Effect of exogenous dopa and tyrosine on amaranthin synthesis and pigment type in Amaranthus

The efrects of exogenously applied DOPA (l-3,4-dihydroxy-phenylalanine) and tyrosine on amaranthin synthesis under a variety of light conditions are described. A possible explanation for the light-sensitive period in development is suggested to be limitation of substrate in the less sensitive stages of development. A yellow pigment tentatively identified as a betaxanthin becomes apparent under exogenous DOPA feeding.     

Effects of light and kinetin on amaranthin synthesis induced by cAMP

The effects of cyclic 3′,5′-adenosine monophosphate (cAMP) on amaranthin synthesis in the dark, or in the presence of kinetin or light were investigated in isolated cotyledons of Amaranthus tricolor and A. caudatus. The results suggest that sites or modes of action of cAMP and kinetin are not separated and differ from those of light and that the nucleotide cannot be considered a messenger involved in amaranthin formation stimulated by kinetin or by light.     

Biosynthesis of amaranthin in Celosia plumosa

Seedlings of a yellow betaxanthin-producing variety of Celosia plumosa when fed with appropriate precursors are capable of synthesizing the red-violet pigment normally present in red varieties of the same species, namely amaranthin. Synthesis of amaranthin occurs in seedlings following administration of betanidin and betanin but much greater accumulation was observed after feeding cycloDOPA and its 5-O-β-d-glucoside. Possible pathways in the biosynthesis of amaranthin are discussed.     

Effects of G protein and cGMP on phytochrome-mediated amaranthin synthesis in Amaranthus caudatus seedlings

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Effects of G protein and cGMP on phytochrome-mediated amaranthin synthesis in Amaranthus caudatus seedlings

The effects of G protein and cGMP on phytochrome-mediated amaranthin biosynthesis inAmaranthus caudatus seedlings were studied. It was shown that G protein agonist cholera toxin induced amarathin synthesis in darkness, whereas G protein antagonist pertussis toxin inhibited red light-induced amaranthin synthesis. Amaranthin synthesis was also induced by exogenous cGMP, while the amaranthin biosynthesis induced by cholera toxin, red light and exogenous cGMP was inhibited by genistein. L Y-83583, an inhibitor of guanylyl cyclase, inhibited the amarenthin synthesis induced both by red light and cholera toxin, while it was not able to inhibit the amaranthin synthesis induced by exogenous cGMP. These results suggest that G protein, guanylyl cyclase and cGMP were the candidates in phytochrone signal transduction chain for red light-induced amaranthin biosynthesis and the red light signal transduction chain might be as follows: red light → phytochrome → G protein → guanylyl cyclase → cGMP.     

Effect of light and exogenously applied precursors on amaranthin synthesis in Amaranthus caudatus

Light stimulates the synthesis of amaranthin in Amaranthus caudatus var. viridis. Evidence suggests that this stimulation is markedly dependent on seedling age. Synthesis is controlled by both a “low-energy” red/far-red reversible phytochrome system and an HER at least partially under phytochrome control. In seedlings exposed to light, synthesis is promoted by exogenously applied DOPA and tyrosine. It is suggested that at least two light-promoted reactions occur in the biosynthetic pathway; one between tyrosine and DOPA and a second between DOPA and amaranthin.     

Photocontrol of betaxanthin synthesis in Celosia plumosa seedlings

Light stimulates the betaxanthin accumulation in Celosia plumosa. The induction is partially reversed by far-red and inhibited by actinomycin D, puromycin, salicylaldoxime and 2,4-dinitrophenol, while 3-(3,4-dichlorophenyl)-1,1-dimethylurea has an inhibitory effect only when photosynthesis is operative. In darkness betaxanthins synthesis is promoted by kinetin.     

光对尾穗苋幼苗内苋红素合成的诱导

不同苗龄的尾穗苋黄化苗对10 min,15Wm~(-2)白光的反应能力不同。光诱导的苋红素合成始于播种后第 20h,至50h合成能力最大,82h以后幼苗对短时光照的反应能力趋于消失。苋红素合成的滞后期为3h,光处理后18h色素积累达到高峰。光调节苋红素合成符合红光—远红光可逆诱导反应等两个基本模式,确证光敏色素参与调控苋红素合成.     

Effect of white and far-red light on betalain formation

Light-induced betalain synthesis has been studied in three species of Amaranthaceae. The results obtained suggest that the response to short-term irradiation with white light is mediated by phytochrome, while the effects of prolonged illumination are controlled by the photosynthetic system. Betalain accumulation stimulated by prolonged far-red irradiation is controlled chiefly by the photosynthetic system, the participation of phytochrome being of minor importance.     

The hormonal control of amaranthin synthesis in Amaranthus caudatus seedlings

Summary Exogenous gibberellic acid, A₃ (GA₃) inhibits phytochrome mediated betacyanin synthesis in seedlings of Amaranthus caudatus. The growth retardants, -chloroethyl-trimethylammonium chloride (CCC), 'isopropyl-4-(triethylammonium chloride)-5-methylphenyl piperidine carboxylate (AMO 1618) and tributyl-2,4,-dichlorobenzylphosphonium chloride (phosphon D) enhance pigment synthesis. Retardant stimulation of pigment synthesis is overcome by GA₃ application. Besides lowering endogenous GA levels the retardants inhibit protein synthesis by as much as 25%. Retardant inhibition of protein synthesis is not overcome by GA₃. The results suggest that amaranthin synthesis in Amaranthus caudatus can be directly controlled by endogenous GA. GA₃ has no effect on kinin induced dark pigment synthesis. Kinins, however, do not overcome GA₃ inhibition of pigment synthesis in the light.Abbreviations AMO 1618 2, 'isopropyl-4-(triethylammonium chloride)-5-methylphenyl piperidine carboxylate - CCC -chloroethyltrimethylammonium chloride - GA₃ Gibberellic acid, A3 - Phosphon D tributyl-2,4,-dichlorobenzylphosphoninm chloride     

Replacement of light by dibutyryl-CAMP and CAMP in betacyanin synthesis

The effect of adenosine 3′,5′-cyclic monophosphate and its N⁶,O^2′- dibutyryl derivative (Bu₂-CAMP) on betacyanin formation in etiolated Amaranthus paniculatus seedlings was investigated. Both substances can replace the action of light in the synthesis of these pigments, the formation of which is controlled by phytochrome. The specificity of this mimicry is underlined by the observations that sodium butyrate does not promote any betacyanin formation and that theophylline enhances the effect of Bu₂-AMP. Puromycin inhibits the induction of betacyanin synthesis by Bu₂-CAMP just as it does the light-induced pigment formation. These findings suggest that phytochrome exerts its controlling role in the synthesis of betacyanins through the agency of CAMP.     

Photoregulation of the Greening Process of Wheat Seedlings Grown in Red Light*

Wheat seedling grown with their shoot bottom exposed to red light (400 μmol m⁻² s⁻¹) either with constant illumination or light-dark cycles did not accumulate chlorophyll. This near-etiolation response was manifested by a critical threshold intensity of red light and did not need continuous illumination. The inhibition of the greening process resulted from reduced synthesis of glutamate-1-semialdehyde and consequent reduction in tetrapyrrole precursor 5-aminolevulinic acid. Red light perceived by the shoot bottom down regulated the protein and/or gene expression of enzymes involved in the biosynthesis of tetrapyrroles. The contents of endogenous cytokinins, i.e., isopentenyl-adenosine and dihydrozeatinriboside, were reduced in seedlings grown in red light having their shoot bottom exposed. Application of exogenous cytokinin and its analogue to roots of seedlings grown in red light reversed the down regulation of the greening process. The reversal of red-light-induced near-etiolation morphogenesis by far-red (200 μmol m⁻² s⁻¹) or blue (25 μmol m⁻² s⁻¹) light suggests that it could be a very high red-irradiance response of phytochrome, in the meristematic layers of the shoot bottom, that works in concert with blue light receptor(s). This work was supported by a competitive grant from the Department of Science and Technology, Govt. of India (DST/SP/SO/A-49/95) to BCT. Suchi Sood Varsha Gupta: Equal contributors     

Effect of continuous far red on betaxanthin and betacyanin synthesis

Seedlings of Celosia plumosa under prolonged irradiation with far red light synthesize chlorophyll α and betaxanthin. Levulinic acid and 2,4-dinitrophenol, inhibitors of chlorophyll synthesis and cyclic photophosphorylation respectively, reduce betaxanthin synthesis. Pigment formation is also inhibited by actinomycin-D and puromycin, but is unaffected by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of noncyclic photophosphorylation. These findings are evidence of the involvement of photosynthesis through cyclic photophosphorylation, in the far red HER associated with betaxanthin synthesis. Under continuous far red seedlings of Amaranthus tricolor synthesize only chlorophyll α. Lack of betacyanin formation is ascribed to the inactive status of the genes involved in the pigment synthesis.     

Phytochrome control of amino acid synthesis in cotyledons of Sinapis alba

Continuous far red light, acting through phytochrome, stimulates the rate of incorporation of density label into amino acids in the cotyledons of Sinapis alba. It is shown that such stimulation leads to increased incorporation of label into proteins. This has important consequences for experiments in which rates of enzyme synthesis in light treated and dark grown plants are compared by labelling methods. The results of some such experiments are re-evaluated.     

The effects of hormones and inhibitors on amaranthin synthesis in seedlings of Amaranthus tricolor

Summary Both gibberellic acid and abscisic acid inhibit the light induced synthesis of amaranthin in Amaranthus tricolor seedlings. The auxin, indolyl-3-acetic acid has no effect. The protein/RNA inhibitors, cycloheximide and 8-azaguanine, also reduced the levels of amaranthin produced.     

Light signaling in plants

Light signals have profound morphogenic effects on plant development. Signals perceived by the red/far‐red absorbing phytochrome family of photoreceptors and the blue/green/ UV‐A absorbing cryptochrome photoreceptor converge on a group of pleiotropic gene products defined by the COP/DET loci to control the pattern of development. The signaling pathway, although still undefined, includes several classic signaling molecules, such as G‐proteins, calcium, calmodulin, and cGMP. A separate signaling pathway is involved in the modulation of the phototropic response. Additional mutants have been identified that affect subsets of light signaling responses. This review provides an overview of our current understanding of the light signaling process, in particular recent genetic and biochemical advances.     

Effect of rare earth element europium on amaranthin synthesis in Amarathus caudatus seedlings

Considering the resemblances between Eu³⁺ and Ca²⁺ in their atomic radius and structures of the valence electron, the effects of Eu³⁺ on amaramthin synthesis in Amarathus caudatus seedling were studied. Eu³⁺ had both promoting and inhibiting effects on amaramthin synthesis. The optimum promoting concentration and half inhibiting concentration of Eu³⁺ to synthesis of amaranthin were 0.4 mmol/L and 2.5 mmol/L, respectively. In the dark, A₂₃₁₈₇ (ions carrier) could carry Eu³⁺ into cells through the Ca²⁺ channel. When Ca²⁺ was chelated with EGTA, the synthesis of amaranthin could be partly retrieved by Eu³⁺. Eu³⁺ treatment could also activate Ca²⁺-ATPase on plasma membrane. Moreover, the sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of total proteins from the plants treated by Eu³⁺ and Ca²⁺ were similar but slightly different in the contents. It suggested that the effects of Eu³⁺ and Ca²⁺ on amaranthin synthesis were similar. After being treated by Eu³⁺ or Ca²⁺, the outside Ca²⁺ could enter into cells to promote synthesis of amaranthin. The results above indicated that Eu³⁺ might replace Ca²⁺ in the calcium/calmidulin-dependent phytochrome signal transduction system and play important roles in plant development by promoting calcium transportation across plasma membrane.     

Regulation by light of chlorophyll synthesis in the cotyledons of Scots pine (Pinus sylvestris) seedlings

Seedlings of gymnosperms, unlike angiosperms, synthesize chlorophyll(ide) (Chl) in darkness (D). In Scots pine cotyledons ( Pinus sylvestris L.) Chl accumulation ceases in D at a low level but Chl accumulation is strongly increased by light, red light (R) being more effective than blue light (B), whereas in Pinus maritima Chi synthesis is almost light-independent. In Scots pine the capacity to form Chl can be increased by R pulses, fully reversible by far-red light, demonstrating the involvement of phytochrome. However, when B- or R–grown seedlings were transferred to D, Chl accumulation stopped immediately irrespective of the level of P_fr (far-red light absorbing form of phytochrome), indicating that the conversion of protochlorophyllide (PChl) is light-dependent. Dose response curves in R and B and simultaneous irradiation with R and B show that R and B are perceived by separate photoreceptors. The immunodetected NADPH-dependent protochlorophyllide oxidoreductase (POR, EC 1.6.99.1), assumed to regulate light-dependent Chl synthesis in angiosperms, is not correlated with the capacity of gymnosperm Chi accumulation in darkness. While two FOR bands could be separated in extracts from dark grown material (38 and 36 kDa) of Pinus sylvestris and P. maritima , only the 38 kDa band disappeared consistently in the light. However. the significance of the more light resistant 36 kDa band for chlorophyll synthesis remains unclear as well.     

Light and chlorophyll gradients within Cucurbita cotyledons

Abstract. Measurement of light within 10–14-d-old green and etiolated Cucurbita pepo cotyledons were made with fibre-optic microprobes to assess the influence of chlorophyll distribution and anatomical variations in mesophyll cell type (spongy versus palisade) on internal light pattern. More than 50% of the pigment in green cotyledons occurred in the upper (adaxial) 300 μm and this gradient strongly influenced the internal propagation of 680 nm light. When the upper (adaxial) surface was irradiated with 680 nm light, almost complete absorption occurred within the first 400 μm (palisade) of approximately 1200-μm-thick cotyledons. In contrast, when lower (abaxial) surfaces were irradiated with 680 nm light, penetration extended throughout the spongy mesophyll to about the 700 μm depth. Measurements of collimaled and scattered light gradients at 550, 680 and 750 nm indicated that collimaled light was rapidly scattered by mesophyll cells. In cotyledons irradiated on the upper surface, spongy mesophyll cells received only scattered light. Furthermore, comparisons of scattered light gradients obtained from cotyledons irradiated on upper and lower surfaces suggested that spongy mesophyll cells scatter light more effectively than palisade cells, probably due to the greater proportion of intercellular air spaces in spongy mesophyll tissue. These data also indicate that both the spectral quality and quantity of light incident on palisade versus spongy mesophyll cells differs, perhaps contributing to developmental and physiological differences between these two mesophyll cell types.     

Comparison of cytokinin activities of 9-substituted N6-benzyladenines in the Cucumis and Amaranthus bioassays

9-Substituted N⁶-benzyladenines were tested for their ability to eliminate the lag phase in and promote chlorophyll synthesis in Cucumis sativus cotyledons and for their effectiveness in eliciting the dark biosynthesis of betacyanin in Amaranthus tricolor cotyledon-hypocotyl explants. The following general relationships were established for dose-responses: (a) 9-ribosidation brought about little (in Amaranthus) or no (in Cucumis) decrease in activity relative to the free base, (b) the presence of a 9-ribose 5′-phosphate group moderately depressed activity in Amaranthus but slightly enhanced activity in Cucumis, (c) the presence of a 9-ribose 3′,5′- cyclic phosphate group depressed activity substantially in both systems, more so in Amaranthus, (d) 9-glucosylation greatly decreased activity, as did 7-glucosylation, while 3-glucosylation depressed activity to a much lesser extent, in both systems, (e) 9-substitution with cyclopentyl, methyl, methoxymethyl, and tetrahydropyranyl groups reduced activity, the first two substituents more so than the last two, and (f) alteration of the 9-riboside group to a 9-[2-O-β-hydroxyethylglycerol] moiety by oxidation- reduction led to complete (in Amaranthus) or nearly complete (in Cucumis) inactivation. Responses to hormone treatment were detectable after dark incubation times as short as 4 hr (in Cucumis) or 8 hr (in Amaranthus).