Differential accumulation of water stress-related proteins, sucrose synthase and soluble sugars in Populus species that differ in their water stress response

Proteins inducible by dehydration and abscisic acid (ABA), have been identified in a number of species and have been suggested to play a role in desiccation tolerance. Recently, we identified a novel boiling-stable protein (BspA) which accumulated in shoots of aspen (Populus tremula L.) cultured in vitro, in response to gradual water stress and ABA application (Pelah et al. 1995. Tree Physiol. 15: 673-678.). Accumulation of BspA, and of the water stress-related protein dehydrin dsp-16 and sucrose synthase from the resurrection plant, Craterostigma plantagineum, was examined in two greenhouse-grown Populus species to investigate the relationship between the presence of the proteins and water stress tolerance. Detached leaves of Populus tomentosa lost more water than Populus popularis, resulting in a significant decrease in leaf water potential. Using electrolyte leakage analysis, it was found that detached leaves of Populus popularis are more tolerant to water stress than those of Populus tomentosa. Using western blots with the corresponding antibodies, we have found in Populus popularis accumulation of BspA and sucrose synthase due to water stress, and the constitutive presence of a dehydrin-like protein. In contrast, a low expression of BspA was found in Populus tomentosa, but not of sucrose synthase and dehydrin-like proteins. Desiccation tolerance in many tissues can be partly attributed to soluble sugars. Analysis of the amount of soluble sugars did not reveal clear-cut differences between the two species, except for significant sucrose accumulation and glucose reduction in water-stressed Populus tomentosa and increase in glucose in water-stressed Populus popularis. The data obtained points to a positive correlation between increased water stress tolerance of one poplar species as compared with another and accumulation of water stress-related proteins and sucrose synthase.