Photocontrol of hypocotyl elongation in light-grown Cucumis sativus L.

An interaction is demonstrated between the effects of phytochrome and cryptochrome (the specific blue-light photoreceptor) in the inhibition of hypocotyl elongation of light-grown cucumber (Cucumis sativus L.) cv. Ridge Greenline seedlings. At certain fluence rates of blue light the total inhibition response is greater than the sum of the separate responses to each photoreceptor. The threshold for response to blue light is reduced at least 30-fold by additional red-light irradiation. The synergistic effect is demonstrated for two different fluence rates of red light. Synergism is mediated by phytochrome in both the cotyledons and the hypocotyl.Abbreviations and symbols BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light - photostationary state of phytochrome - _c calculated      

Sucrose in storage media and cultivar affects post-storage regrowth of <Emphasis Type="Italic">in vitro</Emphasis> Hosta propagules

The goal of this research was to investigate if culturing in high sucrose (5%) liquid media during multiplication phase (stage II) would enhance endogenous sugar levels and dry matter sufficiently to allow storage of in vitro plants in sugar free media without adversely affecting post-storage recovery. Hosta tokudama Newberry Gold (NBG) and Hosta Striptease were cultured in Murashige and Skoog (MS) media containing 5% sucrose during stage II and transferred to rooting phase (stage III) in MS medium without (0%) sucrose or with 3% sucrose for 4weeks. At the end of stage III, cultures were stored, with the remaining media, at 10°C with 5molm^–2s^–1 photosynthetic photon flux (PPF) from cool white fluorescent lamps for 7 or 14weeks with or without a 2-week dark period prior to removal from storage. In both cultivars, stage III plants cultured in 3% sucrose media had higher soluble sugar levels and greater shoot and root biomass than those cultured in 0% sucrose media. Shoot and root soluble sugars decreased during storage. Shoot growth ceased during storage in both media. Root dry matter continued to increase in plants stored in 3% sucrose media but did not change in 0% sucrose media. Plants cultured in 3% sucrose media had less leaf chlorosis and less mortality after 7 or 14weeks of low temperature storage than the plantlets from sugar free media. Extending the storage period from 7 to 14weeks or introduction of 2-week dark period at the end of storage did not affect leaf chlorosis or plant mortality during acclimatization. Post-storage growth varied with the cultivar. Benefit of having sucrose in storage media was to develop a strong root system that aided the acclimatization and post-storage growth following 7 or 14week storage. Sucrose loading by culturing plants in liquid media containing 5% sucrose did not allow storage in sugar free media without adversely affecting post-storage growth in both cultivars.     

Comparative efficiencies of bispecific F(ab′γ)2 and chimeric mouse/human IgG antibodies in recruiting cellular effectors for cytotoxicity via Fcγ receptors

Summary The three forms of Fc receptor carried by monocytes (FcRI, II) and natural killer (NK) cells (FcRIII) are all capable of mediating cell lysis. Here we compare the use of F(ab)₂ bispecific antibodies, specifically targetting individual FcR, and chimeric IgG mouse/human antibodies which are capable of targetting all FcR, for their ability to mediate target cell destruction. The derivatives are prepared by linking hinge sulphydryl residues via tandem thioether bonds, using a bismaleimide crosslinker: Fab from an anti-FcR mAb linked to Fab from a common anti-target mAb (BsAb), or Fab from the common anti-target mouse antibody linked to human Fc (FabFc or bisFabFc). All the derivatives targetting chick red blood cells gave efficient lysis, although different effector cell donors yielded differences in both the lytic levels achieved and the comparative efficiencies of derivatives. In contrast, significant lysis of the guinea pig lymphoblastic leukaemia, L₂C, regularly resulted only via the anti-FcRIII BsAb and the chimeric derivatives. These results suggest that the chimeric, Fc-containing derivatives mediate tumour cell lysis principally through FcRIII on NK cells. This is in contrast to the situation with the chick red blood cells where the chimeric derivatives appear capable of lysing erythrocytes by utilizing either monocytes or NK cells, because significant (50%) lysis occurred with effector cell populations magnetically depleted through either FcRII or FcRIII. A major difference between these two types of antibody derivative was their ability to function in the presence of high concentrations of normal human Fc. The lysis mediated by BsAb reactive with FcRI or II was unaffected by the presence of human Fc at 2.5 mg/ml (a concentration comparable with that yielded by IgG in plasma) whereas the BsAb recognizing FcRIII and all the Fc-containing derivatives were completely inhibited.This work has been supported by Tenovus, the Cancer Research Campaign, the Leukaemia Research Fund, Italfarmaco, Milano, Italy and the Imperial Cancer Research Fund     

High irradiance response promotion of a subsequent light induction response in Sinapis alba L.

Relative quantum responsivity curves for inhibition of hypocotyl elongation in Sinapis alba L. seedlings previously grown in white light confirm that a marked end of day inhibition response can be induced by a monochromatic light treatment (30 min) at the end of the light period. In dark grown seedlings, however, no growth inhibition can be induced by a 30 min monochromatic light treatment. A prerequisite for an induction response appears to be a pretreatment with continuous light. Far red light is most effective with blue and red light showing a lesser effectiveness. The light pretreatment also shows a marked fluence rate dependency with respect to its ability to allow an induction response to manifest itself. The pretreatment required shows all the characteristics of a classical HIR response. The appearance of the effect in plants treated with the herbicide SAN 9789 seems to exclude chlorophyll as being the photoreceptor.Abbreviations SAN 9789 4-chloro-5-(methylamino)-2-(, , -trifluoro-m-tolyl)-3(2H)-pyridazinone - RG9 light long wavelength far red light (Schott RG9 colour glass) - FR far red light - WL white light - BL blue light - RL red light - D darkness - P_tot total phytochrome - P_fr far red absorbing form of phytochrome - HSR high irradiance response     

Inversion of gravitropism by symmetric blue light on the clinostat

Gravitropic stimulation of maize (Zea mays L.) seedlings resulted in a continuous curvature of the coleoptiles in a direction opposing the vector of gravity when the seedlings were rotated on a horizontal clinostat. The orientation of this response, however, was reversed when the gravitropic stimulation was preceeded by symmetric preirradiation with blue light (12.7 mol photons·m^–2). The fluence-response curve of this blue light exhibited a lower threshold at 0.5 mol·m^–2, and could be separated into two parts: fluences exceeding 5 mol·m^–2 reversed the direction of the gravitropic response, whereas for a range between the threshold and 4 mol·m^–2 a split population was obtained. In all cases a very strong curvature resulted either in the direction of gravity or in the opposite orientation. A minor fraction of seedlings, however, curved towards the caryopsis. Furthermore, the capacity of blue light to reverse the direction of the gravitropic response disappeared with the duration of gravitropic stimulation and it depended on the delay time between both stimulations. Thistonic blue-light influence appears to be transient, which is in contrast to the stability observed fortropistic blue-light effects.This work was supported by the Deutsche Forschungsgemeinschaft.     

Uptake of sewage derived nitrogen by<Emphasis Type="Italic"> Ulva rigida</Emphasis> (Chlorophyceae) in Bahía Nueva (Golfo Nuevo,Patagonia, Argentine)

Uptake kinetics of nitrogen derived from sewage–seawater mixtures (2.5–20% v/v effluent) were determined in the laboratory for Ulva rigida (Chlorophyceae) native from Bahía Nueva (Golfo Nuevo, Patagonia, Argentine). In terms of nitrogen concentration, experimental enrichment levels varied between 53.7 and 362.3M of ammonium and between 0.77 and 6.21M of nitrate+nitrite. Uptake rates were fitted to the Michaelis–Menten equation, with the following kinetic parameters: ammonium: V_max = 591.2molg^–1h^–1, K _s=262.3M, nitrate+nitrite: V _max=12.9molg^–1h^–1, K _s=3.5M). Both nutrients were taken up simultaneously, but ammonium incorporation was faster in all cases. The results show a high capability of Ulva rigida to remove sewage-derived nitrogen from culture media. In the field, most of the nitrogen provided by the effluent would be tied up in algal biomass, supporting low nitrogen levels found at a short distance away from the source.     

Oxygen free radicals induced release of lysosomal enzymes in vitro

Summary The effect of oxygen free radicals, generated by xanthine and xanthine oxidase, was studied on the release of lysosomal hydrolase from rat liver lysosomes in vitro. A lysosomal enriched subcellular fraction was prepared, using differential centrifugation technique, from the homogenate of rat liver. The biochemical purity of the lysosomal fraction was established by using the markers of different cellular organelles. Oxygen free radicals were generated in vitro by the addition of xanthine and xanthine oxidase. The release of lysosomal hydrolase (-glucuronidase) from the lysosomal fraction was measured. There was a 3 to 4 fold increase in the release of -glucuronidase activity in the presence of xanthine and xanthine oxidase when compared to that in the absence of xanthine and xanthine oxidase. In the presence of superoxide dismutase (SOD), a scavenger of oxygen free radicals, the xanthine and xanthine oxidase system was unable to induce the release of -glucuronidase activity from the lysosomes. Sonication (2 bursts for 15 sec each) and Lubrol (2 mg/10 mg lysosomal protein) treatment, which are known to cause membrane disruption, also induced the release of -glucuronidase from lysosomal fraction. This release of -glucuronidase by sonication and lubrol treatment was not prevented by SOD. These data indicate that lysosomal disruption is a consequence of oxygen free radicals, generated by xanthine and xanthine oxidase.Abbreviations HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - EGTA Ethylene Glycol Bis-(-aminoethyl ether)N,N,-N,N-tetracetic acid - Tris Tris (hydroxymethyl) aminomethane - SOD Superoxide Dismutase     

Breeding soybeans for the tropics capable of nodulating effectively with indigenousRhizobium spp.

Summary Most soybean varieties fail to nodulate effectively in tropical soils unless inoculated with a competitive strain ofRhizobium japonicum. Developing countries in the tropics, with few exceptions, lack inoculant industries to produce and distribute viable inoculants to small farmers and extension programs to teach them to use inoculant. Several soybean genotypes have been identified that nodulate effectively with many strains of the cowpea inoculation group which is ubiquitous in tropical soils of Africa. Soybean genotypes that nodulate and grow well without inoculant application are called promiscuous. Methodologies for incorporation of the promiscuity character into high-yielding backgrounds are discussed.Supported in part by grant 05-0560 from United Nations Development Program to the International Institute of Tropical Agriculture.     

Phototactic responses in Haematococcus lacustris and its modification by light intensity and the carotenoid biosynthesis inhibitor Norflurazon

At fluence rates below 45 W· m^-2 cells of the flagellate stage of Haematococcus lacustris react only positively phototactically with a rather high degree of orientation (indicated by r values up to 0.66 with the Rayleigh test). The directedness of orientation decreases with decreasing irradiance. The degree of directedness of the phototactic response depends on the intensity of preirradiation: Low light intensity applied after strong light application results in a dark reaction (low r values), low light given after darkness stimulates a rather high degree of directedness of positive phototaxis. Weak blue light (=483 nm; 0.4 W · m^-2) stimulates positive phototactic response, whereas comparable red light (=658 nm; 0.5 W · m^-2) does not.Cells which were grown in a medium containing 10^-4 M Norflurazon (effective in inhibition of carotenoid biosynthesis) although maintaining motility completely lose the ability to react positively phototactically. The possible role of carotenoids in the phototactic orientation is discussed.     

Phytochrome-mediated regulation of β-amylase mRNA level in mustard (Sinapis alba L.) cotyledons

Phytochrome, activated by continuous red light, increases the amount of total polyadenylated RNA during photomorphogenesis of mustard (Sinapis alba L.) cotyledons. In-vitro translation of total polyadenylated RNA in a reticulocyte translation system has shown that the activity of translatable -amylase mRNA is increased by phytochrome about threefold in the 3-d-old cotyledons, based on equal amounts of polyadenylated RNA, and about eightfold on a per-cotyledon basis. Cordycepin prevents the accumulation of translatable -amylase mRNA. It is concluded that the phytochrome-mediated control of -amylase synthesis is exerted on the level of mRNA synthesis. During seedling development in continuous red light, a phytochrome-dependent increase of -amylase mRNA can be observed at least 6 h before the onset of -amylase synthesis. If, after a period of enzyme synthesis, phytochrome action is interrupted by long-wavelength far-red light followed by darkness, -amylase mRNA as well as -amylase synthesis remain at a high level for 8–10 h and then decline sharply. It is concluded that -amylase mRNA, having an apparent lifetime of the order of 8–10 h, can be formed under the influence of phytochrome during early seedling development but it activates -amylase synthesis only after a lag-phase of about 8 h, when the cotyledons acquire competence to synthesize the enzyme. The consequences of these findings for the signal-transduction chain of phytochrome are discussed.Abbreviations EDTA Na₂-ethylenediaminotetraacetic acid - PAGE polyacrylamide gel electrophoresis - poly(A)⁺RNA polyadenylated mRNA - P_r, P_fr red- and far-red-absorbing forms of phytochrome - SDS sodium dodecyl sulfate - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Rooting apple cultivars in vitro: Interactions among light,temperature, phloroglucinol and auxin

Delicious apple (Malus domestica Borkh.) and several of its strains, which have been difficult to root in vitro, were successfully propagated with rooting percentages up to 100%. The combination of treatments used to achieve this result included placing the shoots on rooting medium in the dark at 30°C for the first week of the rooting stage, then moving them to a regime of 16 hr light-8 hr dark at 25°C. The rooting medium contained half strength Murashige and Skoog salts plus 1.2 M thiamine HCl, 0.56 mM myo-inositol, 1 mM phloroglucinol (PG), 1.4 M indolebutyric acid (IBA), 1.3 M gibberellic acid (GA₃), 87.6 mM sucrose, and 7 g l^–1 Difco Bacto agar. Dark treatment applied during the proliferation stage (etiolation) was less effective than one applied at the beginning of the rooting stage. The optimum length of dark treatment during rooting was 4 to 7 days. Increasing the temperature from 25°C to 30°C improved rooting of Delicious, Royal Red Delicious, and Vermont Spur Delicious in the absence of PG but generally had less effect in the presence of PG. Further increase in temperature to 35°C stimulated rooting of Royal Red Delicious but reduced rooting of Vermont Spur Delicious. Transfer of the cuttings to auxin-free medium after 1 week had no effect on percentage rooting and increased the number of roots per cutting for only 1 of 4 cultivars tested and then only in the presence of PG. In general PG stimulated rooting of Delicious and its strains, but had no effect on Golden Delicious.     

Changes of cytoplasmic free Ca2+ in the green alga Mougeotia scalaris as monitored with indo-1, and their effect on the velocity of chloroplast movements

The fluorescent calcium-sensitive dye 1-[2-amino-5-(6-carboxyindol-2-yl)-phenoxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,N,N-tetraacetic acid (indo-1) was loaded by a transplasmalemma pH gradient into filamentous cells and protoplasts of Mougeotia scalaris, such that most of the indo-1 fluorescence originated from the cytoplasm. Incubation of M. scalaris filaments in ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA)-buffered media (-log [Ca²⁺] (=pCa) 8 versus pCa 3) caused a consistent and significant decrease in the cytoplasmic free [Ca²⁺]. Pulses of the fluorescence excitation light (UV-A 365 nm, 0.7 s) caused an increase in cytoplasmic free [Ca²⁺] in M. scalaris that was nearly independent of the external [Ca²⁺] and of chloroplast dislocation by centrifugation. This calcium flux, highest in UV-A light, compared with blue or red light, probably resulted from a release of Ca²⁺ from intracellular stores. Increased cytoplasmic [Ca²⁺] may affect the velocity of chloroplast rotation since UV-A-light-mediated chloroplast movement was faster than in blue or red light. Consistently, the calcium ionophore A23187 and the calcium-channel agonist Bay-K8644 both increased the velocity of the red-light-mediated chloroplast rotation. Based on these and other observations, a Ca²⁺-induced decrease in cytoplasmic viscosity in Mougeotia is presumed to occur.Abbreviations EGTA ethylene glycol-bis-(-aminoethyl ether)N,N,N,N-tetraacetic acid - indo-1 1-[2-amino-5-(6-carboxyindol-2-yl)-phenoxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,N,Ntetraacetic acid - pCa log [Ca²⁺] - P_fr far-red-absorbing form of phytochrome - P_r red-absorbing form of phytochrome - x_G geometric mean Dedicated to Professor Wolfgang Haupt on the occasion of his 70th birthdayThis paper is part of the Ph.D. thesis of U. Russ at the Justus-Liebig-Universitat Giessen (FRG). Part of this work has been presented at a meeting on Calcium and intracellular signalling in plants in Plymouth, UK, Dec. 1990We are indebted to Dr. G. Seibold and Dipl. Phys. H. Weintraut for their advice on the technique of microspectrofluorometry and for allowing access to the microspectrophotometric facilities in the Strahlenzentrum der Justus-Liebig-Universität, Giessen, FRG. We thank Mrs. A. Quanz for reliable culture of the algae and evaluation of the videotapes. Bay-K8644 was a generous gift of Bayer AG, Wuppertal, FRG. U. russ was supported by a scholarship according to the Hessisches Graduierten Förderungsgesetz. This work was supported by the Deutsche Forschungsgemeinschaft.     

Rapid photomodulation of stem extension in light-grownSinapis alba L.

Treatment of the whole of aSinapis alba plant with supplementary far-red light (FR), in back-ground white light (WL), induces a rapid increase in stem extension rate. This rapid increase is regulated by the light environment of the stem itself. Supplementary FR to the stem increases extension rate after a lag period of 10–15 min. A lag period of 3–4 h follows FR irradiation of the leaf, before an increase in extension rate is detectable. When the stem is given supplementary FR, the change in extension rate which is induced increases with increasing FR fluence rate, and with decreasing phytochrome photoequilibrium. There is no difference between the effects of supplementary FR _max 719 nm and supplementary FR _max 739 nm for these relationships. The increase in extension rate induced by supplementary FR is reversed by an increase in the fluence rate of red light (R). These data indicate that the response is controlled by phytochrome photoequilibrium.Abbreviations B blue light - FR far-red light - R red light - WL white light - Pfr far-red absorbing form of phytochrome - Pr red absorbing form of phytochrome - P_tot total phytochrome level (=Pr+Pfr); -Pfr/Ptot, measured - ER difference in stem extension rate, before and after treatment     

A phylogenetic analysis ofLeucaena (Leguminosae: Mimosoideae)

Chloroplast DNA restriction fragment length polymorphisms have been used to reconstruct the maternal phylogeny of all the known taxa in the small neotropical legume genusLeucaena. Three major plastome clades were recognized, but these did not conform with relationships between the taxa proposed on other characters from morphology, cytology or hybridization. The maternal parentage of tetraploids within the genus has been proposed. Evidence for introgression was found between diploidL. diversifolia and tetraploidL. diversifolia. The implications of these results for the origin of the cultivated taxa are discussed.     

Mutants of Arabidopsis thaliana with altered phototropism

Thirty five strains of Arabidopsis thaliana (L.) Heynh. have been identified with altered phototropic responses to 450-nm light. Four of these mutants have been more thoroughly characterized. Strain JK224 shows normal gravitropism and second positive phototropism. However, while the amplitude for first positive phototropism is the same as that in the wild-type, the threshold and fluence for the maximum response in first positive phototropism are shifted to higher fluence by a factor of 20–30. This mutant may represent an alteration in the photoreceptor pigment for phototropism. Strain JK218 exhibits no curvature to light at any fluence from 1 mol·m^-2 to 2700 mol·m^-2, but shows normal gravitropism. Strain JK345 shows no first positive phototropism, and reduced gravitropism and second positive phototropism. Strain JK229 shows no measurable first positive phototropism, but normal gravitropism and second positive phototropism. Based on these data, it is suggested that: 1. gravitropism and phototropism contain at least one common element; 2. first positive and second positive phototropism contain at least one common element; and 3. first positive phototropism can be substantially altered without any apparent alteration of second positive phototropism.Abbreviation WT wild-type     

Fluence-response curves and action spectra for promotion and inhibition of seed germination in wildtype and long-hypocotyl mutants of Arabidopsis thaliana L.

The fluence-response curves of wildtype and long-hypocotyl mutants of Arabidopsis thaliana L. for induction and inhibition of seed germination, expressed as percentage germination on probit scale against logarithm of fluence, are very different in shape. The mutants show reduced photoinhibition of hypocotyl growth in white light compared with wildtype, suggesting they are either mutated in phytochrome, the blue/UV-absorbing photosystem or some other red-absorbing photosystem. Calculations of the amount of the far-red-absorbing form of phytochrome (Pfr), by a given fluence have been made taking into account pre-existing Pfr in the seeds. This pre-existing Pfr can change dramatically the slope of a fluence-response curve. Other factors such as an overriding factor, stimulating germination by a non-phytochrome-related process, the total phytochrome content, the range of normal distribution of logarithm of Pfr requirement of individuals in the population and differential screening can influence the form and-or position of a fluence-response curve. Action spectra calculated for germination induction and for the inhibition of induction for the different genotypes are qualitatively the same, having peaks of effectiveness at 660 nm and 730 nm respectively. In the blue region of the spectrum very little activity is seen in comparison with that of red light. Differences in bandwidth of effectiveness for induction of germination are attributed to different amounts of screening pigments in the seed batches. The long-hypocotyl mutants therefore have a normal phytochrome system operative in the control of seed germination, by short-term irradiation and no other photosystem appears to be involved.Abbreviations and symbols FR far-red light - P phytochrome - Pfr far-red-absorbing form of P - Pr red-absorbing form of P - R red light - SD standard deviation of logarithm Pfr around - logarithm Pfr required for 50% germination - aparent molar conversion cross section - maximum Pfr/Ptot established by a given wave-length - ₀ initial Pfr     

Phototropic fluence-response relations for Avena coleoptiles on a clinostat

Phototropism of Avena sativa L. has been characterized using a clinostat to negate the gravitropic response. The kinetics for development of curvature was measured following induction by a single pulse of blue light (BL), five pulses of BL at 20-min intervals, and this same pulsed-light regime following a 2-h red light (RL) pre-irradiation. A final curvature of about 14° is expressed within 180 min following the single pulse; a final curvature of about 62° in about 240 min following five pulses without pre-irradiation; and a curvature of over 125° in 360 min following five pulses after the RL pre-irradiation. For seedlings not pre-irradiated, the final curvature to five pulses of BL at a total fluence of 9.4 pmol·cm^-2 increases with time of darkness between pulses up to 15 min; with seedlings pre-irradiated with RL, curvature increased more slowly with time of darkness between pulses to a maximum at 35 min. The final curvature induced by a constant fluence of 9.4 pmol·cm^-2 increases linearly with time between the first pulse and last pulse of a five-pulse sequence. The curvature induced by a single BL pulse with a 5-min RL co-irradiation increases with fluence to a maximum of about 60° at about 10 pmol·cm^-2, and then decreases to 0° at about 200 pmol·cm^-2. Curvature induced by five BL pulses following a 2-h RL pre-irradiation increased with fluence from a threshold of about 0.05 pmol·cm^-2 to a maximum of 90° at about 10 pmol·cm^-2, and then gradually decreased with fluence to 50° at 1 000 pmol·cm^-2. Based on these data, it is concluded that the initial photoproduct formed by a BL pulse has a limited lifetime, that there is a kinetic limitation downstream of the photoreceptor pigment for phototropism, and that the additivive effect of pulsed BL is distinct from the potentiating effect of RL on phototropism. Thus, any degree of curvature from 0° to over 90° may be induced by a fluence in the ascending arm of what is traditionally called the first positive phototropic response.Abbreviations BL blue light - RL red light     

Development of an L6 myoblast in vitro model of moniliformin toxicosis

L6 myoblasts were used as an in vitro model to investigate the role of moniliformin and its interaction with monensin in turkey knockdown syndrome and sudden death syndromes in poultry. Cell viability and microscopic and ultrastructural alterations noted in L6 myoblasts cultured in the presence of moniliformin (0.0–0.3 g/l) were compared to those observed in parallel cultures also containing one of the following compounds: selenium (0–0.004 ng/l), thiamine (0–0.3 g/l), or pyruvate (0–0.46 g/l). Marked dilation of the RER, membranous whorls, glycogen deposition, membrane-bound cytoplasmic inclusions and necrosis were observed in myoblasts exposed to 0.03/2-0.30 g moniliformin/l medium. Supplementation of medium with thiamine and pyruvate, or selenium, provided significant protection to cells exposed to 0.0–0.3 g/l or 0.0–0.15 g moniliformin/l, respectively. Dose-dependent differences in protein and ATP production were not detected. Myoblasts grown in medium containing 0–0.15 g moniliformin/l and 7.5–50.0 M A23187, beauvericin or monensin had degrees of cytotoxicity similar to parallel cultures receiving only an ionophore. L6 myoblasts were a useful model of moniliformin toxicosis. The findings of this study suggest cytotoxicity due to moniliformin in L6 myoblasts may be due in part to oxidative damage and altered pyruvate metabolism, and that moniliformin does not predispose myoblasts to ionophore toxicosis. This study supports the results of in vivo investigations in poultry that moniliformin and monensin do not act synergistically to induce knockdown or monensin toxicosis.     

Transient reduction of responsiveness of blue-light-mediated hair-whorl morphogenesis inAcetabularia mediterranea induced by blue light

After a prolonged period of red light the formation of a new whorl of lateral hairs can be induced inAcetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva) by a pulse of blue light. It has previously been shown that the response to blue light obeys the law of reciprocity. In this paper we demonstrate that the responses to blue light are additive only within 10 min after the onset of blue-light treatment, since the responsiveness of the cells is also affected by blue light. One hour after a short blue-light pulse the response to a second blue-light pulse has come to a minimum. After that, the responsiveness is restored in a refractory period of several hours. The fluenceresponse curves for hair-whorl formation at the time of minimum responsiveness are shifted parallel to the original fluence-response curves without preirradiation. Again, the law of reciprocity applies. This indicates an increased light requirement only for the same degree of hair-formation response. The sensitivity to blue light of the reduction of responsiveness response is higher by a factor of about 50 than the induction of hairformation response.     

Mechanism of rapid suppression of cell expansion in cucumber hypocotyls after blue-light irradiation

Rapid suppression of hypocotyl elongation by blue light in cucumber (Cucumis sativus L.) was studied to examine possible hydraulic and wall changes responsible for diminished growth. Cell-sap osmotic pressure, measured by vaporpressure osmometry, was not decreased by blue light; turgor pressure, measured by the pressureprobe technique, remained constant during the growth inhibition; and stem hydraulic conductance, measured by dynamic and static methods, was likewise unaffected by blue light. Wall yielding properties were assessed by the pressure-block technique for in-vivo stress relaxation. Blue light reduced the initial rate of relaxation by 77%, but had little effect on the final amount of relaxation. The results demonstrate that blue irradiation acts to decrease the wall yielding coefficient, but not the yield threshold. Stress-strain (Instron) analysis showed that irradiation of the seedlings had little effect on the mechanical extensibilities of the isolated wall. The results indicate that blue light can reduce cell-wall loosening without affecting bulk viscoelastic properties, and indicate a chemorheological mechanism of cell-wall expansion.Abbreviations and symbols BL blue light - wall yield coefficient - Y wall yield threshold - P turgor pressure - L hydraulic conductance - g radial water-potential gradient supporting cell expansion - osmotic pressure - P_i initial chamber pressure needed to stop growth - P_f final chamber pressure needed to stop growth