Metabolism of Glycollate byLemna minorL. Grown on Nitrate or Ammonium as Nitrogen Source (original) (raw)
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The metabolism of pyruvate in the light in plants with Crassulacean acid metabolism
1979
This thesis is concerned with the pathways for conversion of pyruvate and phosphoenolpyruvate (PEP) to carbohydrate in the light in C A M plants. These 3-carbon substrates are produced by the decarboxylation of malic acid which accumulates in the dark in these plants. It is shown that these 3-carbon compounds are principally converted to carbohydrate by a reversal of glycolysis (gluconeogenesis) and that oxidative metabolism to CO^, and refixation in photosynthesis is probably of minor significance.
Levels of metabolites related to glycolysis in Catharanthus roseus cells during culture☆
Phytochemistry, 1993
The rate of respiration and levels of various compounds that are involved in the metabolism of carbohydrate were determined in suspension-cultured Catharanthus roseus cells that were subcultured at lo-day intervals. Maximum rates of uptake of 0, were found during the lag phase (day 1) and the logarithmic phase (days 4-5). The levels of sucrose, starch and hexose phosphates increased during the first four to six days after inoculation. A decrease in levels of sucrose was detected earlier than in that of starch. The pools of triose phosphates were smaller than those of hexose phosphates during the entire culture period. The level of phosphoenolpyruvate was low when maximum respiratory rates were recorded. By contrast, the accumulation of pyruvate was observed transiently when the rate of respiration began to decrease. The level of ATP increased during first one-day period after transfer of cells to fresh medium and then it decreased. The adenylate energy charge was almost constant (0.76-0.78), apart from an initial increase on day 1 (to 0.85). The level of PPi remained high during the logarithmic phase of growth. These results are discussed in the context of possible mechanisms for the regulation of the metabolism of carbohydrates, and of glycolysis in particular, in cells at different stages of culture.
Phosphoenolpyruvate carboxylase in Hydrilla plants with varying CO 2 compensation points
Photosynthesis Research, 1983
Incubation of the submersed aquatic macrophyte, Hydrilla vertieillata Royle, for up to 4 weeks in growth chambers under winter-like or summer-like conditions produced high (130 to 150 μl CO2/l) and low (6 to 8 μl CO2/l) CO2 compensation points (Γ), respectively. The activities of both ribulose bisphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylases increased upon incubation but the major increase was in the activity of PEP carboxylase under the summer-like conditions. This reduced the ratio of RuBP/PEP carboxylases from 2.6 in high Γ plants to 0.2 in low Γ plants. These ratios resemble the values in terrestrial C3 and C4 species, respectively. Kinetic measurements of the PEP carboxylase activity in high and low Γ plants indicated the Vmax was up to 3-fold greater in the low Γ plants. The Km (HCO3-) values were 0.33 and 0.22 mM for the high and low Γ plants, respectively. The Km (PEP) values for the high and low Γ plants were 0.23 and 0.40 mM, respectively; and PEP exhibited cooperative effects. Estimated Km (Mg2+) values were 0.10 and 0.22 mM for the high and low Γ plants, respectively. Malate inhibited both PEP carboxylase types similarly. The enzyme from low Γ plants was protected by malate from heat inactivation to a greater extent than the enzyme from high Γ plants. The results indicated that C4 acid inhibition and protection were not reliable methods to distinguish C3 and C4 PEP carboxylases. The PEP carboxylase from low Γ plants was inhibited more by NaCl than that from high Γ plants. These analyses indicated that Hydrilla PEP carboxylases had intermediate characteristics between those of terrestrial C3 and C4 species with the low Γ enzyme being different from the high Γ enzyme, and closer to a C4 type. Al incubar la macrofita acuática sumergida (MAS) Hydrilla vertieillata Royle, por un período de hasta 4 semanas en cámaras de crecimiento con condiciones semejantes a las de invierno (bajas temperaturas y días cortos) o de verano (altas temperaturas y dlas largos), se originaron cambios en el punto de compensación de CO2 (Γ) de las plantas a valores de 130 a 150 μl CO2/l y 6–8 μl CO2/l, respectivamente. Las actividades tanto de la RiBP carboxilasa como de la PEP carboxilasa aumentaron durante la incubación, pero el aumento más significativo fué de la actividad de la PEP carboxilasa en las plantas en la condición de verano. Este aumento redujó la relación RiBP/PEP carboxilasa de 2.6 en las plantas con alto Γ a 0.2 en las plantas con bajo Γ. Estos valores se asemejan a los de especies C3 y C4 terrestres, respectivamente. Estudios de la cinética de la PEP carboxilase en plantas de Hydrilla, indican una Vmax de la enzima en plantas con bajo Γ hasta tres veces mayor que la Vmax en plantas con alto Γ. Las Km (HCO3-), Km (PEP) y Km (Mg2+) fueron diferentes en los dos tipos de plantas y la enzima mostró caracteristicas alostéricas en presencia de uno de sus substratos, PEP y del Mg2+. La inhibiclón de la PEP carboxilasa de ambos tipos de plantas (alto y bajo Γ) fué similar en presencia de malato. El malato a su vez fué más eficiente que el aspartato, en la protección de la enzima de plantas con alto Γ, de su inactivación por altas temperaturas. Los resultados indican sin embargo, que la inhibición de las PEP carboxilasas de especies C3 y C4 en presencia de ácidos de 4-C, no es un criterio aceptable para diferenclar entre las PEP carboxilasas de plantas C3 y de plantas C4. La inhibición de la PEP carboxilasa en presencia de NaCl fué un método más preciso en la distinción de ambos tipos de enzimas; la PEP carboxilasa de plantas de Hydrilla con bajo Γ mostró una mayor sensibilidad en presencia del NaCl que la enzima de plantas con alto Γ. Estos estudios indican que la PEP carboxilasa de plantas de Hydrilla tienen caracteristicas que son intermedias entre la de las enzimas de especies terrestres C3 y C4, siendo la enzima de las plantas con bajo Γ más parecida a la de las especies C4.
CO2 Exchange Of Potato Transformants With Reduced Activities Of Glycine Decarboxylase
Elsevier eBooks, 2000
Summary Download full-size image Components of photosynthetic and respiratory CO 2 exchange in photosynthesising leaves of potato ( Solanum tuberosum L., var. Desiree) control plants and of its transformants (P1 and P15) with limited expression of glycine decarboxylase have been determined under normal environmental conditions. The rate of true photosynthesis was highest in leaves of control plants (16.0 μmol CO 2 m - 2 .s - 1 ). In transformant P1 it was 2 times lower while P15 showed an intermediate value. The same relationship was found for the total rate of intracellular decarboxylation in the light: 2.6, 1.3 and 1.8 μmol CO 2 m - 2 .s - 1 in leaves of control plants, P1 and P15, respectively. No differences were detected in the relative rate of intracellular decarboxylation indicating that transformants did not have any advantage with respect to respiratory losses during photosynthesis in the light. In all varieties the main substrates of decarboxylation were primary photosynthates, the contribution of stored photosynthates varied in the range from 15 to 25% the total rate of decarboxylation. The rate of photorespiration exceeded the rate of respiration 7.5 times in control plants and 1.8-2.5 times in transformants. The rate of respiration in the dark was in leaves of control plants 30-40% higher than in leaves of transformants. Light severely, about 20 times, inhibited this component of respiration in control plants but only 1.5 times in P1 and 5.5 times in P15. The specificity of Rubisco, determined in intact leaves in vivo , had significantly higher values in transformants compared to control plants. It has been shown that in transformants a portion of glycine was not decarboxylated by glycine decarboxylase but transported out of the glycolate cycle which results in a change of the stoichiometry between RuBP oxygenation and photorespiration and in an apparent increase of Rubisco specificity. In leaves of transformants the content of non-protein glycine was 3-5 times higher and the content of non-protein serine 6-15 times lower than in leaves of control plants.
PLANT PHYSIOLOGY, 1983
Young bean plants (Phaseolus vulgaris L. var Saxa) were fed with three different types of inorganic nitrogen, after being grown on nitrogen-free nutrient solution for 8 days. The pattern of "CO2 fixation was investigated in photosynthesizing primary leaf discs of 11-day-old plants (3 days with nitrogen source) and in a pulse-chase experiment in 13-day-old plants (5 days with nitrogen source). Ammonium caused, in contrast to nitrate nutrition, a higher level of 14C incorporation into sugar phosphates but a lower incorporation of label into malate, glycolate, glycerate, aspartate, and alanine. The labeling kinetics of glycine and serine were little changed by the nitrogen source. Ammonium feeding also produced an increase in the ratio of extractable activities of ribulose-1,5-bisphosphate carboxylase to phosphoenolpyruvate carboxylase and an increase in dark respiration and the CO2 compensation concentration. Net photosynthesis was higher in plants assimilating nitrate. The results point to stimulated turnover of the photosynthetic carbon reduction cycle metabolites, reduced phosphoenolpyruvate carboxylation, and altered turnover rates within the photosynthetic carbon oxidation cycle in ammonium-fed plants. Mechanisms of the regulation of primary carbon metabolism are proposed and discussed. The effect of NH4' on photosynthetic carbon assimilation has been repeatedly reported (3, 8, 12, 13, 16, 17, 19-23, 27, 29) and the changes in metabolism which occur in response to toxic NH4' concentrations recently reviewed (10). Studies with Chlorella and Medicago sativa suggest that, during NH4' assimilation, photosynthetically fixed carbon is diverted into amino acids at the expense of sucrose synthesis (12, 13, 22). Pyruvate kinase, PEp2 carboxylase, and RuBP carboxylase are all apparently stimulated (8, 12, 13, 20-22), and in isolated spinach cells, photosynthetic 14CO2 fixation increased, in response to the presence of NH4' (29). Supplying C4 and C3 plants with NH4' as compared to NO3 produces, among other effects, changes in the initial carboxylation products, the CO2 compensation point, and the net photosynthetic rate (26), while in maize, NH4' nutrition causes a lower incorporation of label from 14CO2 into malate (3). Further, the addition of NH4' to N03grown cells of Nicotiana tabacum produced an increase in the cellular concentrations of alanine and glutamine, ' This work was supported by Swiss National Science Foundation Project 3.259-0.77.
PLANT PHYSIOLOGY, 1988
The effects of adenine nucleotides on phosphoenolypyruvate carboxylase were investigated using purified enzyme from the CAM plant, Crassula argentea. At 1 millimolar total concentration and with limiting phosphoenolpyruvate, AMP had a stimulatory effect, lowering the K. for phosphoenolpyruvate, ADP caused less stimulation, and ATP decreased the activity by increasing the K. for phosphoenolpyruvate. Activation by AMP was not additive to the stimulation by glucose 6phosphate. Furthermore, AMP increased the K. for glucose 6-phosphate. Inhibition by ATP was competitive with phosphoenolpyruvate. In support of the kinetic data, fluorescence binding studies indicated that ATP had a stronger effect than AMP on phosphoenolpyruvate binding, while AMP was more efficient in reducing glucose 6-phosphate binding. As free Mg2e was held constant and saturating, these effects cannot be ascribed to Mg2+ chelation. Accordingly, the enzyme response to the adenylate energy charge was basically of the "R" type (involving enzymes of ATP regenerating sequences) according to D. E. Atkinson's (1968 Biochemistry 7: 40304034) concept of energy charge regulation. The effect of energy charge was abolished by 1 millimolar glucose 6-phosphate. Levels of glucose 6-phosphate and of other putative regulatory compounds of phosphoenolpyruvate carboxylase were determined in total leaf extracts during a day-night cycle. The level of glucose 6-phosphate rose at night and dropped sharply during the day. Such a decrease in glucose 6phosphate concentration could permit an increased control of phosphoenolpyruvate carboxylase by energy charge during the day.