliage sampled on three harvest dates (October, January and Ap ril) of one seedlot revealed a seasonal variation of a large number pr oteins (76 to 184). Of the seasonally varied proteins, the amino termi nal sequence of several proteins including Pin m III was determined. O ne of the sequences was identified by homology to that of the small su bunit of ribulose biphosphate carboxylase, whose level increased subst antially from fall to spring. The amino terminal sequence of Pin m III had 89% homology to a sugar pine protein, Pin l I. The anti-photosyst em II antibody was used to monitor the annual variation of the extrins ic 23-kDa photosystem II protein, The level of the extrinsic 23-kDa ph otosystem II protein decreased slowly as fall progressed and reached i ts lowest level in December and then increased in early spring indicat ing that this variation is due to photosynthetic activity of the folia ge during the season.