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The Interaction of Auxin and Light in the Growth Responses of Plants

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Abstract

The information presented above suggests that many heretofore unrelated processes which are affected by both light and auxin, including red light induced growth of the Avena coleoptile, the photoperiodic response, leaf expansion, and seed germination, may all have their basis in a common mechanism. All of these processes have approximately the same action spectra with effective peaks at ca. 660O, all are freely reversed by infra-red light, and all appear to be auxin-dependent. It has been shown that in the case of the Avena coleoptile, red light appears to exert its effect through the generation of an auxin-receptive entity, E, within the plant and that infra-red light acts to decompose the active complex ES into an auxin-non-receptive entity. In the coleoptile these processes also proceed thermally although at reduced rates. This is particularly true of the infra-red mediated decomposition of ES. The present paper calls attention to the fact that a concept of the cyclic interconversion of auxin-non-receptive precursor, auxin receptor, and receptor-auxin complex by light and dark can be applied without violence to the interpretation of these varied plant responses. The concept presented, that of the photo-cycle, at once suggests a variety of experimental approaches which may be used to further test its validity in each individual instance.

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... Recently, LIVERMAN and BONNER (41) demonstrated that the growth promoting effect of red light on Avena coleoptile sections cannot be reversed by infrared, unless auxin is added. In the latter case, the promotion by red light is even stronger, and this extra growth can be inhibited by subsequent irradiation with infrared. ...
... These findings will be discussed in greater detail in Chapter VIII. LIVERMAN and STARR (unpublished, quoted in [41]) demonstrated the same phenomenon for leaf growth in Phaseolus. ...
... Several other reactions of the same type have since been described. LEOPOLD and GUERNSEY (40) described experiments in which light induced changes of the respiratory rate in photoperiodically sensitive plants were regulated by a reversible photoreaction of the same type; LIVERMAN and BONNER demonstrated a similar reversibility in light-dependent growth stimulation of Arena coleoptile sections (41). ...
Thesis
Light of various spectral regions (at low or high intensities) supplemented a short day (SD) in white light, or was used alone at high intensity. Two types of relation of wave length to photoperiodic reaction were found: Crucifers were sensitive to blue and infrared (even SD exposure promoted elongation and flowering) and did not respond to 520-700 mμ(so this region inhibited flowering in white light despite its blue component); other plants, e.g. Cosmos bipinnatus and Spinacia oleracea were sensitive to 520-700 mμand showed little or no response to blue and infrared. Flowering of day-neutral plants was not affected by wave length of supplementary light. All species showed strong response to supplementary blue and infrared radiation, by excessive elongation of a part such as internodes, leaves or petioles. The rate depended on light intensity and the process was inhibited by red or green. Light of restricted spectral regions also induced strong formative and biochemical effects. Infrared counteracted red light. 'Monochromatic' light of high intensity perhaps regulated auxin level, whereas the supplementary light might effect its activity or sensitivity to auxin.<p/
... First, the absolute amount of auxin translocated is approximately the same with or without red light treatment, although red light reduces the total auxin produced by a factor of 2. If the amount of auxin in the non-treated plants is above the linear portion of the curve plotting curvature as a function of auxin concentration difference, one would not expect these plants to curve as much as those given red light. Second, Liverman and Bonner (1953) have shown that at least in oat coleoptiles there is yet another phytochromemediated reaction that might affect phototropic sensitivity: oat coleoptile sections exposed to red light are significantly more responsive to applied auxin than those kept in the dark. If the same situation is true for corn, the plants untreated with red light might actually be less sensitive to their own endogenous auxin, and less curvature might be expected on this basis alone. ...
... In the present paper, 15 min red light is only sufficient to induce a small part of the whole sensitivity change, with at least an hour necessary for a maximum effect, and Curry (1957) reported that 10 min red light only caused a 10% shift. Perhaps the shift she found is a reflection of the sort of phytochrome-mediated reaction suggested by Liverman and Bonner (1953), a red-induced increase in sensitivity of the tissue to auxin. If this reaction occurred more rapidly than the hypothesized reaction involving pigment changes, one should find only an increase in the amount of curvature obtainable from a given dosage, but no shift in the position of the dosage-response curve. ...
... The slight change in shape of the dosage-response curve as a consequence of red irradiation, described previously (22), could be a reflection of the change in auxin concentration. The red light-induced change in tissue sensitivity to auxin, described by Liverman and Bonner (15), might also contribute to the change in shape noted above, but cannot account for the sensitivity changes. ...
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Article
In an earlier paper (Mohr 1957) it was described that the formation of anthocyanin and the inhibition of lengthening of the hypocotyl of dark grown seedlings (Sinapis alba) is governed by the action of two photomorphogenic action systems. The one system is the well known “reversible red far-red reaction system” (low energy reaction), the other one is a high energy reaction system which can be called — in reference to the action peaks in the far-red and in the blue — “blue far-red reaction system”. The chemical nature of the absorbing pigments is still unknown. In the present paper another photomorphogenic response of the young dark grown seedlings ofSinapis alba, the light dependent formation of unicellular hairs from epidermal cells of the hypocotyl, has been investigated. It has been shown that this response is also governed by these two reaction systems. These systems have been physiologically separated. Experiments have been presented which evaluate the importance of the assumption that the red absorbing pigment of the reversible red far-red pigment system is reformed from a precursor when the pigment present before irradiation is transformed into the far-red absorbing pigment by an irradiation with red.
Article
Experiments with Salvia occidentalis (SDP) and Hyoscyamus niger (LDP) demonstrated that at least two photoperiodic reactions are involved in the process leading to a long-day effect. The main-light-period reaction is more sensitive to near infra-red and blue light than to red or green light. The effect of near infra-red and blue light can be antagonized by red light. The nightbreak reaction, promoted by red light, is nullified by a relatively short exposure to near infra-red or blue light.Experiments with various plant species on the elongation of internodes have shown that at relatively low intensities red light is more inhibitive than blue light. At relatively high intensities blue light is the most inhibiting spectral region. The inhibiting effect of red light on the elongation of hypocotyls of light-grown gherkin seedlings is antagonized by a subsequent exposure to near infra-red or blue light. The inhibiting effect of red light on the hypocotyl of dark-grown gherkin seedlings is much more pronounced when the seedlings are pre-irradiated with white or blue light.
Article
Throughout their life cycle vascular plants carry at the terminal portions of their axes young cells that retain the ability to divide. They are the so-called meristematic cells which go to form the primary apical meristems. These meristems continually give rise to derivatives, from which new tissues and organs originate; hence they maintain the functions of proliferation and organogenesis that follow segmentation of the zygote. They form the essential organs of vascular plants and lay the primary structure of the shoots and roots; for this reason they may be called shoot meristems or root meristems. The two types of apices, i.e, the shoot and root apices, are very different from each other in their structure, localization, and physiology. This chapter focuses on the caulinary meristematic cells, and discusses the histocytological, biochemical, and experimental research that led to clearer conceptions of the origin, structure, function, and development of the apical cells of shoots. The root meristem, protected by the root cap, produces an independent axis, the root, which gives rise, at some distance from the meristcm, to lateral roots, organs of internal origin that ensure branching of the root axis. The shoot meristem, on the contrary, produces organs of superficial origin on its sides, the leaves, exhibiting bilateral symmetry. These leaves, by becoming united at their bases, form the stem, an axis that is therefore entirely dependent on the leaves.
Article
1In 4-day-old etiolated rice seedlings, 3 mm of the coleoptile tip did mainly perceive the photostimulus to cause the phytochrome-dependent inhibition of coleoptile elongation. At this age, cell elongation occurred most in the middle portion of coleoptiles in the dark, and was reversibly controlled by a brief exposure of the tip to red and far-red light. Thus, the photoperceptive site was evidently separated from the growing zone in intact rice coleoptiles.2The red-light-induced inhibition of coleoptile elongation was nullified by the removal of tip followed by the exogenous application of IAA. The sensitivity of thus treated coleoptiles to IAA was gradually lost during intervening darkness between the irradiation and the decapitation, and a 50% loss was obtained at ca. 6th hour at 26°C.3Polar auxin transport from coleoptile tips was remarkably prevented at the period between, at least, 2nd and 4th hour after red irradiation, and it recovered to the level of dark control by the 6th hour. Far-red light given immediately after red irradiation reversed the yield of diffusible auxin up to that of far-red control.
Article
The rate of oxidative phosphorylation by isolated mitochondria was found to be affected by red (650 m mu ) and far-red (725 m mu ) light. Esterification of adenosine diphosphate to adenosine tripliosphate by rat liver mitochondria is decreased by concomitant or prior irradiation with far-red and increased by red light. The effect of far-red is reversible by red in an alternating sequence. An analogous sensitivity was not found when isolated mitochondria of the Avena seedling were irradiated. However, irradiation of the intact seedling significantly affected the phosphorylative capacity of the mitochondria subsequently isolated. Whether enhancement or inhibition of activity took place depended on the time at which the seedlings were irradiated in the post germinative period. There is apparently no direct correlation between radiationinduced changes in phosphorylative rate and either mitochondrial protein or volume. Impairment of ATP generation is suggested as the biochemical basis for the far-red potentiation of x-ray-induced chromatid aberrations. The photosensitivity of this phosphorylation also suggests its consideration as a metabolic determinart of the photomorphogeneses controlled by red and far-red light. (auth)
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Addition of 6 muM indole-3-acetic acid (IAA) to incubation buffer increases the sensitivity of coleoptile sections cut from dark-grown Avena sativa L. cv. Lodi to red light by a factor of 10,000, relative to the response in the absence of added IAA, without changing the maximum amount of light-induced growth. From 0.03 to 4 muM IAA sections show at least a 100-fold increase in sensitivity to red light relative to the response in the absence of added IAA. In this IAA concentration range, the light-induced increase in elongation shows two phases of response to red-light fluence, which are separated by a plateau. The biphasic fluence-response curve is also characteristic of the red-light-induced stimulation of coleoptile growth in intact dark-grown seedlings. The effect of IAA on the sensitivity of the phytochrome-mediated growth response appears to be on some step in the transduction of the phytochrome signal, rather than on the growth response itself.
Article
The repeated exposure of Pisum (pea) plants to red light brings into operation an apparent synthesis of phytochrome which is not observed in material kept in the dark. This process shows some temperature compensation but has an optimum at 26 degrees ; it is irreversibly inhibited by 10(-4)m cycloheximide and 10 mug/ml actinomycin D. It is also inhibited by the auxins indoleacetic acid, naphthalene acetic acid and 2,4-dichlorophenoxyacetic acid at 10(-4)m but in these cases the inhibition is completely reversed when the auxin is washed out of the tissue. Antiauxins 2,4,6-trichlorophenoxyacetic acid and p-chlorophenoxy isobutyric acid, while strongly inhibiting growth have little effect on apparent synthesis. Other growth regulators and the precursor of tetrapyrrole synthesis, delta-aminolevulinic acid, have no consistent effect on the process, but 3 x 10(-4)m cobalt (II) nitrate is inhibitory. The capacity for apparent synthesis decreases as the cells approach maturity. The results may be explained by either de novo synthesis of phytochrome, or by a transformation process resembling in some respects the dark reversion of Pfr to Pr. The physiological role of apparent synthesis is suggested.
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The uptake and accumulation of exogenous indoleacetic acid-(14)C by intact rice coleoptiles were examined. The absorption of exogenous indoleacetic acid was controlled by phytochrome, while the subsequent accumulation of this indoleacetic acid in various portions of the coleoptile was complex, and the effect of red light in this system was small compared to the alteration of the uptake of indoleacetic acid by red light. The absorption of indoleacetic acid exhibited two phases: the first occurring during the first 3-hour portion of the incubation was an inhibition, while the second was a promotive effect at about the 5th hour of incubation. Both of these effects were red, far redreversible, implicating phytochrome in this effect. Neither the destruction nor the immobilization of this exogenous indoleacetic acid apeared to be greatly affected by red light irradiation. The principal interaction between phytochrome and indoleacetic acid appears to occur during the absorption of exogenous indoleacetic acid. This effect may be related to the control by phytochrome of the amount of auxin which diffuses from coleoptile tips.
Article
Growth response of coleoptile segments excised from 3-day-old seedlings of wheat (Triticum vulgare cv. Baart) to gibberellic acid, indoleacetic acid, and 2,4-dichlorophenoxyacetic acid, to red light, and to several microtubule disorganizers depends on the initial position of the excised segment in the intact coleoptile. Red light, 660 nm, stimulates the growth of the apical cells, but inhibits markedly the growth of the cells in the basal region of the coleoptile. The effects of red light are independent of sucrose, gibberellic acid, indoleacetic acid, and 2,4-dichlorophenoxyacetic acid, even though these substances themselves markedly affect the growth of the coleoptile segments. Concentractions of the microtubule disorganizers, vinblastine sulfate, cupric chloride, urea, and colchicine, which do not alter significantly the growth of the dark control apical segments, substantially repress the promotive effects of red light or auxin on the increase in length of the apical cells of the coleoptile. This suggests that stimulation by red light and by auxin involves microtubule production. Microtubule disorganizers repress the growth of elongating cells of the coleoptile, yet on the other hand, auxin and irradiation do not alter significantly the response of basal cells to the microtubule disorganizing agents. We hypothesized that light and growth regulators induce polymerization of nonaggregated microtubule subunits, resulting in faster growth.
Article
The elongation of hypocotyl segments cut from etiolated Cucumis sativus seedlings is not affected by a single red light exposure at the start of the 20-hour growth period, but is inhibited by brief exposures repeated each hour or two even though these give no greater total energy. The inhibition is annulled if each red exposure is followed by far-red. The time course of phytochrome transformations in this tissue after a single red light exposure, followed spectrophotometrically, shows no anomalous characteristics that might correlate with the unusual pattern of responsiveness to red light. In intact seedlings, hypocotyl elongation responds similarly, but the opening of the hypocotyl hook is saturated by a single initial red light treatment. Excised hypocotyl segments on water alone appear insensitive to repeated red light treatment, but the growth increments caused by the addition of potassium ion, 2-propanol or cobaltous ion, or by leaving the cotyledons attached, are all inhibited roughly 40%. However, continuous white light inhibits the entire growth increment, reducing elongation to that of the water controls. Some implications of these results for current hypotheses and future investigations on the mechanisms of growth regulation by light are discussed.
Article
1The gibberellins are metabolic products of the fungus Gibberella fujikuroi (conidial state Fusarium moniliforme). Three gibberellins are known: gibberellic acid (C19H22O6), gibberellin A1 (C19H24O6) and gibberellin A2 (C19H26O6). A structure for gibberellic acid has been proposed. Gibberellin A1 is a dihydro derivative of gibberellic acid. The structure of gibberellin A2 has not yet been established.2The biological activity of all three gibberellins is, as far as is known at present, zqualitatively similar; no truly quantitative comparisons have been reported. In describing biological results below, the abbreviation GA may refer to any one gibberellin or to mixtures.3The most characteristic effects of GA on shoot growth are increased inter-node extension, increased leaf-growth and enhanced apical dominance.4Under some circumstances, with some plant species, treatment with GA does not stimulate growth of intact roots, though some root sections do respond by increased growth. High concentrations of GA are only slightly inhibitory, results in increased dry weight. This is mainly due to increased carbon fixation and is believed to be a secondary effect of increased leaf growth.5Not all plants respond to GA by increased shoot growth and the effect on some species is greater than that on others. In species in which dwarf mutants are known, the dwarf may frequently be induced by GA to grow in a form in-distinguishable from that of the tall phenotype, genetically tall plants themselves being unaffected.6Many forms of dormancy are broken by GA. These include seed dormancy, dormancy of potato tubers and dormancy of shoot internodes and buds.7GA will induce flowering of long-short-day plants kept permanently in short-day photoperiods. I t will induce stem growth and, in long-day photoperiods but possibly not in short days, flowering in cold-requiring biennial long-day plants.8It inhibits flowering of short-day plants in inductive short-day photoperiods. I t will induce stem growth and, in long-day photoperiods but possibly not in short days, flowering in cold-requiring biennial long-day plants. It inhibits flowering of short-day plants in inductive short-day photoperiods.9In its effects on vegetative cell extension GA has certain similarities to the auxins but there are also differences. The most important differences are: (a) auxins greatly increase cell-extension in excised tissue sections, whereas GA has little effect; (6) GA induces marked cell extension in shoots of some intact plants, whereas exogenous auxins have little effect; (c) auxins inhibit root growth strongly, but GA does not.10There is evidence from several sources that GA only influences cell extension if auxin is present.11Comparison of the growth rate of excised pea internode sections with the growth rate of comparable tissues in intact plants, using untreated and GA-treated plants as sources of both types of material, has led to the conclusion that the endogenous auxins of plants are limited in their effects, and that growth is correspondingly limited, by 'an inhibitory system'GA acts by neutralizing the effects of this inhibitory system.12The work of Galston (1957) suggests that this inhibitory system might be an auxin-destroying enzyme. Not all experimental observations are completely compatible with this view.13In its effects on leaf expansion and on some forms of dormancy, GA simulates light. In most photoperiodically sensitive plants, light, particularly in the form of long-day photoperiod, induces increased shoot growth; GA has a similar effect. The internode-inhibiting effects of light are not simulated by GA, which always promotes growth; on the other hand, GA does not physiologically reverse such inhibitions.14GA also breaks certain forms of dormancy broken in natural conditions by exposure to low temperature (vernalization).15In its effects on flowering GA also simulates light. By inducing flowering of long-day plants and long-short-day plants in short days it acts as if by extension of the light period; in inhibitory flowering in short-day plants in inductive short-day photocycles it simulates a light break in the dark period. The action spectrum of he light-induced effects mentioned in this paragraph and in paragraph 13 is similar, red light (650 mp) being most active. Characteristically an inducing exposure to red light may be reversed by an exposure to far-red (735 mμ).16In cold-requiring biennials GA simulates vernalization.17GA is not florigen, the postulated flowering hormone common both to short-day plants and long-day plants.18Hormones with physiological properties similar to those of GA have been detected in several plant tissues. The active material has been isolated from Phaseolus seeds and shown to be gibberellin A,. It is suggested that growth regulation in plants is based on a balance of auxins, GA-like hormones and a growth-inhibitory system.19Effects of photoperiod on plants are not confined to flowering. In general, short-day photoperiods tend to induce retarded shoot extension and dormancy; shoot extension is accelerated and dormancy broken by exposure to long-day photoperiods, to low temperature, or to exogenous GA.20There is thus a fundamental unity in the effects of GA on plant development, in which GA closely simulates effects usually induced in nature either by exposure to light or by vernalization. Accordingly, the explanation already offered (paragraphs 11 and 18 of this Summary) of the effects of GA on vegetative growth of day-neutral plants, may be extended to cover phenomena of flowering and dormancy.21A hypothetical scheme is presented to explain regulation of growth and flowering, based primarily on the activity of GA-like hormones; this scheme is a modification of those proposed by Borthwick et al. (1952) and Liverman & Bonner (1953). It may be summarized as follows: In response to light, GA-like hormones are formed in leaves, a physiologically inactive, or less active, precursor (P) being an intermediary. The hormone is converted slowly back to P in darkness, more rapidly if the leaves are exposed to far-red light. If the leaf is then exposed to red light once more, the hormone is again formed from P. Thus in long-day conditions increasing concentrations of the hormone will be built up but in short-days concentrations will be much lower. If it is supposed that high levels of GA-like hormone induce flowering in long-day plants but that flowering of SDP only takes place when levels of the hormone are low, the flowering and vegetative responses of both types of plant to light and to exogenous GA can be accounted for. This scheme can be adapted to explain other light-induced responses, and also the effects of vernalization if it is assumed that low-temperature treatments also are concerned with synthesis of GA-like hormones.
Article
In seeking a simple, red light-promoted straight growth test in which phytochrome assays may be conducted without interference by protochlorophyll, the response of excised Avena coleoptile segments to red and far-red light was re-examined. The elongation of apical (non-decapitated) segments is promoted by a brief exposure to red light, and this effect is almost completely nullified by an immediately subsequent exposure to far-red light. Although growth promotion by red light occurs in distilled water alone, the effect is greater on a medium consisting of 0.02 M phosphate buffer, pH 6.2 to 6.4, with 1 to 2% sucrose. Over the pH range 4.5 to 7.4, dark-growth decreases with increasing pH, but the absolute increment brought about by red light is nearly constant. Elongation appears to be entirely the result of increased cell size. Contrary to previous reports, similar results can be obtained with subapical (decapitated) coleoptile segments, although the absolute magnitude of the response is reduced.
Article
SUMMARYA 3 hours lasting irradiation with red light 27 hours after moistening of Avena seeds does not repress the growth of the mesocotyls completely. A second irradiation with red light 72 hours after moistening further reduces mesocotyl growth. In contrast red light enhances slightly but significantly the growth of the coleoptiles. Total seedling growth is reduced.
Chapter
Auch der Zustand der nichtwachsenden, aber lebenden und aktiven Zelle ist, wie wir wissen, dynamisch charakterisiert, als Gleichgewichtszustand, in dem der dauernd ablaufende Stoffabbau durch eine Synthese gleichen Umfanges bilanzmäßig kompensiert ist (Rittenberg und Mitarbeiter 1939, Vickery und Mitarbeiter 1939, Hevesy und Mitarbeiter 1940, Schoenheimer 1942, MacVicar und Burris 1948, Mazia und Prescott 1955 u. a.). Überwiegen die Synthesen die abbauenden Vorgänge, so arbeitet die Zelle mit Stoffgewinn, sie wächst. Diese Art des Wachstums, die wir, soweit wir nur die Zunahme der plasmatischen Zellbestandteile ins Auge fassesn, als Plasmawachstum bezeichnen, ist die fundamentale, die gewöhnlich auch den anderen Wachstumsformen, dem Teilungswachstum und dem Streckungswachstum, vorauszugehen hat, diese auch zum Teil noch begleitet.
Chapter
In diesem Bericht sind die Veröffentlichungen aus den Jahren 1953 und 1954 zusammengefaßt, die sich mit genetischen und genphysiologischen Fragen befassen. In einzelnen Fällen war es zum Verständnis der neueren Untersuchungen notwendig, auf ältere Arbeiten zurückzugreifen, die in den vorigen Referaten nicht berücksichtigt wurden. Die Gewichtsverteilung auf wenige, im Mittelpunkt der Diskussion stehende Probleme hat sich nur geringfügig verändert. Um die Orientierung zu erleichtern und den Anschluß an die früheren Berichte zu wahren, wurde daher im wesentlichen die Reihenfolge der Abschnitte aus den letzten Bänden beibehalten.
Chapter
Der vorliegende Berichtsabschnitt ist durch ein weiteres Ansteigen der vielfältigen Untersuchungen auf dem Gebiet der Strahlenbiologie gekennzeichnet. Es erscheint praktisch unmöglich, selbst wichtige Arbeiten gebührend zu berücksichtigen, und es sind Beschränkungen erforderlich. Trotz der vielen Untersuchungen zeigt sich, daß wir von einem Verständnis der Wirkung der verschiedenen Strahlungen im lebenden Gewebe noch weit entfernt sind. Nachdem in den letzten Jahren bekannt wurde, welche hervorragende Bedeutung neben den direkten Trefferwirkungen die indirekten Strahleneffekte (vgl. Fortschr. Bot. 15) besitzen, hat sich deren Untersuchung sehr stark ausgedehnt, und die Wendung des Interesses der biologischen Strahlenforschung von rein physikalischen Gesichtspunkten zur chemischen Betrachtungsweise ist augenfällig [vgl. z. B. Gray 1954 (3), (4); oder auch Wels (2)]. Aber bereits der Ausgangspunkt des ganzen Problems, die Radiochemie des Wassers und der einfachsten Lösungen, ist noch keineswegs wirklich geklärt. So ist es nicht verwunderlich, daß die viel komplexeren Verhältnisse in Zellen und Geweben zwar in breitester Front untersucht wurden, im ganzen aber erst ein Anfang der ursächlichen Aufklärung der Strahlenwirkung erreicht worden ist. Auch die Abhängigkeit der Strahlenwirkung von den vor, während und nach der Bestrahlung herrschenden physikalischen, chemischen und biologischen Bedingungen, wie Temperatur, Anwesenheit der verschiedensten Stoffe, dem Entwicklungszustand der untersuchten Zellen und Gewebe usw., ist immer stärker Gegenstand der Forschung geworden.
Chapter
Light, perceived and transduced by a number of photoreceptors, is known to regulate or modify many aspects of plant growth and development. Beginning with seed germination and ending with fruiting and senescence, light can regulate processes which can also be modified by plant hormones. This has been taken as circumstantial evidence that light may be exerting its influence via plant hormones, and considerable research effort has been directed toward elucidating the role of plant hormones in light-mediated processes. The two areas of light and plant hormone research that have received the most attention are de-etiolation and photoperiodism (see Vince-Prue, Chap. 9 this Vol.). While the emphasis, by necessity, of this chapter is on plant hormones in de-etiolation, we include relevant work on other aspects of photomorphogenesis and plant hormones.
Chapter
Als „Licht“ bezeichnen wir jene Strahlung, die beim Menschen die Lichtempfindung verursacht, also nur Strahlung zwischen etwa 400 und 750 mµ Wellenlänge. Daß dieses „Licht“ beim Menschen die „Lichtempfindung“ verursacht, ist für die Phänomene, die hier zur Diskussion stehen, belanglos. Es wäre wohl besser, bei allen physikalischen und pflanzen- bzw. tierphysiologischen Untersuchungen den Begriff „Licht“ zu vermeiden. Man sollte generell von Strahlung sprechen und diese durch die Wellenlänge näher definieren. Um der Kürze willen werden jedoch auch wir den Begriff im Sinn obiger Definition verwenden. Den an das langwellige Rot anschließenden Spektralbereich nennen wir „langwelliges = nahes Ultraviolett“. Wir behandeln experimentelle Resultate, die durch Bestrahlung mit Strahlung zwischen 320 und 800 (— 1000) mµ gewonnen wurden. Die Grenze im nahen Infrarot ist dadurch gegeben, daß es bisher nicht möglich war, jenseits dieser Grenze mit Sicherheit spezifische physiologische Strahlungseffekte nachzuweisen. Die Absorption von Quanten im Bereich des Infrarot scheint lediglich in unspezifischen thermischen Effekten zu resultieren. Die alleinige Beeinflussung der Schwingungs- bzw. Rotationsenergie der vielatomigen organischen Moleküle führt offenbar nicht zu spezifischen Stoffwechseländerungen. Im infraroten Bereich würde auch, falls spezifische Strahlungseffekte nachweisbar wären, die zwischen 800 und 1000 mµ einsetzende, starke Absorption des Wassers eine Interpretation von Wirkungsspektren sehr erschweren.
Chapter
This review is restricted to phytochrome-mediated light effects and to the generally recogniz’d five classes of natural hormones, auxins, gibberellins, cytokinins, abscisic acid and ethylene. Other environmental conditions having morphogenic effects in relation to phytochrome and hormone actions are included when they are relevant to our objective. Aspects of flower induction are mentioned when an interaction between phytohormones and phytochrome is evident.
Chapter
The discovery of the gibberellins stems from studies of a soil-borne disease of rice, the so-called bakanae disease, caused by infection by the fungus Gibberella fujikuroi. The classical publications, describing the critical steps in this discovery of a new series of plant growth-regulating compounds, are those of Kurosawa (170) who in 1926 first showed that cell-free filtrates from cultures of the fungus contained a growth-promoting principle, and Yabuta and Hayashi (340) who in 1939 first obtained crystalline active material for which they coined the name gibberellin. Until 1954 virtually all publications on these substances were Japanese; access to the numerous early Japanese publications has been greatly simplified for many readers by the publication by Stodola (292) of his invaluable Source Book on Gibberellin, 1828–1957.
Article
Briggs, Winslow R. (Stanford U., Stanford, Calif.) Red light, auxin relationships, and the phototropic responses of corn and oat coleoptiles. Amer. Jour. Bot. 50(2): 196–207. Illus. 1963.— Red light decreases the phototropic sensitivity of corn (Zea mays Burpee ‘Golden Cross Bantam’) and oat (Avena saliva ‘Victory’) coleoptiles. The decrease is reflected by a shift of the curve ploting log dosage vs. response to higher dosages, as described in the literature. In the absence of red light treatment, 1,000 meter-candle-seconds (mcs) white light induces first negative curvature in oats and almost no curvature in corn, which appears to lack the mechanism for first negative curvature. Immediately following a 2-hr red light treatment, the same white light dosage induces almost maximum first positive curvature both in corn and in oat coleoptiles. The increase in curvature obtained reflects the decreased phototropic sensitivity of both plants shown by the dosage-response curve shift. After red treatment, the effect of red light remains maximal for an hour, decaying to the level of non-red-treated plants within another 2 hr. Red light suppresses auxin production by corn coleoptiles. The effect decays after the end of red treatment. Both changes follow time courses parallel to those for the phototropic sensitivity changes. The 1,000 mcs light dosage induces lateral transport of auxin both in red-treated and untreated corn coleoptiles, despite the lack of curvature of the latter. Red light does not induce a circadian rhythm for the phototropic sensitivity changes in oats, is not effective if administered after phototropic induction, and its effect is probably mediated by phytochrome. The hypothesis, not original with this paper, that red light induces an increase in the amount of pigment mediating second positive curvature most closely accounts for the results obtained. Pertinent literature is discussed.
Article
Red light enhances the geotropic response of excised Avena coleoptiles. With higher dosages this enhancement occurs in the main in the upper centimeter of the organ and is compensated by a decrease in the geotropic response of the base. In both of these aspects the red light induced alterations are dosage dependent in the range of irradiancies investigated (from 2000 to 240 000 erg/cm2; intensity: 1000 erg/cm2 sec). The influence of even a relatively small dosage of red light (2000 erg/cm2) is evident for at least four hours after the illumination. Possible relations with phototropic phenomena are discussed. From the current hypotheses about the mechanism of the red light-induced alterations in tropic responses, that of red light influencing the pigment system active in phototropic perception is considered to be the least attractive one.
Article
Investigations were conducted with etiolated seedlings of Avena on the influence of red, far red and blue light on: a.the growth of sections of coleoptile and mesocotylb.the geotropic reactions of coleoptile and mesocotylc.guttation of the seedlings. The experiments were carried out in darkness, the experimental irradiations excepted. Two systems of reactions to light appear to be present in the seedlings. One of them shows a very low saturation value of about 1 erg cm−2 for red and far red light, the sensitivity to blue light being much lower than for the former wavelengths. This system was found in section growth and the geotropic reaction. The other system shows a dependency on the amount of light energy applied up to at least 105 erg cm−2 for red, far red and blue light. In this system the sensitivity to far red light is much lower than to red light and about as high as to blue light. This system was found to affect guttation and the shape of the geotropic curves of the seedlings. The latter system appears to exert its influence through changes in transport rates of water and solutes, as is indicated by its influence on guttation. From the results is concluded that this change in the rate of water transport influences the transport rates of auxins and, consequently, the relative growth rates of different parts of the seedlings. Connections of the conclusions drawn with some data from the literature on phototropism are discussed.
Article
Growth of decapitated Avena sativa coleoptile segments, of coleoptile segments which included the tip, and of coleoptiles of intact seedlings was compared in darkness and in light of different wavelengths. In all instances, both in light and in darkness, coleoptile growth in intact seedlings exceeded that of decapitated coleoptile segments, while the growth of decapitated segments was greater than that of segments which included the tip. The expansion of decapitated coleoptile segments is insensitive to light, the resulting growth being comparable to that in darkness. The growth of apical coleoptile segments is inhibited, in comparison with control segments incubated in darkness, at 510—565 nm, but stimulated at 605—700 run. Growth of the coleoptiles of intact Avena seedlings is inhibited at 455—565 nm and at 660—700 rim, though not at intermediate wavelengths.
Article
Abstract Optimal conditions for studying the elongation response to a 1 mmol m−2, 2-min pulse of red light in subapical coleoptile sections from dark-grown oat (Avena sativa L. ev. Lodi) seedlings have been determined. A technique for obtaining standard-length coleoptile sections without exposing either seedlings or sections to any light has been developed, and is described. The optimal conditions found were: sampling time, 12 h after irradiation; buffer conditions, 5 mol m−3 potassium phosphate with 5% (w/v) sucrose (pH 5.9). The optima were determined by obtaining the time course for light-induced growth under various conditions. The red light-induced growth response is linear until 12 h after irradiation, when it undergoes an interruption. Optimal incubation conditions were determined by varying the buffer contents systematically and measuring the responses at the optimal lime determined. The results indicate a distinct difference between auxin-induced and light-induced growth responses. Even with variations of basal growth rate and several incubation conditions, the red light-induced elongation appears to be of a constant magnitude, to persist for a constant time period. and to exhibit a constant lag period between irradiation and the onset of response. The use of sections that were produced and handled in complete darkness yielded an unusual response to fusicoccin. A linear, high growth rate in response to I mmol m−3 FC was observed for more than 12 h, both in the irradiated sections and in the dark controls.
Article
Sutmmitary. Therepeated exposureofPisum(pea)plants toredlight brings into operation an apparentsynthesis ofphytochrome whichisnotobservedinmaterial keptinthedark.Thisprocess showssome temperature compensation buthasan optimumat260;itisirreversiibly inhibited by10-4M cycloheximide and10jg/ml actinomycin D. Itisalsoinhibited bytheauxinsindoleacetic acid, naphthalene acetic acidand2,4-dichlorophenoxyacetic acidat10-4 M butinthesecasestheinhibition is completely reversed whentheauxiniswashedoutofthetissue. Antiauxins 2,4,6-tri- chlorophenoxyacetic acidandp-chlorophenoxy isobutyric acid, whilestrongly inhibit- inggrowthhavelittle effect on apparentsynthesis. Othergrowthregulators and theprecursor of tetrapyrrole synthesis, &-aminolevulinic acid,haveno consistent effect on theprocess,but3 X 10-4 M cobalt(II)nitrate isinhibitory. Thecapacity forapparent synthesis decreases as thecellsapproach maturity. The results may be explained byeither denovo synthesis ofphytochrome, or bya transformation process resembling insome respects thedarkreversion ofPfrtoPr. Thephysiological role ofapparent synthesis issuggested.
Article
Abstract— Red light (around 6,550 Å.) and far-red light (around 7,300 Å) have been administered to excised first internodes of etiolated oat seedlings, and their effects upon growth by elongation have been studied. It has been found that red light inhibits much more the elongation produced bv gibberellic acid (GA) than that produced by 3-indolylacetic acid (IAA). Far-red light acts synergistically with GA in promoting elongation, but not with IAA. The effect of far-red is localized in the node and in the first 4 mm below the node, at least when the seedlings are 63 hr old. The stimulatory effect of the far-red radiation is observed when seedlings are younger than 65 hr or older than 69 hr after sowing. Except for a gradual decrease with age, there is no such two-peaked pattern for the sensitivity to red light. Red light promotes the elongation of the node and of the 2 mm-zone of the first internodes immediately below it. It inhibits the elongation of the zone comprised between 2 and 10 mm below the node. Various types of experiments could not demonstrate a true reversal of the red effect by far-red light and vice-versa. They indicated rather an additive effect of the inhibitory and stimulatory properties characteristic of each type of radiation.
Article
It is characteristic of a great number of biologically active substances that the responses which they elicit are twofold, low concentrations of the material promoting a particular activity, and higher concentrations inhibiting it. This is the case with the auxin-induced growth responses of plants. An active auxin such as indole acetic acid (IAA) brings about and is essential to growth in length of stems, hypocotyls and other plant organs including the Avena coleoptile.
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Report of work supported in part by the National Science Foundation and in part by the Lederle Laboratories Division, American Cyanamid Co. 1 Schneider, C. L., Am. J. Bot., 28, 878 (1941). Went, F. W., and Thimann, K. V., Phytohormones, Macmillan Co., New York, 1937. 2 Liverman, J., and Lang, A., Abst. Ann. Meeting Am. Soc. Plant Physiol., Cornell, 1952, p. 36. 3 Thurlow, J., and Bonner, J., Am. J. Bot., 34, 603 (1947). Bonner, J., and Thurlow, J., Bot. Gaz., 110, 613 (1949). 4 Galston, A. W., and Baker, R., Am. J. Bot. (1953); (in press).
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14 Salisbury, F., and Liverman, J., Abst. Ann. Meeting Am. Soc. Plant Physiol., Western Sect., Santa Barbara, 1953.
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10 Borthwick, H. A., Hendricks, S. B., Parker, M. W., Toole, E. H., and Toole, V. K., PROC. NATL. AcAD. Sci., 38, 662 (1952). Flint, L. H., and McAlister, E. D., Smith. Misc. Publ., 94, No. 5 (1935). .11 Hamner, K. C., and Bonner, J., Bot. Gaz., 100, 388 (1938).
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17 Miller, C. O., Arch. Biochem. Biophys., 32, 216 (1951).
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r Foster, R. J., McRae, D. H., Bonner, J., PROC. NATL. ACAD. ScI., 38, 1014 (1952).
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