THE EFFECTS OF HIGH SALINITY, WATER-DEFICIT, AND ABSCISIC-ACID ON PHOSPHOENOLPYRUVATE CARBOXYLASE ACTIVITY AND PROLINE ACCUMULATION IN MESEMBRYANTHEMUM-CRYSTALLINUM CELL-CULTURES

It has been established from previous studies in the halophyte Mesembr yanthemum crystallinum that saline conditions induce the synthesis of phosphoenolpyruvate carboxylase (PEPC), the performance of Crassulacea n acid metabolism (CAM), and the production of compatible solutes such as proline. The objective of the present study was to determine wheth er factors causing the induction of these processes in leaves were als o effective in tissue cultures of M. crystallinum grown under differen t conditions. In heterotrophically (sucrose)-grown calli of M. crystal linum, low levels of NaCl (10 to 25 mM) were required for optimum grow th, while increasing concentrations of salt up to 200 mM caused a prog ressive decline in growth. Addition of salt to the culture medium caus ed a progressive increase in proline accumulation (13 fold increase in calli grown in 200 mM NaCl compared with calli grown without salt) bu t had little affect on PEPC activity in calli grown in sucrose media i n the dark or light. Addition of 10(-7)M abscisic acid in the presence of 200 mM NaCl doubled the proline content in light-grown calli, whil e abscisic acid alone had no affect. However, growth with 10(-7) to 10 (-5)M abscisic acid had no affect on levels of PEPC in dark or light-g rown calli, in contrast to the previously reported induction of this e nzyme and CAM by provision of abscisic acid to whole plants. Water str ess (imposed by addition of polyethylene glycol) and low levels of NaC l (10 mM) in combination caused a large increase in proline content in heterotrophically cultured cells, whereas neither were effective alon e. In photomixotrophic cell cultures, obtained by replacement of sucro se by soluble starch as the external carbon supply, there was a much h igher chlorophyll content, and a limited salt induced increase in PEPC activity (4-fold enhancement during a 12-d, 200-mM, salt-shock period ).