Light Spectral Quality Research Articles

Action spectra of microalgal photosynthesis and depth distribution of spectral scalar irradiance in a coastal marine sediment of Limfjorden, Denmark

The role of complementary spectral utilization of light for the zonation of different groups of oxygenic phototrophic organisms in sediments was studied. The marine sediment was covered by a dense population of diatoms with an underlying population of cyanobacteria. Action spectra for photosynthesis and spectral scalar irradiance, E0, were measured directly in the sediment at a spatial resolution of 0.1 mm by the use of oxygen and light microsensors. The action spectrum for the diatoms was similar to the attenuation spectrum of the scalar irradiance, K0, in the diatom layer with Chl.a. and carotenoids being the major photosynthetic pigments. The action spectrum of the cyanobacteria showed photosynthesis maxima at the absorption regions of Chl.a. and phycocyanin. The measured depth distribution of spectral scalar irradiance and the action spectra of diatoms and cyanobacteria were used to calculate the spectral quality for photosynthesis of the 400–700 nm light to which the two populations were exposed. This spectral quality was compared to that of the light incident on the sediment surface. Due to preferential extinction of wavelengths, at which their photosynthetically active pigments had maximal absorption, the relative light quality for diatoms was reduced to 85% of the quality of d incident light at a similar total quantum flux. This effect was partly due to spectral alterations of light backscattered from the underlying sediment with cyanobacteria. The cyanobacteria at the bottom of the euphotic zone, in contrast, experienced a light spectrum which was favorably altered, to 10% in quality, due to absorption by the overlying diatoms. It was concluded that these changes in spectral light quality can be considered as only one of more factors explaining the zonation of the two phototrophic populations, and that total light intensity and the chemical microenvironment are probably more important factors.

Action spectra of microalgal photosynthesis and depth distribution of spectral scalar irradiance in a coastal marine sediment of Limfjorden, Denmark

The role of complementary spectral utilization of light for the zonation of different groups of oxygenic phototrophic organisms in sediments was studied. The marine sediment was covered by a dense population of diatoms with an underlying population of cyanobacteria. Action spectra for photosynthesis and spectral scalar irradiance, E 0, were measured directly in the sediment at a spatial resolution of 0.1 mm by the use of oxygen and light microsensors. The action spectrum for the diatoms was similar to the attenuation spectrum of the scalar irradiance, K 0, in the diatom layer with Chl. a. and carotenoids being the major photosynthetic pigments. The action spectrum of the cyanobacteria showed photosynthesis maxima at the absorption regions of Chl. a. and phycocyanin. The measured depth distribution of spectral scalar irradiance and the action spectra of diatoms and cyanobacteria were used to calculate the spectral quality for photosynthesis of the 400–700 nm light to which the two populations were exposed. This spectral quality was compared to that of the light incident on the sediment surface. Due to preferential extinction of wavelengths, at which their photosynthetically active pigments had maximal absorption, the relative light quality for diatoms was reduced to 85% of the quality of d incident light at a similar total quantum flux. This effect was partly due to spectral alterations of light backscattered from the underlying sediment with cyanobacteria. The cyanobacteria at the bottom of the euphotic zone, in contrast, experienced a light spectrum which was favorably altered, to 10% in quality, due to absorption by the overlying diatoms. It was concluded that these changes in spectral light quality can be considered as only one of more factors explaining the zonation of the two phototrophic populations, and that total light intensity and the chemical microenvironment are probably more important factors.

Adaptation of cyanobacteria to environmental stimuli: new steps towards molecular mechanisms

Dating from the Pre-Cambrian era, cyanobacteria have a long history of adaptation to the Earth's environment. By evolving oxygen via photosynthetic reactions similar to those of plants and green algae, these prokaryotes were essential to the evolution of the present biosphere. They continue to make a large contribution to the equilibrium of the Earth's atmosphere by production oxygen and removing carbon dioxide. To survive in extreme or variable environments, cyanobacteria have developed specific regulatory systems, in addition to more general mechanisms equivalent to those of other prokaryotes or photosynthesis eukaryotes. Specific regulatory systems control the differentiation of specialized nitrogen-fixing cells and of cell types facilitating the dispersion of species. In the past decade, considerable progress has been made towards understanding the expression of the cyanobacterial genome in response to variations in the intensity and spectral quality of incident light and in response to nutritional conditions, especially carbon, nitrogen and sulphur sources. These studies have provided insights into the relationships between carbon and nitrogen intermediary metabolism, and a start towards understanding of the interconnected pathways which lead from the perception of environmental signals to the regulation of enzyme activities and gene expression. Cyanobacterial regulatory mechanisms share common features with those of other prokaryotes, but are unique since these essentially photo-autotrophic organisms must maintain a proper cellular C/N balance, in spite of dailty variations in incident light. Thus an appropriate coordination between photosynthesis and other metabolic processes must be achieved through control of the catalytic activity of key enzymes by reducing equivalents and ATP produced by photosynthetic or respiratory electron transport. Recently discovered kinases/phosphatases act by post-translational modification of specific proteins which probably act as signal transducers or modulators of gene expression in a manner similar to the well-known two-component regulatory systems described in other bacteria. In this overview, we present our current knowledge on the molecular aspects of the biology of cyanobacteria, as well as on their mechanisms of resistance to metal ions and their responses to metabolic stress.

Adaptation of cyanobacteria to environmental stimuli: new steps towards molecular mechanisms

Dating from the Pre-Cambrian era, cyanobacteria have a long history of adaptation to the Earth's environment. By evolving oxygen via photosynthetic reactions similar to those of plants and green algae, these prokaryotes were essential to the evolution of the present biosphere. They continue to make a large contribution to the equilibrium of the Earth's atmosphere by production oxygen and removing carbon dioxide. To survive in extreme or variable environments, cyanobacteria have developed specific regulatory systems, in addition to more general mechanisms equivalent to those of other prokaryotes or photosynthesis eukaryotes. Specific regulatory systems control the differentiation of specialized nitrogen-fixing cells and of cell types facilitating the dispersion of species. In the past decade, considerable progress has been made towards understanding the expression of the cyanobacterial genome in response to variations in the intensity and spectral quality of incident light and in response to nutritional conditions, especially carbon, nitrogen and sulphur sources. These studies have provided insights into the relationships between carbon and nitrogen intermediary metabolism, and a start towards understanding of the interconnected pathways which lead from the perception of environmental signals to the regulation of enzyme activities and gene expression. Cyanobacterial regulatory mechanisms share common features with those of other prokaryotes, but are unique since these essentially photo-autotrophic organisms must maintain a proper cellular C/N balance, in spite of dailty variations in incident light. Thus an appropriate coordination between photosynthesis and other metabolic processes must be achieved through control of the catalytic activity of key enzymes by reducing equivalents and ATP produced by photosynthetic or respiratory electron transport. Recently discovered kinases/phosphatases act by post-translational modification of specific proteins which probably act as signal transducers or modulators of gene expression in a manner similar to the well-known two-component regulatory systems described in other bacteria. In this overview, we present our current knowledge on the molecular aspects of the biology of cyanobacteria, as well as on their mechanisms of resistance to metal ions and their responses to metabolic stress.

Effect of Light Quality on the Organization of Chloroplast Thylakoids of Pinus nigra Arn.

Summary Cotyledons of black pine ( Pinus nigra Arn.) seedlings grown under different irradiance and spectral quality of light have adapted in such a manner as to have the light quality effecting predominantly the Chl a/b ratio, the polypeptide structure of Chl a/b proteins of the LHC-2 and the ratio of the reaction centres of the PS2/PS1 Chl a proteins. The most pronounced differences of the Chl a/b and Chl a/ carotenoid ratios occurred in red and blue light. Red effected the greatest accumulation of Chl b , followed by the greatest accumulation of Chl a/b proteins of the LHC-2 complex. The proportion of the PS2/PS 1 Chl a protein core was lower in all light qualities than in the white of the same irradiance. The examined light qualities proved favourable for the excitation of PS2. The Chl a/b ratio in chloroplasts of plants grown in either blue, green or yellow did not follow the level of LHC-2 proteins.

Response of Soybean Photosynthesis and Chloroplast Membrane Function to Canopy Development and Mutual Shading

The effect of natural shading on photosynthetic capacity and chloroplast thylakoid membrane function was examined in soybean (Glycine max. cv Young) under field conditions using a randomized complete block design. Seedlings were thinned to 15 plants per square meter at 20 days after planting. Leaves destined to function in the shaded regions of the canopy were tagged during early expansion at 40 days after planting. To investigate the response of shaded leaves to an increase in available light, plants were removed from certain plots at 29 or 37 days after tagging to reduce the population from 15 to three plants per square meter and alter the irradiance and spectral quality of light. During the transition from a sun to a shade environment, maximum photosynthesis and chloroplast electron transport of control leaves decreased by two- to threefold over a period of 40 days followed by rapid senescence and abscission. Senescence and abscission of tagged leaves were delayed by more than 4 weeks in plots where plant populations were reduced to three plants per square meter. Maximum photosynthesis and chloroplast electron transport activity were stabilized or elevated in response to increased light when plant populations were reduced from 15 to three plants per square meter. Several chloroplast thylakoid membrane components were affected by light environment. Cytochrome f and coupling factor protein decreased by 40% and 80%, respectively, as control leaves became shaded and then increased when shaded leaves acclimated to high light. The concentrations of photosystem I (PSI) and photosystem II (PSII) reaction centers were not affected by light environment or leaf age in field grown plants, resulting in a constant PSII/PSI ratio of 1.6 +/- 0.3. Analysis of the chlorophyll-protein composition revealed a shift in chlorophyll from PSI to PSII as leaves became shaded and a reversal of this process when shaded leaves were provided with increased light. These results were in contrast to those of soybeans grown in a growth chamber where the PSII/PSI ratio as well as cytochrome f and coupling factor protein levels were dependent on growth irradiance. To summarize, light environment regulated both the photosynthetic characteristics and the timing of senescence in soybean leaves grown under field conditions.

Hormogonium Differentiation in the Cyanobacterium Calothrix: A Photoregulated Developmental Process.

Hormogonium differentiation is part of the developmental cycle in many heterocystous cyanobacteria. Hormogonia are involved in the dispersal and survival of the species in its natural habitat. The formation of these differentiated filaments has been shown to depend on several environmental conditions, including spectral light quality. We report here morphological and ultrastructural changes associated with the formation of hormogonia, as well as optimal light conditions required for their differentiation in the cyanobacterium Calothrix sp PCC 7601. The action spectrum for hormogonium differentiation is similar to that which triggers complementary chromatic adaptation because red and green radiation display antagonistic effects in both cases. However, these two photoregulated processes also show major differences. Transcription analyses of genes that are specifically expressed during hormogonium differentiation, as well as of genes encoding phycobiliproteins, suggest that two different photoregulatory pathways may exist in this cyanobacterium.

光質の相違がイヨカン果実の品質に及ぼす影響

To study the basis of pigment for mationin Iyo fruit, the ffect of spectral quality of light on color development was examined. In the first experiment, white, yel1ow, pink, red, blue, and violet cellophane bags were used. Fruit of 'Miyauchi' Iyo were bagged on 2 August and 1 September and kept covered until they were harvested on 9 Jan, The harvested Iyo fruits were used for the second experiment. On 13 January, the uncovered fruits were irradiated with 100W mercury vapor lamp. The spectral quality of the lamp wasred (600 to 700nm).1.Results of the August bagging revealed that the unbagged control fruit had the highest a value; fruits in the white or yellow bags had intermediate a values, whereas, those in the blue, red, and violet had the lowest values. The light intensities in the white and yellow bags were higher than were those in the pink bags; the light intensities in the blue, red, and violet bags were lowest and the colord evelopment of the fruit with in was poorest. In the autumn bagging experiment, fruit color was most intense in the red bags.2.Red light irradiation promoted pigment for mation in stored fruit. Color development tended to highest at the stem end area of the fruit where light impinged on the surface directly; it was intermediate in the equatorial area and lowest at the stylar end.3.Sugar content in the peel increased in response to the irradiation, Among the sugars, increase in sucrose was greatest.4.Our results stress that red light irradiation with 100W mercury vapor lamp is useful for promoting colord evelopment of Iyo fruit during storage.

PHOTOCONTROL OF DIOSCOREA ALATA PLANTLET GROWTH IN VITRO

The effects of light spectral quality on Discorea alata cv, Oriental in vitro grown plantlets were investigated. Cultured nodes were treated with red (R) or far-red (FR) light at the end of a 14 hr photoperiod. End-of-day (EOD) light treatments did not affect organogenesis. EOD FR light increased average internode lengths as compared to plantlets treated with EOD R light. The EOD FR enhancement of internode elongation was reversed by following the FR with R suggesting the involvement of phytochrome. There were no residual light effects on subsequent plantlet development from subcultured nodes or potted plantlets after EOD light treatments were terminated.

Primary production in the North Pacific gyre: a comparison of rates determined by the 14C, O 2 concentration and 18O methods

Primary production was measured at 28°N/155°W, north of Hawaii, during the late summer of 1985, using three independent in vitro techniques: (1) the 18O method, in which gross oxygen production is determined from the rate at which 18O-labelled O 2 is produced from 18O-labelled H 2O, (2) the O 2 light/dark bottle method, and (3) the H 14CO 3 − assimilation method. For samples incubated in situ, rates of gross O 2 production, determined with 18O, are similar to rates calculated by oxygen changes in light/dark bottles. 14C productivities range from ∼60 to 100% of 18O gross production. Assuming PQ ⩾ 1, this implies that 14C production is ⩾65% of gross C assimilation. However, in samples incubated on board ship (with neutral density filters at 35% of incident light intensity, and at surface seawater temperatures), the rates of gross oxygen production measured with 18O were up to two times the rates measured with light/dark bottles, and 2–3 times the rates of 14C production. We believe that the increase in O 2 cycling and carbon cycling implied by these data is an artifact reflecting the response of metabolism to some condition of shipboard incubation, possible the spectral quality of light.

Changes in alkaline phosphatase activity and phosphate uptake in P-limited phytoplankton, induced by light intensity and spectral quality

Alkaline phosphatase activity and P uptake were determined in P-limited Dunaliella tertiolecta, Thalassiosira pseudonana, Phaeodactylum tricornumtum, and Prymnesium parvum grown under different light intensities and colors. Both intracellular and extracellular enzyme activities varied with the intensity and quality of light in a species-specific manner. The spectral composition of the light also affected P uptake kinetics. No correlation was found between enzyme activity and Vmax both within a species and for pooled data for all four species, indicating that the change in uptake kinetics and enzyme activity was not related to P limitation, but induced by the light conditions. Changes in the optimum N:P ratio induced by light were also not related to P uptake kinetics or enzyme activity. These data suggest that light conditions may in themselves have profound effects on species competition for limiting nutrients. Furthermore, since both alkaline phosphatase activity and P uptake were influenced by the prevailing light conditions we suggest that these parameters be used cautiously when determining the P nutritional status of phytoplankton in nature.

Changes in alkaline phosphatase activity and phosphate uptake in P-limited phytoplankton, induced by light intensity and spectral quality

Changes in alkaline phosphatase activity and phosphate uptake in P-limited phytoplankton, induced by light intensity and spectral quality

Germination response of Galium spurium L. to light

SummaryThe effects of intensity, duration and spectral quality of light were investigated on the germination of Galium spurium L. Light inhibited germination and the degree of this inhibition was related to the intensity and duration of exposure to light beyond the initial 36‐h imbibition period. Subsequent dry storage for up to 7 weeks and reincubation in the dark did not remove this inhibitory effect, indicating that a secondary dormancy was induced by continuous exposure to light. Germination was completely inhibited with intermittent 1‐h exposures of light every 3, 7 or 11 h for 8 days. Red, far‐red and blue light inhibited germination and the degree of inhibition was related to the duration of exposure. Far‐red light was more inhibitory than red or blue light. Green light promoted germination slightly. Nitrate salts in the medium during light exposure did not prevent the onset of light‐induced dormancy. In subsequent dark incubation, light‐induced dormancy was overcome by the addition of nitrates and, to a lesser extent, by kinetin and GA3.

Reversible effects of moderately elevated temperature on the distribution of excitation energy between the two photosystems of photosynthesis in intact avocado leaves

Initial (Fo), maximum (Fm) and steady-state (Fs) levels of modulated chlorophyll fluorescence were measured in intact avocado leaves (Persea americana Mill.) during state 1-state 2 transitions using a combination of modulated and non-modulated lights with synchronized detection. Under normal temperature conditions (20°C), transition from state 2 to state 1 was associated with a substantial increase (about 20%) in Fm and Fo whereas the Fm/Fo ratio remained constant, reflecting increased absorption cross-section of PS II. On the contrary, at moderately elevated temperature (35°C), these fluorescence changes were very limited, indicating marked inhibition of the state regulation. The fraction of light distributed to PS II (β) was calculated from the Fo, Fm and Fs levels for both types of leaves. In control leaves, β varied from 48% (in state 2) to values as high as 58% (in state 1). In contrast, mild heat treatment resulted in β values close to 50% in both states, indicating the inability of heated leaves to reach extreme state 1. The results suggested that avocado leaves under moderately elevated temperature conditions are blocked in a state close to state 2. This effect was shown to occur in a non-injurious temperature range (as shown by the preservation of the (photoacoustically monitored) oxygen evolution activity) and to be rapidly reversed upon lowering of the temperature. Thermally induced development of state 2 (independent on the light spectral quality) could possibly be a protective mechanism to avoid photodamage of the heat-labile PS II by high light intensities which usually accompany heat stress in the field.

A quantitative analysis of light distribution between the two photosystems, considering variation in both the relative amounts of the chlorophyll-protein complexes and the spectral quality of light

A quantitative analysis of light distribution between the two photosystems, considering variation in both the relative amounts of the chlorophyll-protein complexes and the spectral quality of light

Effects of particulate peat on the behavior and physiology of the Jamaican reef-building coral Montastrea annularis

Corals in an in situ respirometer exposed to suspended peat during the day greatly decreased net oxygen production, probably due to a reduction of intensity and spectral quality of light reaching the symbiotic zooxanthellae. Net production returned to pre-exposure levels after the chambers were cleared; the corals showed no behavioral effects. In contrast, after exposure during the night, corals displayed clearing behavior (such as extreme distension of the coenosarc and trapping of peat particles in thick clumps of mucus) and an increase in respiration rate comparable to the decrease in net production observed during the daytime exposure. The following morning, net production values were significantly lower than pre-exposure production values although ambient light intensity was slightly higher. This decrease in production as well as a 22% reduction of chlorophyll content in the coral tissue indicated loss of zooxanthellae from the stressed corals. Long-term exposure to such a stress could reduce coral growth rates and substantially alter coral reef communities.

Coexistence of photosynthetic microorganisms with growth rates depending on the spectral quality of light

Coexistence of photosynthetic microorganisms with growth rates depending on the spectral quality of light

Coexistence of photosynthetic microorganisms with growth rates depending on the spectral quality of light

A new equation for the growth rate of photosynthetic microorganisms is derived. It is based on a series formulation of the mechanism of photosynthesis and it has the form of a functional of the spectral qualities of light. Using this functional to model their growth it is shown that populations of photosynthetic microorganisms can coexist in the same homogeneous environment even though they compete for the available light.

Influence of Spectral Quality of Light on Pollen Tube Elongation in Arachis hypogaea

The effect of light of different wave lengths (red RL, blue BL, yellow YL, green GL and far-red FR) on pollen tube elongation has been studied in Arachis hypogaea . Short exposure of pollen to RL caused enhanced tube elongation and this effect was reduced by FR and BL. The effects of RL and FR were mutually reversible. Similarly, the inhibitory effect of blue light could be overcome by IAA and riboflavin separately whereas acetylcholine and GA 3 mimicked the RL effect. The activities of peroxidase (PO) and malate dehydrogenase (MDH) were increased by RL and IAA whereas BL increased the activity of IAA-oxidase. The regulatory role of light of different spectral composition in controlling pollen tube elongation is discussed.

Lighting systems in major New Zealand controlled environment facilities

The lighting systems used in New Zealand in the Department of Scientific and Industrial Research (DSIR) Climate Laboratory controlled environment rooms, the Forest Research Institute (FRI) tree growth rooms, and the DSIR-designed reach-in controlled environment chambers are described. All lighting systems are based on high-pressure discharge lamps which can be used with varying amounts of incandescent light supplementation. The main lighting type used in the Climate Laboratory controlled environment rooms is the high-pressure metal halide lamp, that in the FRI rooms the high-pressure mercury-vapour fluorescent lamp with internal reflector, and that in the reach-in chambers a high-pressure mercury halide lamp. Details of lighting rig design, of irradiance levels obtainable, vertical and horizontal light distribution patterns and spectral quality are presented for each system. The photosynthetic irradiance levels available at 2–3 m below the lighting systems in all of these controlled environment systems are high (180–200 W m −2 PAR). In the Climate Laboratory and FRI growth rooms peak sunlight values of approximately 400 W m −2 PAR (approximately 10,000 ft.c.) have been achieved. A discussion of the performance of these systems is also presented.