EVIDENCE FOR A 26kDA VEGETATIVE STORAGE PROTEIN IN THE STEM SAPWOOD OF MATURE PEDUNCULATE OAK

The distribution of total soluble proteins was investigated in the sapwood of 20-year-old Quercus robur L. at leaf shedding (October) and after leaf expansion (June) in order to assess seasonal changes in soluble protein content at whole tree level. The content of total soluble proteins was 10 times lower than that of starch. In October, the top sapwood segments stored significantly more soluble proteins than other organs. In the below canopy stem, up to 80% of the proteins present during October were mobilized for spring growth, as compared to only 50-60% of the starch. As oak trees produce a large fraction of annual radial growth before spring-leaf expansion, vegetative storage proteins (VSP) in the stem are hydrolyzed and a part of the resulting free amino acids pool should be used to sustain wood formation. A 26kDa VSP was isolated by SDS-PAGE. At leaf shedding, this VSP represented up to 50% of the soluble proteins, while it was absent in June. This suggests this protein was remobilized to sustain early growth. The use of this 26kDa VSP as a marker for spring growth reactivation capacity is proposed.