The modulation of the conversion of l-aminocyclopropane-l-carboxylic acid to ethylene by light

Endogenous ethylene production of tobacco leaves was similar in light and in darkness. However, the rate of conversion of exogenously applied l-aminocyclopropane-l-carboxylic acid (ACC) to ethylene was reversibly inhibited by light. Virus-stimulated ethylene production, during the hypersensitive reaction of tobacco leaves to tobacco mosaic virus, was likewise inhibited by light. Under such circumstances ethylene production is limited at the level of the conversion of ACC to ethylene. Inhibition of the increase in ACC-stimulated ethylene production by cycloheximide and 2-(4-methyl-2,6-dinitroanilino)-N-methyl-propionamide after shifting leaf discs from light to darkness indicated that de novo protein synthsis was involved. Regulation of ACC-dependent ethylene production by reversible oxidation/reduction of essential SH groups, as suggested by Gepstein and Thimann (1980, Planta 149, 196–199) could be excluded. Instead, regulation of the ACC-converting enzyme at the level of both synthesis/degradation and activation/inactivation is suggested. Phytochrome was not involved in light inhibition, but low intensities of either red or blue light decreased the rate of ACC conversion. Dichlorophenyldimethylurea counteracted the inhibitory effect of light, indicating that (part of) the photosynthetic system is involved in the light inhibition. The ethylene production of Pharbitis cotyledons grown in darkness or light, either in the presence of absence of the inhibitor of carotenoid synthesis, SAN 9789 (norflurazon), supported this view.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - DCMU dichlorophenyldimethylurea - MDMP 2-(4-methyl-2,6-dinitroanilino)-N-methyl-propionamide - SAM S-adenosylmethionine - SH groups sulfhydryl groups - TCA trichloroacetic acid - TMV tobacco mosaic virus     

Effects of light and regulators on senescence-related changes in soluble proteins in detached oat (Avena sativa L.) leaves

The rate of senescence and the two-dimensional pattern of soluble proteins from detached oat leaves senescing in either darkness or light were analyzed, and compared to those of leaves in which senescence was delayed by application of the cytokinin benzyladenine or enhanced through the action of abscisic acid.Senescence of detached leaves in light did not differ significantly from senescence in attached leaves on intact plants. In darkness, protein was lost at a higher rate than in light, but several individual proteins showed relative increases. Notably, proteins previously characterized as high-molecular-weight proteins and senescence-associated proteins (Klerk et al., 1992) increased. Changes observed during incubation in light or darkness appeared to be related to this condition rather than the rate or progress of senescence. Cytokinins delayed and abscisic acid accelerated the changes in protein pattern compared to water. Beside changes previously identified in leaves senescing on the plant, detached leaves show alterations that reflect their condition of incubation rather than their developmental progress.Abbreviations 2D-PAG two-dimensional polyacrylamide gel electrophoresis - ABA abscisic acid - BA N⁶-benzyladenine - BSA bovine serum albumin - EDTA ethylenediamine tetraacetic acid - IEF isoelectric focusing - Rubisco ribulosebisphosphate carboxylase/oxygenase - SDS sodium dodecyl sulfate - Tris tris (hydroxymethyl) aminomethane     

Effect of red light and gibberellic acid on lipid metabolism in germinating spores of the fern Anemia phyllitidis

The spores of the fern Anemia phyllitidis contain abundant quantities of lipid as reserve material. Germination of these spores can be induced either by red light or, even in the dark, by gibberellic acid. The effects of both these factors on lipid degradation, lipase and isocitrate lyase activities, and on the fatty acid composition have been studied in the course of the germination process. During germination in darkness with gibberellic acid, the fatty acid composition remained similar to that in the ungerminated spore. In contrast, when spores were germinated in red light, α-linolenic acid was synthesized. Little activity of lipase and isocitrate lyase could be detected in the dry spore. Red light or gibberellic acid affected a dramatic increase of the activities of these enzymes. Lipid breakdown and lipase activity were more active in red light, however. Permanent stimuli were necessary for growth and complete lipid degradation. Induction of germination simultaneously with both factors revealed an additivity of the effects of red light and gibberellic acid.     

Factors increasing ethylene production enhance the sensitivity of root growth to auxins

Light inhibits root elongation, increases ethylene production and enhances the inhibitory action of auxins on root elongation of pea ( Pisum sativum L. cv. Weibulls Marma) seedlings. To investigate the role of ethylene in the interaction between light and auxin, the level of ethylene production in darkness was increased to the level produced in light by supplying 1-aminocyclopropane-1-carboxylic acid (ACC) or benzylaminopurine (BAP). Ethylene production was measured in excised root tips after treatment of intact seedlings for 24 h, while root growth was measured after 48 h. Auxin, at a concentration causing a partial inhibition of root elongation, did not increase ethylene production significantly. A 4-fold increase in ethylene production, caused either by light, 0.1 μ M ACC or 0.1 μ M BAP, inhibited root elongation by 40–50%. The auxins 2,4-dichlorophenoxyacetic acid and indolebutyric acid applied at 0.1 μ M inhibited root elongation by 15–25% in darkness but by 50–60% in light. Supply of ACC or BAP in darkness enhanced the inhibitory effects of auxins to about the same extent as in light. The inhibition caused by the auxins as well as by the BAP was associated with swelling of the root tips. ACC and BAP treatment synergistically increased the swelling caused by auxins. We conclude that auxin and ethylene, when applied or produced in partially inhibitory concentrations, act synergistically to inhibit root elongation and increase root diameter. The effect of light on the response of the roots to auxins is mediated by a light-induced increase in ethylene production.     

A phytochrome-mediated alteration from stem to rosette growth on chicory root explants in vitro

Chicory root explants (Cichorium intybus L. var. foliosum) of two cultivars, taken before and after hydroponic forcing, were cultured in vitro in complete darkness supplemented with red and far-red light treatments. Using 5 min red light per day, the strong stem elongation occurring in complete darkness was converted to rosette formation. This reaction was reversed to stem elongation (accompanied by leaf formation) adding 15 min far-red light after the red light. Fifteen min far-red light per day alone caused the same reaction as 5 min red/15 min far-red light. Far-red light followed by red light caused rosette formation. In stems, formed under complete darkness in vitro, the presence of phytochrome was shown. No phytochrome was detected in the root fragment itself.Abbreviations R red light - FR far-red light - GA gibberellinic acid - A absorbance - FW fresh weight     

Effects of abscisic acid,cytokinins, and light on isoflavonoid phytoalexin accumulation inPhaseolus vulgaris L.

Cotyledons ofPhaseolus vulgaris L. contain small amounts of phaseollin and kievitone. Isolating the cotyledons from the plant does not alter phaseollin levels. Kievitone levels, however, although not affected in light-incubated cotyledons, increased rapidly in dark-incubated cotyledons. Abscisic acid (ABA) at 10^-4 M stimulated the accumulation of phaseollin in excised cotyledons in both light and darkness, whereas benzylaminopurine (BAP) increased these levels only in the light. The kievitone level was influenced by ABA and BAP only in dark-incubated cotyledons, i.e., inhibited at 10^-4 M. When excised cotyledons were treated with mercuric chloride, both phaseollin and kievitone accumulated rapidly in both light and darkness. The effect of ABA on these cotyledons was similar to that on non-treated cotyledons. The results demonstrate that the synthesis of the two phytoalexins is regulated by separate mechanisms and indicate that the phytoalexin composition is dependent on the physiological condition of the cotyledons. ABA and BAP may play a role in the resistance response of the plant.Abbreviations ABA abscisic acid - BAP benzylaminopurine     

2-Amino-4-Phosphonobutyric Acid Exerts a Light-Dependent Effect on Post-Gabaculine Levels of Retinal γ-Aminobutyric Acid (GABA): Evidence that ON Synaptic Pathways Regulate Retinal GABAergic Transmission

Abstract: The effects of light, 2-amino-4-phosphonobutyric acid (APB), and kainic acid on rat retinal γ-aminobutyric acid (GABA)-ergic transmission were studied by measuring levels of retinal GABA following subcutaneous injection of gabaculine, an irreversible inhibitor of GABA-transaminase. Post-gabaculine levels of retinal GABA in light-exposed rats were significantly greater than those in rats held in darkness. The synaptic mechanism of this effect of light was examined by measuring post-gabaculine levels of retinal GABA in rats placed into either lighted or darkened conditions after receiving unilateral intravitreal injections of APB, a glutamate analogue that selectively decreases the activity of ON synaptic pathways in the retina. APB attenuated the post-gabaculine accumulation of GABA in rats held in the light, but not in those placed into darkness. Furthermore, the light-dependent increment in post-gabacu line accumulation of retinal GABA was entirely APB sensitive, and the effect of APB was entirely light dependent. In contrast to APB, kainic acid stimulated the post-gabaculine accumulation of retinal GABA in vivo. Our findings suggest that APB and kainic acid influence GABAergic transmission at different sites in the retina and that some retinal GABAergic neurons are either ON or ON-OFF amacrine cells.     

Events surrounding the early development of euglena chloroplasts: v. Control of paramylum degradation

The degradation of the storage carbohydrate, paramylum, is induced by light in wild-type Euglena gracilis Klebs var. bacillaris Pringsheim and in a mutant, W₃BUL, which lacks detectable plastid DNA. Treatment of wild type with cycloheximide in the dark produces 60% as much paramylum breakdown as light, whereas treatment with levulinic acid in the dark yields a slightly greater response than light. Both cycloheximide and levulinic acid produce a greater paramylum breakdown in the light than they do in the dark. Treatment of W₃BUL with levulinic acid in darkness produces a larger paramylum degradation than light, with values similar to wild type in the light. Treatment of W₃BUL with cycloheximide induces paramylum degradation in darkness, and as with wild type, light is slightly stimulatory in the presence of both cycloheximide or levulinic acid. Streptomycin brings about only a very small amount of paramylum breakdown in the dark and only slightly inhibits breakdown in the light. Thus paramylum breakdown induced by light does not require the synthesis of proteins on cytoplasmic or plastid ribosomes. A model which explains these results postulates the existence of a protein which inhibits paramylum breakdown. When the synthesis of this protein is prevented either by light, cycloheximide, or by levulinic acid acting as a regulatory analog of delta amino levulinic acid, paramylum breakdown takes place. Because levulinic acid is a better inducer than light in W₃BUL, W₃BUL may not be able to form as much delta amino levulinic acid in light as wild type. The small amount of induction by streptomycin is viewed as a secondary regulatory effect attributable to interference with plastid protein synthesis which affects regulatory signals from the plastid to the rest of the cell.     

An unusual effect of the far-red absorbing form of phytochrome: Photoinhibition of seed germination inBromus sterilis L.

Seeds ofBromus sterilis L. germinated between 80–100% in darkness at 15° C but were inhibited by exposure to white or red light for 8 h per day. Exposure to far-red light resulted in germination similar to, or less than, that of seeds maintained in darkness. Germination is not permanently inhibited by light as seeds attain maximal germination when transferred back to darkness. Germination can be markedly delayed by exposure to a single pulse of red light following 4 h inhibition in darkness. The effect of the red light can be reversed by a single pulse of far-red light indicating that the photoreversible pigment phytochrome is involved in the response. The response ofB. sterilis seeds to light appears to be unique; the far-red-absorbing form of phytochrome (Pfr) actually inhibiting germination.Abbreviations Pr red absorbing form of phytochrome - Pfr far-red absorbing form of phytochrome     

Interaction of jasmonic acid with some plant growth regulators in the control of apple (Malus domestica) embryo germination

Embryos isolated from dormant apple seeds were treated with jasmonic acid (JA), gibberellin A₃ (GA₃), abscisic acid (ABA) and hydrogen cyanide in darkness and in light. The chemicals were present in the culture medium continuously and simultaneously or applied for 2 days and in different sequences. All treatments stimulated embryo germination except ABA, which was strongly inhibitory. Additive effects of JA with light and with GA₃ on embryo germination were observed, whereas ABA interacted synergically with JA, HCN and light. ABA and GA₃ were most effective when applied early during embryo incubation, but the late JA treatment was more stimulatory. It is concluded that JA does not act on the regulatory pathway that is initiated by light and which leads to embryo germination through gibberellin accumulation and alkaline lipase activation. ABA and HCN appear to be involved in the control of this pathway. JA and ABA may be involved in the control of alkaline lipase activity, independently of this regulatory chain.Abbreviations ABA abscisic acid - GA₃ gibberellin A₃ - JA jasmonic acid     

Dark requirement for cell regeneration and colony formation by mesophyll protoplasts ofNicotiana plumbaginifolia Viv.

Summary The protoplasts ofNicotiana plumbaginifolia required darkness for cell regeneration and colony formation. Maximal plating efficiency of the protoplasts could be achieved by keeping the cultures in dark instead of light or dark/light sequence. Only two days of darkness prior to the illumination at 400 or 3,000 lux resulted in appreciable plating efficiency, than those of light from the beginning, but these values could not match the high plating efficiency in total darkness.     

Formation of kynurenic and xanthurenic acids from kynurenine and 3-hydroxykynurenine in the dinoflagellate Lingulodinium polyedrum: role of a novel,oxidative pathway

The dinoflagellate Lingulodinium polyedrum (syn. Gonyaulax polyedra) was used as a model organism for studying the effects of high and low physiological oxidative stress on the formation of kynurenic and xanthurenic acids from kynurenine and 3-hydroxykynurenine. Cell were incubated with the precursors and exposed to light (high physiological stress due to photosynthetically formed oxidants) or kept in darkness (low stress). In cultures of less than 0.5 ml cell volume/l of medium, cells took up approximately one half of 0.1 mM extracellular kynurenine within 18 h. The amino acid was partially converted to kynurenic acid, most of which was released to the medium; however, intracellular concentrations of the product were by approximately 10-fold higher than extracellular levels. Rates of kynurenic acid release exceeded by far those explained by kynurenine and tryptophan aminotransferase activities, the latter representing an additional source of kynurenic acid formation via indole-3-pyruvic acid. Light enhanced the release of kynurenic acid by approximately 4-fold; these rates were further increased by exposure to continuous light. Diurnal rhythmicity of kynurenic acid release was clearly exogenous and did not match with the circadian pattern of kynurenine or tryptophan aminotransferase activities; no rhythm was detected in constant darkness. Similar findings were obtained on turnover of 3-hydroxykynurenine to xanthurenic acid and release of the product to the medium. However, light/dark differences were relatively smaller, and additional products were formed, according to HPLC data obtained with electrochemical detection. Results are most easily explained on the basis of a recently discovered pathway of kynurenic acid formation from kynurenine, involving either non-enzymatic oxidation by H(2)O(2) or, at higher rates, enzymatic catalysis by hemoperoxidase. A corresponding mechanism may exist for the hydroxylated analogue.     

Effects of red and blue light on the composition and morphology of maize kernels grown in vitro

Growth and development of plants are known to be affected by exposure to red and blue light. Mechanisms by which light quality influences gene expression in maize (Zea mays L.) embryos have not been explored. Maize kernels can be cultured in vitro allowing experimental manipulation of environmental factors during seed development. We used the in vitro kernel culture system to investigate the response of developing maize seeds, which normally develop without exposure to light, to controlled light quality. Kernels grown under red light accumulated more dry weight than those grown in darkness, whereas kernels grown under blue light accumulated less. Reciprocal color shift experiments showed that light quality during the first week in culture had more influence on kernel weight than during the subsequent three weeks in culture. Soluble sugars were higher in both light treatments than in darkness. Blue-grown kernels had higher amino acid and lower lipid levels than red-or dark-grown kernels. Embryo morphology was markedly affected by red light, under which the upper shoot axis was longer than under blue light or in darkness. Embryo morphology was influenced by light quality during the later stages of development rather than the first week. We suggest, based on these results, that gene expression in the embryo and endosperm of developing maize seeds is sensitive to light quality, and the mechanism and time dependence of this effect warrant further study. In vitro maize kernel culture affords a convenient system for such light quality experiments.     

Relationship between light conditions and behavior of the freshwater snail Biomphalaria glabrata (Say)

The influence of light upon behavior of Biomphalaria glabrata was investigated in snails submitted for 48 h to one of the following regimes: normal light cycle, continuous darkness, continuous light. Time-lapse cinematography was used to provide data about snail locomotor activity in response to (a) continuous light or darkness; (b) light or dark phases; (c) light transitions. Snails were significantly less active under continuous light than under continuous or intermittent darkness. Under the normal light cycle, the activity rate was significantly higher in the dark than in the light. Changes from light to dark corresponded to increases in the activity rate which persisted long afterwards. No significant variation in activity occurred upon changes from dark to light.     

Effect of salicylic acid on protein composition of Tatar buckwheat Fagopyrum tataricum calluses with different ability for morphogenesis

The effect of salicylic acid on the content of soluble proteins and individual polypeptides in Tatar buckwheat Fagopyrum tataricum calluses differing in ability for morphogenesis was studied. Changes in the protein composition of the calluses cultivated in the dark and in the light indicated the higher sensitivity of the non-morphogenic callus. Different response of callus cultures to salicylic acid and conditions of cultivation (light, darkness) is suggested to be associated with the antioxidant defense system, which is, in particular, characterized by the hydrogen peroxide content in the calluses. Salicylic acid increased the H₂O₂ content in non-morphogenic calluses more strongly than in morphogenic calluses, and the difference was more significant for the calluses cultivated in the light.Translated from Biokhimiya, Vol. 70, No. 3, 2005, pp. 390–396.Original Russian Text Copyright © 2005 by Maksyutova, Galeeva, Rumyantseva, Viktorova.     

Survival of Chromatium vinosum at low light intensities

The effect of low irradiation on the viability of Chromatium vinosum was investigated. Cultures were precultivated at 1,000 lux (=0.1/h). Then, before the substrate was depleted, illumination was changed to either complete darkness or about 30 lux. Previously, the latter light intensity had been found not to promote growth.The parameters assayed were viability, protein, bacteriochlorophyll, ATP, RNA, DNA, absorbance (E ₂₆₀) of the supernatant, and total anthron-positive material.The data show that irradiation insufficiently high to promote growth, results in viability percentages as high as 90% after 8 days, whereas cultures incubated in complete darkness are virtually dead by then. Neither in the light nor in the dark a degradation of protein or cell wall hexoses was observed. The RNA content also remained constant. However, particularly in the dark cultures DNA was found to decrease concomitant with increased E ₂₆₀ readings of the supernatant. It is considered unlikely that such essential macromolecules are degraded to serve the maintenance energy requirements. The ecological impact of the observations is discussed.Non-Standard Abbreviations PHB poly--hydroxybutyric acid - Bchl Bacteriochlorophyll     

Senescence in wheat leaves: is a cysteine endopeptidase involved in the degradation of the large subunit of Rubisco?

In wheat (Triticum aestivum L.), leaf senescence can be initiated by different factors. Depending on the plant system (intact plants or detached leaves) or the environmental conditions (light, nutrient availability), the symptoms of senescence differ. The aim of this work was to elucidate the catabolism of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC. 4.1.1.39) under various senescence-inducing conditions. Leaf senescence was initiated in intact plants by darkness or by N-deprivation and in leaf segments by exposure to light or darkness. Depending on the treatment, a 50 kDa fragment of Rubisco was observed. The formation of this fragment was enhanced by leaf detachment and low light. In segments exposed to high light and in intact plants induced to senesce by N-deprivation, the fragment was essentially absent. Since an antibody against the N-terminus of a large subunit of Rubisco (LSU) did not cross-react with the fragment, it appears likely that a smaller fragment was removed from the N-terminus of LSU. Inhibitor studies suggest that a cysteine endopeptidase was involved in the formation of the 50 kDa fragment. Non-denaturing-PAGE followed by SDS-PAGE revealed that the fragment was produced while LSU was integrated in the holoenzyme complex, and that it remained there after being produced. It remains open how the putative endopeptidase reaches the stromal protein Rubisco. The results indicate that depending on the senescence-inducing conditions, different proteolytic enzymes may be involved. The involvement of vacuolar proteases must be considered as occurring during LSU degradation, which takes place in darkness, low light or under carbon limitation.     

Darkness improves growth and delays necrosis in a nonchlorophyllous habituated sugarbeet callus: Biochemical changes

The transfer of light-cultured green normal (N) and white habituated (HNO) sugarbeet callus to darkness reduced the growth of N callus and improved growth and delayed necrosis in the HNO callus. The decrease of dry matter of N callus under darkness was accompanied by a reduced content of carotenoids and by decreased CO₂ fixation, which was compensated by an increased dependency on externally supplied sucrose. The levels of some organic nitrogen compounds such as glutamate, proline, and free polyamines were not affected by transfer to darkness of N or HNO callus. Darkness decreased ethylene emissions in both callus types. In the HNO callus, the sucrose growth dependency and the CO₂ fixation were unaffected by darkness. Chlorophylls were absent both in light and darkness, whereas some carotenoids were accumulated in the HNO callus only in dark conditions. In another connection, a significant increase of peroxidase activity, which did not occur in the N callus, was induced by darkness in the HNO callus. A decreased content of thio-barbituric acid (TBA)-reactive substances was measured in the HNO callus transferred to darkness, whereas an increase was noticed in the N callus placed in the same conditions. These metabolic changes and the reduction of cellular damage in darkness revealed light-induced stress reactions leading to necrosis and to reduced growth of HNO callus. It appeared that darkness allowed the HNO callus to avoid the photooxidation stress. Therefore, the favorable effect of darkness on HNO growth might be explained by the suppression of photooxidative damage due to the absence of carotenoids. The higher peroxidase activity in the HNO callus maintained in darkness raised the problem of heme synthesis in this heterotrophic callus.