Streckungshemmung durch FUDR bei den Hypokotylen von Sinapis alba

Summary Seedlings of Sinapis alba which were grown in light for 24, 48 and 72 h after 36 h of dark treatment renew elongation when transferred to dark again. The rate of elongation decreases with increased light treatment. The per cent as well as absolute inhibition of elongation by FUDR decreases with the duration of light treatment. The shortening of the hypocotyl is due mainly to the inhibition of cell elongation. The inhibition is not directly proportional to DNA synthesis at any particular time.Plants without cotyledons are less inhibited than those with cotyledons. Cytosine arabinoside is inhibitory only at high concentrations. According to these results elongation inhibition by FUDR does not involve the entire DNA-synthesis.     

Rasch ablaufende Änderungen im Gehalt an löslichen Zuckern und Zellwandkohlenhydraten bei der phytochrominduzierten Photomorphogenese des Senfkeimlings (Sinapis alba L.)

Summary Short term changes in the soluble sugar, starch, and cell-wall carbohydrate content of the mustard seedling have been studied in the different organs during phytochrome induced photomorphogenesis in continuous far-red. The program was: imbibition of seeds 36 hrs dark far-red irradiation. Kinetics have been followed up to 12 hrs after the onset of irradiation.There are no substantial changes in carbohydrate content in the cotyledons and the radicle. In the cotyledons in far-red after a lag-phase of 3 hrs, there is a decrease in oligosaccharide content, and after a lag-phase of 6 hrs, an increase in cell-wall synthesis. The reducing sugar and starch content is not altered upon irradiation. In the radicle immediately after the onset of far-red, there is a temporary rise in the reducing sugar and cell-wall carbohydrate content. However, 6 hrs later the values in far-red again parallel those of the dark control.The important phytochrome dependent changes take place in the hypocotyl. In far-red after a lag-phase of 3 hrs the glucose accumulation is markedly retarded, the sucrose and starch content no longer increased, and the fructose content even decreases below the 3 hrs value. The glucose: fructose ratio, which is constant in dark, is shifted in favour of glucose. The lag-phase of phytochrome controlled hypocotyl elongation is about 1 hr, the lag-phase of the inhibition of cell-wall carbohydrate synthesis is in about the same order of magnitude.There seems to be neither any immediate connection between sugar content and cell-wall carbohydrate synthesis, as shown by the difference in lag-phases, nor does there seem to be any direct relationship between hypocotyl inhibition and overall synthesis of cell-wall material. The relative inhibition of cell-wall synthesis is less than one third of that of hypocotyl elongation (Figs. 5,6). Apparently phytochrome controls hypocotyl elongation by influencing the cell-wall structure.In spite of the fact that fat degradation is higher in far-red than in dark and respiration higher in dark than in far-red (Friederich, 1968), 6 hrs after the onset of far-red the increase of total carbohydrate content declines compared with that in dark. This finding leads to the conclusion that the efficiency of the fat-carbohydrate-transformation is higher in dark than in far-red.     

Further biological characteristics of galactoglucomannan oligosaccharides

The biological activity of cell wall-derived galactoglucomannan oligosaccharides (GGMOs) was dependent on their chemical structure. Galactosyl side chains linked to the glucomanno-core influenced their inhibition of elongation growth of pea (Pisum sativum L. cv. Tyrkys) stem segments induced by 2,4-dichlorophenoxyacetic acid (2,4-D). Reduction of the number of galactosyl side chains in GGMOs caused stimulation of the endogenous growth. Modification on the glucomanno-reducing end did not affect significantly the activity of these oligosaccharides. GGMOs inhibited also the elongation induced by indole-3-acetic acid (IAA) and gibberellic acid (GA₃). In the presence of IAA the elongation growth was inhibited to 20 – 35 % after 24 h of incubation depending on GGMOs concentrations (1 μM, 10 nM, 0.1 nM), similarly as in the presence of 2,4-D, which confirms the hypothesis of GGMOs antiauxin properties. The elongation induced by GA₃ was inhibited to 25 – 60 %, however, the time course of inhibition was different compared with IAA and 2,4-D. The highest inhibition was determined already after 6 h of incubation with a significant decrease after this time. The results indicated a competition between GGMOs and growth regulators.     

Investigations of the turnover of the putative cellulose-synthesizing particle “rosettes” within the plasma membrane ofFunaria hygrometrica protonema cells

Summary In youngFunaria protonemata the influence of various inhibitors and treatments on cell elongation, fine-structure, and particle rosettes within the plasma membrane, putative parts of cellulose synthase complexes, was investigated. Cycloheximide (3×10^–5M) inhibited growth, reduced the number of rosettes and evened the gradient of rosette distribution at the beginning of treatment. The cell fine-structure was unaffected. Actinomycin D (10^–5M and 10^–4) caused an initial but transient decrease in rosette number. Alterations in cell elongation and fine-structure have not been observed. Application of 2.6-dichlorobenzonitrile (10^–5 M) for some minutes reduced the number of rosettes remarkably, while cell elongation seemed to be normal after the filaments had been transferred back to normal medium. An incubation of 2 h or longer stopped growth and caused cells to burst. The number of rosettes then rose to about 50% of the control values. When applied for 7 h biofluor (5×10^–4 M) promoted growth slightly, but generally it retarded it when used for a longer time. It did not markedly affect the number of rosettes. A short heat stock stopped elongation, caused the disappearance of rosettes and affected the structure of the mitochondria and of the Golgi apparatus. Plasmolysed cells did not grow and, initially, did not have rosettes. At reduced turgor, wider cells are formed. Freeze fracturing under UHV conditions and shadowing at very low specimen temperature revealed a small, central depression in the 8 nm rosette particles, suggesting that they are composed of subunits. Our results provide further evidence that the rosettes are parts of the cellulose synthase complexes. Their existence clearly depends on protein synthesis and on the constitution of the plasma membrane, but not on cellulose crystallization.     

The Inhibition by Cytokinin of Auxin-Promoted Elongation in Excised Soybean Hypocotyl

The experiments characterize the inhibition by kinetin of auxin-promoted elongation in excised hypocotyl sections of 3-day soybean seedlings (Glycine max cv. Hawkeye 63). It was found that concentrations of kinetin above 4.2 μM did not further inhibit auxin-promoted elongation. Kinetin is as potent an inhibitor of elongation as actinomycin D or cycloheximide. Tissue incubated for 3 or 5 h in the absence of auxin or cytokinin would, upon addition of auxin, exhibit a new growth rate similar to that of tissue grown in auxin for the entire incubation period. Similarly, tissue grown for 3 and 5 h in the presence of auxin would revert to the control rate of elongation upon addition of kinetin. A 10 to 30 min preincubation in kinetin yielded the tissue incapable, for the ensuing 6 h, of increasing its rate of elongation in response to auxin. Zeatin and isopentenyladenine were more potent than kinetin and benzyladenine in the inhibition of elongation. Levels of ethylene produced in the presence of auxin plus cytokinin indicated that it was not involved in this auxin-cytokinin interaction. Kinetin by itself did not promote elongation; nor did it enhance auxin-promoted elongation at low auxin concentrations.     

Kinetic study of the toxicity of zinc and lead ions to the heavy metals accumulating fungus Paecilomyces marquandii

Studies have been carried out to determine the toxicity of zinc and lead ions to germinating spores and hyphal growth of heavy metal accumulating fungus Paecilomyces marquandii (former Verticillium marquandii). Inhibitive concentration (IC₅₀) of zinc and lead ions was assayed by three different methods: image analysis, nephelometric on-line measurement and microcalorimetry. A kinetic model of spore germination and germ tube elongation was formulated and used as an auxiliary tool to determine IC₅₀ values upon image analysis data. The inhibitive effect of Zn²⁺ and Pb²⁺ to P. marquandii spores was mathematically described by the Edwards equation. Comparing the obtained IC₅₀ values, lead ions occurred to be more toxic to the germinating spores of P. marquandii than zinc ions (2.80 and 5.20 mM, respectively), although zinc ions induced a more significant delay in the development of the hyphae (13.84 h for 5 mM of Zn²⁺ and 9.30 h for 5 mM of Pb²⁺), which was demonstrated by the lengthened lag-phase (spore-swelling phase).     

The stability of the postulated wall-loosening enzyme in acid-induced growth

Long-term pretreatments with cycloheximide (CH) caused inhibition of subsequent acidinduced growth of Avena coleoptile segments, but only after 6 or more h of CH treatment. These results together with previous, published evidence with frozen-thawed tissue are consistent with the hypothesis that there exists a wall-loosening enzyme responsible for acid-induced elongation and that it has a half-life of at least 7–8 h.     

Correlative inhibition of lateral bud growth in Phaseolus vulgaris L. timing of bud growth following decapitation

Summary On intact, 3-week-old plants of Phaseolus the larger bud in the axils of the primary leaves shows slow, continuous elongation growth. Release from correlative inhibition can be detected within 30 min following decapitation. When 0.1% indoleacetic acid in lanolin is applied to the decapitated stem stump, the lateral bud shows slow growth during the first 7 h, then stops completely for a further 15 h but after 2 days a further gradual increase in length is observed.The movement of ¹⁴C-labelled assimilates from the subtending primary leaf into the lateral bud increases following removal of the shoot apex. When indole acetic acid is applied to decapitated plants the ability of the buds to import ¹⁴C increases for 5–7 h and then declines to a negligible amount. Little or no radioactivity from tritiated indoleacetic acid is transported into the lateral buds of decapitated plants during the first 48 h following removal of the apex and it appears that rapid metabolism of the compound occurs in the stem tissues.     

Influence of Auxin on Young's Modulus in Stems and Roots of Pisum and the Theory of Changing the Modulus in Tissues

The effect of auxin on elastic extensibility has been investigated by means of the resonance frequency melhod in Pisum, sativum. The time lag for the decrease in Young's modulus E, caused by IAA, was between 2 and 3 minutes in etiolated stem internodes. The time lag for growth was about 7 minutes. The measurements of E in root segments were only qualitative owing to the structural characteristics; IAA decreases E in roots as it does in stems, but only in the region where IAA is assumed to enhance elongation. The connexion between elastic modulus and growth is discussed with reference to other investigations. The assumption has been made that a decrease in elastic modulus indicates a change in the cell wall which in some way is conducive to growth (induction of elongation). The theoretical possibilities of changing E have been discussed with reference to the formula for water fluxes. Both a change in a cell wall properly and a change in the cytoplasmic permeability are able to cause a change in E in the same way as auxin does. An early action of auxin must be located in the cell-wall-plasmalemma region.     

Evidence against the involvement of phytochrome in UVB-induced inhibition of stem growth in green tomato plants

The effects of UVB on the kinetics of stem elongation of wild type (WT) and photomorphogenic mutants of tomato were studied by using linear voltage transducers connected to a computer. Twenty-one or twenty-six-day-old plants, grown in 12 h white light (150 μmol m⁻² s⁻¹ PAR)/12 h dark cycles, were first transferred to 200 μmol m⁻² s⁻¹ monochromatic yellow light for 12 h, then irradiated with 0.1 or 4.5 μmol m⁻² s⁻¹ UVB for 12 h and finally kept in darkness for another 24 h. The measurements of the kinetics of stem elongation started after 4 h under yellow light. Significant differences in stem growth during the irradiation with yellow light, as well as during the dark period, were found between the genotypes. In darkness, the magnitude of stem growth followed the order: tri > AC = fri > MMau > hp1. Two factors determined the large differences of growth in darkness: 1) the different stem elongation rate (SER) and 2) the different duration of the growing phase among the genotypes. In darkness the stem growth of au and hp1 mutants lasted for about 18 h, whereas it continued for the whole experimental period (36 h) in the other genotypes. UVB irradiation substantially reduced elongation growth of all genotypes (4.5 μmol m⁻² s⁻¹ being more effective than 0.1 μmol m⁻² s⁻¹). Both fluence rates of UVB induced a detectable reduction of SER already after 15 min of irradiation. Red light inhibited, while far red light promoted stem growth of all the genotypes tested. fri (phyA null), tri (phyB1 null), hp1 (exhibiting exaggerated phytochrome responses) mutants and WT tomato showed similar levels of UVB–induced inhibition of growth, while the aurea mutant showed the largest growth inhibition during the 12 h of irradiation. These results indicate that phytochrome is not directly involved in UVB control of stem elongation. The results of dichromatic irradiations UVB + red or UVB + far red indicate the presence of distinct and additive action of UVB photoreceptor and of the phytochrome system in the photoregulation of stem growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigations of the turnover of the putative Cellulose-synthesizing particle “rosettes” within the plasma membrane ofFunaria hygrometrica protonema cells

Summary YoungFunaria protonemata were treated with Monensin (10^–6 M) and Cytochalasin (CB) (2×10^–5 M). The influence of the inhibitors on a) elongation growth, b) cell fine structure and c) particle rosettes within the plasma membrane after freeze fracture was observed. Monensin stopped cell growth, caused swelling of the mitochondria and plastids and inhibited the secretory activity of the Golgi apparatus within about 15 minutes. The number of rosettes in the PF of the plasma membrane was distinctly reduced after 4–5 minutes and decreased further to only very few after 30 minutes. The tip to base gradient in distribution was maintained for a long time. The effects were reversible, regeneration occurred within 3 hours. CB treatment showed no effect on elongation growth and cell fine structure. The number of rosettes, however, was strongly reduced within 3 minutes exposure time and their distribution was nearly uniform then. Number and tip to base gradient increased again after 6 minutes intoxication. The results are discussed in regard to the turn over of the rosettes.Abbreviations CB Cytochalasin B - PF protoplasmic fracture face - F-vesicle flat vesicle - F-Actin filamentous actin - G-Ac-tin globular actin     

Reversal of 5-fluorodeoxyuridine-caused growth inhibition in intact and excised etiolated hypocotyls of Sinapis alba L. by thymidine

Summary The elongation growth in etiolated, intact seedlings and excised hypocotyl segments of Sinapis alba is inhibited by FdUrd in the same fashion, and in either case there is a direct correlation between FdUrd concentration and inhibition of elongation growth. Removal of the roots reduced elongation; however, the percentage inhibition by FdUrd remained the same. Therefore, the growth inhibition by FdUrd is not a consequence of root growth inhibition.The growth inhibition in excised hypocotyls cultured on synthetic media is inversely proportional to the size of the segments, and of the seedlings from which they are taken. Elongation of the smaller segments is more sensitive to FdUrd than that of the larger ones. Anatomical observations showed that the inhibition of growth elongation by FdUrd in the hypocotyl segments is due to inhibition of cell elongation, and not of cell division. Root formation is inhibited in all isolated segments.The growth inhibition by FdUrd could be reversed by dThd but not by uridine, and this reversibility depended upon the FdUrd concentration. When FdUrd inhibition is partial (up to 10^-7M) relatively high dThd concentration (up to 100 fold) are required for complete reversal; when inhibition is maximal relatively lower dThd concentrations effect a complete or near-complete reversal. Irreversible, unspecific effects of FdUrd were not found.These experiments confirm that DNA synthesis is involved in cell elongation of the hypocotyls even when the apical meristem and roots are removed, and that the growth inhibition by FdUrd is not a nonspecific, toxic effect.Abbreviations FdUrd 5-fluorodeoxyuridine - dThd thymidine     

Response of actin microfilaments during phytochrome-controlled growth of maize seedlings

Summary In seedlings of maize (Zea mays L. cv. Percival), growth is controlled by the plant photoreceptor phytochrome. Whereas coleoptile growth is promoted by continuous far-red light, a dramatic block of mesocotyl elongation is observed. The response of the coleoptile is based entirely upon light-induced stimulation of cell elongation, whereas the response of the mesocotyl involves light-induced inhibition of cell elongation. The light response of actin microfilaments was followed over time in the epidermis by staining with fluorescence-labelled phalloidin. In contrast to the underlying tissue, epidermal cells are characterized by dense longitudinal bundles of microfilaments. These bundles become loosened during phases of rapid elongation (between 2–3 days in irradiated coleoptiles, between 5–6 days in dark-grown coleoptiles). The condensed bundles re-form when growth gradually ceases. The response of actin to light is fast. If etiolated mesocotyls are transferred to far-red light, condensation of microfilaments can be clearly seen 1 h after the onset of stimulation together with an almost complete block of mesocotyl elongation. The observations are discussed in relation to a possible role of actin microfilaments in the signal-dependent control of cell elongation.     

Role of abscisic acid in cotton fiber development

Fibers of three cotton cultivars varying widely in their final fiber length, i.e., long staple (Gossypium hirsutum H-4), middle staple (G. Hirsutum H-8), and short staple (G. Arboretum G. Cot-15) were analyzed to study the role of ABA in fiber elongation and dry matter accumulation, in vivo and in vitro. The fibers were analyzed for different growth parameters and endogenous ABA content during the entire period of their development using indirect ELISA by raising the antibodies against ABA. From growth analysis, cotton fiber development was divided into four distinct phases, (i) initiation, (ii) elongation, (iii) secondary thickening, and (iv) maturation. An inverse correlation between final fiber length and ABA content was observed in all the cultivars. In long staple cultivar (H-4), rapid ABA accumulation started after fiber had attained peak elongation growth while, in short staple cultivar (G. Cot-15), ABA accumulation was observed even during elongation growth. Significant inhibition in length of short and middle staple cultivars as compared to long staple cultivar was observed in in vitro grown fibers when media were supplemented with ABA (1, 3, and 5 mg/l). The addition of growth promoters like NAA and GA, along with ABA, has reduced the inhibition in fiber elongation in all the cultivars. These results suggest a regulatory role of ABA in cotton fiber elongation along with auxins and gibberellins. Published in Russian in Fiziologiya Rastenii, 2006, Vol. 53, No. 1, pp. 68–74. The text was submitted by the authors in English.     

The early time course of the inhibition of stem growth of etiolated pea seedlings by fluorescent light

The stem elongation responses of etiolated peas (Pisum sativum L.) to fluorescent light (35–45 mol.m^t-2.s^-1) were recorded using high resolution position transducers. Continuous fluorescent light decreased growth by 70% within 9 min. The growth rate declined to 5% of the control over the next 2 h and remained at this level for 7 h. Pulses of fluorescent light ranging from 8 s to 34 min led to partial suppression of growth and resulted in a complex kinetic response. The distinctive kinetics of blue and red light inhibition were apparent as components of the responses to non-saturating levels of fluorescent light. The rapid suppression of growth by blue light was not affected by concomitant red light. The lag time for the onset of red light inhibition was not affected by concomitant blue, but the rate of inhibition appeared accelerated.     

Effects of submergence on development and gravitropism in the coleoptile of Oryza sativa L.

Caryopses of rice (Oryza sativa L. cv. Sasanishiki) were germinated in air or under water. In submerged seedlings a twofold increase in coleoptile growth rate and an inhibition of root growth was observed. The amount of starch in the amyloplasts of submerged coleoptiles was substantially reduced compared to the air-grown control plants and plastids had a proplastidic character. During the rapid elongation of coleoptiles under water, the osmotic concentration of the press sap remained constant, whereas in air-grown coleoptiles a decrease was measured. Determination of curvature of gravistimulated air-grown and submerged shoots was carried out by placing the coleoptiles horizontally in air of 98% relative humidity. Air-grown coleoptiles reached a vertical orientation within 5 h after onset of gravistimulation. In coleoptiles germinated under water the first signs of consistent negative gravitropic bending occurred after 4–5 h and curvature was complete after 24 h. During the first 5 h of gravistimulation the water-grown coleoptiles grew at an average rate of 0.39 mm·h^–1, whereas in air-grown coleoptiles a rate of 0.27 mm·h^–1 was measured. Concomitant with the delayed onset of gravitropic bending of the water-grown coleoptiles, a change in plastid ultrastructure and an increase in starch content was observed. We conclude that the gravitropic responsiveness of the rice coleoptile depends on the presence of starch-filled amyloplasts.We wish to thank H.-J. Ensikat for technical assistance with the scanning electron microscopy. Supported by the Bundesminister für Forschung und Technologie and the Deutsche Forschungsgemeinschaft.     

Brassinolide application to Lepidium sativum seeds and the effects on seedling growth

Brassinosteroids have been reported to accelerate plant growth when applied to seeds. We examined the effects of seed treatment with brassinolide on early growth of Lepidium sativum (cress). Submicromolar and micromolar concentrations of brassinolide inhibited root growth within 48 h after seed treatment. Germination of cress was not affected by brassinolide. The inhibition of cress root growth by brassinolide was time specific in terms of eliciting the response. Untreated germinated seeds transferred to filter paper moistened with brassinolide solution did not exhibit the same level of root inhibition as treated seeds. Brassinolide (2 m) had no effect on ethylene levels, suggesting that at this concentration brassinolide is acting independently of ethylene to inhibit cress root elongation. Also, brassinolide had no effect on DNA synthesis within 24 h after seed treatment, but synthesis was reduced after 48 h. The results of this study illustrate a significant specific effect on very early cress root growth by seed treatment with brassinolide.Abbreviations BR brassinosteroid(s) - SDS sodium dodecyl sulfate - TCA trichloroacetic acid - ACC 1-aminocyclopropane-1-carboxylic acid     

Allelopathic Substance Exuded from a Serious Weed, Germinating Barnyard Grass (Echinochloa crus-galli L.), Roots

The allelopathy of a serious weed, barnyard grass (Echinochloa crus-galli L.), was investigated. Root exudates of young barnyard grass showed allelopathic effects and plant-selective activity and inhibited root elongation of all plants tested. With respect to shoot growth, the exudates did not show inhibition of barnyard grass only. The allelopathic substance was isolated and identified as p-hydroxymandelic acid by NMR. p-Hydroxymandelic acid strongly inhibited shoot growth and root elongation of all plants tested. The effects of three congeners of p-hydroxymandelic acid were tested on rice shoot growth. In the biological activity exhibited in rice, shoot growth was related to the hydroxyl groups. Received October 7, 1998; accepted March 29, 1999     

Comparative Effects of Indoleacetic Acid and Gibberellic Acid on Growth of Decapitated Etiolated Epicotyls of Pisum sativum cv. Alaska

Measurements were made of the growthof the sub-apical region of decapitated, etiolated epicotyls of Pisum sativum L. cv. Alaska after treatments with indoleacetic acid (IAA), gibberellic acid (GA) and triiodobenzoic acid (TIBA). Growth was measured either at the end of a 2-day period, at short intervals during growth, or was monitored continuously for 2–3 h using a position-sensing transducer. In experiments measuring growth after 2 days, high levels (0.1–10 μg/plnat) of IAA caused expansion, whereas similar levels of GA caused elongation. When both hormones were applied together, the effects of IAA were dominant and expansion ensued, even when GA was present at 100 times the amount of IAA. Very low amounts of IAA (0.5–5 ng/plant), however, caused elongation. The elongation elicited by high GA or low IAa was inhibited to a similar extent by TIBA and this inhibition of elongation was associated with an increased expansion at the extreme tip. When application of the hormones was delayed, GA-induced elongation was reduced considerably, IAA-induced elongation was lessened somewhat and IAA-induced expansion was partially converted into elongation. In experiments measuring elongation at short intervals, high levels of IAA caused rapid elongation followed after 3 to 6 h by expnasion. Both GA and low levels of IAA extended the duration of elongation with little apparent effect on the rate of growth. In fast-growth experiments, low, intermediate and high levels of IAA doubled the rate of elongation with a lag period of about 20 min, whereas GA had at most a very slight stimulatory effect on the growth rate. It is concluded that the main role of GA in this system is to maintain physiological levels of IAA in the growing zone and that the level of IAA present determines whether elongation or expansion will take place.