Pod removal responsive change in phytohormones and its impact on protein degradation and amino acid transport in source leaves of Brassica napus

To investigate the regulatory role of ethylene in the source-sink relationship for nitrogen remobilization, short-term effects of treatment with different concentrations (0, 25, 50, and 75 ppm) of ethephon (2-chloroethylphosphonic acid, an ethylene inducing agent) for 10 days (EXP 1) and long-term effects at 20 days (Day 30) after treatment with 100 ppm for 10 days (EXP 2) on protein degradation and amino acid transport in foliar sprayed mature leaves of Brassica napus (cv. Mosa) were determined. In EXP 1, endogenous ethylene concentration gradually increased in response to the treated ethephon concentration, leading to the upregulation of senescence-associated gene 12 (SAG12) expression and downregulation of chlorophyll a/b-binding protein (CAB) expression. Further, the increase in ethylene concentration caused a reduction in protein, Rubisco, and amino acid contents in the mature leaves. However, the activity of protease and expression of amino acid transporter (AAP6), an amino acid transport gene, were not significantly affected or slightly suppressed between the treatments with 50 and 75 ppm. In EXP 2, the enhanced ethylene level reduced photosynthetic pigments, leading to an inhibition of flower development without any pod development. A significant increase in protease activity, confirmed using in-gel staining of protease, was also observed in the ethephon-treated mature leaves. Ethephon application enhanced the expression of four amino acid transporter genes (AAP1, AAP2, AAP4, and AAP6) and the phloem loading of amino acids. Significant correlations between ethylene level, induced by ethephon application, and the descriptive parameters of protein degradation and amino acid transport were revealed. These results indicated that an increase in ethylene upregulated nitrogen remobilization in the mature leaves (source), which was accompanied by an increase in proteolytic activity and amino acid transport, but had no benefit to pod (sink) development.

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Effects of cimaterol on protein synthesis, protein degradation, amino acid transport and acetate oxidation in sheep external intercostal muscle

Nutrition Research ◽

10.1016/s0271-5317(05)80091-0 ◽

1988 ◽

Vol 8 (11) ◽

pp. 1287-1296 ◽

Cited By ~ 3

Author(s):

M.A. Wilson ◽

C. Zhong ◽

N.E. Forsberg ◽

R.H. Dalrymple ◽

C.A. Ricks

Keyword(s):

Protein Synthesis ◽

Amino Acid ◽

Protein Degradation ◽

Amino Acid Transport ◽

Intercostal Muscle ◽

Acid Transport ◽

Acetate Oxidation

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N use efficieny and amino acid transport in rape (Brassica napus L.)

Plant Nutrition ◽

10.1007/0-306-47624-x_12 ◽

2001 ◽

pp. 28-29 ◽

Cited By ~ 1

Author(s):

J. Tilsner ◽

G. Lohaus

Keyword(s):

Amino Acid ◽

Brassica Napus ◽

Amino Acid Transport ◽

Acid Transport ◽

Brassica Napus L ◽

N Use

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Protein turnover, growth and proliferation in CHO cells. Variation within and between mutant classes for salvage pathway enzymes

Biochemical Journal ◽

10.1042/bj2820049 ◽

1992 ◽

Vol 282 (1) ◽

pp. 49-57 ◽

Cited By ~ 2

Author(s):

J M Gunn ◽

M R Brancheau

Keyword(s):

Protein Synthesis ◽

Amino Acid ◽

Protein Degradation ◽

Amino Acid Transport ◽

Cho Cells ◽

Protein Turnover ◽

Transport Protein ◽

Clonal Variation ◽

Acid Transport ◽

Salvage Pathways

We have examined the clonal variation in rates of amino acid transport, protein synthesis, protein degradation, growth and proliferation for CHO cells with mutations in the purine and pyrimidine salvage pathways. First we compared three clonal cell lines, each with a different mutation, with the heterozygous parental line AT3-2. Overall, the correlation between rates of protein turnover, growth and proliferation was excellent. The slower growth and proliferation of one mutant, AB3 (TK-, APRT-), is explained by a low intrinsic rate of protein synthesis coupled with a smaller response in rates of amino acid transport, protein synthesis and protein degradation to insulin, serum and dexamethasone. Secondly, we compared seven aza-adenine-resistant and 14 thioguanine-resistant mutants of AT3-2 and found significant differences in control and insulin-stimulated rates of protein turnover both within and between mutant populations. A significant difference between the populations was unexpected because each individual cell line was cloned from a spontaneous pre-existing mutation in AT3-2, and each population should have the same average rate. Remarkably, all 24 mutants had lower rates of protein synthesis than AT3-2. We cannot explain the data solely in terms of mutations in the salvage pathways. Rather, we propose that the mutant survivors have randomly down-regulated the intrinsically fixed growth factor-regulated pathways of protein turnover, resulting in a broad spectrum of lower metabolic rates.

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Effects of insulin and anchorage on hepatocytic protein metabolism and amino acid transport

Journal of Cell Science ◽

10.1242/jcs.48.1.1 ◽

1981 ◽

Vol 48 (1) ◽

pp. 1-18

Author(s):

A. Poli ◽

P.B. Gordon ◽

P.E. Schwarze ◽

B. Grinde ◽

P.O. Seglen

Keyword(s):

Protein Synthesis ◽

Amino Acid ◽

Protein Degradation ◽

Amino Acid Transport ◽

Protein Synthesis Inhibitor ◽

Acid Transport ◽

Synthesis Inhibitor ◽

Insulin Effect ◽

High Amino Acid ◽

Amino Acid Concentrations

Insulin partially inhibits endogenous protein degradation in isolated hepatocytes. The inhibition seems to specifically affect the lysosomal pathway of degradation, since it is not additive to the effects of lysosome inhibitors such as propylamine and leupeptin. The insulin effect is potentiated by intermediate concentrations of amino acids, but is largely abolished at high amino acid concentrations which suppress degradation maximally, suggesting that the hormone may exert its effect indirectly by acting upon the more basal amino acid control mechanism. Glucagon, which stimulates protein degradation, similarly displays its effect only in the presence of intermediate amino acid concentrations. The insulin inhibition is not affected by the aminotransferase inhibitor, aminooxyacetate, indicating that it is not due to interference with amino acid metabolism. Protein synthesis furthermore does not seem to be required, since a significant insulin effect can be seen in the presence of the protein synthesis inhibitor, cycloheximide. The issue is, however, complicated by the fact that cycloheximide itself inhibits protein degradation to approximately the same extent as does insulin. Insulin stimulates uptake of the amino acid alpha-aminoisobutyrate (AIB), but not the uptake of valine, indicating a specific stimulation of ‘A’-type transport. Cycloheximide similarly stimulates AIB uptake, without completely obfuscating the transport effect of insulin. Neither protein synthesis, protein degradation, amino acid transport, nor the effects of insulin were affected by cell-to-substratum anchorage (attachment and spreading) in any detectable way.

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