Journal of Experimental Botany, Vol. 38, No. 186, pp. 67-76, January 1987 The Permeability of Ammonia, Methylamine and Ethylamine in the Charophyte Chara corallina (C. australis) RAYMOND J. RITCHIE Section of Biochemistry, Molecular and Cell Biology, Division of Biological Sciences, Cornell University, Ithaca, New York, 14853 U.S.A. Received 20 August 1986 ABSTRACT Ritchie, R. J. 1987. The permeability of ammonia, methylamine and ethylamine in the charophyte Chara corallina (C. australis).—J. exp. Bot. 38: 67-76. The permeabilities of the amines, ammonia (NH 3 ), methylamine (CH 3 NH 2 ) and ethylamine (CH 3 CH 2 NH 2 ) in the giant-celled charophyte Chara corallina (C. australis) R.Br. have been measured and compared. The permeabilities were corrected for uptake fluxes of the amine cations. Based on net uptake rates, the permeability of ammonia was 6-4 + 0-93 /im s" 1 (n = 38). The permeabilities of methylamine and ethylamine were measured in net and exchange flux experiments. The permeabili- ties of methylamine were not significantly different in net and exchange experiments, nor to that of ammonia (P mclk ,\ zmtac = 60±0-49 (ims"'(» = 44)). In net flux experiments the apparent perme- ability of ethylamine was slightly greater than that of ammonia and methylamine (/^yumine, ne , = 8-4+ 1-2 fxm s" 1 (n = 40)) but the permeability of ethylamine based on exchange flux data was significantly higher (/"nhyumme. exchange = 14± l-2/«n s" 1 (n = 20)). Methylamine can be validly used as an ammonium analogue in permeability studies in Chara. The plasmalemma of Chara has acid and alkaline bands; little diffusion of uncharged amines would occur across the acid bands. The actual permeability of amines across the alkaline bands is probably about twice the values quoted above on a whole cell basis i.e. the permeability of ammonia across the permeable part of the plasmalemma is probably about 12 fim s~'. Key words—Chara, permeability, ammonia, methylamine. Correspondence to: Section of Biochemistry, Molecular and Cell Biology, Division of Biological Sciences, Cornell University, Ithaca, New York, 14853 U.S.A. INTRODUCTION Ammonia is the preferred source of fixed nitrogen for many plants, fungi and bacteria (Kleiner, 1981). A major difficulty in studies of nitrogen uptake and metabolism is that a convenient nitrogen radioisotope is not readily available but it has been demonstrated that, for some organisms and physiological conditions, 14 C-methylamine can be used as an ammonia analogue in many organisms (Hackette, Skye, Burton, and Segel, 1970); for a review see Kleiner (1981). The weakly basic amines (R-NH 2 ), ammonia (NH 3 ), methylamine (CH 3 NH 2 ) and ethylamine (CH 3 CH 2 NH 2 ) have pK a s of 9-25, 10-65 and 10-75 respectively at 25 °C. The relative abundance of the two forms in solutions at a known pH can be calculated using the Henderson-Hasselbalch equation. The permeability (Pj) of a chemical species (j) is a measure of the ability of the species to © Oxford University Press 1987