Temperature Features of Enzymes Affecting Crassulacean acid Metabolism

Abstract

Summiilary. Enzymes involved in malic acid production via a pathway with 2 carboxylation reactions and in malic acid conversion via total oxidation have been demonstrated in mitochondria of Bryophyllurn tutbiflorumn Harv. Activation of the mitochondria by Tween 40 was necessary to reveal part of the enzyme activities. The temperature behaavior of the enzymes has been investigated, revealing optimal activity of acid-producing enzymes at 350. Even at 530 the optimum for acid-converting enzymes was not yet reached. From the simultaneous action of acid-producing and acid-converting enzyme systems the overall result at different temperatures was estajblished. Up to 150 the net result was a malic acid prodduction. Mloderate temperattures brought about a decrease in this accumulation, which was partly accompanied by a shift to isocitrate production, while at higher temperatures total oxidation of the acids exceeded the production. (21,22,24) and P-enol(pyrtuvate carboxylase has been stuggested as catalyzing the CO., fixatioin. The oxaloacetic acid produiced can be converted to malic acid by malate dehydrogenase, which was also demonstrable in the leaf extracts. A second carboxylation reaction in the acid-synthesizing pathway was proposed on the basis of the constant labeling of malic acid, produced by leaves in 14CO9 (6). The ratio of radioactivity fotund in carbon-4 to that in carbon-I was constantly 2:1 tunder a great variety of conditions, while the labeling of carbon-2 and carbon-3 could never be detected. This was explained by assuming an acid synthesis via carboxylation of ribulose 1,5-di,P to glvcerate 3-P, followed by conversion of glycerate 3-P to P-enolpyruvate, a second carboxylation (resulting in oxaloaceti;c acid) and reduction to malic acid. This pathway implies participation of the oxidative pentose phosphate pathway, so that the following reaction sequence for acid production can be proposed: starch glucose 6-P --ribulose 1,5-diP glycer.ate 3-P P-enolpyruvate -* malate.For acid conversion a role is attributed to the malic enzyme (22,23), which converts malate to pyruvate, followed by total oxidation of this product by the tricarboxylic acid cycle (7,14).That the acid accutmulation is a result of the dominance o-f acid-synthesizing enzymes at low temperatures, while the acid decrease is a consequence of the fact that conversion exceecds production at higher temperatures was demonstrated by Bennet-Clark (3)

In Vitro Characterization of Thermostable CAM Rubisco Activase Reveals a Rubisco Interacting Surface Loop

“…We note that such a mechanism would not be available to plants using crassulacean acid metabolism (CAM) growing in a desert environment, where Calvin-Benson-Bassham cycle function will be taking place in the light, with the stomata closed to minimize water loss (Borland et al, 2014). Consequently, we reasoned that, like other enzymes required during daytime, CAM activases should be relatively thermostable (Brandon, 1967;Luttge, 2004). Any potential temperature fuse function should not be conserved in CAM Rca proteins.…”

Isolation of Mesophyll Cells from Sedum telephium Leaves

“…Section B occurs primarily in the light, particularly the photosynthetic reductive pentose phosphate cycle and the formation of PEP from pyruvate. In the light, the entire scheme in Figure 3 may operate, and in the dark only section A is (7). We have experiments in progress on identification of the products of '4CO2 fixation which show that the predicted labeled products of both light and dark metabolism in Figure 3 can be observed with these isolated S. telephium cells.…”

“…Table IV There are some methods available for decreasing the amount of acidity in CAM plants. By increasing temperature in the night, the acid accumulation at night is diminished (7,18). Changes in the duration of light, such as exposure of leaves for at least 24 hr to light (18) will lower the acid content.…”

Germinación y reclutamiento de clusia spp. (linneo) en un bosque muy húmedo tropical colombiano Fragmentado

“…El género Clusia spp. presenta árboles marcadamente umbrófilos, y como muchas otras plantas, necesita en los primeros estadios de vida varias horas luz (hl) para su desarrollo, más teniendo en cuenta que es el único árbol neotropical con Metabolismo Ácido de las Crasuláceas CAM (Lûttge, 2006), por lo cual son imperativas varias hl ligadas a altas temperaturas que aseguran la dinámica del metabolismo (Brandon, 1967). Lo anterior refuerza que los efectos de temperatura están fuertemente ligados a los de luminosidad y estos a la sanidad fisiológica de la especie vegetal (Haag-Kerwer et al 1992) El agua y los nutrientes, por su parte, determinan mancomunadamente las condiciones para la emergencia de las plántulas y su posterior crecimiento.…”