The synthesis of phosphoenolpyruvate carboxylase in imbibing sorghum seeds

1991 ◽  
Vol 69 (2-3) ◽  
pp. 141-145 ◽  
Author(s):  
Eli Khayat ◽  
Erwin B. Dumbroff ◽  
Bernard R. Glick
Keyword(s):  
Enzyme Activity ◽  
Seed Development ◽  
Phosphoenolpyruvate Carboxylase ◽  
Bisphosphate Carboxylase ◽  
Seeds Germination

When sorghum seeds were imbibed either in the light or in the dark, the presence of newly synthesized phosphoenolpyruvate carboxylase (PEPC) could be detected immunologically after approximately 6 h. In addition, both PEPC mRNA and enzyme activity were detected in extracts of dry seeds prior to imbibition. By contrast, ribulose-1,5-bisphosphate carboxylase mRNA, protein, and activity, as well as chlorophyll, were not detected even after 24 h of imbibition. These observations suggest that the nonphotosynthetic form of PEPC is synthesized during seed development and may play an important role in the germinative process.Key words: phosphoenolpyruvate carboxylase, sorghum seeds, germination, ribulose-1,5-bisphosphate carboxylase.

Possible involvement of phosphoenolpyruvate carboxylase and NAD-malic enzyme in response to drought stress. A case study: a succulent nature of the C4-NAD-ME type desert plant, Salsola lanata (Chenopodiaceae)

2017 ◽  
Vol 44 (12) ◽  
pp. 1219
Author(s):  
Zhibin Wen ◽  
Mingli Zhang
Keyword(s):  
Enzyme Activity ◽  
Drought Stress ◽  
Phosphoenolpyruvate Carboxylase ◽  
Malic Enzyme ◽  
C4 Plants ◽  
Leaf Water Content ◽  
Transcriptional Level ◽  
Desert Plant ◽  
Severe Stress ◽  
Real Time Quantitative Pcr

The co-ordination between the primary carboxylating enzyme phosphoenolpyruvate carboxylase (PEPC) and the further decarboxylating enzymes is crucial to the efficiency of the CO2-concentrating mechanism in C4 plants, and investigations on more types of C4 plants are needed to fully understand their adaptation mechanisms. In this study we investigated the effect of drought on carboxylating enzyme PEPC, and the further decarboxylating NAD-malic enzyme (NAD-ME) of Salsola lanata Pall. (Chenopodiaceae) – an annual succulent C4-NAD-ME subtype desert plant. We investigated enzyme activity at the transcriptional level with real-time quantitative PCR and at the translational level by immunochemical methods, and compared S. lanata with other forms of studied C4 plants under drought stress. Results showed that only severe stress limited PEPC enzyme activity (at pH 8.0) of S. lanata significantly. Considering that PEPC enzyme activity (at pH 8.0) was not significantly affected by phosphorylation, the decrease of PEPC enzyme activity (at pH 8.0) of S. lanata under severe stress may be related with decreased PEPC mRNA. The suggestion of increased phosphorylation of the PEPC enzyme in plants under moderate stress was supported by the ratio of PEPC enzyme activity at pH 7.3/8.0, as PEPC enzyme is inhibited by L-malate and the evidence of the 50% inhibiting concentration of L-malate. NAD-ME activity decreased significantly under moderate and severe stress, and coincided with a change of leaf water content rather than the amount of α-NAD-ME mRNA and protein. Leaf dehydration may cause the decrease of NAD-ME activity under water stress. Compared with other C4 plants, the activities of PEPC and NAD-ME of S. lanata under drought stress showed distinct features.

Genetic Manipulation of Key Photosynthetic Enzymes in the C4 Plant Flaveria bidentis

1997 ◽  
Vol 24 (4) ◽  
pp. 477 ◽  
Author(s):  
Robert T. Furbank ◽  
Julie A. Chitty ◽  
Colin L.D. Jenkins ◽  
William C. Taylor ◽  
Stephen J. Trevanion ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Malate Dehydrogenase ◽  
Genetic Manipulation ◽  
Photosynthetic Performance ◽  
Covalent Modification ◽  
Wild Type ◽  
Bisphosphate Carboxylase ◽  
Photosynthetic Enzymes ◽  
Flaveria Bidentis

The NADP-malic enzyme type C4 dicot Flaveria bidentis (L.) Kuntze was transformed with antisense and cosense gene constructs that resulted in specific decreases in single photosynthetic enzymes. The enzymes targeted were ribulose-1,5-bisphosphate carboxylase/oxygenase [EC 4.1.1.39] (Rubisco), pyruvate, Pi dikinase [EC 2.7.9.1] (PPDK) and NADP malate dehydrogenase [EC 1.1.1.82] (NADP-MDH). These enzymes were chosen as targets because they have low activity compared to photosynthetic rates (Rubisco), are subject to complex covalent regulation (NADP-MDH), or both (PPDK). T1 progeny of a number of lines of these transformants were examined for the effects of these gene constructs on enzyme levels and photosynthetic performance. Rubisco antisense transformants expressing between 15 and 100% of wild-type enzyme activity were obtained. Pyruvate, Pi dikinase antisense lines were obtained with 40–100% wild-type levels. NADP malate dehydrogenase sense constructs caused a co-suppression of enzyme activity with some lines containing less than 2% of wild- type activity. Under saturating illumination, the control coefficients for these enzymes were determined to be up to 0.7 for Rubisco, 0.2–0.3 for PPDK and effectively zero for NADP-MDH. The implications of these observations for the regulation of photosynthetic flux and metabolism in C4 plants and the role of regulation by covalent modification are discussed.

Regulation of Phosphoenolpyruvate Carboxylase in Zea mays by Protein Phosphorylation and Metabolites and Their Roles in Photosynthesis

1996 ◽  
Vol 23 (1) ◽  
pp. 25 ◽  
Author(s):  
Y Gao ◽  
KC Woo
Keyword(s):  
Zea Mays ◽  
Enzyme Activity ◽  
Protein Phosphorylation ◽  
Photosynthetic Rate ◽  
Phosphoenolpyruvate Carboxylase ◽  
Strong Inhibitor ◽  
Physiological Concentration ◽  
Crude Extracts ◽  
Maize Leaves

The effects of metabolites, protein phosphorylation and malate inhibition on phosphoenolpyruvate carboxylase (PEPC) activity were investigated at pH 7.0 in partially purified enzyme from maize leaves. Glycine, glucose 6-phosphate or alanine stimulated the activity two- to three-fold. Glycine and glucose 6-phosphate increased the affinity for PEP by factors of eight and four respectively. These metabolites changed the response of the enzyme activity to pH. Activity increased between pH 6.8 and 8.0 by 10-fold in the absence and 26% in the presence of these metabolites. In vitro phosphorylation of PEPC increased the activity two-fold in the absence but not in the presence of these metabolites. Malate was a strong inhibitor of PEPC, the KI value being 0.25-0.5 mM. Protein phosphorylation and the above metabolites increased the Ki value by factors of three and 12 respectively, but they synergistically increased the Ki 50-fold, thus providing maximal protection against malate inhibition. In the crude extracts from light- and dark-adapted leaves in the presence of a physiological concentration of malate (20 mM), PEPC activity comparable to the photosynthetic rate was obtained only from the light-adapted leaves in the presence of metabolites indicating that both light-induced protein phosphorylation and metabolic activators were essential for PEPC activation during photosynthesis. We propose that both these factors act synergistically to modulate PEPC during photosynthesis in maize.

Inhibitory Action of Glufosinate on Photosynthesis

1993 ◽  
Vol 48 (3-4) ◽  
pp. 369-373 ◽  
Author(s):  
Aloysius Wild ◽  
Christine Wendler
Keyword(s):  
Enzyme Activity ◽  
Calvin Cycle ◽  
Atmospheric Conditions ◽  
Direct Inhibition ◽  
Carboxylase Activity ◽  
Bisphosphate Carboxylase ◽  
Transamination Reaction ◽  
Ribulosebisphosphate Carboxylase ◽  
High Concentrations ◽  
Respiratory Conditions

Glufosinate (phosphinothricin) irreversibly blocks the glutamine synthetase which subsequently gives rise to an accumulation of ammonium and to a strong decrease in some amino acids, especially glutamine and glutamate.Under atmospheric conditions (400 ppm CO2, 21% O2) glufosinate causes a rapid inhibition of photosynthesis, too. H ow ever, under non-photo respiratory conditions (1000 ppm CO2, 2% O2) only a slight inhibition of photosynthesis occurs with glufosinate. Since under both conditions an accumulation of ammonium occurs, it is concluded that inhibition of photosynthesis is not induced by the higher concentrations of ammonium. The results rather suggest that the absence of amino donors in the glycolate pathway leads to a break-down of the transamination reaction of glyoxylate to glycine. This causes an inhibition of photorespiration and as a further consequence the inhibition of photosynthesis. There are two hypotheses for explaining this phenomenon. One of them supposes that the blockade in the glycolate pathway produces a lack of Calvin cycle intermediates which subsequently is the cause of the inhibition of photo synthesis. The other one suggests a direct inhibition of the ribulose-1,5-bisphosphate carboxylase by the accumulation of glyoxylate and P-glycolate.After treatment with different intermediates of the Calvin cycle and photorespiration to gether with glufosinate no decrease in the inhibition of photosynthesis could be measured. This suggests that the inhibition of photosynthesis is not induced by a depletion of intermediates of the Calvin cycle.Tests on the effect of glyoxylate and P-glycolate on ribulosebisphosphate carboxylase activity showed that in crude leaves extracts the enzyme activity can only be inhibited by high concentrations of these substances. However, in intact spinach chloroplasts the enzyme activity can be blocked by using much lower concentrations of glyoxylate. This may indicate that the ribulosebisphosphate carboxylase activase is affected by this metabolite and that this may be the reason for an inhibition of photosynthesis after treatment with glufosinate.

The inorganic carbon requirements for nitrogen assimilation

1991 ◽  
Vol 69 (5) ◽  
pp. 1139-1145 ◽  
Author(s):  
David H. Turpin ◽  
Greg C. Vanlerberghe ◽  
Alan M. Amory ◽  
Robert D. Guy
Keyword(s):  
Amino Acid ◽  
Phosphoenolpyruvate Carboxylase ◽  
Nitrogen Assimilation ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Sufficient Conditions ◽  
Acid Synthesis ◽  
Amino Acid Synthesis ◽  
Bisphosphate Carboxylase ◽  
N Assimilation

In the green alga Selenastrum minutum (Naeg.) Collins the assimilation of NH4+ into the full suite of protein amino acids requires at least three separate and distinct inorganic carbon fixing reactions, catalyzed by the enzymes ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC), and carbamoyl phosphate synthetase. In this paper we examine the requirements for CO2 fixation of NH4+ assimilation in this organism. When grown under N-sufficient conditions, NH4+ assimilation is directly dependent upon photosynthetic CO2 fixation to provide carbon skeletons for amino acid synthesis. When cultured under N-limited conditions, the cells accumulate starch, which is then available for amino acid synthesis. This alleviates the requirement of photosynthetic CO2 fixation for NH4+ assimilation. N-limited cells, however, still exhibit a nonphotosynthetic CO2 requirement for N assimilation that is mediated through PEPC. This activity of PEPC increases during N assimilation to replenish TCA cycle intermediates consumed during amino acid synthesis. The in vivo activity of this enzyme is tightly regulated so that there are ~0.3 moles C fixed per mole N assimilated. In S. minutum PEPC is regulated primarily by the ratio of glutamine/glutamate, thus providing a mechanism by which primary NH4+ assimilation modulates the supply of carbon for amino acid biosynthesis. Activation of PEPC during NH4+ assimilation occurs in both the light and the dark. Key words: dissolved inorganic carbon, nitrogen assimilation, phosphoenolpyruvate carboxylase, photosynthesis, amino acid synthesis, respiration.

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