Involvement of Ethylene in Phytochrome-mediated Carotenoid Synthesis

Accumulation of carotenoid pigments in the shoot apex of etiolated pea (Pisum sativum cv. Alaska) seedlings is completely prevented by ethylene. Under certain conditions carotenoid synthesis is normally controlled by endogenously produced ethylene. The gas completely inhibits carotenoid synthesis induced either by continuous white light or brief illumination with red light, but only partially inhibits light-induced chlorophyll formation. Far red illumination followed by red illumination reverses the action of red light on carotenoid synthesis. Red light-induced carotenogenesis is partly or wholly caused by phytochrome-mediated inhibition of ethylene biosynthesis.     

Phytochrome-mediated Carotenoids Biosynthesis in Ripening Tomatoes

Red light induced and far red light inhibited carotenoid biosynthesis in ripening tomatoes (Lycopersicon esculentum Mill.) when compared to controls kept in the dark. Red illumination following far red illumination reversed the inhibitory action of far red light on carotenoid biosynthesis, suggesting a phytochrome-mediated process. Quantitation of individual carotenoids favored the hypothesis of two separate carotenoid biosynthetic pathways in tomatoes.     

Formation of chlorophyll B, and the fluorescence properties and photochemical activities of isolated plastids from greening pea seedlings

Chlorophyll b was first detectable after 10 minutes of illumination of etiolated pea seedlings (Pisum sativum L. var Greenfeast) with continuous white light. The chlorophyll a/b ratio decreased from 300 at 10 minutes to 15 after 1 hour. There was little change in the chlorophyll a/b ratio between 1 and 2 hours, and it declined to 3 between 2 and 5 hours of illumination. In red light, the time courses of total chlorophyll synthesis and chlorophyll a/b ratio were similar to those in white light for the first 5 hours of illumination. But with increasing time of illumination with red light, there was an increase in the chlorophyll a/b ratio to 7 after 30 hours. Illumination with white light of very low intensity also gave high chlorophyll a/b ratios. Seedlings which had been illuminated for varying periods and then returned to darkness always showed an increase in chlorophyll a/b ratio during the dark period. It is concluded that the synthesis of chlorophyll b is controlled by light.     

Light-induced Polysome Formation in Etiolated Leaves: Kinetics of Inhibition by Antibiotics

Red light-induced, far red light-reversible increase in etiolated bean (Phaseolus vulgaris, var. Asgrow Valentine) leaf polyribosomes was shown to be sensitive to actinomycin D, cycloheximide, and rifampicin inhibition. Actinomycin prevented response to red light if administered simultaneously with a 10-minute illumination, had no immediate effect if given 2 hours after illumination, but was again rapidly inhibitory at 4 and 6 hours. The effects of actinomycin and far red light were more than additive.     

In the presence of red light,cucumber and possibly other host plants lose their attractability to the melon thrips <Emphasis Type="Italic">Thrips palmi</Emphasis> (Thysanoptera: Thripidae)

The melon thrips, Thrips palmi Karny (Thysanoptera: Thripidae), is a serious agricultural pest of many crops. Previous studies have shown that red light decreases the number of Thrips palmi in greenhouses. In order to understand how red light affects T. palmi, we examined the behavioral responses to host plants that were irradiated with a red light-emitting diode panel (660 nm) in an environment with natural or fluorescent (normal-white) light. When T. palmi were allowed to move freely around in the experimental arena, we found that fewer individuals were attracted to plants irradiated by red light than to plants under normal light illumination. We then used a sticky trap of green coloration to exclude olfactory and visual stimuli associated with the host plants in order to test binary choice behavior in T. palmi. The number of thrips attracted to the green sticky trap irradiated with red light was approximately half of that without red light irradiation. This is the first study to show that an addition of red light can change the behavior of insects, leading to an avoidance of green targets in an environment of normal illumination.     

The role of xanthoxin in the inhibition of pea seedling growth by red light

Intermittent periods of red light illumination inhibit the growth of dwarf pea seedlings within 1 day and stop length increase completely in 3 days. Cis,trans-xanthoxin is synthesized within the plant during the 1st day of illumination and reaches a maximum level on the 3rd day. The red light treatment also causes an increase in the levels of violaxanthin, linoleic acid and peroxidase, lipoxygenase and carotene-bleaching activities in the plant. The possible control of xanthoxin production is discussed.     

Relation of Phytochrome-enhanced Geotropic Sensitivity to Ethylene Production

Brief exposure of etiolated pea (Pisum sativum cv. Alaska) seedlings to red light enhances subsequent development of geotropic curvature of the stem. Both this response and inhibition of ethylene production by red light become maximal 8 hours after illumination. Very low concentrations of applied ethylene inhibit development of geotropic curvature, whereas hypobaric treatment enhances geotropic sensitivity by removing endogenous ethylene. Increased geotropic sensitivity after illumination is accompanied by increased lateral migration of ³H-indoleacetic acid in response to gravity, and ethylene inhibits this lateral migration. It is suggested, therefore, that red light-enhanced geotropic sensitivity is caused by increased lateral auxin transport resulting from a reduction in ethylene production after illumination.     

Effects of light quality on the circadian rhythm of leaf movement of a short-day-plant

Studies were made of the effects of blue, green, red and far-red (FR) light on the circadian rhythm of leaf movement of Coleus blumei × C. frederici, a short day plant. Under continuous illumination with blue light, there was a significant lengthening of the period of the rhythm to about 24.0 hr, as compared to 22.5 hr in continuous darkness. Under continuous red light, the period length was significantly shortened to 20.5 hr. Under continuous green or FR, the period length was not significantly different from the dark control. It was observed that under continuous FR illumination, the leaves tended to oscillate in a more downward position. Eight-hr red light signals were effective in advancing the phase of the rhythm as compared to a control under continuous green light. Blue light signals were effective in delaying the phase of the rhythm. FR light signals were ineffective in producing either delay or advance phase shifts. Far-red light did not reverse the effects of either red or blue light signals. On the basis of these results it is suggested, that pigments which absorb blue or red light, rather than phytochrome, mediate the effect of light on the circadian rhythm of leaf movement.     

Redox Processes in the Blue Light Response of Guard Cell Protoplasts of Commelina communis L

Guard cell protoplasts from Commelina communis L. illuminated with red light responded to a blue light pulse by an H⁺ extrusion which lasted for about 10 minutes. This proton extrusion was accompanied by an O₂ uptake with a 4H⁺ to O₂ ratio. The response to blue light was nil in darkness without a preillumination period of red light and increased with the duration of the red light illumination until about 40 minutes. However, acidification in response to a pulse of blue light was obtained in darkness when external NADH (1 millimolar) was added to the incubation medium, suggesting that redox equivalents necessary for the expression of the response to blue light in darkness may be supplied via red light. In accordance with this hypothesis, the photosystem II inhibitor 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (10 micromolar) decreased the acidification in response to blue light more efficiently when it was added before red light illumination than before the blue light pulse. In the presence of hexacyanoferrate, the acidification in response to a blue light pulse was partly inhibited (53% of control), suggesting a competition for reducing power between ferricyanide reduction and the response to blue light.     

Photoreduction and Oxidation of Cytochrome f in Bundle Sheath Cells of Maize

The photo-oxidation of cytochrome f (cytochrome c₅₅₄) in bundle sheath cells isolated from leaves of maize (Zea mays var. DS 606A) has been compared with that in intact maize leaf and in isolated pea leaf cells (Pisum sativum L.). In all cases, illumination with red light caused a negative absorbance change at 554 nm which was attributed to the oxidation of cytochrome f. The extent of this change was greater using monochromatic red light at wavelengths above 700 nm compared with wavelengths below 700 nm. 3-(3,4-Dichlorophenyl)-1, 1-dimethylurea abolished this difference in bundle sheath cells. After illumination for 1 minute or longer in bundle sheath cells, reduction of cytochrome f in the dark was rapid only if the wavelength of the illuminating light was below 700 nm. In the presence of 3-(3,4-dichlorophenyl)-1, 1-dimethlyurea, reduction was slow after illumination at all wavelengths.     

Modulation of a mitochondrial function by oat phytochrome in vitro

Previous data in the literature have indicated that phytochrome could alter the rate of reduction of exogenously added NADP by a pea mitochondrial preparation in vitro. These results could not be duplicated using a mitochondrial preparation isolated from etiolated oat seedlings. Further experimentation demonstrated that the addition of Pr to the preparation, in combination with a far red light illumination, could significantly reduce the rate of oxidation of NADH by the external dehydrogenases of oat mitochondria. This response was characterized by a 15% decrease in reaction velocity at saturating substrate concentrations and a 2-fold increase in apparent K_m as compared to values obtained after Pfr plus red light treatment. The response was photoreversible, the rate of oxidation of exogenous NADH being determined by the last light illumination given to the mitochondrial preparation. The interaction between phytochrome and the mitochondria was apparently occurring at the level of the inner mitochondrial membrane. A requirement for these results was that the mitochondria be isolated from plants that were illuminated with white or red light before extraction; mitochondria from unirradiated plants showed no dehydrogenase response to treatments with phytochrome plus actinic light.     

Phytochrome control of oscillating levels of phenylalanine ammonia lyase in Hordeum vulgare shoots

Five-day-old etiolated barley shoots respond to brief illumination with red light by increasing their level of PAL ca 50% within 5 hr. When assayed s     

Phytochrome-mediated Electric Potential Changes in Oat Seedlings

Brief exposures to red light induce far red-reversible changes of 5 to 10 millivolts magnitude in the upper 1 centimeter of etiolated Avena coleoptiles. The changes begin within 15 seconds of the start of illumination and they continue for at least 12 minutes. The changes were measured using a flowing solution of 10 mm KCl to contact the surface of the coleoptile. A dark-grown coleoptile shows no change in response to far red light unless it first receives red light treatment. The second of two red light exposures is ineffective without an intervening far red treatment. Some characterization of these electric responses to light is presented.     

Phytochrome mediated regulation of sucrose phosphate synthase activity in maize

The extractable activity of sucrose phosphate synthase was determined in etiolated seedlings of maize (Zea mays L.), soybean (Glycine max [L.] Merr.), and sugar beet (Beta vulgaris L.) following treatments of changing light quality. A 30-minute illumination of 30 microeinsteins per square meter per second white light produced a three-fold increase in sucrose phosphate synthase activity at 2 hours postillumination when compared to seedlings maintained in total darkness. Etiolated maize seedlings treated with 3.6 microeinsteins per square meter per second of red and far-red light showed a 50% increase and a 50% decrease in sucrose phosphate synthase activity, respectively, when compared to etiolated maize seedlings treated with white light. Maize seedlings exposed for 30 minutes to red followed by 30 minutes to far-red showed an initial increase in sucrose phosphate synthase activity followed by a rapid decrease to control level. Neither soybean or sugar beet sucrose phosphate synthase responded to the 30-minute illumination of white light. Phytochrome is involved in sucrose phosphate synthase regulation in maize, whereas it is not responsible for changes in sucrose phosphate synthase activity in soybean or sugar beet.     

Changes in Succinyl CoA Synthetase Activity in Etiolated Bean Leaves Caused by Illumination

The illumination of etiolated bean leaves (Phaseolus vulgaris) causes an increase in the activity of succinyl coenzyme A synthetase. Continuous white light or short periods of red or blue light followed by darkness will induce an increase with the highest activity at about 6 hr after the onset of illumination. Thereafter the activity decreases so that at 12 hr it is the same as the initial dark activity. Treatment with cycloheximide before illumination prevents the increase in activity. A number of other enzymes have been studied in an attempt to determine the significance of the transient nature of the changes in succinyl CoA synthetase activity.     

Phytochrome control of two low-irradiance responses in etiolated oat seedlings

Light-induced coleoptile stimulation and mesocotyl suppression in etiolated Avena sativa (cv. Lodi) has been quantitated. Etiolated seedlings showed the greatest response to light when they were illuminated 48 to 56 hours after imbibition. Two low-irradiance photoresponses for each tissue have been described. Red light was 10 times more effective than green and 1,000 times more effective than far red light in evoking these responses. The first response, which resulted in a 45% mesocotyl suppression and 30% coleoptile stimulation, had a threshold at 10⁻¹⁴ einsteins per square centimeter and was saturated at 3.0 × 10⁻¹² einsteins per square centimeter of red light. This very low-irradiance response could be induced by red, green, or far red light and was not photoreversible. Reciprocity failed if the duration of the red illumination exceeded 10 minutes. The low-irradiance response which resulted in 80% mesocotyl suppression and 60% coleoptile stimulation, had a threshold at 10⁻¹⁰ einsteins per square centimeter and was saturated at 3.0 × 10⁻⁸ einsteins per square centimeter of red light. A complete low-irradiance response could be induced by either red or green light but not by far red light. This response could be reversed by a far red dose 30 times greater than that of the initial red dose for both coleoptiles and mesocotyls. Reciprocity failed if the duration of the red illumination exceeded 170 minutes. Both of these responses can be explained by the action of phytochrome.     

Induction of delta-Aminolevulinic Acid Formation in Etiolated Maize Leaves Controlled by Two Light Systems

A short illumination of etiolated maize (Zea mays) leaves with red light causes a protochlorophyll(ide)-chlorophyll(ide) conversion and induces the synthesis of δ-aminolevulinic acid (ALA) during a subsequent dark period. In leaves treated with levulinic acid, more ALA is formed in the dark than in control leaves. Far red light does not cause a conversion of protochlorophyll(ide) into chlorophyll(ide) and does not induce accumulation of ALA in the dark. Both red and far red preilluminations cause a significant potentiation of ALA synthesis during a period of white light subsequent to the dark period. The results indicate a dual light control of ALA formation. The possible role of phytochrome and protochlorophyllide as photoreceptors in this control system is discussed.     

Effect of Light with Different Spectral Composition on Cell Growth and Pigment Composition of the Membranes of Purple Sulfur Bacteria <Emphasis Type="Italic">Allochromatium minutissimum</Emphasis> and <Emphasis Type="Italic">Allochromatium vinosum</Emphasis>

The effect of light with different spectral composition: white, red and blue-green (the first one is absorbed by all the pigments of the cell, and the second and the third ones are absorbed by bacteriochlorophyll and carotenoids, respectively) on culture growth, carotenoid synthesis, and assembly of the light-harvesting complexes was studied for the purple sulfur bacteria Allochromatium (Alc.) minutissimum MSU and Alc. vinosum ATCC 17899. The working hypothesis on the growth of bacteria under blue-green illumination (absorbed by carotenoids) resulting in the inhibition of cell growth was tested. When equalizing the light by luxes, the intensity of illumination for each luminous flux was 1800 lx (white and red light, 4 W/m²; bluegreen light, 0.4 W/m²). The growth of the cells was recorded in white and red light, while in blue-green light an insignificant increase was observed only for Alc. vinosum at the end of the experiment (7–9 days). Regardless of the spectral composition of the light the B800-850 type LH2 complex was always assembled in Alc. minutissimum membranes, and two short-wave LH2 complexes of В800-820 and В800-840 type were assembled in the membranes of Alc. vinosum. Upon smoothing and increasing the luminous flux up to 6 W/m² for every illumination mode, both cultures grew with approximately equal rates in blue-green light. In the membranes of Alc. minutissimum and Alc. vinosum the same types of LH2 complexes were assembled as in the case of 1800 lx illumination. It was found that blue-green light did not inhibit cell growth. At illumination of the cells collected at the end of the experiment with blue-green light for 6 h, no photooxidation of BChl850 was registered. However, in the membranes from the cells oxygen-saturated at isolation, ~50% of BChl850 was oxidized after 30 minutes of illumination. In the course of cell growth, oxygen is probably completely consumed and anaerobic conditions develop inside the cell. Under these conditions, formation of reactive oxygen species, BChl photooxidation and inhibition of the cell growth become impossible.     

Assembly of LH2 light-harvesting complexes in Rhodopseudomonas palustris cells illuminated by blue and red light

We investigated the formation of the B800-850 complex in cells of the bacterium Rhodopseudomonas palustris AB illuminated by red and blue light under anaerobic growth conditions. Under red illumination, the B800-850 complex was assembled with a reduced absorption band at 850 nm. The results of re-electrophoresis of the B800-850 complex and oxidation in the presence of potassium iridate suggest its heterogeneity. It may be a mixture of two complexes (B800 and B800-850). The B800-850 complex lacks the capacity for conformational transitions if assembled under blue illumination. Accordingly, the light-harvesting complex assembled in the blue light contains polypeptides that are not synthesized under normal conditions or at increased or decreased light intensities. The mechanism of regulation of the synthesis of the polypeptides of light-harvesting the B800-850 complex and its dependence on the spectral composition of the light is discussed.