Light-induced synchrony of cell division in the protonema of the fern,Pteris vittata

Summary In protonemata of Pteris vittata grown for 6 days under red light, which brings about a marked depression of mitotic activity, the first division of the cells was synchronously induced by irradiation with blue light, and subsequent cell divisions were also promoted. The peak of the mitotic index reached a maximum of about 70% at 11.5 hrs, and 90% of all protonemata divided between the 11th and 13th hour after exposure to blue light. When the protonemata were continuously irradiated with blue light, synchronism of the next cell division in the apical cells decreased to a mitotic index of about 30%, and further divisions occurred randomly.The synchronization of cell division was found to be a combined effect of red and blue light. Red light maintained the cells in the early G₁ phase of the cell cycle; blue light caused the cells to progress synchronously through the cell cycle, with an average duration of 12 hr. By using ³H-thymidine, the average duration of the G₁, S, G₂ and M phases was determined to be about 3.5, 5, 2.5 and 1 hr, respectively.Synchronous cell division could be induced in older protonemata grown for 6 to 12 days in red light and even in protonemata having two cells. It could be repeated in the same protonema by reexposure to red light for 24 hrs or more before another irradiation with blue light.     

Anatomical features of pepper plants (Capsicum annuum L.) grown under red light-emitting diodes supplemented with blue or far-red light

Pepper plants (Capsicum annuum L. cv., Hungarian Wax) were grown under metal halide (MH) lamps or light-emitting diode (LED) arrays with different spectra to determine the effects of light quality on plant anatomy of leaves and stems. One LED (660) array supplied 90% red light at 660 nm (25nm band-width at half-peak height) and 1% far-red light between 700-800nm. A second LED (660/735) array supplied 83% red light at 660nm and 17% far-red light at 735nm (25nm band-width at half-peak height). A third LED (660/blue) array supplied 98% red light at 660nm, 1% blue light between 350-550nm, and 1% far-red light between 700-800nm. Control plants were grown under broad spectrum metal halide lamps. Plants were gron at a mean photon flux (300-800nm) of 330 micromol m-2 s-1 under a 12 h day-night photoperiod. Significant anatomical changes in stem and leaf morphologies were observed in plants grown under the LED arrays compared to plants grown under the broad-spectrum MH lamp. Cross-sectional areas of pepper stems, thickness of secondary xylem, numbers of intraxylary phloem bundles in the periphery of stem pith tissues, leaf thickness, numbers of choloplasts per palisade mesophyll cell, and thickness of palisade and spongy mesophyll tissues were greatest in peppers grown under MH lamps, intermediate in plants grown under the 660/blue LED array, and lowest in peppers grown under the 660 or 660/735 LED arrays. Most anatomical features of pepper stems and leaves were similar among plants grown under 660 or 660/735 LED arrays. The effects of spectral quality on anatomical changes in stem and leaf tissues of peppers generally correlate to the amount of blue light present in the primary light source.     

Photoregulation of asymmetric cell division followed by rhizoid development in the fern Ceratopteris prothalli

Strap-shaped prothalli of CERATOPTERIS: richardii grown in the dark have an apical meristem, a subapical elongation zone and a basal growth cessation zone [Murata et al. (1997) Plant Cell Physiol. 38: 201]. When the dark-grown prothalli were irradiated with continuous white light, marginal cells of the elongation zone divided asymmetrically, and the resulting smaller cells developed into rhizoids. The asymmetric division was also induced by brief irradiation of red light. The effect of red light was cancelled by subsequent irradiation of far-red light, indicating that the asymmetric division was regulated by phytochrome. Since the response to red light was not observed at 10(1) J m(-2) and saturated at 10(2) J m(-2) and the response is photoreversible by far-red light, the photoresponse was classified as a low-fluence response of phytochrome. Although the asymmetric division was induced by brief irradiation of red light, continuous irradiation of white, blue or red light was necessary to induce rhizoid growth. These results indicate that asymmetric division and subsequent cell growth are independently regulated by light in CERATOPTERIS: prothalli.     

Light-quality and irradiance-level control of light-harvesting complex of photosystem 2 in maize mesophyll cells. Evidence for a low fluence-rate threshold in blue-light reduction of mRNA and protein

Levels of pigment-proteins and mRNA coding for proteins associated with the light-harvesting complex of photosystem 2 (LHCP2) were reduced in maize ( Zea mays L. cv. OP Golden Bantum) plants grown for 14 days in 8.0 nmol m^-2s^-1 of blue light compared to those in plants grown under an equal irradiance of red light. At the same time, there was a small increase in steady state levels of mRNA for the Dl protein of PS2 (psbA) in blue-grown plants. The reduction of LHCP2 mRNA and the increase in psbA mRNA were observed in both 5- and 10-day-old blue-light-grown leaves, but the degree of reduction or increase was much greater in 10-day-old leaves. Maize grown under 6 different mixtures of blue and red light, each with a total irradiance level of 8.0 μmol m^-2 s^-1, showed the same degree of LHCP2 mRNA reduction relative to red light. This is different from the behavior of psbA which increased in a linear manner with increasing amounts of blue light. The amounts of Chi a and Chi b in these mixed-light samples were not significantly different froi those found in pure red light. This indicates that a low fluence level of blue light, even when combined with red light, is sufficient to reduce equilibrium levels of proteins and mRNA of LHCP2, and this reduction is independent of pigment formation. It also suggests that the mechanisms of blue-light regulation of mRNA may operate differently at the nuclear and chloroplast levels.     

Effect of light quality on the organization of photosynthetic electron transport chain of pea seedlings

The activity of NADP and O₂ photoreduction by water is essentially higher in chloroplasts isolated from pea seedlings (Pisum sativum L.) grown under blue light as compared with that from plants grown under red light. In contrast, the photoreduction of NADP and O₂ with photosystem I only is practically the same or even lower in chloroplasts isolated from plants grown under blue light. The addition of plastocyanin does not affect the rate or the extent of NADP photoreduction by water in the chloroplasts isolated from plants grown under blue light, whereas it sharply activates NADP reduction in the chloroplasts isolated from plants grown under red light. The extent of the light-induced oxidation of cytochrome f is appreciably higher in chloroplasts isolated from plants grown under blue light. Cytochrome b₅₅₉ plays the predominant role in the oxidoreductive reactions of these chloroplasts. Furthermore, the fluorescence measurements indicate more effective transfer of excitation energy from chlorophyll to the photosystem II reaction center in chloroplasts isolated from plants grown under blue light.     

Abstracts of papers read at the winter meeting at the university of Newcastle Upon Tyne

Young plants of Laminaria hyperborea collected from the field were grown for 2·5–4 weeks in blue, green, red and white (simulated underwater) light fields at 5, 20 and 100 μmol m^-2s^-1. The absolute concentrations of all pigments showed little variation with irradiance in green and white light, but decreased in high irradiances of red and blue light. The ratio of fucoxanthin to chlorophyll a also increased in the latter treatments, as did the chlorophyll c:a ratio in bright red light. There was little difference in the action spectrum for photosynthesis between the different light qualities at any one irradiance, but the action spectra for plants grown at 100 μmol m^-2s^-1 showed deeper troughs and higher peaks than those for plants grown at lower irradiances. Gross photosynthesis per unit of thallus area at 10 μmol m^-2s^-1 decreased in plants with low total pigment concentrations, but the photosynthesis per unit of pigment concentration increased. This suggestion of self-shading of pigment molecules within the algal thalli was supported by a flattening of the action spectrum in plants with higher chlorophyll a contents. The variations observed between the action spectra for different plants could thus be attributed to the decrease in pigment content at high irradiances, and not to the light quality in which the plants were grown.     

Electrical Changes in the Apical Cell of the Fern Gametophyte during Irradiation with Photomorphogenetically Active Light

Electrophysiological procedures were used to evaluate cellular responses of fern (Onoclea sensibilis L.) gametophytes to photomorphogenetically active light. Red, far red, and blue light caused rapid changes in the membrane potential of the apical cell of the gametophyte filament; other cells in the filament were not similarly responsive. Measurements made with one electrode in the apical cell revealed that the membrane potential depolarized in red light and repolarized in far red light. Irradiation with blue light caused a hyperpolarization, the rapidity of which was dependent on a red light pretreatment. More refined measurements with one electrode in the tip of the apical cell and another in the base of the cell showed that both red and blue light treatments cause the apical cell to behave as a dipole. Because of the profound, long-term morphological changes that follow light irradiation in this organism, it was hoped to use it to elucidate the role that electrical parameters play in determining subsequent developmental events.     

Blue light delays commitment to cell division in Chlamydomonas reinhardtii

In this study, we describe the effect of red and blue light on the timing of commitment to cell division in Chlamydomonas reinhardtii. The time point and cell size after which cells can complete their cell cycle with one division round were determined for cultures that were exposed to various red and blue light periods. We show that the commitment point of cells grown in blue light is shifted to a later time point and a larger cell size, when compared with cells grown in red light. This shift was reduced when cultures were exposed to shorter blue light periods. Furthermore, this shift occurred only when exposure to blue light started before the cells attained a particular size. We conclude that the critical cell size for cell division, which is the cell size at which commitment to cell division is attained, is dependent on spectral composition.     

The effect of light quality on the growth and development of in vitro cultured Doritaenopsis plants

The influence of light quality on growth and development of in vitro grown Doritaenopsis hort. (Orchidaceae) plants was investigated. Growth parameters like leaf and root fresh/dry mass and leaf area were highest with plants grown under red plus blue light emitting diodes (LEDs). Leaf length was greater with the plants grown under red LED. Carbohydrate (starch, sucrose, glucose and fructose) and leaf pigment (chlorophylls and carotenoids) biosynthesis of the plants was significantly increased in plants grown under red plus blue LEDs compared to red or blue LED and fluorescent light treatments. This study suggests that the production of quality Doritaenopsis plants is possible by culturing the plants in vitro under a mixture of blue plus red light sources.     

Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting

Red light-emitting diodes (LEDs) are a potential light source for growing plants in spaceflight systems because of their safety, small mass and volume, wavelength specificity, and longevity. Despite these attractive features, red LEDs must satisfy requirements for plant photosynthesis and photomorphogenesis for successful growth and seed yield. To determine the influence of gallium aluminium arsenide (GaAlAs) red LEDs on wheat photomorphogenesis, photosynthesis, and seed yield, wheat (Triticum aestivum L., cv. 'USU-Super Dwarf') plants were grown under red LEDs and compared to plants grown under daylight fluorescent (white) lamps and red LEDs supplemented with either 1% or 10% blue light from blue fluorescent (BF) lamps. Compared to white light-grown plants, wheat grown under red LEDs alone demonstrated less main culm development during vegetative growth through preanthesis, while showing a longer flag leaf at 40 DAP and greater main culm length at final harvest (70 DAP). As supplemental BF light was increased with red LEDs, shoot dry matter and net leaf photosynthesis rate increased. At final harvest, wheat grown under red LEDs alone displayed fewer subtillers and a lower seed yield compared to plants grown under white light. Wheat grown under red LEDs+10% BF light had comparable shoot dry matter accumulation and seed yield relative to wheat grown under white light. These results indicate that wheat can complete its life cycle under red LEDs alone, but larger plants and greater amounts of seed are produced in the presence of red LEDs supplemented with a quantity of blue light.     

Light Regulation of delta-Aminolevulinic Acid Biosynthetic Enzymes and tRNA in Euglena gracilis

Chlorophyll synthesis in Euglena, as in higher plants, occurs only in the light. The key chlorophyll precursor, δ-aminolevulinic acid (ALA), is formed in Euglena, as in plants, from glutamate in a reaction sequence catalyzed by three enzymes and requiring tRNA^Glu. ALA formation from glutamate occurs in extracts of light-grown Euglena cells, but activity is very low in dark-grown cell extracts. Cells grown in either red (650-700 nanometers) or blue (400-480 nanometers) light yielded in vitro activity, but neither red nor blue light alone induced activity as high as that induced by white light or red and blue light together, at equal total fluence rates. Levels of the individual enzymes and the required tRNA were measured in cell extracts of light- and dark-grown cells. tRNA capable of being charged with glutamate was approximately equally abundant in extracts of light- and dark-grown cells. tRNA capable of supporting ALA synthesis was approximately three times more abundant in extracts of light-grown cells than in dark-grown cell extracts. Total glutamyl-tRNA synthetase activity was nearly twice as high in extracts of light-grown cells as in dark-grown cell extracts. However, extracts of both light- and dark-grown cells were able to charge tRNA^Glu isolated from light-grown cells to form glutamyl-tRNA that could function as substrate for ALA synthesis. Glutamyl-tRNA reductase, which catalyzes pyridine nucleotide-dependent reduction of glutamyl-tRNA to glutamate-1-semialdehyde (GSA), was approximately fourfold greater in extracts of light-grown cells than in dark-grown cell extracts. GSA aminotransferase activity was detectable only in extracts of light-grown cells. These results indicate that both the tRNA and enzymes required for ALA synthesis from glutamate are regulated by light in Euglena. The results further suggest that ALA formation from glutamate in dark-grown Euglena cells may be limited by the absence of GSA aminotransferase activity.     

Light-quality and irradiance effects on pigments, light-harvesting proteins and Rubisco activity in a chlorophyll- and light- harvesting-deficient soybean mutant

Soybean ( Glycine max [L.] Merrill) plants, normal green (Clark L1) and mutant yellow (Clark y₉y₉), were grown in (1) full-spectrum solar irradiation; (2) either red plus far-red or blue plus far-red; (3) either red or blue light with no far-red light. Young leaves harvested from first (1TF) trifoliolate or fifth (5TF) trifoliolate stages of development showed that the mutant plants express pigment and protein deficiencies as a direct function of irradiance. Response of the mutant to light quality indicates that blue light slightly enhances expression of the mutation at higher irradiances. Direct response of light-harvesting proteins of photosystem 2 (LHCP2) and light-harvesting protein of photosystem 1 (LHCP1) to light quality increases the ratio of LHCP1/LHCP2 in blue light compared to that in red or red/far-red light. Rubisco proteins and Rubisco activity (leaf area basis) are directly related to irradiance level but are enhanced in blue light over equal irradiance red. This enhancement is not shown in the presence of far-red light.     

Der Einfluß von Rot-und Blaulicht auf die Hillaktivität von Acetabularia-Chloroplasten

Summary Hill activity (reduction of trichlorophenol indophenol) of chloroplasts isolated after various times from the unicellular alga Acetabularia mediterranea grown under red light conditions decreases with time. After 2 weeks the amount of Hill activity is only about 30–40% of that at the beginning of the red light treatment. On the other hand, Hill activity of chloroplasts from cells grown under blue light does not change remarkably during the course of the experiment. Transfering cells to blue light after 2 weeks in red light results in an increase of Hill activity within 48–72 hours up to the level of Hill activity in cells grown in blue light.It is concluded that the observed changes in the rate of photosynthesis in red and in blue light (Schaeel and Clauss, 1968) are due to an alteration of the photosynthetic apparatus. Apparently processes are affected which are somehow involved in the light reactions.

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Die Arbeit wurde durch Mittel der DFG gefördert. Mein Dank gilt Frau Ingrid Maass für die sorgfältige Mitarbeit bei den Versuchen.     

Photosynthetic characteristics of rice leaves grown under red light with or without supplemental blue light

In rice plants grown under red light supplemented with blue light (red/blue-light PPFD ratio was 4/1), photosynthetic rates per unit leaf area measured under white light at 1,600 and 250 micromol m-2) s-1 were higher than those in the plants grown under red light alone. The higher photosynthetic rates were associated with higher total N content of leaves, which was accompanied by larger amounts of key components of photosynthesis-limiting processes, including Rubisco, Cyt f, Chl and LHCII. These results suggested that the increase in total N content of leaves induced by supplemental blue light enhanced both light-saturated and light-limited photosynthesis.     

Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting

Red light-emitting diodes (LEDs) are a potential light sourcefor growing plants in spaceflight systems because of their safety,small mass and volume, wavelength specificity, and longevity.Despite these attractive features, red LEDs must satisfy requirementsfor plant photosynthesis and photomorphogenesis for successfulgrowth and seed yield. To determine the influence of galliumaluminium arsenide (GaAIAs) red LEDs on wheat photomorphogenesis,photosynthesis, and seed yield, wheat (Triticum aestivum L.,cv. ‘USU-Super Dwarf’) plants were grown under redLEDs and compared to plants grown under daylight fluorescent(white) lamps and red LEDs supplemented with either 1% or 10%blue light from blue fluorescent (BF) lamps. Compared to whitelight-grown plants, wheat grown under red LEDs alone demonstratedless main culm development during vegetative growth throughpreanthesis, while showing a longer flag leaf at 40 DAP andgreater main culm length at final harvest (70 DAP). As supplementalBF light was increased with red LEDs, shoot dry matter and netleaf photosynthesis rate increased. At final harvest, wheatgrown under red LEDs alone displayed fewer subtillers and alower seed yield compared to plants grown under white light.Wheat grown under red LEDs+10% BF light had comparable shootdry matter accumulation and seed yield relative to wheat grownunder white light. These results indicate that wheat can completeits life cycle under red LEDs alone, but larger plants and greateramounts of seed are produced in the presence of red LEDs supplementedwith a quantity of blue light. Key words: Triticum aestivum L., red light, blue light, subtillering, bioregenerative advanced life support     

The effect of light quality on leaf production and development of in vitro-cultured plants of Alternanthera brasiliana Kuntze

We investigated the influence of light quality on the leaf development of Alternanthera brasiliana Kuntze (Amaranthaceae) grown in vitro. Growth parameters including specific leaf mass, thickness, and leaf density were lowest in plants grown under red light. Blue light induced the largest number of leaves/plant, and the largest thickness and area of the leafblade. Green and red lights induced the smallest leaf areas. The thickness of the abaxial-face epidermis and spongy parenchyma of the plants was significantly reduced in plants grown under red light. The thickness of the palisade parenchyma and upper epidermis were significantly increased in plants grown under blue light, compared to the other fluorescent-light treatments. The specific spectral band also influenced the differentiation of mesophyll cells. In the dark and under red light, the mesophyll was homogenous; and in the dark and under green light, the leaves were more compact. Under blue light, the cells displayed the characteristic palisade morphology. The results showed that the increase of a specific parenchyma type was related to a specific spectral band. All spectral-quality treatments reduced the numbers of stomata and trichomes. The results for green light were in some respects similar to those for red light, and in other respects similar to those for blue light, probably because phytochromes and cryptochromes are green-light receptors. This study indicated that Alternanthera plants have strong morphological plasticity induced by light. The results suggest that high-quality Alternanthera can be achieved by culturing the plants in vitro under a combination of blue and red light.     

RESPONSE OF PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE) TO LIGHT OF DIFFERENT SPECTRAL QUALITIES AND IRRADIANCES: GROWTH AND PIGMENTATION1

Growth and pigment concentrations of the, estuarine dinoflagellate, Prorocentrum mariae-lebouriae (Parke and Ballantine) comb. nov., were measured in cultures grown in white, blue, green and red radiation at three different irradiances. White irradiances (400–800 nm) were 13.4, 4.0 and 1.8 W · m^?2 with photon flux densities of 58.7 ± 3.5, 17.4 ± 0.6 and 7.8 ± 0.3 μM quanta · m^?2· s^?1, respectively. All other spectral qualities had the same photon flux densities. Concentrations of chlorophyll a and chlorophyll c were inversely related to irradiance. A decrease of 7- to 8-fold in photon flux density resulted in a 2-fold increase in chlorophyll a and c and a 1.6- to 2.4-fold increase in both peridinin and total carotenoid concentrations. Cells grown in green light contained 22 to 32% more peridinin per cell and exhibited 10 to 16% higher peridinin to chlorophyll a ratios than cells grown in white light. Growth decreased as a function of irradiance in white, green and red light grown cells but was the same at all blue light irradiances. Maximum growth rates occurred at 8 μM quanta · m^?2· s^?1 in blue light, while in red and white light maximum growth rates occurred at considerably higher photon flux densities (24 to 32 μM quanta · m^?2· s^?1). The fastest growth rates occurred in blue and red radiation. White radiation producing maximum growth was only as effective as red and blue light when the photon flux density in either the red or blue portion of the white light spectrum was equivalent to that of a red or of blue light treatment which produced maximum growth rates. These differences in growth and pigmentation indicate that P. mariae-lebouriae responds to the spectral quality under which it is grown.     

Effect of different light qualities on the ultrastructure, thylakoid membrane composition and assimilation metabolism of Chlorella fusca

Chlorella fusca (Shihira et Krauss) strain C-1.1.10 was grown under three different light qualities (red, white or blue light) in homocontinuous cultures. Under electron microscopy, blue light cultures showed enlarged cells, thinner cell walls and lower starch content than red light cells. Under blue light, the degree of stacking of the thylakoid membranes was significantly lower than under white or red light conditions. Changing the light from blue to red the ratio of exposed to appressed membranes was doubled. Compared to red light cells, blue light cells exhibited higher photosynthetic rates per chlorophyll molecule and contained less chlorophyll per dry weight. Blue light stimulated the content of soluble protein as well as that of soluble carbohydrates. The dry weight productivity per unit time was enhanced under blue light conditions. The thylakoid protein complexes which are generally assumed to be localized in the exposed membranes were found in higher concentrations under blue light than under red light. In blue light, both the Photosystem II/Photosystem I ratio and the ratio of light-harvesting chlorophyll protein to P-700 chlorophyll a -protein were lower than in red light. Blue light cells contained twice the concentration of cytochrome f , which correlates well with their higher photosynthetic capacity. When altering the light quality, the degree of change in the reaction center complexes was much lower than expected given the corresponding degree of change in the ratio of exposed to appressed membranes. These results are discussed in light of the question as to whether the variation in the stoichiometry of the laterally distributed complexes can be explained by changes in the degree of stacking alone.     

Daylength and development in four species of Ceramiaceae (Rhodophyta)

Developmental patterns in four species of Ceramiaceae were determined using excised thallus apices grown under a range of light periods. Models of thallus development and organization based on these patterns are presented. Increased rates of apical cell division, greater growth of apical fragments and increased average cell size were found with increasing number of hours light per day between 8–16 and 16–8 h. No aspect of growth investigated was associated with photoperiodic phenomena, and growth occuring during the light break (8-7.5-1-7.5 h) was intermediate between that in 8–16 and 12–12 h. Three patterns of cell elongation were found in the four species in which (1) cell age, (2) cell age and position and (3) cell age, cell position and light period determined cell length at different axial cell positions. Elongation was followed within cells, along axes ofAntithamnion spirographidis for plants grown under different day lengths. Three regions of development were found along main axes: (1) an apical region in which basipetal expansion was greater than acropetal expansion. (2) a zone of stability with equal elongation in apical and basal growth region of cells, and (3) a basal region with greater acropetal expansion. With increasing daylength, the zone of stability was extended to greater ranges of cell length.