Water-stress response in aspen (populus tremula): Differential accumulation of dehydrin, sucrose synthase, GAPDH homologues, and soluble sugars

In a previous study we identified a novel 66-kD boiling-stable protein (BspA) that accumulates in cultured shoots of aspen (Populus tremula L.) in response to gradual water stress and ABA application, as well as to osmotic and cold stresses (Airman et al., 1996; Pelah et al., 1995). BspA was found to be the major heat-stable water stress-responsive protein in aspen. Here, the expression of other water-stress responsive proteins - DSP 16 (dehydrin), cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and sucrose synthase - was studied in aspen roots and shoots. These proteins were identified immunologically using polyclonal antibodies isolated from the resurrection plant Craterostigma plantagineum. A 43-kD homologue and a 31-kD homologue of dehydrin were found to accumulate in roots and shoots of aspen after water stress in a tissue specific manner. Shoots and roots of intact plantlets subjected to ABA application accumulated a 33-kD dehydrin homologue. A sucrose synthase homologue (90 kD) accumulated in water-stressed shoots and was constitutively present at high levels in control and water-stressed roots harvested from intact plantlets. GAPDH, a key enzyme in the glycolysis and gluconeogenesis pathways, exhibited some accumulation in shoots in response to water stress. Sugar analysis revealed that water stress results in increased sucrose and decreased glucose levels in the aspen leaves. The data presented here suggest that the water-stress-response mechanisms present in herbaceous plants are also present in woody plants. Woody plants subjected to water stress accumulate dehydrin-like proteins and specific enzymes such as sucrose synthase and GAPDH, which may play a dominant role in sugar metabolism under these conditions.