Compartmentation of Organic Acids in Corn Roots II. The Cytoplasmic Pool of Malic Acid

Lips, S. H.; Beevers, Harry

doi:10.1104/pp.41.4.713

Cited by 44 publications

(25 citation statements)

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“…Lips and Beevers (12) provided evidence for a cytoplasmic and a mitochondrial pool of malate in corn root cells. In leaf cells of Kalanchoe, rapid transport of malate to a storage pool and slow transport to a metabolically active pooi have been postulated at low temperatures (5).…”

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Temperature Features of Enzymes Affecting Crassulacean acid Metabolism

Brandon

1967

Plant Physiol.

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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)

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confidence: 99%

Temperature Features of Enzymes Affecting Crassulacean acid Metabolism

Brandon

1967

Plant Physiol.

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“…More recently a double labeling method, in which the disappearance of 1'C and 3H from malate in the tissue following a pulse of bicarbonate 14C plus acetate-3H was measured, allowed the demonstration of 2 separate pools of malate, neither of which appeared to be in the vacuole (3,4). One of these pools, that labeled by acetate-3H, was associated with the tricarboxylic acid cycle and the other, labeled by CO-fixation from bicarbonate-14C, did not readily enter the cycle.…”

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Compartmentation of Organic Acids in Corn Roots. III. Utilization of Exogenously Supplied Acids

Steer

Beevers

1967

Plant Physiol.

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“…The direct influence of bicarbonate has been demonstrated by Steward and Preston (36) and by Jackson and Coleman (16) and is evident in the early work of Ulrich (43), and of Poole and Poel (32). While phosphate at pH 7.5 elicits extensive organic acid synthesis (17,18,23,35), phosphate at pH 5.0 has no effect (26). Maruyama et al (27) have directly implicated bicarbonate as the reactive species in carboxylation mediated by peanut cotyledon PEP carboxylase by noting the distribution of SQ in OAA and inorganic phosphate following the fixation of 10-labeled bicarbonate.…”

Section: Materiais and Methodsmentioning

confidence: 96%

“…Furthermore, studies with root tips have shed light on the availability of cytoplasmic malate to mitochondrial metabolism (23).…”

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Bicarbonate Fixation and Malate Compartmentation in Relation to Salt-induced Stoichiometric Synthesis of Organic Acid

Jacoby

Laties

1971

Plant Physiol.

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The relationship of malate synthesis to K absorption from solutions of K2SO4 and KHCO3 was compared in nonvacuolate barley (Hordeum vulgare) root tips and whole excised roots. The comparison has permitted separation of the process which evokes organic acid synthesis from that which leads to stoichiometry between net acid equivalents formed and excess K+ absorbed from K2SO4, on the one hand, and total K+ absorbed from KHCOs, on the other. Both in tips and in roots K+ uptake from 20 mN salt solution exceeds malate synthesis in the first hour. In vacuolate roots the expected stoichiometry is achieved with time. When root tips are transferred to dilute CaSO4, malate is rapidly metabolized, and K+ is lost to the solution. By contrast, in excised whole roots the malate level remains unchanged, the salt-induced organic acid presumably being retained in the vacuole. In excised roots malonate leads to a marked drop in malate levels in untreated roots as well as in roots which have experienced salt-induced net malate synthesis. In consequence, it is contended that malonate makes available normally sequestered vacuolar malate.The general hypothesis is offered that the bicarbonate level of the cytoplasm controls organic acid synthesis by phosphoenolpyruvate carboxylase, and that the cytoplasmic bicarbonate level is raised either by exchange of cytoplasmic HI for external cation, or by bicarbonate absorption directly. Stoichiometry, in turn, is achieved by the accumulation in the vacuole of the double salt of malate.The time-honored observation linking organic acid synthesis in plant tissue to preferential cation uptake is still attended by the primordial questions of what elicits synthesis, and why there is a stoichiometric relationship between the equivalents of acid produced and the excess of cation absorbed over the counter anion taken up. It has been amply established that the organic acid synthesis which accompanies excess cation absorption is the result of dark CO, fixation (3,14,17,18,43), and it remains to determine the manner in which one or more of the multiplicity of carboxylating enzyme sys-

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Compartmentation of Organic Acids in Corn Roots II. The Cytoplasmic Pool of Malic Acid

Cited by 44 publications

References 8 publications

Temperature Features of Enzymes Affecting Crassulacean acid Metabolism

Temperature Features of Enzymes Affecting Crassulacean acid Metabolism

Compartmentation of Organic Acids in Corn Roots. III. Utilization of Exogenously Supplied Acids

Bicarbonate Fixation and Malate Compartmentation in Relation to Salt-induced Stoichiometric Synthesis of Organic Acid

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