Induction of Crassulacean Acid Metabolism in Mesembryanthemum crystallinum by High Salinity: Mass Increase and de Novo Synthesis of PEP-Carboxylase

Intact plants of the halophilic species Mesembryanthemum crystallinum were induced to exhibit Crassulacean acid metabolism by irrigation with nutrient solution containing 500 millimolar NaCl. During the induction period, the extractable activity of phosphoenolpyruvate carboxylase (PEPcase) increased approximately 40-fold. This increase was linearly correlated with a mass increase of PEPcase protein as measured by single radial immunodiffusion. De novo synthesis of PEPcase protein was shown by immunoprecipitation of the newly synthesized, radioactively labeled protein in leaf discs from salt-treated plants. Nontreated plants were characterized by a low level of the enzyme and low rates of PEPcase synthesis. Synthesis of this enzyme in leaf discs was correlated with the concentration of NaCl in the nutrient solution during growth.