Action of red and far red light on ribosome formation in cabbage seedlings

The action of light on ribosome formation was examined in the cabbage seedlings, a system extensively used in the studies of anthocyanin synthesis. Ribosomes were extracted 18 h after the beginning of the irradiation and separated by sucrose gradient centrifugation. In the cotyledons of dark-grown cabbage seedlings, a brief red light induces an increase both in total ribosomes and in the fraction present as polysomes; the effect of red light is reversed by far red light, indicating the involvement of phytochrome in polysome formation in cabbage seedlings. Continuous red and continuous far red light are about equally effective in bringing about an increase of total ribosomes and of the polysome fraction. Streptomycin, which inhibits chlorophyll synthesis and chloroplast development, and enhances anthocyanin synthesis in cabbage seedlings, causes a decrease of total ribosomes and of the fraction present as polysomes. In hypocotyls, the red-far red reversibility is evident only for the polysome content and streptomycin does not decrease the polysome/monosomo ratio as it does in cotyledons.     

Comparison of the action of light on ribosomal RNA synthesis in cabbage and mustard seedlings

We have compared the action of light on ribosomal RNA synthesis in mustard and cabbage seedlings, two of the most frequently used systems for the studies of anthocyanin synthesis. The level of RNA (both t-RNA and r-RNA) “stored” in mustard dry seeds is much lower than in cabbage dry seeds. The kinetics of RNA synthesis in cabbage and mustard seedlings exposed to light are very different: In cabbage seedlings, light produces no apparent stimulation of cytoplasmic r-RNA synthesis, while it does increase plastid r-RNA synthesis. On the other hand, in mustard seedlings, light promotes both cytoplasmic and plastid ribosomal RNA synthesis. Streptomycin, which inhibits chlorophyll formation and chloroplast development while having no effect (mustard) or enhancing (cabbage) anthocyanin synthesis in these two systems, is in both cases an effective inhibitor of plastid r-RNA synthesis, but not of cytoplasmic r-RNA synthesis.     

Polyamine requirement for streptomycin action on protein synthesis in bacteria

Self-association between various heparan sulphate species and oligosaccharide fragments thereof have been studied by affinity chromatography. Polysaccharides or oligosaccharides were coupled to agarose and free chains were applied at low concentrations (less than or equal to 2 mg/ml) in 0.15 M NaCl to minimize self-association between free chains. The results show that the interaction may be specific. Heparan sulphate chains chiefly bind to gels substituted with cognate chains, i.e. the same kind or closely similar ones. Oligosaccharides of the general structure glucosamine-(iduronate/glucuronate-glucosamine)n--O--C(=CH2)--CHO were prepared by periodate oxidation/alkaline elimination and also coupled to agarose via the --CHO group. Cognate heparan sulphate chains were bound to this affinity matrix with the same affinity as in the case of heparan-sulphate--agarose. Free oligosaccharides were not bound to oligosaccharide-agarose, nor to the corresponding heparan-sulphate--agarose. Oligosaccharides of the same size and containing only iduronate were ineffective as affinity ligands. It is concluded that the segments comprising both iduronate and glucuronate may serve as contact zones in the heparan sulphate/heparan sulphate self-association and that the strength of binding is dependent on cooperative interactions between a number of such zones. The putative contact zones, as ligands on the matrix, showed an emerging lack of specificity as non-associating or unrelated and associating chains were bound to this gel. This is ascribed to a randomization of the contact zones which, in the polymeric chains, are placed in their proper register by the intervening (glucuronate-N-acetylglucosamine)n segments.     

Effectiveness of intermittent light treatments on anthocyanin synthesis in dark-grown and light-pretreated seedlings

Differences in the extent of anthocyanin production between intermittent light treatments with short and long dark intervals between successive irradiations are more pronounced in dark-grown than in light-pretreated cabbage seedlings. This observation is consistent with the hypothesis, based on destruction kinetics data, that there might be two pools of phytochrome, a labile one and a stable one, present in different proportions in dark-grown and light-pretreated seedlings, and suggests that light-dependent changes of the stable to labile phytochrome ratio might be physiologically significant in the photoregulation of photomorphogenic responses.     

Action spectrum and characteristics of the light activated disappearance of phytochrome in oat seedlings

The action spectrum for the light-activated destruction of phytochrome in etiolated Avena seedlings has been determined. There are 2 broad maxima, one between 380 and 440 mμ, the other between 600 and 700 mμ. peaking at about 660 mμ. On an incident energy basis, the red region of the spectrum is more efficient than the blue by about one order of magnitude in activating phytochrome disappearance. Both the red absorbing as well as the far-red absorbing forms of phytochrome are destroyed after exposure of Avena seedling to either red or blue light.

From the action spectrum and photoreversibility of pigment loss, we conclude that phytochrome acts as a photoreceptor for the photoactivation of its metabolically-based destruction. We suggest that another pigment might also be associated with the disappearance of phytochrome in oat seedlings exposed to blue light.

     

Action of streptomycin and dihydrostreptomycin on human chromosoms in vitro

Summary Comparative investigations concerning the action of streptomycin (SM) and dihydrostreptomycin (DHSM) on human chromosomes in vitro revealed a strong effectivity of SM in inducing achromatic lesions (AL) while DHSM is ineffective in this respect. Chromatid breaks (B) and isochromatid breaks (B) are not induced by the two streptomycins. Chromatid translocations (RB') were found only 3 times in all concentrations tested. The intrachromosomal distribution of the streptomycin-induced AL is very similar to the distribution of AL induced with the alkylating agent Chinon I and the thioxanthon derivative Miracil D. The view is discussed that the appearance of achromatic lesions cannot be interpreted as an indicator for a mutagenic activity of an agent.     

Photocontrol of anthocyanin synthesis: I. Action of short, prolonged, and intermittent irradiations on the formation of anthocyanins in cabbage, mustard, and turnip seedlings

Red far red reversibility (phytochrome control) of anthocyanin synthesis can be easily demonstrated for the response induced by short (5 minutes) and relatively short (4 hours) irradiation. Red far red reversibility of the response induced by longer irradiations can be demonstrated by the use of cyclic irradiations alternating short exposures to red and far red light.     

Action of red light on indole-3-acetic-acid status and growth in coleoptiles of etiolated maize seedlings

Brief irradiation of intact etiolated seedlings of maize (Zea mays L.) with red light (R; 30 W cm^-2, 10 min) reduces the amounts of diffusible and free (solvent-extractable) indole-3-acetic acid (IAA) obtainable from excised coleoptile tips. The effect is transient, the lowest level (30% of the dark control) occurring at about 3 h after irradiation. The free-IAA content of the whole coleoptile and the diffusible-IAA yield from the base of the same organ are similarly reduced, whereas the conjugated-IAA content of the coleoptile is not affected. These results support the view that R inhibits the production of IAA at the coleoptile tip. It is further shown that R inhibits biosynthesis of [³H]IAA from [³H]tryptophan supplied to the coleoptile tip. The shapes of the fluence-response curves obtained for the reduction of the diffusible-IAA yield by R and far-red light (FR) indicate the participation of two photoreactive systems. One has thresholds at 10^-3 W s cm² of R, five orders of magnitude less than the minimum required for the appearance of spectrophotometrically measurable far-red-absorbing form of phytochrome (Pfr) in vivo, and 10^-1 W s cm^-2 of FR; its response is linear to the logarithm of fluence exceeding five orders of magnitude. The other system is seen above 10² W s cm^-2 as an increase in the slope of the fluenceresponse curve; its response is FR reversible and related to the Pfr level of total photoreversible phytochrome. Both systems inhibit biosynthesis of IAA from tryptophan. Elongation of the coleoptile is stimulated by R; the stimulation is most apparent in the apical region, and is saturated with a fluence at which bo detectable pfr is formed. Farred light can also saturate this response. Since the endogenous IAA concentration in the coleoptile appears not to be in the inhibitory range, it is concluded that the stimulation of coleoptile elongation is not the result of changes in free-IAA levels.Abbreviations FR far-red light - IAA indole-3-acetic acid - Pfr phytochrome in the far-red-absorbing form - Pr phytochrome in the red-absorbing form - R red light     

Action of phenylephrine on protein synthesis in liver cells.

The alpha-adrenergic agonist phenylephrine was found to inhibit protein labelling from [3H]valine in isolated liver cells. This effect is only observable under conditions of partial Ca2+ depletion and in cells displaying maximal rates of protein labelling, i.e. cells isolated from fed animals or from starved animals when incubated in the presence of alanine. The ability of phenylephrine to inhibit protein labelling at near-saturating concentrations of the amino acid precursor indicates that this alpha-agonist actually decreases the rate of protein synthesis. The possibility that phenylephrine acts by making cellular Ca2+ availability further limiting can be ruled out, since alanine stimulates protein labelling under conditions of severe Ca2+ depletion obtained by pretreatment of the cells with EGTA. The following observations indicate that the phenylephrine action may be mediated by an increase in cellular cyclic AMP content: (1) a close relationship was found between the abilities of phenylephrine to inhibit protein labelling and to increase cyclic AMP content; (2) cyclic AMP mimics the phenylephrine action only in cells partially depleted of Ca2+; (3) the alpha 1-antagonist prazosin, which inhibited the phenylephrine-mediated increase in cyclic AMP, also abolished the effect on protein synthesis.     

Coaction between phytochrome and blue/UV light in anthocyanin synthesis in seedlings

Light-mediated mass production of blue/UV absorbing pigments, anthocyanin and/or other flavonoid compounds, can be considered an adaptive mechanism to protect a plant against high levels of short wavelength sunlight. Comparative studies of light-mediated formation of anthocyanin in seedlings of higher plants have been performed. As a result of Darwinian evolution, a seedling may be expected to form considerable amounts of pigment only when necessary and only to the extent required for protection ('economy principle'). The four species investigated with regard to light-mediated synthesis of anthocyanin in seedlings (mustard, milo, tomato, wheat), differ greatly with regard to their photoperception. Phytochrome is involved in the photoresponse in all cases. We conclude that the P_fr-mediated differential gene activation leading to anthocyanin synthesis is the core of the response. However, the different species differ greatly with regard to the red, blue and UV light dependent processes they perform in order to establish sensitivity towards phytochrome (P_fr), or to amplify sensitivity towards P_fr.     

Amino acid metabolism and protein synthesis in streptomycin resistant Vibrio El Tor.

Metabolic activities in relation to protein synthesis and amino acid utilization are altered in Vibrio El Tor after development of resistance towards streptomycin. Efficiency of in vivo and in vitro protein synthesis is markedly reduced in streptomycin resistant Vibrio El Tor. The rate of incorporation of 14C-amino acids into protein, uptake of 14C-valine and oxidation of certain amino acids are also altered.