ANALYSIS OF CDNA CLONES ENCODING SUCROSE-PHOSPHATE SYNTHASE IN RELATION TO SUGAR INTERCONVERSIONS ASSOCIATED WITH DEHYDRATION IN THE RESURRECTION PLANT CRATEROSTIGMA-PLANTAGINEUM HOCHST

Sucrose-phosphate synthase (SPS) is a key enzyme in the regulation of sucrose metabolism, being responsible for the synthesis of sucrose 6-p hosphate from fructose 6-phosphate and uridine 5'-diphosphate-glucose. We report on the isolation and characterization of cDNA clones encodi ng SPS from Craterostigma plantagineum Hochst., a resurrection plant i n which the accumulation of sucrose is considered to play an important role in tolerance to severe protoplastic dehydration. Two distinct cl asses of cDNAs encoding SPS were isolated from C. plantagineum, and ar e represented by the clones Cpsps1 and Cpsps2. The transcripts corresp onding to both cDNAs decrease to very low levels in dehydrating leaves of C. plantagineum. Only the Cpsps1 transcript occurs in the roots, w here it is present at a higher level than in leaves and increases upon dehydration of the plant. Higher enzymatic activities have been deter mined in protein extracts of dehydrated tissues compared with untreate d tissues, which correlates with an increase in protein levels. It is suggested that the overall regulation of SPS is strongly influenced by the changing composition of the cytoplasm in C. plantagineum leaves d uring the dehydration-rehydration cycle.