Enzymic Activities Associated with the Ability of Aerial and Submerged Forms ofLittorella uniflora(L.) Aschers to perform CAM

Abstract

Groenhof, A. C., Smirnoff, N. and Bryant, J. A. 1988. Enzymic activities associated with the ability of aerial and submerged forms of Littorella uniflora (L.) Aschers to perform CAM.—J. exp. Bot. 39: 353-361. The submerged form of Littorella uniflora shows a full CAM mode of photosynthesis as shown by diel acid fluctuations and elevated activities (in comparison to non-submerged leaves) of the enzymes phosphoeno/pyruvate carboxylase (PEPC) and NADP-malic enzyme. Non-submerged plants exhibit no diel fluctuations of acidity and no changes in activity of NADP-malic enzyme or PEPC. PEPC activity is low and NADP-malic enzyme is not detectable. Further characterization of PEPC extracted from submerged plants during the light and dark periods of a diel cycle shows that the enzyme extracted in the dark is more active. In addition, the enzyme shows a decrease in Km (PEP) and an increase in Kmax in the presence of glucose-6-phosphate, whilst in the presence of malate K„ (PEP) is increased and Vmax decreased; this response to malate is only observed in the light and at pH 7-2. Molecular weight determinations using a Sephacryl S-300 column show that the enzyme extracted from plants during the dark period has an apparent mol. wt. of 375 KDa and the enzyme extracted from plants during the light period has an apparent mol. wt. of 307 KDa. Key words—Littorella uniflora (shoreweed), Crassulacean acid metabolism, PEP carboxylase, malic enzyme. Correspondence to: Department of Biological Sciences, University of Exeter, Washington Singer Laboratories, Perry Road, Exeter EX4 4QG, U.K.