Mesembryanthemum crystallinumplants were grown for 10 weeks in soil culture and, during the final 3 weeks, watered with NaCl solutions varying in concentration between 50 and 500 mM. Plants show an increasingly less negative net CO2balance and increased malate accumulation in the leaves during the dark with increasing NaCl concentration. There is a positive net CO2balance above 100 mM with a maximum at 350 mM NaCl. Plants watered with 350 mM NaCl do not display this characteristic feature of crassulacean acid metabolism (CAM) initially,i.e.during the first week after the commencement of NaCl treatment. However, after this adaption period net CO2balance during the dark begins to approach a positive value. Malate accumulation in the leaves during the dark increases rapidly after the first week of NaCl treatment, reaching a constant level after about 3 weeks. Leaves which develop after commencement of NaCl treatment produce less malate during the dark than leaves which were already present at the onset of NaCl watering. Na+content in the leaves is higher than Cl-content when plants are watered with NaCl solutions. Four-and-a-half-month-old plants grown under soil culture without addition of NaCl also exhibit CAM, probably because of ion uptake from the soil which causes increase in Na+and Cl-contents in the leaves. Na2SO4, KCl and K2SO4have effects similar to those of NaCl on gas exchange reactions ofMesembryanthemum crystallinum.
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