Aspartic‐C<sup>14</sup> Acid Metabolism in Leaves, Roots, and Stems

Naylor, Aubrey W.; Rabson, R.; Tolbert, N. E.

doi:10.1111/j.1399-3054.1958.tb08250.x

Cited by 41 publications

(19 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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). Besides their entry into chloroplasts, amino acids can also be absorbed by isolated leaf cells (5), leaf slices (17)(18)(19), and excised leaves (9,10,(21)(22)(23). Presently, the only evidence for carrier mediation in amino acid uptake by such photosynthetic cells is for an unnatural amino acid analog, AIB2 (18).…”

mentioning

confidence: 99%

Amino Acid Uptake by Pea Leaf Fragments

Cheung

Nobel²

1973

Plant Physiol.

View full text Add to dashboard Cite

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.

show abstract

mentioning

confidence: 99%

Amino Acid Uptake by Pea Leaf Fragments

Cheung

Nobel²

1973

Plant Physiol.

View full text Add to dashboard Cite

show abstract

“…The action of homoserine in inhibiting growth is difficult to explain, since it has no known effect on any enzyme of the pathway. In some plants, such as germinating peas (14), homoserine can accumulate to high concentrations. Growth inhibition by lysine or threonine is probably due to feedback inhibition of aspartokinase as was shown in the isolated enzyme (Fig.…”

Section: Discussionmentioning

confidence: 99%

Aspartokinase in Lemna minor L

Wong¹,

Dennis²

1973

Plant Physiol.

View full text Add to dashboard Cite

The growth of Lemna minor was followed by means of frond number, fresh weight, and dry weight measurements in the presence of various amino acids at a concentration 0.25 mM. Lysine inhibited growth but not to the same extent as threonine and homoserine. Isoleucine was also an inhibitor of growth. In the presence of methionine there was some growth for 2 to 3 days, but by 5 days most of the plants appeared to be dead. When lysine and threonine were added together, there was no growth at all, and the plants were dead after 5 days. This effect of lysine + threonine could be reversed by adding methionine or homoserine to the growth medium.The isolated aspartokinase from Lemna showed inhibition by lysine and higher concentrations of threonine. When these amino acids were added together at low concentrations, there was a concerted inhibition of the aspartokinase. It is suggested that some effects of amino acids on the growth of L. minor can be explained on the basis of a concerted feedback control of aspartokinase.The amino acids isoleucine, threonine, homoserine, methionine, and lysine are all derived from aspartate in bacteria and in plants (4-6, 14, 15 MATERIALS AND METHODS Growth of L. minor. Sterile fronds of L. minor were obtained by the method of Hillman (10). The plants were grown under sterile conditions in 250-ml Erlenmeyer flasks, each containing 100 ml of the following growth medium: MgSO, 2 mM; Ca(NOJ),, 7 mm; KNO,, 5 mM; KHaPO, 2 mM; sucrose, 10 mM; FeNaEDTA, 38 1M; H.BO., 46 ,iM; MnCl,, 9.2 FiM; CUSO4, 3.2 ,uM; ZnSO4, 1.8 p,m; Na,MoO4, 4.1 lAm; CoClk,3 ,m; and each of the L-amino acids (0.25 mM) tested. The final pH was 6.0. In all cases, sterile conditions were achieved by autoclaving the growth medium at 15 p.s.i. for 15 min and by transferring the Lemna in a sterile cabinet.Usually, one plant consisting of three to four fronds was transferred to the growth medium, and the cultures were grown in a growth cabinet of 26 C and in continuous light with an intensity of 1000 ft-c. The growth of the plants was determined by the number of fronds, the fresh weight, and dry weight. All tests were run in duplicates and the experiments were repeated three times. Preparation of Aspartokinase. Fronds of L. minor were harvested, washed with distilled water, and dried of excess water. They were ground in a Waring Blendor for 1 min with acetone precooled to -15 C. The homogenate was filtered through a Biichner funnel and washed thoroughly with cold acetone until the filtrate was colorless. The slightly green powder was dried and then stored at -15 C.The acetone powder was suspended in 0.05 M TES (pH 8.0) in a ratio of 1:20 w/v. After stirring for 30 min the suspension was filtered through eight layers of cheesecloth and then centrifuged at 20,000g for 20 min. The crude extract was fractionated with saturated ammonium sulfate, and the frac-

show abstract

“…Bilinski aindI McConnell (2), V-ogel (35), and Navlor, Rabson and Tol,bert (24) concluided that threoinine was synthesized from aspartate in plants.…”

Section: Discussionmentioning

confidence: 99%