Uptake of Amino Acids and Other Organic Compounds by <i>Lemna paucicostata</i> Hegelm. 6746

Datko, Anne H.; Mudd, S. Harvey

doi:10.1104/pp.77.3.770

Cited by 37 publications

(29 citation statements)

References 25 publications

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“…[ relative to that of L-serine itself (770 nl/frond min [6]). Paper chromatography (solvent B) or electrophoresis at pH 7.0 of aliquots of the methanol-water-soluble fractions showed that all of the tissue radioactivity moved with serine, none with Pserine.…”

Section: U(m -T) Tmentioning

confidence: 99%

“…Initial rates of uptake of P-serine were measured over 5 to 20 min periods as described (6). Other Methods Chromatographic systems and solvents previously designated as A through E were used as described (32) of radioactivity in particular compounds which had been subjected to several sequential purification steps have been described (7,8,31,32 ,32P]GP-EA was assumed to have come into isotopic equilibrium) were used to calculate the "'C specific radioactivity (dpm/nmol) of the ['C,`2P]GP-EA.…”

Section: Uptakesmentioning

confidence: 99%

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Synthesis of Ethanolamine and Its Regulation in Lemna paucicostata

Mudd¹,

Datko²

1989

Plant Physiol.

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The metabolism of ethanolamine and its derivatives in Lemna paucicostata has been investigated, with emphasis on the pathway for synthesis of phosphoethanolamine, a precursor of phosphatidylcholine in higher plants. In experiments involving labeling of intact plants with radioactive serine, ambiguities of interpretation due to entry of radioactivity into methyl groups of methylated ethanolamine derivatives were mitigated by pregrowth of plants with methionine. Difficulties due to labeling of diacylglyceryl moieties of phospholipids were avoided by acid hydrolysis of crucial samples and determination of radioactivity in isolated serine or ethanolamine moieties. The results obtained from such experiments are most readily reconciled with the biosynthetic sequence: seine --ethanolamine --phosphoethanolamine phosphatidylethanolamine. A possible altemative is: serine phosphatidylserine -. phosphatidylethanolamine -i ethanolamine --phosphoethanolamine. Cell-free extracts of L. paucicostata were shown to produce CO2 from the carbon originating as C-1 of serine at a rate sufficient to satisfy the demand for ethanolamine moieties. A number of experiments produced no support for a hypothetical role for phosphoserine in phosphoethanolamine formation. Uptake of exogenous ethanolamine commensurately down-regulates the synthesis of ethanolamine moieties (considered as a whole, and regardless of their state of derivatization at the time of their formation). In agreement with previous observations, uptake of exogenous choline down-regulates the methylation of phosphoethanolamine, without being accompanied by secondary accumulation of a marked excess of ethanolamine derivatives.findings bring to the fore the question of the biosynthetic origin in higher plants of P-EA, a compound crucial to initiation of each of these metabolic pathways. One route to P-EA, each of the component steps of which has been demonstrated in higher plants, involves the decarboxylation of PtdSerine:PtdSerine --PtdEA + CO2 (reaction 1)PtdSerine decarboxylase activity has been demonstrated in extracts of spinach leaves, chiefly in the 100,000g supernatant fraction (26,27 Plant Physiol. Vol. 91, 1989 10, 18), contribution to EA formation. EA is a widespread constituent of higher plants (23), but a decarboxylase unequivocally acting on free serine (5, 10) has not, to our knowledge, been reported.Once EA is formed, the pathway to P-EA may be completed by EA kinase:This kinase is well known in higher plants (29,30), including Lemna (32,33).An alternative route to P-EA, entirely speculative at the moment (32), would involve the decarboxylation of P-serine:Evidence (reviewed and summarized by Keys [21 ]) is available suggesting that P-serine may be formed in at least some higher plants from the photosynthetic and glycolytic intermediate, P-glycerate, by successive oxidation and transamination.An additional uncertainty related to P-EA metabolism in higher plants is whether this compound can be converted to PtdEA by a sequence analogous to that for the c...

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Section: U(m -T) Tmentioning

confidence: 99%

Section: Uptakesmentioning

confidence: 99%

Synthesis of Ethanolamine and Its Regulation in Lemna paucicostata

Mudd¹,

Datko²

1989

Plant Physiol.

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“…In a recent survey of the capacity of Lemna paucicostata to take up organic compounds, it was found that this plant possesses specific and distinct systems for the transport of eight groups of organic compounds (4). Among these is a system which transports ethanolamine, and another which transports choline.…”

mentioning

confidence: 99%

“…velocity . substrate concentration) (4), in units of nl/frond-min. Frond-d, calculated as described (1), was multiplied by 1440 to obtain frond-min.…”

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Uptake of Choline and Ethanolamine by Lemna paucicostata Hegelm. 6746

Datko

Mudd²

1986

Plant Physiol.

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Lemna paucicostata Hegelm. 6746 possesses specific systems for uptake of choline and ethanolamine. Each is distinct from the six other systems for uptake of organic compounds so far identified in this plant. Both systems show biphasic kinetics, so that uptake by them can be described as the composite result of two Michaelis-Menten processes. Inhibitor studies are reported which indicate the very strict structural specificity of each system. The kinetic constants of choline uptake are such that, at an external concentration of 0.65 micromolar, the total requirement of the plant for this compound would be met, 41% via the high affinity system and 59% via the lower. At an external concentration of 2.4 micromolar ethanolamine, an amount of this compound sufficient to form the total choline of the plant would be supplied, 59% via the high affinity system and 41% via the lower. These, and other observations, strongly support the physiological importance of these systems under natural conditions. radioactive medium. This was followed by a 20-min washout incubation in nonradioactive medium. Plant samples were then harvested and the radioactivity in TCA-soluble and -insoluble fractions measured (2). Uptake is expressed as clearance (i.e. velocity . substrate concentration) (4), in units of nl/frond-min. Frond-d, calculated as described (1), was multiplied by 1440 to obtain frond-min. Estimates of clearance and of extent of inhibition of uptake were made by measuring uptake from solutions of specified concentration. Clearance as a function of substrate concentration was measured by increasing substrate concentration by addition of nonradioactive substrate.When uptake was measured as disappearance of radioactivity from the medium, plants were inoculated into 600 ml medium containing the specified concentration of '4C-labeled substrate. At suitable intervals, frond number was determined and medium was sampled for determination of radioactivity, allowing calculation ofclearance for each interval. Inoculum size and sampling intervals were chosen so that there was no more than a 10% decrease in substrate concentration due to uptake during each interval.In a recent survey of the capacity of Lemna paucicostata to take up organic compounds, it was found that this plant possesses specific and distinct systems for the transport of eight groups of organic compounds (4). Among these is a system which transports ethanolamine, and another which transports choline. Here we report the results of further studies of these two transport systems, providing data upon their kinetic parameters and their specificities. It RESULTS Under the standard growth conditions employed (5) Lemna paucicostata Hegelm. 6746 doubles each 35.2 h (SD ± 1.7, n = 4) (3). Plant colonies, each usually consisting of 3 to 6 fronds (6), float on the surface ofthe aqueous medium from which they absorb nutrients. The mean wet weight of a frond is 509 Ag (3); the mean surface area is 4.8 mm2 (determined as described [2]).The uptakes ofcholine and ethanolamine by...

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Applications of the aquatic higher plant Lemna gibba for ecotoxicological assessment

Greenberg

Huang

Dixon

1992

Journal of Aquatic Ecosystem Health

104

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Although higher plants represent a significant portion of the total biomass in some aquatic environments, their use in ecosystem evaluation has lagged behind that of other organisms. This is partly due to a lack of convenient aquatic higher plant systems that can be employed for ecotoxicological assessment. However, the aquatic C-3 monocot Lemna gibba has many attributes that makes it useful for ecosystem health assessment. In this report, using examples from the literature and our research, some of the applications Lemna has for environmental research are discussed. Toxicant impacts on Lemna can be readily assessed in terms of growth; the plants multiply quickly and changes in biomass (which doubles approximately every 2 days) can be accurately measured by counting leaves. The plants are small, allowing for simultaneous multiple replication. The small size also makes the lighting conditions easy to control; sunlight can be accurately simulated and specific spectral regions can be enhanced or deleted. Lemna is amenable to in vivo chlorophyll and photosynthesis assays, which make excellent companion endpoints for growth. The plants assimilate chemicals directly from the growth medium, facilitating controlled toxicant application. Furthermore, Lernna has a high bioconcentration capacity, indicating a potential for use in bioremediation technologies.

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Uptake of Amino Acids and Other Organic Compounds by Lemna paucicostata Hegelm. 6746

Cited by 37 publications

References 25 publications

Synthesis of Ethanolamine and Its Regulation in Lemna paucicostata

Synthesis of Ethanolamine and Its Regulation in Lemna paucicostata

Uptake of Choline and Ethanolamine by Lemna paucicostata Hegelm. 6746

Applications of the aquatic higher plant Lemna gibba for ecotoxicological assessment

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