CHARACTERIZATION OF BSPA, A MAJOR BOILING-STABLE, WATER-STRESS-RESPONSIVE PROTEIN IN ASPEN (POPULUS-TREMULA)

We identified a novel 66 kDa boiling-stable protein (BspA) in cultured shoots of aspen (Populus tremula L.) which was highly expressed in re sponse to gradual water stress. The BspA protein, which was highly exp ressed as early as 1 h after initiation of a drought treatment, accumu lated during progressive water stress, decreased on rehydration, and w as expressed in response to abscisic acid (ABA) application, as detect ed by SDS-PAGE protein analysis and Western blotting. Anti-BspA antibo dies also cross-reacted with a 119 kDa protein. The 119 kDa protein wa s also induced by water stress, but it was detected only in the total protein fraction and not in the heat-stable fraction. The BspA protein cross-reacted with antibodies raised against a water-stress-responsiv e protein isolated from the African resurrection plant Craterostigma p lantagineum Hochst. The N-terminal amino acid sequence of BspA was det ermined and exhibited high homology with the wheat germins GF-2.8 and GF-3.8. The BspA protein was the only major, water-stress-responsive b oiling-stable protein detected in aspen.