Antagonisms between Kinetin and Amino Acids: Experiments on the Mode of Action of Cytokinins.
TL;DR: In this article, the maintenance of chlorophyll in darkened first leaves of oats was used as a bioassay for cytokinins in pea (Pisum sativum) roots.
Abstract: The maintenance of chlorophyll in darkened first leaves of oats was used as a bioassay for cytokinins in pea (Pisum sativum) roots. No cytokinin was found (in contrast with earlier reports on sunflower roots); however, the extracts contained two or more substances antagonistic to cytokinin, i. e., promoting the yellowing in this test. Because the most active of these appeared to be an amino acid, individual amino acids were examined for their ability to modify the greening reaction. As a result, l-serine was found to have these properties. It promotes yellowing whether the greening agent is kinetin, indoleacetic acid, or adenine; it is, therefore, not functioning as a specific cytokinin antagonist. Its action is due to promoting proteolysis. Its d-isomer is inactive. l-Arginine, which alone does not cause chlorophyll retention and only weakly inhibits proteolysis, strongly antagonizes the action of l-serine, and thus prevents the yellowing; this effect is specific, and the only other effective serine antagonist found, although much weaker, is l-threonine. The action of arginine is not due to its preventing serine uptake, but rather the action parallels the serine-arginine antagonism previously described for nitrate reductase induction. A novel interpretation of the effect of amino acids on this process is therefore put forward. In studies of the RNase in darkened oat leaves, serine was found to have no effect; however, kinetin strongly inhibits the normal rise in the level of RNase which occurs in the isolated leaf. Kinetin also maintains the integrity of the cell membranes. A variety of evidence leads to the conclusion that the primary action of kinetin on the leaf is to inhibit proteolysis, rather than to promote protein synthesis.
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TL;DR: In this review, different classes of senescence-related genes are defined and progress towards isolating such genes is reported and a range of internal and external factors which appear to cause leafsenescence is considered.
Abstract: SUMMARY
Leaf senescence is a hiphly-controlled sequence of events comprising the final stage of development. Cells remain viable during the process and new gene expression is required. There is some similarity between senescence in plants and programmed cell death in animals. In this review, different classes of senescence-related genes are defined and progress towards isolating such genes is reported. A range of internal and external factors which appear to cause leaf senescence is considered and various models for the mechanism of senescence- initiation are described. The current understanding of senescence at the wrganelle and molecular levels is presented. Finally, same ideas are mooted as to why senescence occurs and why it should be studied further.
734 citations
TL;DR: The role played by accumulated amino acids in plants varies from acting as osmolyte, regulation of ion transport, modulating stomatal opening, and detoxification of heavy metals to affecting synthesis and activity of some enzymes, gene expression, and redox-homeostasis.
Abstract: Plants subjected to stress show accumulation of proline and other amino acids. The role played by accumulated amino acids in plants varies from acting as osmolyte, regulation of ion transport, modulating stomatal opening, and detoxification of heavy metals. Amino acids also affect synthesis and activity of some enzymes, gene expression, and redox-homeostasis. These roles played by amino acids have been critically examined and reviewed.
507 citations
TL;DR: The senescence-promoting substance of wormwood as detected by the oat (Avena sativa L. cv "Victory") leaf assay has been identified as (-)-methyl jasmonate, methyl (1S, 2R)-3-oxo-2-(2'-cis-pentenyl)-cyclopentane-1-acetate, by gas-liquid chromatography-mass spectrometry and optical rotatory dispersion.
Abstract: The senescence-promoting substance of wormwood (Artemisia absinthium L.) as detected by the oat (Avena sativa L. cv “Victory”) leaf assay has been identified as (−)-methyl jasmonate, methyl (1S, 2R)-3-oxo-2-(2′-cis-pentenyl)-cyclopentane-1-acetate, by gas-liquid chromatography-mass spectrometry and optical rotatory dispersion. Its senescence-promoting effect was much stronger than that of abscisic acid, and even at such a low concentration as 1 to 2.5 micrograms per milliliter, it could completely eliminate the anti-senescence action of 2 micrograms per milliliter kinetin. Comparing the biological activity of the (−)- with the (±)-forms of methyl jasmonate, it seemed that only the (−)-form was biologically active.
444 citations
Book•
01 Jan 1989
TL;DR: The dominant objective of Biochemistry and Physiology of Plant Hormones is to summarize, in a reasonably balanced and comprehensive way, the current state of fundamental knowledge regarding the major kinds of hormones and the phytochrome pigment system.
Abstract: Biochemistry and Physiology oj Plant Hormones is intended primarily as a textbook or major reference for a one-term intermediate-level or advanced course dealing with hormonal regulation of growth and development of seed plants for students majoring in biology, botany, and applied botany fields such as agronomy, forestry, and horticulture. Additionally, it should be useful to others who wish to become familiar with the topic in relation to their principal student or professional interests in related fields. It is assumed that readers will have a background in fundamental biology, plant physiology, and biochemistry. The dominant objective of Biochemistry and Physiology oj Plant Hor mones is to summarize, in a reasonably balanced and comprehensive way, the current state of our fundamental knowledge regarding the major kinds of hormones and the phytochrome pigment system. Written primarily for students rather than researchers, the book is purposely brief. Biochemical aspects have been given priority intentionally, somewhat at the expense of physiological considerations. There are extensive citations of the literature-both old and recent-but, it is hoped, not so much documentation as to make the book difficult to read. The specific choices of publications to cite and illustrations to present were made for different reasons, often to illustrate historical develop ment, sometimes to illustrate ideas that later proved invalid, occasionally to exemplify conflicting hypotheses, and most often to illustrate the current state of our knowledge about hormonal phenomena."
334 citations
TL;DR: The principal metabolites formed from zeatin by the roots of intact Z. mays seedlings were adenosine-5′-phosphate, zeat in riboside, adenine,Adenosine and an unknown compound termed Y.mays which was isolated and identified as 9-glucosylzeatin.
Abstract: [3H]Zeatin was supplied through the transpiration stream to radish (Raphanus sativus L.) seedlings with roots excised. Formation of dihydrozeatin was not detected but numerous other metabolites were formed, including adenine, adenosine, AMP, zeatin riboside and zeatin riboside-5′-monophosphate. However, in labelled seedlings which had been left in water for 15 h, an unknown compound (raphanatin) was the dominant metabolite and accounted for about 25% of the total radioactivity extracted. A procedure for the isolation of this metabolite was devised and yielded 70 μg from 1600 seedlings. Raphanatin was characterized by mass and ultraviolet spectra and has been identified as 7-glucosylzeatin. It is an active and very stable metabolite which was located mainly in the cotyledon laminae and may be a storage form of the hormone. In contrast, labelled nucleotides, the other major metabolites of zeatin, were largely confined to the hypocotyls and petioles. Zeatin riboside-5′-monophosphate was the dominant metabolite in hypocotyls of de-rooted seedlings supplied with zeatin for 0.5–2 h. The majority of the radioactivity in the xylem sap was due to zeatin, but about 10% was present as zeatin riboside; nucleotides accounted for less than 10% of the radioactivity and labelled raphanatin was not detected.
308 citations
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113 citations
TL;DR: Activity so defined was shown by a variety of microorganisms, such as yeast, Penicillium qlaucum, and Asperqillus niqer, and by Bacillus coli, Bacillus proteus, and staphylococcus and it is apparent that these ester bonds may be broken without the separation of phosphoric acid from any of the four nucleotides.
54 citations
TL;DR: Brown as mentioned in this paper reported that ammonium sulphate, aspartic acid, glutamic acid, potassium nitrate and asparagine, at concentrations supplying equivalent quantities of nitrogen, showed progressive increases in their capacity to increase the dry weight and nitrogen content of barley embryos cultured for a period of one week.
Abstract: Brown (I906) has described the results of an early investigation on the ability of mature, isolated cereal embryos to utilize organic forms of nitrogen. He reported that ammonium sulphate, aspartic acid, glutamic acid, potassium nitrate and asparagine, at concentrations supplying equivalent quantities of nitrogen, showed progressive increases in their capacity to increase the dry weight and nitrogen content of barley embryos cultured for a period of one week. Out of these nitrogen sources only asparagine produced an increase in the growth in length of the roots, while all, with the possible exception of ammonium sulphate, produced an increase in the length attained by the shoot system. Phenylalanine, tyrosine and leucine were distinctly inhibitory to growth. So far as the author is aware, there have been no other recent reports of comparable studies on the ability of isolated cereal embryos to utilize organic forms of nitrogen for growth. The purpose of the present investigation was to assess the value of amino acids as sources of nitrogen for the growth of mature oat embryos isolated from their endosperm. Particular attention has been given to interactions occurring between amino acids in their effects on the growth of the embryos. A note on some of the experiments described has appeared elsewhere (Harris, I953a).
43 citations
TL;DR: No significant changes in the composition of chromatin were found when the excised barley leaves were floated on water or on kinetin solution in the dark, but increases in the activities ofchromatin associated ribonuclease and deoxyribonucleasing in leaves floated onWater drastically suppressed the increases in these enzymes.
42 citations