The Effects of Red, Far-red, and Blue Light on the Geotropic Response of Coleoptiles of Zea mays

The effects of red, far-red, and blue light on the geotropicresponse of excised coleoptiles of Zea mays have been investigated.Seedlings were grown in darkness for 5 or 6 days, exposed tovarious light treatments, and then returned to darkness fordetermination of the geotropic response. The rate of response of the coleoptiles is decreased after theyhave been exposed to red light (620–700 mµ, 560ergs cm^–2sec^–1 for the 24 hrs, but not for the 4hrs, preceding stimulation by gravity. Furthermore, their rateof response is greatly reduced if they are exposed to red lightfor 10 min and then returned to darkness for 20 hrs before geotropicstimulation. At 25° C an interval of 6 to 8 hrs elapses between a 10-minexposure to red light and the first detectable decrease in thegeotropic response of the coleoptile. This interval can be lengthenedby exposing the seedlings to low temperatures (0° to 2°C) after the light treatment but cannot be greatly shortenedby increasing the duration of exposure to red light. Using a standard procedure of exposing 5-day-old etiolated seedlingsto light for various times, replacing them in darkness for 20hrs and then determining the response of the coleoptiles to4 hrs geotropic stimulation, it has been found that: (a) Exposureto red light for 15 sec significantly decreases the geotropiccurvature of the coleoptiles and that further reduction occurson increasing the length of the light treatment to 2 and 5 min.(b) Far-red light has no effect on the geotropic response ofthe coleoptiles but it can completely reverse the effect ofred light. After repeated alternate exposure to red and far-redlight the geotropic response of the coleoptile is determinedby the nature of the last exposure, (c) Complete reversal ofthe effect of red light by far-red radiation only occurs whenexposure to far-red follows immediately after exposure to red.The reversing effect of far-red radiation is reduced if a periodof darkness intervenes between the red and far-red light treatments,and is lost after a dark interval of approximately 2 hrs. The effect of red light on the rate of geotropic response ofthe coleoptiles is independent of their age and length at thetime of excision. Blue light acts in a similar way to red light, but the seedlingsare less sensitive to blue than to red light. Coleoptiles grown throughout in a mixture of continuous, weak,red, and far-red light have a lower rate of geotropic responsethan etiolated coleoptiles.     

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.     

Kulturverfahren zur Bestimmung der Salz- und Über-flutungsverträglichkeit vonPuccinellia spp. (Gramineae)

In the ecology ofPuccinellia species (P. maritima, P. distans, P. retroflexa andP. limosa of the German flora described to date) two environmental factors seem to be very important: the salinity of the soil or of the tidal sea water and, especially in regard toP. maritima, the periodical inundation during the tidal cycle. The latter species forms an important community (Puccinellietum maritimae) a few decimetres above the middle tide level. The other species seem to be specialized to localities of higher levels. Some 450 natural localities covered withP. maritima on the western coasts of Schleswig-Holstein (W. Germany) have been analysed with respect to the type of plant community, dominance ofP. maritima, frequency of inundations, level above or below middle tide level, and soil factors (for instance: Cl-ion content, electrical conductivity, pH, clay content, etc.). Physiological experiments have been carried out in greenhouses, experimental grounds, and culture-rooms to test the effects onP. maritima (number 57 from the optimal level within the Puccinellietum maritimae of the banks of the River Eider) of soil composition, light intensity and daylength, temperature, inundation, etc.P. maritima grows with long creeping stolons at daylengths of 16 hrs and more; it forms a caespitose tufted plant at daylengths of 12 hrs and less (light intensity: 10,000 lux and more). Optimal growth occurs between 17° and 23° C and under conditions of artificial flooding up to soil surface twice a day (for about 10 minutes) by artificial sea water of 25 ‰ S. Two culture techniques have been developed for testing growth and survival after 8 weeks under greenhouse conditions (20° C or more; 10,000 lux or more; 15 hrs daylength or more, after comparable pre-cultivation over 8 weeks under 12 hrs day and artificial light conditions; sand + 3 % peat). The first technique has been used for testing salt tolerances between 0 and 60 ‰ S (artificial sea water), the second for testing inundation tolerances (0–2.5 hrs inundation twice a day; artificial sea water of 25 ‰ S). Considering different proveniences ofPuccinellia species on German coasts, it became clear thatPuccinellia exhibits broader ecological and morphological than taxonomical variabilities. WithinP. maritima, for example, several ecological types can be separated. This finding indicates the possibility of isolating different ecological types for specific localities in land reclamation areas.     

The regreening of nitrogen-deficient Chlorella fusca

Chlorella fusca, strain 211-15, cells degreened in a nitrogen-deficient mineral growth medium in the light for 4–6 weeks were regreened for up to 24 hrs in a nitrogen rich medium that leads to synchronous cell division at 24–26 hrs. Structural changes in the plastid membranes during the regreening period were observed by thin section and freeze-fracture electron microscopy. Nitrogen-deficient plastids were found to have non-appressed lamellae, prolamellar body-like membrane aggregations, and only 2 types of freeze-fracture face. At this time no photosynthetic oxygen evolution could be demonstrated. After 6 hrs regreening the plastid lamellae had fused to form bands of appressed lamellae and the four types of freeze-fracture face, described previously, were visible. At this time photosynthetic oxygen evolution could be demonstrated. After 24 hrs regreening the plastids had an appearance typical of normally grown Chlorella and had commenced to divide. Supporting evidence for these developmental stages is presented from isolated chloroplast particle fractions. An unusual type of cell wall proliferation was observed in the nitrogen-deficient Chlorella cells that resulted in the laying down of several walls, each with a trilaminar component.     

Effects of red light on the growth of intact wheat and barley coleoptiles

The final lengths of intact dark-grown coleoptiles vary with species and cultivar. The growth distribution pattern in the apical 25-mm growing zone and the absolute amount of growth in each zone depend on the age and species of the coleoptile. A comparative study of several cultivars of wheat, Triticum vulgare, and barley, Hordeum vulgare, indicates that the growth distribution pattern in 30- to 38-mm coleoptiles varies with the species and cultivar. In barley, there are two patterns of growth distribution among the several cultivars, whereas in wheat, all cultivars exhibit a common zonal growth pattern. The total growth of coleoptiles, initially 30 to 38 mm in length, during a 24-hour dark incubation period is the same in dark-grown coleoptiles as in those irradiated with 3 minutes of red (660 nm) light prior to the incubation period. The growth distribution pattern in the growing zone of this 30- to 38-mm coleoptile is, however, altered by red light. Growth of the apical 5-mm zone is stimulated by red light and the zonal growth 5 to 10 mm below the apex is only slightly affected, whereas growth in the zones 10 to 15 to 20, and 20 to 25 mm below the apex is inhibited. This growth distribution pattern in irradiated coleoptiles changes as the coleoptile increases in length. The response of a zone following exposure to red light is dependent upon the age of the seedlings irradiated. The over-all effect of red light on growth of the intact coleoptile varies with the length of the coleoptile. In young seedling 20 to 29 mm in length, the cells of the coleoptile can compensate for the effects of red light, with the over-all growth of the dark-grown and irradiated coleoptile about the same. As the seedling grows older, the cells of the coleoptile can no longer make up for the effects of red light, and the over-all effect changes from compensation to pronounced inhibition.     

DAY AND NIGHT KINETICS OF GROWTH RATE IN GREEN,BROWN, AND RED SEAWEEDS1

Growth rates in terms of area increase per 30 min were measured in flat thalli of several seaweed, species by means of computer-assisted image analysis, at 12 h light per day and a photon fluence rate of 20 μmol · m^-2· s^?1. Light fields included white fluorescent, imitated underwater, blue, green, and red light. In the green alga Ulva pseudocurvata Koeman et Hoek, blue light caused an immediate reduction of thallus area and growth rate after the onset of light, whereas green light and red light resulted in an initial peak in growth rate followed by inhibition 60 min after the onset of light. More growth was observed in darkness than in blue light in U. pseudocurvata. All brown and red algae tested, with Laminaria saccharina (L.) Lamour. and Palmaria palmata Stackh. as the main investigated species, grew faster during the day than during the night, irrespective of light quality during the main light phase. The upper intertidal red alga Porphyra umbilicalis (L.) J. Ag. achieved most of its thallus expansion per 24 h during the first 3 h of the light phase, with maximum growth rates of 2–3% increase in area per hour. Maximal growth rates were 0.7% for juvenile laminarian sporophytes and were lower than this in Palmaria palmata and other perennial red algae. The temporary growth inhibition by light in Ulva pseudocurvata suggests photomorphogenetic events, similar to the kinetics of stem elongation in higher plant seedlings after blue or red light pulses in darkness.     

Arrest of Nuclear Division in Plasmodium through Blockage of Erythrocyte Surface Exposed Ribosomal Protein P2

Malaria parasites reside inside erythrocytes and the disease manifestations are linked to the growth inside infected erythrocytes (IE). The growth of the parasite is mostly confined to the trophozoite stage during which nuclear division occurs followed by the formation of cell bodies (schizogony). The mechanism and regulation of schizogony are poorly understood. Here we show a novel role for a Plasmodium falciparum 60S stalk ribosomal acidic protein P2 (PfP2) (PFC0400w), which gets exported to the IE surface for 6–8 hrs during early schizogony, starting around 26–28 hrs post-merozoite invasion. The surface exposure is demonstrated using multiple PfP2-specific monoclonal antibodies, and is confirmed through transfection using PfP2-GFP. The IE surface-exposed PfP2-protein occurs mainly as SDS-resistant P2-homo-tetramers. Treatment with anti-PfP2 monoclonals causes arrest of IEs at the first nuclear division. Upon removal of the antibodies, about 80–85% of synchronized parasites can be released even after 24 hrs of antibody treatment. It has been reported that a tubovesicular network (TVN) is set up in early trophozoites which is used for nutrient import. Anti-P2 monoclonal antibodies cause a complete fragmentation of TVN by 36 hrs, and impairs lipid import in IEs. These may be downstream causes for the cell-cycle arrest. Upon antibody removal, the TVN is reconstituted, and the cell division progresses. Each of the above properties is observed in the rodent malaria parasite species P. yoelii and P. berghei. The translocation of the P2 protein to the IE surface is therefore likely to be of fundamental importance in Plasmodium cell division.     

High antioxidant capability interacts with respiration to mediate two Alexandrium species growth exploitation of photoperiods and light intensities

Light drives phytoplankton photosynthesis, so phytoplankton in their living habitats must exploit variable light levels and exposure durations, depending upon seasons, latitudes, depths and mixing events. Comparative growth, physiology and biochemical compositions were explored for the small Alexnadrium minutum (˜40 μm³ biovolume) and large Alexandrium catenella (˜9300 μm³ biovolume), globally wide spread coastal toxic red tide dinoflagellates, responding to a matrix of photoperiods (Light:Dark, 8:16, 16:8 and 24:0) and growth light irradiances. Smaller A. minutum grew faster under shorter photoperiods across growth light levels, while larger A. catenella grew fastest under longer photoperiods at the lowest applied light level. Photosystem II function responded largely to the instantaneous growth light level across photoperiod lengths, while the cell biovolume-based respiration, antioxidant capacity as well as cell composition responded more to photoperiod duration than to light level. These complex photophysiological responses resolved into linear correlations between growth rate versus cellular antioxidant activity and versus dark respiration, indicating that respiration energizes cellular antioxidant systems to benefit the growth of the cells. These results show the growth responses of Alexandrium species to light levels across photoperiods vary with species, and possibly with cell size. Together with previous results this puts a note of caution on meta-analytical extrapolations of physiological responses to light intensity derived from studies applying different photoperiods to different taxa, because different taxa show differential, even opposite growth responses to photoperiods and light intensities.     

Persistent Photoreversibility of Leaf Development

Far red light reversal of red light induced leaf expansion and enzyme changes were investigated in seedlings of Phaseolus vulgaris var. Black Valentine. In etiolated plants growth, anthocyanin accumulation and increases in glyceraldehyde-3-phosphate dehydrogenase and glycolic acid oxidase activities induced by a 10 min red irradiation were stopped by a 7 min far red irradiation given 17, 24, or 48 hr after activation. Etiolated seedlings illuminated for 24 hr with white light and seedlings grown in continuous light remained sensitive to far red reversal. This suggests that the far red sensitive receptor does not decay with time but remains associated with the site of its regulatory functions.     

Short term phytochrome control of oat coleoptile and pea epicotyl growth

Continuous recordings of the effect of light on oat (Avena sativa L. cv. Victory) coleoptile and pea (Pisum sativum L. cv. Alaska) epicotyl growth were made. Using a single excised coleoptile 10 minutes of red light was found to promote growth after a latent period of 46 minutes. The stimulation was transient and was not far red-reversible. Blue and far red light also promoted growth with similar kinetics. The action of continuous red or far red light was similar to that of 10-minute light. The growth of the intact pea third internode (as well as excised segments) was strongly inhibited by red light, with a latent period of 80 minutes. This effect was far red-reversible, and far red and blue light caused only a slight inhibition of growth.     

Growth, greening, and phytochrome in etiolated spirodela (lemnaceae)

Two species of Spirodela were grown aseptically in a simple mineral medium containing sucrose. Weak red light (15 erg cm⁻² sec⁻¹) enhanced dark growth of S. oligorrhiza, whereas weak far red light (15 erg cm⁻² sec⁻¹) when given after the red light reduced this effect.     

Influence of photoperiods on the growth rate and biomass productivity of green microalgae

The effect of different photoperiods: 24 h illumination and a 12:12-h light/dark (12L:12D) cycle on the growth rate and biomass productivity was studied in five algal species: Neochloris conjuncta, Neochloris terrestris, Neochloris texensis, Botryococcus braunii and Scenedesmus obliquus. The green microalgae examined differ in the reproduction mode. Continuous illumination stimulated the growth of B. braunii and S. obliquus more effectively than the growth of the microalgal species from the genus Neochloris. However, under shorter duration of light of the same intensity (12L:12D cycle), the growth of all the three species of Neochloris was stimulated. Under continuous illumination, the specific growth rate in the first phase of B. braunii and S. obliquus cultures was higher than the growth rate of Neochloris, whereas under the 12L:12D cycle, the specific growth rate of all the three Neochloris species was generally higher than that in B. braunii and S. obliquus. As a result, the light regime influenced algal biomass productivity differently. The maximum biomass productivity was obtained in B. braunii and S. obliquus cultures carried out at continuous illumination. All the Neochloris species produced biomass more efficiently at the 12L:12D cycle, which was two–threefold higher than that of B. braunii and S. obliquus. The unicellular species of the green microalgae from the genus Neochloris, examined for the first time in this study, are promising prospective objects for algal biotechnology.     

Growth and development temperature influences level of tolerance to high light stress

The influence of growth and development temperature on the relative tolerance of photosynthetic tissue to high light stress at chilling temperatures was investigated. Two tuber-bearing potato species, Solanum tuberosum L. cv Red Pontiac and Solanum commersonii were grown for 4 weeks, at either 12 or 24°C with 12 hours of about 375 micromoles per second per square meter of photosynthetically active radiation. Paired leaf discs were cut from directly across the midvein of leaflets of comparable developmental stage and light environment from each species at each growth temperature treatment. One disc of each pair was exposed to 1°C and about 1000 micromoles per second per square meter photosynthetically active radiation for 4 hours, and the other disc was held at 1°C in total darkness for the same duration. Photosynthetic tissue of S. tuberosum, developed at 12°C, was much more tolerant to high light and low temperature stress than tissue developed under 24°C conditions. Following the high light treatment, 24°C-grown S. tuberosum tissue demonstrated light-limited and light-saturated rates that were approximately 50% of their paired dark controls. In contrast, the 12°C-grown tissue from S. tuberosum that was subjected to the light stress showed only a 18 and 6% reduction in light-limited and light-saturated rates of photosynthetic oxygen evolution, respectively. Tissue from 24°C-grown S. commersonii was much less sensitive to the light stress than was tissue from S. tuberosum grown under the same conditions. The results presented here demonstrate that: (a) acclimation of S. tuberosum to lower temperature growth conditions with a constant light environment, results in the increased capacity of photosynthetic tissue to tolerate high light stress at chilling temperature and (b) following growth and development at relatively high temperatures S. commersonii, a frost- and heat-tolerant wild species, has a much greater tolerance to the high light stress at chilling temperature than does S. tuberosum cv Red Pontiac, a frost-sensitive cultivated species.     

Dormancy in bulbils of several herbaceous plants: Effects of photoperiod,light, temperature,oxygen and gibberellic acid

Effects of some environmental conditions (photoperiod, white and colored lights, temperature, partial oxygen pressure) and growth regulators (gibberellic acid, 2-chloroethyltrimethylammonium chloride) on induction and release of dormancy of the bulbils ofDioscorea batalas, Laportea bulbifera, Elatostema involucratum andSedum bulbiferum were investigated. Bulbils were formed under short-day conditions inLaportea andElatostema, under long-day conditions inSedum, and irrespective of photoperiods inDioscorea. In all species exceptSedum, immature bulbils required light, particularly blue or far red, for sprouting (photo-sprouting stage), and mature bulbils required a cold treatment (thermo-sprouting stage). The duration of photo-sprouting and thermo-sprouting stages and the degree of dependency on light or low temperature of sprouting differed from species to species. Sprouting of chilled mature bulbils of these species was promoted by light, especially by red or green light. Both immature and mature bulbils ofSedum sprouted under short-day conditions. Continuous irradiation with blue, far-red and green light markedly inhibited their sprouting. Oxygen at high concentration inhibited the sprouting of immature bulbils inDioscorea; in the other species it promoted sprouting regardless of the maturation of the bulbils. Applications of gibberellic acid caused the sprouting of bulbils the absence of light, chilling or photoperiodic treatment in all species exceptDioscorea, in which gibberellic acid inhibited sprouting. Polyphenol oxidase activity was very high in the homogenates ofDioscorea bulbils, and increased further when the bulbils had been treated with gibberellic acid. In the other species, little or no such activity was observed.     

Phytochrome Control of Cell Wall-bound Hydroxyproline Content in Etiolated Pea Epicotyls

The red light inhibition of growth of the intact pea (Pisum sativum L. cv. Alaska) third internode was correlated with an increase in the content of cell wall-bound hydroxyproline. These changes were detected 3 hours after irradiation, and possibly at 1 hour. Far red light reversed the effects of red light. The iron chelator α,α′-dipyridyl reversed the red light effects on both growth and hydroxyproline content. Using segments incubated in vitro, no phytochrome-mediated change in hydroxyproline content could be observed, perhaps because of an overwhelming wounding response. If plants were irradiated in situ and grown for 8 hours before excision and incubation of segments, some enhancement of hydroxylation by red light was detectable both colorimetrically and radioisotopically. The red light inhibition of segment growth was reversed by α,α′-dipyridyl. These results are examined in reference to the role of extensin in normal and induced growth cessation.     

Locomotor activity rhythm in four wrasse species under varying light conditions

Under controlled laboratory conditions, the locomotor activity rhythms of four species of wrasses (Suezichthys gracilis, Thalassoma cupido, Labroides dimidiatus andCirrhilabrus temminckii) were individually examined using an actograph with infra-red photo-electric switches in a dark room at temperatures of 21.3–24.3°C, for 7 to 14 days. The locomotor activity ofS. gracilis occurred mostly during the light period under a light-dark cycle regimen (LD 12:12; 06:00-18:00 light, 18:00-06:00 dark). The locomotor activity commenced at the beginning of the light period and continued until a little before the beginning of dark period. The diel activity rhythm of this species synchronizes with LD. Under constant illumination (LL) this species shows distinct free-running activity rhythms varying in length from 23 hrs. 39 min. to 23 hrs. 47 min. Therefore,S. gracilis appears to have a circadian rhythm under LL. However, in constant darkness (DD), the activity of this species was greatly suppressed. All the fish showed no activity rhythms in DD conditions. After DD, the fish showed the diel activity rhythm with the resumption of LD, but this activity began shortly after the beginning of light period. The fish required several days to synchronize with the activity in the light period. Therefore,S. gracilis appeared to continue the circadian rhythm under DD. InT. cupido, the locomotor activity commenced somewhat earlier than the beginning of the light period and continued until the beginning of the dark period under LD. The diel activity rhythm of this species synchronizes with LD. Under LL, four of the five specimens of this species tested showed free-running activity rhythms for the first 5 days or longer varying in length from 22 hrs. 54 min. to 23 hrs. 39 min. Although the activity of this species was suppressed under DD, two of five fish showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 38 min. to 23 hrs. 50 min. under DD. Therefore, it was ascertained thatT. cupido has a circadian rhythm. InL. dimidiatus, the locomotor activity rhythm under LD resembled that observed inT. cupido. The diel activity rhythm of this species synchronizes with LD. Under LL, four of seven of this species showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 07 min. to 25 hrs. 48 min. Although the activity of this species was suppressed under DD, three of five fish showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 36 min. to 23 hrs. 41 min. under DD. Therefore, it was ascertained thatL. dimidiatus has a circadian rhythm. Almost all locomotor activity of C.temminckii occurred during the light period under LD. The diel activity rhythm of this species coincides with LD. Under LL, two of four of this species showed free-running activity rhythms throughout the experimental period. The lengths of such free-running periods were from 23 hrs. 32 min. to 23 hrs. 45 min. Although the activity of this species was suppressed under DD, one of the four fish showed free-running activity rhythms throughout the experimental period. The length of the free-running period was 23 hrs. 21 min. under DD. Therefore,C. temminckii appeared to have a circadian rhythm. According to field observations,S. gracilis burrows and lies in the sandy bottom whileT. cupido, L. dimidiatus, andC. temminckii hide and rest in spaces among piles of boulders or in crevices of rocks during the night. It seems that the differences in nocturnal behavior among the four species of wrasses mentioned above are closely related to the intensity of endogenous factors in their locomotor activity rhythms.     

Action Spectrum for Resetting the Circadian Phototaxis Rhythm in the CW15 Strain of Chlamydomonas: I. Cells in Darkness

We have developed protocols for phase shifting the circadian rhythm of Chlamydomonas reinhardtii by light pulses. This paper describes the photobiology of phase-resetting the Chlamydomonas clock by brief (3 seconds to 15 minutes) light pulses administered during a 24 hour dark period. Its action spectrum exhibited two prominent peaks, at 520 and 660 nanometers. The fluence at 520 nanometers required to elicit a 4 hour phase shift was 0.2 millimole photon per square meter, but the pigment that is participating in resetting the clock under these conditions is unknown. The fluence needed at 660 nanomoles to induce a 4 hour phase shift was 0.1 millimole photon per square meter, which is comparable with that needed to induce the typical low fluence rate response of phytochrome in higher plants. However, the phase shift by red light (660 nanometers) was not diminished by subsequent administration of far-red light (730 nanometers), even if the red light pulse was as short as 0.1 second. This constitutes the first report of a regulatory action by red light in Chlamydomonas.     

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.     

Red light and carbon dioxide differentially affect growth,lipid production,and quality in the microalga, <Emphasis Type="Italic">Ettlia oleoabundans</Emphasis>

Ettlia oleoabundans, a freshwater unicellular green microalga, was grown under different light qualities ± carbon dioxide-enriched air to determine the combined effects on growth and lipid production of this oleaginous species. Keeping total light intensity constant, when a portion of the cool white was replaced by red, volumetric lipid yield increased 2.8-fold mainly due to the greater yield of oleic acid, a desirable biodiesel precursor. Only 30 min of red light treatment was sufficient to increase lipid yield and quality to the same level as cultures provided red light for >14 days, indicating the potential role of red light in stimulating lipid production of this species. Carbon dioxide enrichment via air sparging enhanced exponential growth, carbon conversion efficiency, and nutrient consumption. Together, these results showed that light quality plays an important role in microalgal lipid production. Adjustment in light quality and gas delivery efficiency with carbon dioxide enrichment improved lipid yield and quality in this and possibly other oleaginous algal species.     

Genetic analysis of the role of gibberellin in the red light inhibition of stem elongation in etiolated seedlings

Red light causes a reduction in the extension growth of dark-grown seedlings. The involvement of gibberellin in this process was tested by screening a number of gibberellin synthesis and gibberellin response mutants of Pisum sativum L. for the kinetic response of stem growth inhibition by red light. Gibberellin deficient dwarfs, produced by mutant alleles at the Le, Na, and Ls loci, and gibberellin response mutants produced by mutant alleles at the La and Cry², Lka, and Lkb loci were tested. Extension growth of expanding third internodes of dark-grown seedlings was recorded with high resolution using angular position transducers. Seedlings were treated with red light at a fluence rate of 4 micromoles per square meter per second either continuously or for 75 seconds, and the response was measured over 9 hours. With certain small exceptions, the response to the red light treatments was similar in all the mutants and wild types examined. The lag time for the response was approximately 1 hour and a minimum in growth rate was reached by 3 to 4 hours after the onset of the light treatment. Growth rate depression at this point was about 80%. Seedlings treated with 75 seconds red light recovered growth to a certain extent. Red/far-red treatments indicated that the response was mediated largely by phytochrome. The similar responses to red light among these wild-type and mutant genotypes suggest that the short-term (i.e. 9 hour) response to red light is not mediated by either a reduction in the level of gibberellin or a reduction in the level or affinity of a gibberellin receptor.