The Dark Fixation of CO 2 by Succulent Leaves: Metabolic Changes Subsequent to Initial Fixation.

Abstract

Succulent plants are characterized by a diurnal rhythm of dark acidification and light deacidification. Concomitant with the acidification there is a loss of stored carbohydrate while in the light, organic acids are converted to carbohydrate (3). That CO2 fixa-tion in the dark is directly linked with the formation of acids was conclusively-demonstrated by Thurlow and Bonner (20) using C1402 and excised leaves of Bryophyllum crenatum. Thomas and his co-workers (19) have confirmed the relationship of CO2 fixa-tion and acid synthesis by elegant physiological ex-periments in which CO2 uptake was correlated with increased acid formation. Analysis of several compounds synthesized during the dark fixation has been made by Varner and Bur-rell (22). Excised B. calycinum leaves were exposed to C1402 for 2.5 hours in total darkness, and the or-ganic acids and carbohydrates isolated by chromatog-raphy on silica gel columns. The acids isolated were malic, succinic, oxalic, citric, and iso-citric-the same acids which had been identified chemically by Pucher (11). Stutz and Burris (18) extended the work of Varner and Burrell by exposing a wide variety of leaves from higher plants to C1402 in the dark, sep-arating the acids by column chromatography and measuring their specific activities. Ranson (13) em-ployed the technique of paper chromatography and radioautography to identify aspartate and glutamate