Nitrogen metabolism in leaves

McKee, H. S.

doi:10.1007/978-3-642-94733-9_25

Cited by 14 publications

(5 citation statements)

References 130 publications

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“…But a simpler way in which the tryptophan levels could be elevated is by the degradation of proteins. The free amino-acid pools in plant tissues represent only a small proportion, often less than 5 yo, of the total amino acids which can be released by the hydrolysis of the proteins (Allsop, 1948;McKee, 1958). In living cells, where there is a steady turnover of proteins, proteolysis presumably contributes to the steady-state pools of free amino acids.…”

Section: The Biochemical Control Of Auxin Productionmentioning

confidence: 99%

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The Production of Hormones in Higher Plants

Sheldrake¹

1973

Biological Reviews

106

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SUMMARY Although much is known about the effects of plant hormones and their role in the control of growth and differentiation, little is known about the way in which hormone production is itself controlled or about the cellular sites of hormone synthesis. The literature on hormone production is discussed in this review in an attempt to shed some light on these problems. The natural auxin of plants, indol‐3yl‐acetic acid (IAA) is produced by a wide variety of living organisms. In animals, fungi and bacteria it is formed as a minor by‐product of tryptophan degradation. The pathways of its production involve either the transamination or the decarboxylation of tryptophan. The transaminase route is the more important. In higher plants auxin is also produced as a minor breakdown product of trypto phan, largely via transamination. In some species decarboxylation may occur but is of minor importance. Tryptophan can also be degraded by spontaneous reaction with oxidation products of certain phenols. The unspecific nature of the enzymes involved in IAA production and the probable importance of spontaneous, nonenzymic reactions in the degradation of tryp to phan make it unlikely that auxin production from tryptophan can be regulated with any precision at the enzymic level. The limiting factor for auxin production is the availability of tryptophan, which in most cells is present in insufficient quantities for its degradation to occur to a significant extent. Tryptophan levels are, however, considerably elevated in cells in which net protein breakdown is taking place as a result of autolysis. An indole compound, glucobrassicin, occurs in Brassica and a number of other genera. It breaks down readily to form a variety of products including indole aceto‐nitrile, which can give rise to IAA. There is, however, no evidence to indicate that glucobrassicin is a precursor of auxin in vivo. Conjugates of IAA, e.g. IAA‐aspartic acid and IAA‐glucose, are formed when IAA is supplied in unphysiologically high amounts to plant tissues. These and other IAA conjugates occur naturally in developing seeds and fruits. There is no persuasive evidence for the natural occurrence of IAA‐protein complexes. Tissues autolysing during prolonged extraction with ether produce IAA from tryptophan released by proteolysis. IAA is produced in considerable quantities by autolysing tissues in vitro. During the senescence of leaves proteolysis results in elevated levels of trypto phan. Large amounts of auxin are produced by senescent leaves. Coleoptile tips have a vicarious auxin economy which depends on a supply of IAA, IAA esters and other compounds closely related to IAA from the seed. These move acropetally in the xylem and accumulate at the coleoptile tip. The production of auxin in coleoptile tips involves the hydrolysis of IAA esters and the conversion of labile, as yet unidentified compounds, to IAA. There is no evidence for the de novo synthesis of IAA in coleoptiles. Practically all the other sites of auxin production are sites of both meristematic ...

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Section: The Biochemical Control Of Auxin Productionmentioning

confidence: 99%

“…In living cells, where there is a steady turnover of proteins, proteolysis presumably contributes to the steady-state pools of free amino acids. But when net protein degradation occurs, €or example in senescent leaves, the levels of free amino acids are elevated considerably (Chibnall, 1939;McKee, 1958).…”

Section: The Biochemical Control Of Auxin Productionmentioning

confidence: 99%

The Production of Hormones in Higher Plants

Sheldrake¹

1973

Biological Reviews

106

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“…The classical investigations by Prianishnikov show that, when carbohydrates are supplied, asparagine accumulates in the darkgrown seedlings (McKee 1962). Viets, Whitehead and Moxon (1947) and others have confirmed the accumulation of amides.…”

Section: Introductionmentioning

confidence: 89%

“…Apparently the role of amides is to detoxicate the ammonia by combining it with the distal carboxyl group of aspartic and glutamic acids. The appearance of both ammonia and amino acids is a consequence of the protein breakdown in the dark, caused by the lack of carbohydrates for respiration (see a review of McKee 1958).…”

Section: Introductionmentioning

confidence: 99%

Free Amino Acids in the Leaves of Salvinia natans and Azolla filiculoides Grown in Light and Dark

Lähdesmäki

1968

Physiologia Plantarum

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Free amino acids were determined quantitatively by thin-layer chromatography and identified by various chromatographic methods in the leaves of two floating water ferns. Special interest was paid to the amount of y-amino butyric acid.Water soluble nitrogen compounds increase in the leaves of botb plants during the growth of three to four weeks in darkness. Compounds especially accumulating are ammonia and the amides asparagine and glutamine. The amount of most proper amino acids is reduced in the dark, except y-amino butyric acid, which, in addition to amides, is the main amino compound increasing in darkness. 0.1 M HCl extracts the greatest amount of nitrogen compounds of low molecular weight from the dried leaves of the experimental plants. If we denote the amount of the dissolved amino compounds as tOO per cent, we can say that water extracts 96 per cent of the amino compounds, and that an 80 per cent ethanol solution extracts 79 per cent of these compounds. P.hysiol. Plant., 21,196S [1097] '

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“…The rapid onset of senescence in nitrogenstarved plants is not surprising in view of the large proportion of the element that is fixed in cell components -especially protein -so that major disruption may be expected to follow its mobilization and withdrawal (Girardin et al 1985 , 6). Even in the leaves of plants that have not been nitrogen-starved the decrease in protein content in senescent leaves is due less to inability to synthesize it than to a drain of soluble nitrogen compounds to the developing newer organs of the plant (Walkley 1940;McKee 1958).…”

Section: (Ii) Responses To Phosphorus and Nitrogen Deficiencymentioning

confidence: 99%

The effects of severe mineral nutrient deficiencies on the demography of leaves

1987

Proc. R. Soc. Lond. B.

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Plants of flax (Linum usitatissimum) were grown in sand culture and provided with only deionized water or full nutrient solution or with nutrient solutions lacking nitrogen, phosphorus, potassium or calcium. The plants were exposed to these different nutritional régimes throughout their growth cycle, or the régimes were changed after 31 days of growth. The responses to the various treatments were measured by demographic methods, treating the foliage of a plant as a population of leaves. Leaves were allocated to cohorts as they unfolded so that leaf birth rates and death rates could be determined and survivorship could be related to age. The procedure allowed the process of senescence to be distinguished from ageing. The birth rate of leaves (as a measure of the activity of shoot apices) appeared to regulate the death rate of leaves on the same plant, presumably by determining in some way when minerals were withdrawn from older leaves. The linkage between birth and death rates was closest when potassium was deficient, and this is attributed to the high mobility of potassium in the plants. On calcium-deficient plants the older leaves had very long lives and low, eventually zero, leaf birth rates. Plants grown in deionized water produced very few leaves and leaf birth rate rapidly fell to zero but a few of the leaves had exceptionally long lives. The effects of mineral deficiencies on leaf demography are discussed in relation to known differences in the roles and mobilities of the various elements in plants and their different influences on leaf senescence. It is argued that the loss of nutrients from older leaves is a cause of, rather than a result of, leaf senescence.

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Nitrogen metabolism in leaves

Cited by 14 publications

References 130 publications

The Production of Hormones in Higher Plants

The Production of Hormones in Higher Plants

Free Amino Acids in the Leaves of Salvinia natans and Azolla filiculoides Grown in Light and Dark

The effects of severe mineral nutrient deficiencies on the demography of leaves

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