Analysis of cDNA Clones Encoding Sucrose-Phosphate Synthase in Relation to Sugar lnterconversions Associated with Dehydration in the Resurrection Plant

Sucrose-phosphate synthase (SPS) is a key enzyme in the regulation of sucrose metabolism, being responsible for the synthesis of sucrose 6-phosphate from fructose 6-phosphate and uridine 5 ' diphosphate-glucose. W e report on the isolation and characterization of cDNA clones encoding SPS from Craferosfigma planfagineum Hochst., a resurrection plant in which the accumulation of sucrose is considered to play an important role in tolerance to severe protoplastic dehydration. Two distinct classes of cDNAs encoding SPS were isolated from C. plantagineum, and are represented by the clones Cpspsl and CpspsZ. l h e transcripts corresponding to both cDNAs decrease to very low levels in dehydrating leaves of C. plantagineum. Only the Cpspsl transcript occurs in the roots, where it is present at a higher leve1 than in leaves and increases upon dehydration of the plant. Higher enzymatic activities have been determined in protein extracts of dehydrated tissues compared with untreated tissues, which correlates with an increase in protein levels. I t is suggested that the overall regulation of SPS is strongly influenced by the changing composition of the cytoplasm in C. plantagineum leaves during the dehydration-rehydration cycle.