Factors for induction of crassulacean acid metabolism in the facultative halophyte Mesembryanthemum crystallinum L
1997
Saitou, K. (Kyushu Univ., Fukuoka (Japan). Faculty of Agriculture) | Kubota, F. | Agata, W.
In Mesembryanthemum crystallinum L. leaves exhibiting C3 photosynthesis, crassulacean acid metabolism (CAM), as characterized by high PEP carboxylase and NADP-malic enzyme activities and malate synthesis in the dark, was induced by exposure to 400 mM NaCl, 400 mM KCl or 400 mM Na2SO4 in the nutrient medium over two weeks. However, the activity of PEP carboxylase and NADP-malic enzyme in the 400 mM Na2SO4-treated plants were higher than those in the 400 mM NaCl- or 400 mM KCl-treated plants, though the leaf water potential in the 400 mM Na2SO4-treated plants was almost identical to that in the 400 mM NaCl- or 400 mM KCl-treated plants. The activities of PEP carboxylase and NADP-malic enzyme increased by exposing the plant roots to 140 g.l(-1) polyethylene glycol 6,000 (PEG) or by lowering the culture solution to the tips of roots as well. However, the enzymatic activities in plants which were exposed to 105 g.l(-1) PEG plus 100 mM Nacl were higher than those in the 140 g.l(-1) PEG-treated plants, though the leaf water potential in the 105 g.l(-1) PEG plus 100 mM Nacl-treated plants was almost identical to that in the 140 g.l(-1)-treated plants. These results show that M. crystallinum shifts its mode of carbon assimilation from the C3 pathway to CAM in response to water stress, but this effect of water stress was enhanced by salt if the leaf water potential is low
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