ENZYMATIC RESPONSES TO WATER-STRESS IN DETACHED LEAVES OF THE CAM PLANT KALANCHOE-BLOSSFELDIANA POELLN

Total extractable activity (''capacity'') of phosphoenolpyruvate carbo xylase (EC 4.1.1.31, PEPC), phosphofructokinase (EC 2.7.1.1, PKF), ald olase (EC 4.1.2.7), phosphoglycerate mutase (EC 5.4.2.1, PGM), enolase (EC 4.2.1.11), glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G-6-PD H) and phenylalanine ammonia lyase (EC 4.3.1.5, PAL) was measured in l eaves detached from the CAM plant Kalanchoe blossfeldiana grown under long days (C3-performing). The isolated leaves were maintained 36 h un der 280 mumol m-2 s-1 PAR, at 27-degrees-C, under drought (50% relativ e air humidity). A 50% water deficit was brought about in the leaves b y the treatment. Control leaves were kept with petioles immersed in wa ter. Under water stress but not in the control leaves, the capacities of PEPC, PGM and enolase showed a short-term and correlative increase. Immunotitration techniques established that the increase in PEPC was due to de novo synthesis of the enzyme. The capacity of PAL dropped un der drought, following a kinetic inverse of that of PEPC. No effect of the treatment could be demonstrated on PFK, aldolase and G-6-PDH. The responses did not occur in darkness or under red light. Stomatal clos ure in the water-stressed leaves resulted in depletion of the small ma late pool present in the C3-performing leaves at the beginning of the treatment. The increase in enzyme capacities was not followed by induc tion of CAM operation. The results are a further demonstration that en zymatic responses upon stress are triggered in the CAM pathway and in the surrounding network as early steps preceding the actual CAM syndro me.