Two Amino-acid Carriers in Pea Chloroplasts

Nobel, Park S.; Cheung, Yuk-Ngai Stephen

doi:10.1038/newbio237207a0

Cited by 13 publications

(6 citation statements)

References 10 publications

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“…The mechanism was saturated at about 50 mM. Both of these studies (2,18), as well as studies on amino acid uptake by isolated chloroplasts (15), indicate uptake of amino acids by some carrier mechanism (9). Watson and Fowden (21) have reported an active and a nonmetabolic component to uptake of phenylalanine and tyrosine by seedling root tips.…”

Section: Discussionmentioning

confidence: 98%

Long Distance Translocation of Sucrose, Serine, Leucine, Lysine, and Carbon Dioxide Assimilates

Peterson¹,

Housley²,

Schrader³

1977

Plant Physiol.

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To establish whether several amino acids were equally able to enter the phloem of oat (Avena sativa L.) plants and be transported, several 14C-labeled amino acids were applied individually to an abraded spot on a fully expanded source leaf. The base of an immature sink leaf was monitored with a GM tube for time and rate of arrival of radioactivity.Transport of '4C-sucrose and "4CO2 assimilates was measured for a comparison. The applied L-serine, L-lysine, and L-leucine, as weli as sucrose, entered the phloem and were transported to the sink leaf at rates between 1.16 and 1.83 cm/min. Transport velocity for CO2 assimilates was 1.57 cm/min. A heat girdle near the top of the source leaf sheath blocked most transport, which indicated that transport was primarnly through the phloem. Mass transfer rates for amino acids were only 3% as great as that for sucrose, suggesting different mechanisms of entry for sucrose than for amino acids into the phloem. The higher percentage of CO2 assimilates mobilized to the sink leaf was attributed to the greater surface area of minor veins accessible to loading, as compared to those compounds supplied via an abraded spot. Serine was extensively metabolized in the source leaf, and radioactive products in the sink leaf mirrored those in the source leaf. Most radioactivity of lysine and leucine remained within these compounds in the source, path, and sink tissues. We conduded that there was no barrier to entry of amino acids into the phloem and transport therein. Data do not suggest a specific mechanism for entry of amino acids into the phloem. ity in the amino acid fraction of the flag leaf blade or its sheath (Cataldo, Schrader, and Peterson, unpublished data). The possible existence of some mechanism for limiting the entry of amino acids into the transport path was suggested by this observation.There are few previous reports on amino acid transport in the phloem of gramineous species. Yamaguchi and Islam (22) applied several 14C-labeled amino acids to the first leaf of barley (Hordeum vulgare L.) seedlings. Whole plant autoradiography after 24 hr revealed radioactivity in the expanding second leaf and the roots, which indicated probable phloem mobility. With the exception of applied valine, the translocated products were not identified. Amounts of radioactivity extracted from the bud varied among different applied amino acids, suggesting greater transport of some than of others.The objective of our experiments was to determine if several amino acids were able to enter the phloem with equal facility, and be transported from a source to a sink tissue. We applied radioactive amino acid solutions to an abraded spot on a fully expanded source leaf, and monitored an expanding sink leaf with a GM tube for the arrival of radioactivity. We selected L-serine, an amino acid which was rapidly labeled during photosynthesis in '4C02, and L-leucine and L-lysine, amino acids in which label had not been detected (Cataldo et al., unpublished data). The movement of sucrose, which is known to be...

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Section: Discussionmentioning

confidence: 98%

Long Distance Translocation of Sucrose, Serine, Leucine, Lysine, and Carbon Dioxide Assimilates

Peterson¹,

Housley²,

Schrader³

1977

Plant Physiol.

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“…One carrier is specific for glycine and certain aliphatic amino acids (L-alanine, L-leucine, L-isoleucine, and L-valine); another carries L-serine, L-threonine, and Lmethionine (15). Apparently, a third carrier that transports dicarboxylates is actually located in the inner of the two chloroplast limiting membranes and it can translocate aspartate and glutamate (7,8).…”

mentioning

confidence: 99%

“…Carrier-mediated amino acid uptake across the two limiting membranes of chloroplasts has recently received considerable attention (7,8,15). One carrier is specific for glycine and certain aliphatic amino acids (L-alanine, L-leucine, L-isoleucine, and L-valine); another carries L-serine, L-threonine, and Lmethionine (15).…”

mentioning

confidence: 99%

Amino Acid Uptake by Pea Leaf Fragments

Cheung

Nobel²

1973

Plant Physiol.

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Amino acid uptake into leaf fragments of Pisum sativum depended on metabolism. Glycine uptake was optimal at 30 C and could be supported by respiration and by photosynthesis. Based on studies with an electron flow cofactor, inhibitors, and uncouplers, the energy source for glycine uptake was apparently ATP.The energy-dependent transport of glycine was mediated by a carrier that had a broad specificity for neutral and positively charged L-amino acids. It readily translocated 15 such L-amino acids into the cells, but had a very low affinity for L-aspartate, L-glutamate, D-amino acids, and a-aminoisobutyrate. The Ki for competitive inhibition of glycine uptake by another amino acid was equal to the Km for the uptake of that competing species.

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“…The reflection coefficients for certain aldopentoses and amino acids are also low for another organelle. Specifically, the ~j's for pea chloroplasts are 0.00 for D-ribose, 0.43 for D-xylose, 0.47 for D-lyxose, and 0.01 to 0.06 for glycine, L-alanine, L-threonine, L-phenylalanine and L-methionine [16,17,23]. A carrier for aldopentoses and two others for amino acids occur in the limiting membranes of pea chloroplasts, which facilitate the penetration of these compounds and thereby keep their reflection coefficients low [16,23].…”

Section: Discussionmentioning

confidence: 99%

“…Use of reflection coefficients to study the permeability of organelles has recently been successfully applied to chloroplasts [16,17,23]. Here we will use this new approach based on irreversible thermodynamics to examine mitochondria.…”

mentioning

confidence: 99%

Mitochondrial permeability for alcohols, aldoses, and amino acids

Nobel

1973

J. Membrain Biol.

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Summary. Mitochondria isolated from potato tubers were placed in solutions containing various alcohols, aldoses, or neutral amino acids. Based on the osmotic responses in the different media, the reflection coefficients and hence the relative permeabilities of the nonelectrolytes could be determined. The reflection coefficients (afs) of the potato tuber mitochondria for alcohols became progressively larger as hydroxymethyl groups were added to the molecule, viz. If we increase the osmotic pressure in a solution bathing cells or organelles, water will flow out of them. Such osmotic responses are often described by the Boyle-Van't Heft relation, which refers to the equilibrium situation when the internal osmotic pressure (re ~) equals the external osmotic pressure (n~ By the Boyle-Van't Hoff relation, the osmotic pressure (~~ or rc ~) times the volume of the aqueous compartment within the cell or organelle is constant at a given temperature. If we increase the concentration of some solute in the bathing solution and thereby increase n ~ water will leave the internal aqueous compartment so that n~ again becomes the same as n ~ The classical Boyle-Van't Hoff relation presupposes that the membranes are permeable only to water [15].19 J. Membrane Biol. 12

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Two Amino-acid Carriers in Pea Chloroplasts

Cited by 13 publications

References 10 publications

Long Distance Translocation of Sucrose, Serine, Leucine, Lysine, and Carbon Dioxide Assimilates

Long Distance Translocation of Sucrose, Serine, Leucine, Lysine, and Carbon Dioxide Assimilates

Amino Acid Uptake by Pea Leaf Fragments

Mitochondrial permeability for alcohols, aldoses, and amino acids

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