Action Spectrum in the Ultraviolet Region for Phototropism of Bryopsis Rhizoids

The phototropic response of the rhizoid of the marine coenocyticgreen alga Bryopsis plumosa to ultraviolet light (250–350nm) was investigated. The rhizoid exhibited negative bendingthat was due to bulging upon absorption of light in the UV region,as well as in the visible region, of the spectrum. The negativebending might not be a result of the inhibition of growth onthe irradiated side of the apical hemisphere by UV irradiationbecause growth inhibition was observed after bending had reacheda maximum within one to two hours. The action spectrum obtainedfrom fluence rate-response curves had a pronounced peak at 260nm and a small peak at 310 nm. The quantum effectiveness at260 nm was about five times that in the visible region. Phenylaceticacid (PAA), a potent inhibitor of flavin photoreactions, inhibitedthe phototropic response to both UV light and blue light withoutany obvious effect on tip growth. The inhibition of the phototropicresponse to blue light by PAA was partially overcome by rinsingthe alga with riboflavin-containing medium, which result suggeststhe involvement of flavins in the phototropism of Bryopsis rhizoids. (Received February 6, 1995; Accepted June 19, 1995)     

Action spectrum of negative phototropism in Boergesenia forbesii

The rhizoid of Boergesenia forbesii, a gigantic unicellulargreen alga, exhibited negative phototropism. The bending processat 32?C followed Weber-Fechner's law and Bunsen- Roscoe's law.The minimum light energy inducing the phototropic bending was30 J.m^–2 at 467 nm and 32?C. The action spectrum of thisnegative phototropism had two distinct peaks at 380 and 443nm, with shoulders at 430 and 470 nm and a trough around 410run. Light of wavelengths longer than 502 nm was ineffective.The structure of the spectrum agrees well with that reportedfor the positive phototropism of Avena coleoptiles and otherplant parts. (Received February 24, 1979; )     

Phototropism in a red alga, Griffithsia pacifica

In the red alga, Griffithsia pacifica, shoot portions of a plantare positively phototropic and rhizoids are negatively phototropic.We have studied the phototropic response of rhizoids which elongateby tip growth. For 45 min after the beginning of unilateralillumination a rhizoid grows straight, then phototropic curvaturebegins and continues rapidly until the rhizoid is growing awayfrom the light. Curvature is 70–80% complete after 3 hr.If the unilateral stimulus is given for a short time (15 min),curvature again begins at 45 min. However, within an additional30–45 min the rhizoid stops growing away from the lightand wanders back towards its original direction of growth. Phototropismis elicited by light of wavelengths from 350 nm to 500 nm; inlight of wavelengths above 550 nm, little, if any, responseoccurs. ¹Present address: Division of Natural Sciences, University ofCalifornia, Santa Cruz, California 95064, U.S.A. (Received December 10, 1976; )     

Culturing the Segments of Bryopsis hypnoides Lamouroux Thalli Regenerated from Protoplast Aggregations

Bryopsis hypnoides Lamouroux was regenerated In vitro from the protoplasm squeezed out from wild algae and the regenerated Individuals had an advantage over Indlvlduala from the wild In terms of growth. Culturing of segments of thalll also showed that segments from the regenerated algae grew better than those from individuals from the wild. The segment that corresponds to a part of a cell, at least a part of the protoplasm, can develop Into a mature Individual, Including rhlzold and thallus, suggesting that a multlnucleate alga, such as B. hypnoides, Is different from higher plants, whose totlpotancy Is based on an Intact cell （or protoplasm）. Further cultivation of mature Individuals from segments Indicated that the organelles In the thallus had two ways In which they could survive when the alga was on the decline： （Ⅰ） the organelles were transferred Into a ball with a gelatinous envelope through a formed pipe and the ball seemed to be capable of being propagated; and （Ⅱ） the organelles were aggregated In the thallus and then moved to the outside. An Interesting result Is that one organelle aggregation located outside the thallus germinated and developed Into a mature alga, although most organelle aggregations gradually lost vitality and died. The results of the present study reveal that the aggregation of organelles can regenerate a stronger organism than Individuals from the wild owing to the complete exchange of genetic material and may possibly enable organelles to survive in unfavorable surroundings.     

Growth and phototropic bending in Boergesenia rhizoid

The rhizoid of Boergesenia forbesii. a coenocytic green alga,exhibited typical tip growth. The growth stopped at temperatureslower than 15?C and was promoted by red light but inhibitedby blue light (430 nm). The rhizoid showed negative phototropicbending caused by blue light, and the mode of bending was the"bulging" type. The dioptric effect was not involved in thisnegative phototropism. The phototropicbending process was modifiedgreatly by temperature. At low temperature (18?C), bending didnot occur but the phototropic effect could be accumulated andstored. The accumulated effect appeared as a bending in thedark when the temperature was raisedto 25?C. This accumulatedphototropic effect, designated "stored bending", attenuatedat a half-life of 1.5 hr at 18?C in the dark. (Received February 24, 1979; )     

Negative Phototropism in the Rhizoid of Bryopsis plumosa

Negative phototropism in the rhizoid of Bryopsis plumosa wasanalyzed. The growth zone of the rhizoid was confined to theapical hemisphere, as is typical of tip growth. Upon unilateralillumination, the rhizoid bent away from the light source witha "bulging" manner. The photoreceptive site for phototropismwas also restricted to the apical hemisphere. The action spectrumfor this negative phototropism was determined from fluence-responsecurves that were obtained after fixing the duration of illuminationat 60 min and varying the fluence rate between 0.1 and 3.0 Wm^-2. The action spectrum had a large peak at 467 nm and smallerpeaks at 378 and 414 nm, resembling the action spectra of certainother blue-light responses. (Received November 29, 1995; Accepted May 29, 1995)     

Positive Phototropism in the Thallus of Bryopsis plumosa

Positive phototropism in the thallus of the marine coenocyticgreen alga Bryopsis plumosa was investigated in terms of themode of bending, the photosensitive zone and the effectivenessspectrum. The bending occurred as a consequence of a differencein growth rate between the illuminated and the shaded sidesof the thallus. Elongation on the shaded side was stimulatedwhile that on the illuminated side was inhibited. However, theoverall elongation rate was barely affected. Illumination witha fine beam revealed that a zone from approximately 80 to 120µm below the tip was the most photosensitive. The effectivenessspectrum showed that blue light (<550 nm) was most effective,with light at 467 nm having maximal effectiveness. (Received November 29, 1994; Accepted May 29, 1995)     

Negative phototropic response of rhizoid cells in the fern Adiantum capillus-veneris

In general, phototropic responses in land plants are induced by blue light and mediated by blue light receptor phototropins. In many cryptogam plants including the fern Adiantum capillus-veneris, however, red as well as blue light effectively induces a positive phototropic response in protonemal cells. In A. capillus-veneris, the red light effect on the tropistic response is mediated by phytochrome 3 (phy3), a chimeric photoreceptor of phytochrome and full-length phototropin. Here, we report red and blue light-induced negative phototropism in A. capillus-veneris rhizoid cells. Mutants deficient for phy3 lacked red light-induced negative phototropism, indicating that under red light, phy3 mediates negative phototropism in rhizoid cells, contrasting with its role in regulating positive phototropism in protonemal cells. Mutants for phy3 were also partially deficient in rhizoid blue light-induced negative phototropism, suggesting that phy3, in conjunction with phototropins, redundantly mediates the blue light response.     

光照对蕨类植物配子体假根向重力性的影响

对８种蕨类植物配子体假根向重力性反应的研究结果表明,除卷柏Ｓｅｌａｇｉｎｅｌｌａ ｔａｍａｒｉｓｃｉｎａ Ｓｐｒｉｎｇ配子体假根无向重力性反应并且其生长方向与光照方向无关外,其它７种的配子体假根均有向重力性反应,并且假根的向重力性反应在配子体发育初期,因光照的方向不同而异,表现为负向光性。随着配子体发育至片状体阶段,光对其向重力性反应的影响逐渐减弱,而重力的影响增强。在蕨类植物配子体发育初期,光对     

Wirkung von Vorbestrahlung mit Rot- oder Blaulicht auf die geotropische Empfindlichkeit von Maiskoleoptilen

The early geotropic downward bending of corn (Zea mays L.) coleoptiles was found to be influenced by red and blue light. The coleoptiles were illuminated from above and kept in the dark for defined intervals; afterwards they were positioned horizontally and their curvature was monitored for 40 min. After illumination with red light and a 120 min interval and early upward bending instead of an early downward bending was found. This effect was nullified by a far-red illumination administered immediately after exposure to red light. These results indicate that the phytochrome system influences the geotropic reaction. After illumination with blue light and a 30 min interval little downward bending was found. This result corresponds well with the findings of earlier authors who measured the late geotropic reaction, on the basis of the hypothesis that the strength of the early downward bending is a measure of the geotropic sensitivity. The dose-effect curve of the blue light influence on geotropic sensitivity, measured by early downward bending, is very similar to the dose-effect curve of the phototropic curvature of corn coleoptiles. This fact together with the earlier finding of similar adaptation times of about 30 min suggests the existence of some common transducers in the reaction chain of phototropism and geotropism.

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Abkürzungen HR Hellrot - DR Dunkelrot - D Dunkel - WT Wartezeit - DK Dunkelkontrolle     

Reception of far-ultraviolet light in Phycomyces: antagonistic interaction with blue and red light

Phototropism experiments were done with sporangiophores of the fungus Phycomyces blakesleeanus to characterize the interaction between far-UV, blue and red light. Far-UV light elicits negative phototropism (bending away from the light source) while blue light elicits positive phototropism (bending toward the light source). In contrast, red light above 600 nm is phototropically inert. Phototropism was analyzed with light regimens of bilateral or unilateral irradiation with far-UV and blue light. Under bilateral irradiation, in which the two light sources were facing each other, blue light partially inhibited the far-UV-elicited phototropism. A fluence-response curve for this inhibition showed that blue light was maximally effective at fluence rates which exceeded 3 to 57 times that of the far-UV. Tonic red light, which was given from above, abolished to a large extent the antagonistic action of blue light. With a regimen of unilateral irradiation, i.e. when far-UV and blue light were given from the same side, a phototropic balance could be achieved with approximately equal fluence rates of blue and UV light. Above or below this critical balance point the bending was either negative or positive. In this setup the effect of tonic red light was complex. First, it caused an enhancement of the positive or negative bending, and second, it caused at some fluence rates a sign reversal from positive to negative phototropism. The balance point itself was only marginally affected. The data cannot be explained on the basis of a single photoreceptor and support the previous notion of separate far-UV and blue-light receptors. The antagonism between these two receptors probably occurs on the level of a red-light-absorbing receptor intermediate. Received: 16 November 1997 / Accepted: 18 December 1997     

Blue‐light‐induced PIN3 polarization for root negative phototropic response in Arabidopsis

Root negative phototropism is an important response in plants. Although blue light is known to mediate this response, the cellular and molecular mechanisms underlying root negative phototropism remain unclear. Here, we report that the auxin efflux carrier PIN‐FORMED (PIN) 3 is involved in asymmetric auxin distribution and root negative phototropism. Unilateral blue‐light illumination polarized PIN3 to the outer lateral membrane of columella cells at the illuminated root side, and increased auxin activity at the illuminated side of roots, where auxin promotes growth and causes roots bending away from the light source. Furthermore, root negative phototropic response and blue‐light‐induced PIN3 polarization were modulated by a brefeldin A‐sensitive, GNOM‐dependent, trafficking pathway and by phot1‐regulated PINOID (PID)/PROTEIN PHOSPHATASE 2A (PP2A) activity. Our results indicate that blue‐light‐induced PIN3 polarization is needed for asymmetric auxin distribution during root negative phototropic response.     

Red light enhancement of the phototropic response of etiolated pea stems

In the subapical third internode of 7-day-old etiolated pea seedlings, the magnitude of phototropic curvature in response to continuous unilateral blue illumination is increased when seedlings are pre-exposed to brief red light. The effect of red light on blue light-induced phototropism becomes manifest maximally 4 or more hours after red illumination, and closely parallels the promotive action of red light on the elongation of the subapical cells. Ethylene inhibits phototropic curvature by an inhibitory action on cell elongation without affecting the lateral transport of auxin. Pretreatment of seedlings with gibberellic acid causes increased phototropic curvature, but experiments using ¹⁴C-gibberellic acid indicate that gibberellic acid itself is not laterally transported under phototropic stimuli. Neither red light nor gibberellic acid treatment has any promotive effect on blue light-induced lateral transport of ³H-indoleacetic acid. Under conditions where phototropic curvature is increased by red light treatment, low concentrations of indoleacetic acid applied in lanolin paste to the apical cut end of the seedling cause an increased elongation response in subapical tissue. This could explain increased phototropic curvature caused by red light treatment.     

Development of adventive embryos in cauline leaves of Sargassum macrocarpum (Fucales, Phaeophyta)

Spontaneous formation and development of adventive embryos were observed in cauline leaves of Sargassum macrocarpum in laboratory culture. Semi-spherical swellings, which were 200–250 μm in diameter, arose from the surface of cauline leaves of thalli cultured for 4 months from zygotic embryos. Swellings became cylindrical protuberances and grew into ‘daughter’ thalli with one or two small cauline leaves. These thalli detached from ‘mother’ thalli and attached to the surface of culture vessels by rhizoids produced within 1 week after detachment. Each daughter thallus developed into an individual thallus exhibiting the same morphological processes as zygotic embryos.     

Anomalous gravitropic response of Chara rhizoids during enhanced accelerations

Centrifugal accelerations of 50-250 g were applied to rhizoids of Chara globularis Thuill. at stimulation angles (alpha) of 5-90 degrees between the acceleration vector and the rhizoid axis. After the start of centrifugation, the statoliths were pressed asymmetrically onto the centrifugal flank of the apical cell wall. In contrast to the well-known bending (by bowing) under 1 g, the rhizoids responded in two distinct phases. Following an initial phase of sharp bending (by bulging), which is similar to the negatively gravitropic response of Chara protonemata, rhizoids stopped bending and, in the second phase, grew straight in directions clearly deviating from the direction of acceleration. These response angles (beta) between the axis of the bent part of the rhizoid and the acceleration vector were strictly correlated with the g-level of acceleration. The higher the acceleration the greater was beta. Except for the sharp bending, the shape and growth rate of the centrifuged rhizoids were not different from those of gravistimulated control rhizoids at 1 g. These results indicate that gravitropic bending of rhizoids during enhanced accelerations (5 degrees < or = alpha < or = 90 degrees) is caused not only by subapical differential flank growth, as it is the case at 1 g, but also by also by the centripetal displacement of the growth centre as was recently discussed for the negative gravitropism of Chara protonemata. A hypothesis for cytoskeletally mediated polar growth is presented based on data from positive gravitropic bending of Chara rhizoids at 1 g and from the anomalous gravitropic bending of rhizoids compared with the negatively gravitropic bending of Chara protonemata. The data obtained are also relevant to a general understanding of graviperception in higher-plant organs.     

DEVELOPMENTAL CHANGES IN THE ALGAL COENOCYTE CAULERPA PROLIFERA (SIPHONALES) AFTER INVERSION WITH RESPECT TO GRAVITY

The algal coenocyte Caulerpa prolifera produces three types of organs, each with a different orientation. The effect of gravity in controlling the development of these organs was investigated. We inverted plants by rotating them 180° around the horizontal rhizome axis, then compared development of the inverted plants with plants matched by size and differentiation. Quantitative data were obtained from photographic records. After inversion the site of organ differentiation was changed with no change in the timing: the next rhizoid (and all subsequent ones) differentiated on the “now-under side” of the inverted rhizome, the next leaf formed on the “now-upper side.” Despite the fast change in the site of organ differentiation, other parameters were not changed by inversion (e.g., rate of elongation of rhizomes or leaves, rate of formation of leaves or rhizoids). Because such changes also occurred in plants with balanced lighting from two sides, it is clear that gravity alone can control these changes without reinforcement from top illumination. After leaves were initiated, they did not change their orientation, showing neither positive phototropism (at our light levels) nor negative geotropism, even when elongating substantially. Torsion of the rhizome tip did not precede the change in site of rhizoid initiation.     

Oriented growth of Blastocladiella emersonii in gradients of ionophores and inhibitors.

To investigate whether ion currents help to localize growth and development of Blastocladiella emersonii, we grew the organisms in gradients of various ionophores and inhibitors. Gradients were generated by placing into the culture fine glass fibers coated with insoluble inhibitors; in some cases, inhibitors were adsorbed onto beads of ion-exchange resin. Organisms growing in many of these gradients exhibited a striking tendency for the thalli to grow toward the fiber. This proved to be misleading; the cells grew not toward the source of the ionophore but into the unoccupied zone of inhibition adjacent to the fiber. Fibers coated with gramicidin-D induced marked effects on the growth of the rhizoids, which were greatly enlarged and grew toward and onto the fiber. None of the other inhibitors produced such effects, except for beads coated with the proton conductors tetrachlorosalicylanilide and compound 1799. The results suggest that orientation of rhizoid growth results from enhancement of proton flux across the plasma membrane. Growth of the rhizoids was also strongly oriented by gradients of inorganic phosphate and an amino acid mixture; gradients of glucose, K+, Ca2+, and glutamate were ineffective. We propose that a major physiological function of the rhizoid is to transport nutrients to the thallus. Finally, we examined the effects of a series of benzimidazole antitubulins as well as the cytochalasins. These did not orient growth but grossly perturbed the pattern of cellular organization, producing small spherical cells with multiple stunted rhizoids. The findings are interpreted in terms of the interaction of an endogenous transcellular proton current with elements of the cytoskeleton in the determination of form.     

Action Spectrum of Coccolith Formation

The action spectrum of coccolith formation in Coccolithus huxleyi was determined by measuring the uptake of carbon-14 in coccoliths in four-hour experiments as a function of light intensity at each of seven wavelengths. An action spectrum | of photosynthetic carbon assimilation was obtained at the same time. The coccolith action spectrum had peaks at wavelengths of about 440 nm and 670 nm. probably corresponding to the regions of maximum cellular absorption and carbon assimilation. However, blue light appeared to be relatively more efficient in coccolith formation than in carbon assimilation. The results suggest that light-dependent coccolith formation may be catalyzed by two photochemical reactions, one mediated by chloroplast pigments and the other by some pigment absorbing specifically in the blue part of the spectrum.     

PHYTOCHROME KINASE SUBSTRATE1 regulates root phototropism and gravitropism

Light promotes the expression of PHYTOCHROME KINASE SUBSTRATE1 (PKS1) in the root of Arabidopsis thaliana, but the function of PKS1 in this organ is unknown. Unilateral blue light induced a negative root phototropic response mediated by phototropin 1 in wild-type seedlings. This response was absent in pks1 mutants. In the wild type, unilateral blue light enhanced PKS1 expression in the subapical region of the root several hours before bending was detectable. The negative phototropism and the enhanced PKS1 expression in response to blue light required phytochrome A (phyA). In addition, the pks1 mutation enhanced the root gravitropic response when vertically oriented seedlings were placed horizontally. The negative regulation of gravitropism by PKS1 occurred even in dark-grown seedlings and did not require phyA. Blue light also failed to induce negative phototropism in pks1 under reduced gravitational stimulation, indicating that the effect of pks1 on phototropism is not simply the consequence of the counteracting effect of enhanced gravitropism. We propose a model where the background level of PKS1 reduces gravitropism. After a phyA-dependent increase in its expression, PKS1 positively affects root phototropism and both effects contribute to negative curvature in response to unilateral blue light.     

Osmotic adjustment in Spirulina platensis

Unilateral irradiation of maize (Zea mays L.) seedlings results in a fluence-rate gradient, and hence below saturation, a gradient of the far-red-absorbing form of phytochrome (Pfr). The Pfr-gradients established by blue, red and far-red light were spectrophotometrically measured in the mesocotyl. Based on these Pfr-gradients and the fluence-response curves of phytochrome photoconversion the fluence-rate gradients were calculated. The fluence-rate gradient in the blue (460 nm) was steeper than that in the red (665 nm), which in turn was steeper than that in the far-red light (725 nm). The fluence-rate ratios front to rear were 1:0.06 (460 nm), 1:0.2 (665 nm), and 1:0.33 (725 nm). The assumption that phytochrome-mediated phototropism of maize mesocotyls is caused by local phytochrome-mediated growth inhibition was tested in the following manner. Firstly, the Pfr response curve for growth inhibition was calculated; these calculations were based on measurements of Pfr-gradients and data from red-light-induced phototropism. Secondly, the Pfr response curve for growth inhibition was used as a basis for calculating fluence-response curves for blue-and far-red-light-induced phototropism. Finally, these calculated results were compared with experimental data. It was concluded that the threshold for phytochrome-mediated phototropism of maize mesocotyls reflects the apparent photoconversion cross section of phytochrome whereas the maximal inducable curvature depends on the steepness of the light (Pfr) gradient across the mesocotyl.Abbreviations Pfr far-red-absorbing form of phytochrome - Ptot total phytochrome - Fr far-red light