THE MECHANISM OF DAYLENGTH PERCEPTION IN THE RED ALGA ACROSYMPHYTON PURPURIFERUM1

The red alga Acrosymphyton purpuriferum (J. Ag.) Sjöst. (Dumontiaceae) is a short day plant in the formation of its tetrasporangia. Tetrasporogenesis was not inhibited by 1 h night-breaks when given at any time during the long (16 h) dark period (tested at 2 h intervals). However, tetrasporogenesis was inhibited when short (8 h) main photoperiods were extended beyond the critical daylength with supplementary light periods (8 h) at an irradiance below photosynthetic compensation. The threshold irradiance for inhibition of tetrasporogenesis was far lower when supplementary light periods preceded the main photoperiod than when they followed it (<0.05 μmol·m⁻²·s⁻¹ vs. 3 μmol·m⁻²·s⁻¹). The threshold level also depended on the irradiance given during the main photoperiod and was higher after a main photoperiod in bright light than after one in dim light (threshold at 3 μmol·m⁻²·s⁻¹ after a main photoperiod at ca. 65 μmol·m⁻²·s⁻¹ vs. threshold at <0.5 μmol·m⁻²·s⁻¹ after a main photoperiod at ca. 35 μmol·m⁻²·s⁻¹). The spectral dependence of the response was investigated in day-extensions (supplementary light period (8 h) after main photoperiod (8 h) at 48 μmol·m⁻²·s⁻¹) with narrow band coloured light. Blue light (λ= 420 nm) was most effective, with 50% inhibition at a quantum-dose of 2.3 mmol·m⁻². However, yellow (λ= 563 nm) and red light (λ= 600 nm; λ= 670 nm) also caused some inhibition, with ca. 30% of the effectiveness of blue light. Only far-red light (λ= 710 nm; λ= 730 nm) was relatively ineffective with no significant inhibition of tetrasporogenesis at quantum-doses of up to 20 mmol·m⁻².     

STIMULATION OF LIGHT-SATURATED PHOTOSYNTHESIS IN LAMINARIA (PHAEOPHYTA) BY BLUE LIGHT1

The light-saturated rate of photosynthesis in blue light was 50-100% higher than that in red light for young sporophytes of Laminaria digitata (Huds.) Lamour., although photosynthetic rates were slightly higher in red than in blue light at low irradiances. Short exposures to low irradiances (e.g. 2 min at 20 μmol · m^?2· s^?1) of blue light also stimulated the subsequent photosynthesis of Laminaria sporophytes in saturating irradiances of red light but had little effect on photosynthesis in low irradiances of red light. The full stimulatory effect of short exposures to blue light was observed within 5 min of the blue treatment and persisted for at least 15 min in red light or in darkness. Thereafter, the effect began to decline, but some stimulation was still detectable 45 min after the blue treatment. The degree of stimulation was proportional to the logarithm of the photon exposure to blue light over the range 0.15-2.4 mmol · m^?2, and the effectiveness of an exposure to 0.6 mmol · m^?2at different wavelengths was high at 402-475 nm (with a peak at 460-475 nm) but declined sharply at 475-497 nm and was minimal at 544-701 nm. Blue light appears, therefore, to exert a direct effect on the dark reaction of photosynthesis in brown algae, possibly by activating carbon-fixing enzymes or by stimulating the uptake or transport of inorganic carbon in the plants.     

CRITICAL LEVELS OF LIGHT AND TEMPERATURE REGULATING THE GAMETOGENESIS OF THREE LAMINARIA SPECIES (PHAEOPHYCEAE)1

Gametophytes of three Laminaria species occurring near Helgoland, North Sea, were cultivated 4 wk in a 12:12 LD regime at different temperatures in artificial light fields, and in the sea at different water depths. In the artificial light fields underwater spectral distribution was simulated according to Jerlov water Types 5, 7, 9. Blue light in the simulated light fields amounted to 17, 12 or 4% of total quanta. The rate of vegetative growth did not depend on spectral distribution, was light-saturated at 4–6 W · m^?2, and increased with temperature up to 15 C. L. saccharina (L.) Lamour. exhibited the highest tolerance towards temperature, light and UV. Gametophytes survived 1 wk at 21 C ± 0.1, but not 22 C ± 0.1. Gametophytes of L. hyperborea (Gunn.) Fosl. and L. digitata (Huds.) Lamour. survived 1 wk at 20 C ± 0.1, but not at 21 C ± 0.1. In sunlight, and in the light field of a xenon lamp, 50% of L. saccharina gametophytes were killed by a quantum dose of 50 μEin · cm^?2, and 100% of the plants by 90 μEin · cm^?2. Approximately half of these quantum doses killed the corresponding percent of the other species gametophytes. Appreciably higher quantum doses were survived in visible light, with red being the most detrimental. Fertility depended on a critical quantum dose of blue light which decreased almost exponentially with decreasing temperature. The quantum dose (400–512 nm) required for induction of fertilization of 50% of the female gametophytes (males react similarly) was 90 μEin · cm^?2 at 5 C, 110 μEin · cm^?2 at 10 C, 230 (560 in L. digitata)μEin · cm^?2 at 15 C, and 560 (L. hyperborea) or about 850 (other 2 species) μEin · cm^?2 at 18 C. In the sea the gametophytes survived the dark winter months in the unicellular stage, with almost no vegetative growth of the primary cell, due to lack of light. In early spring the female gametophytes matured in the unicellular, and the males in a few-celled stage at the depth of 2 m, as did the laboratory cultures under conditions inducing maximal fertility.     

DOES LIGHT QUALITY AFFECT THE SINKING RATES OF MARINE DIATOMS?1

Although the spectral quality of light in the ocean varies considerably with depth, the effect of light quality on different physiological processes in marine phytoplankton remains largely unknown. In cases where experiments are performed under full spectral irradiance, the meaning of these experiments in situ is thus unclear. In this study, we determined whether variations in spectral quality affected the sinking rates of marine diatoms. Semicontinuous batch cultures of Thalassiosira weissflogii (Gru.) Fryxell et Hasle and Ditylum brightwellii (t. West) Grunow in Van Huerk were grown under continuous red, white, or blue light. For T. weissflogii, sinking rates (SETCOL method) were twice as high (～0.2 m·d^?1)for cells grown under red light as for cells grown under white or blue light (～0.08 m·d^?1), but there were no significant differences in carbohydrate content (～105 fg·μm^?3) or silica content (～ 17 fg·μ^?3) to account for the difference in sinking rates. Thalassiosira weissflogii grown under blue light was significantly smaller (495 μm³) than cells grown under red light (661 μm³), which could contribute to its reduced sinking rate. However, cells grown under white light were similar in size to those grown under red light but had sinking rates not different from those of cells grown under blue light, indicating the involvement of factors other than size. There were no significant differences in sinking rate (～0.054 m·d^?1) or silica content (～20 fg·μm^?3) in D. brightwellii grown under red, white, or blue light, but cells grown under red light were significantly (20%) larger and contained significantly (20%) more carbohydrate per μm³ than cells grown under white or blue light. Spectral quality had no consistent effect on sinking rate, biochemical composition (carbohydrate or silica content), or cell volume in the two diatoms studied. The similarity in sinking rate of cells grown under white light compared to those grown under blue light supports the ecological validity of sinking rate studies done under white light.     

GROWTH AND MORPHOLOGY OF YOUNG GAMETOPHYTES OF PORPHYRA ABBOTTAE (RHODOPHYTA): EFFECTS OF ENVIRONMENTAL FACTORS IN CULTURE1

Growth, blade shape and blade thickness of young gametophytes of Porphyra abbottae Krishnamurthy cultured from conchospores were determined at various combinations of temperature (8, 10, 12° C), photon flux density (17.5, 70, 140 μmol·m-^?2·S^?1), nutrient concentration (5, 25, 50, 100% f medium) and water motion (0, 50, 100, 150 rpm). Growth (as surface area) was light-saturated at 70 μmol· m^?2· S^?1, light-inhabited at 140 μmol·m^?2· S^?1, and nutrient-saturated an 25% f medium. Temperature had no significant effect on growth. Water motion and nutrients had an interactive effect on growth, with water motion having the greatest effect at the lowest nutrient concentrations. Water motion enhanced growth even at saturating nutrient concentrations. Blade length / width ratio was greater in low light (2.5) than in saturating light (1.9); with increasing water motion the ratio increased from 1.2 to 2.4. Blade thickness (53-88 μm) was greatest at the highest nutrient concentrations and at the lowest water motion levels. Temperature and light did not have a consistent effect on blade thickness.     

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m^?2·s^?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m^?2·s^?1 for P. oedogonia (0.247 d^?1) and 25°C and 500 μmol·m^?2·s^?1 for Spirogyra sp. (0.224 d^?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m^?2·s^?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m^?2·s^?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt^?1) than did P. oedogonia (1.35–3.08 μg·mg fwt^?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.     

PHOTOINHIBITION OF MECHANICALLY STIMULABLE BIOLUMINESCENCE IN THE AUTOTROPHIC DINOFLAGELLATE CERATIUM FUSUS (PYRROPHYTA)1

Ceratium fusus (Ehrenb.) Dujardin was exposed to light of different wavelengths and photon flux densities (PFDs) to examine their effects on mechanically stimulable bioluminescence (MSL). Photoinhibition of MSL was proportional to the logarithm of PFD. Exposure to I μmol photons·m^?2s^?1 of broadband blue light (ca. 400–500 nm) produced near-complete photoinhibition (≥90% reduction in MSL) with a threshold at ca. 0.01 μmol photons·m^?2·s^?1. The threshold of photoinhibition was ca. an order of magnitude greater for both broadband green (ca. 500–580 nm) and red light (ca. 660–700 nm). Exposure to narrow spectral bands (ca. 10 nm half bandwidth) from 400 and 700 nm at a PFD of 0.1 μmol photons·m^?2·s^?1 produced a maximal response of photoinhibition in the blue wavelengths (peak ca. 490 nm). A photoinhibition response (≥ 10%) in the green (ca. 500–540 nm) and red wavelengths (ca. 680 nm) occurred only at higher PFDs (1 and 10 μmol photons·m^?2·s^?1). The spectral response is similar to that reported for Gonyaulax polyedra Stein and Pyrocystis lunula Schütt and unlike that of Alexandrium tamarense (Lebour) Balech et Tangen. The dinoflagellate's own bioluminescence is two orders of magnitude too low to result in self-photoinhibition. The quantitative relationships developed in the laboratory predict photoinhibition of bioluminescence in populations of C. fusus in the North Atlantic Ocean.     

EFFECT OF TEMPERATURE,LIGHT AND pH ON GROWTH,PHOTOSYNTHESIS AND RESPIRATION OF THE DINOFLAGELLATE PERIDINIUM CINCTUM FA. WESTII IN LABORATORY CULTURES1

Optimum light, temperature, and pH conditions for growth, photosynthetic, and respiratory activities of Peridinium cinctum fa. westii (Lemm.) Lef were investigated by using axenic clones in batch cultures. The results are discussed and compared with data from Lake Kinneret (Israel) where it produces heavy blooms in spring. Highest biomass development and growth rates occurred at ca. 23° C and ≥50 μE· m^?2·s¹ of fluorescent light with energy peaks at 440–575 and 665 nm. Photosynthetic oxygen release was more efficient in filtered light of blue (BG 12) and red (RG 2) than in green (VG 9) qualities. Photosynthetic oxygen production occurred at temperatures ranging from 5° to 32° C in white fluorescent light from 10 to 105 μE·m^?2·s^?1 with a gross maximum value of 1500 × 10^?12 g·cell^?1·h^?1 at the highest irradiance. The average respiration amounted to ca. 12% of the gross production and reached a maximum value of ca. 270·10^?12 g·cell^?1·h^?1 at 31° C. A comparison of photosynthetic and respiratory Q₁₀-values showed that in the upper temperature range the increase in gross production was only a third of the corresponding increase in respiration, although the gross production was at maximum. Short intermittent periods of dark (>7 min) before high light exposures from a halogen lamp greatly increased oxygen production. Depending on the physiological status of the alga, light saturation values were reached at 500–1000 μE·m^?2·s^?1 of halogen light with compensation points at 20–40 μE·m^?2·s^?1 and I_k-values at 100–200 μE·m^?2·s^?1. The corresponding values in fluorescent light in which it was cultured and adapted, were 25 to 75% lower indicating the ability of the alga to efficiently utilize varying light conditions, if the adaptation time is sufficient. Carbon fixation was most efficient at ca. pH 7, but the growth rates and biomass development were highest at pH 8.3.     

NONEQUILIBRIUM RATES OF PHOTOSYNTHESIS AND RESPIRATION UNDER DYNAMIC LIGHT SUPPLY1

To identify processes that might account for differences in growth rates of rhodophytes under constant and dynamic light supply, we examined nonequilibrium gas exchange by measuring time courses of photoinduction, loss of photoinduction, and respiration rates immediately after the light–dark transition. Using the rhodophyte species Palmaria palmata (Huds.) Lamour and Lomentaria articulata (Huds.) Lyngb., we compared the effects of growth-saturating constant photon flux density (PFD) (95 μmol photons · m^?2· s^?1) to those of a dynamic light supply modeled on canopy movements in the intertidal zone (25 μmol photons · m^?2· s^?1 background PFD plus light flecks of 350 μmol photons · m^?2· s^?1, 0.1 Hz). The time required for P. palmata and L. articulata to be fully photoinduced was not affected by the dynamics of light supply. L. articulata required only 6 min of illumination with either fluctuating or constant light to be completely induced compared to 20 min for P. palmata. The latter species also lost photoinduction more rapidly than did L. articulata in the dark. There was no significant decline in photoinduction state for either species at the background PFD. The time courses of respiration after illumination with constant and fluctuating light were significantly different for P. palmata but not for L. articulata when the total photon dose was equal. In general, gas exchange of P. palmata appeared to be particularly sensitive to the temporal distribution of light supply whereas that of L. articulata was sensitive to the amplitude of variations, being photoinhibited at high PFD. These results are discussed in terms of the different mechanisms of inorganic carbon acquisition in the two species.     

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.     

Effects of light intensity and quality on phycobiliprotein accumulation in the cyanobacterium <Emphasis Type="Italic">Nostoc sphaeroides</Emphasis> Kützing

Objectives

To assess the effects of light intensity and quality on the growth and phycobiliproteins (PBP) accumulation in Nostoc sphaeroides Kützing (N. sphaeroides).

Results

Dry weights, dry matter, protein, chlorophyll and PBP contents were higher under 90 μmol m^?2 s^?1 than under other intensities (both higher and lower). Phycocyanin and allophycocyanin increased with light intensity while phycoerythrin decreased. Fresh weights, protein and PBP contents increased at the highest rates under blue light. Red light resulted in higher values of dry matter, phycocyanin and chlorophyll a.

Conclusion

White light at 90 μmol m^?2 s^?1 or blue light 30 μmol m^?2 s^?1 were optimal for the growth and phycobiliprotein accumulation in N. sphaeroides.

     

LIGHT DEPENDENCE OF GROWTH AND PHOTOSYNTHESIS IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Phaeodactylum tricornutum Bohlin was maintained in exponential growth over a range of photon flux densities (PFD) from 7 to 230 μmol·m^?2s^?1. The chlorophyll a-specific light absorption coefficient, maximum quantum yield of photosynthesis, and C:N atom ratio were all independent of the PFD to which cells were acclimated. Carbon- and cell-specific, light-satuated, gross photosynthesis rates and dark respiration rates were largely independent of acclimation PFD. Decreases in the chlorophyll a-specific, gross photosynthesis rate and the carbon: chlorophyll ratio and increases of cell- or carbon-specific absorption coefficients were associated with an increase in cell chlorophyll a in cultures acclimated to low PFDs. The compensation PFD for growth was calculated to be 0.5 μmol·m^?2s^?1. The maintenance metabolic rate (2 × 10^?7s^?1), calculated on the basis of the compensation PFD, is an order of magnitude lower than the measured dark respiration rate(2.7 × 10^?6mol O₂·mol C^?1s^?1). Maintenance of high carbon-specific, light-saturated photosynthesis rates in cells acclimated to low PFDs may allow effective use of short exposures to high PFDs in a temporally variable light environment.     

COMPARISONS OF SALT-MARSH FUCOID PRODUCTION ESTIMATED FROM THREE DIFFERENT INDICES1

Production of Ascophyllum nodosum (L.) LeJolis ecads and Fuscus vesiculosus L. was calculated from measurements of in situ growth, seasonal variations in standing-crops and seasonal variations in photosynthetic capacity. A computer model for predicting daily, monthly and yearly net production from photosynthesis data was constructed. This model used daily irradiation, actual biomass of algae/m² contributing to production and photosynthesis vs. light intensity relationships as data inputs. Comparison of production estimated from in situ growth, standing-crops and photosynthesis indicated that both marsh fucoids turn over biomass twice per year. Total net production of both fucoids, estimated from photosynthesis data, was ca. 315 g C · m^?2· yr^?1. On the other hand, production of both fucoids calculated from standing-crop data was only 155 g C · m^?2· yr^?1.     

Quality and intensity of light affect <Emphasis Type="Italic">Lippia gracilis</Emphasis> Schauer plant growth and volatile compounds in vitro

The aim of this study was to evaluate the effects of different intensities and quality of light and explant type on the growth of and volatile compounds in Lippia gracilis in vitro. The treatments were as follows: light intensities of 26, 51, 69, 94, or 130 µmol m^?2 s^?1 from fluorescent lamps and light-emitting diode (LED) lamps at different wavelengths, namely, white, red, blue, and combinations of red and blue light at ratios of 2.5:1 and 1:2.5, respectively, and two explant types, namely, nodal and apical segments. On the 30th day of culture on half-strength Murashige and Skoog (Physiol Plant 15(3):473–497, 1962) medium, growth, production of photosynthetic pigments, chlorophyll a and b, total chlorophyll, carotenoids, and volatile constituents (using headspace gas chromatography-mass spectrometry) were analyzed. The light quality and intensity significantly influenced the in vitro growth of L. gracilis. The apical segments were superior in all parameters evaluated compared to nodal segments. The number of segments plantlet^?1, root length, and leaf, shoot, root, and total weight were higher with increasing light intensity, especially under the 94 µmol m^?2 s^?1 treatment, for both explant types. The red light showed the highest leaf (32.28 mg plantlet^?1) and total (58.33 mg plantlet^?1) dry weight of all the light qualities. Major constituents, namely, ρ-cymene, γ-terpinene, thymol, carvacrol, and E-caryophyllene, were identified, regardless of light conditions. The amount and composition of volatile compounds varied according to light intensity and quality. Low intensity (26 µmol m^?2 s^?1) increased γ-terpinene content (12.42%) and concomitantly decreased carvacrol (38.52%). Blue LED light showed higher production of carvacrol (48.11%).     

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.     

LIGHT REQUIREMENTS FOR MONOSPORE GERMINATION IN BANGIA ATROPURPUREA (RHODOPHYTA)1

Monospore germination, in Bangia atropurpurea (Roth) C. Ag. [= B. fuscopurpurea (Dillw.) Lyngb.] is light-dependent. In white light, the percent germination increases with increasing photon fluence rate until the response is saturated at 35 μmol · m^?2· s^?1. At a saturating photon fluence rate in an 18:6 h L:D cycle, 9 days are required for maximum germination. Green light is the most effective spectral region for monospore germination, although the process can occur in red and blue light if sufficiently high photon fluence rates are provided. Monospore germination and photosynthetic oxygen evolution are completely inhibited by DCMU at a concentration of 1 × 10^?6 M. Germination is reduced in a low CO₂ atmosphere and does not occur in the dark when glucose, maltose or inositol are supplied. It is concluded that photosynthesis is required for monospore germination.     

Effects of diurnal fluctuations in light intensity on the efficiency of growth of Skeletonema costatum (Grev.) Cleve (Bacillariophyceae) in a cyclostat

The effects of diurnal variations in light intensity on the biomass characteristics and the efficiency of daily growth of Skeletonema costatum (Grev.) Cleve were evaluated. The relative importance of changes in carbon specific rates of respiration and organic release to the efficiency of growth was determined. Light intensity was either constant at 130 μE · m^?2 · s^?1 during the light period or fluctuated throughout the light period from 500 to 10 μE · m^?2 · s^?1 at rates of either 1 or 12 cycles · day^?1. Total daily light was equivalent for all light regimes at 5.6 E · m^?2 · day^?1.Daily rates of growth remained comparable at ≈ 1 · day^?1 under constant and fluctuating light regimes. Cell size as daily mean carbon · cell^?1, nitrogen · cell^?1 and cellular volume was decreased under diurnally varying light whereas daily mean chlorophyll a · cell^?1 was unaffected.Rates of respiration, organic release and gross production were elevated several fold under diurnally varying light in comparison to constant light. Net growth efficiency decreased from 0.69 under constant light to values of 0.50 and 0.38 under 1 and 12 cycles · day^?1, respectively. Decreased efficiency of growth under diurnally fluctuating light resulted mostly from greater respiratory activity while organic release remained < 10% of gross production. Increased rates of gross production reflected enhancement in the efficiency of carbon fixation with fluctuating light.     

CRITICAL IRRADIANCE LEVELS AND THE INTERACTIVE EFFECTS OF QUANTUM IRRADIANCE AND DOSE ON GAMETOGENESIS IN THE GIANT KELP,MACROCYSTIS PYRIFERA1

Gametophytes of Macrocystis pyrifera (L.) C. Ag. were cultured under a series of quantum irradiances in three photoperiod regimes. The quantum irradiances in each photoperiod were adjusted to provide equal daily irradiation dosages between photoperiods which allowed a critical examination of the interactions between quantum irradiance and quantum dose in determining gametophyte fertility. The lowest quantum irradiance which stimulated gametogenesis in more than 50% of the female gametophytes was 5 μE·m^?2·s^?1. The saturating irradiance was ca. 10 μE·m^?2·s^?1 at photoperiods of 12 h or greater. In terms of daily quantum dose, the lowest dose at which greater than 50% gametogenesis occurred was 0.2 E·m^?2·d^?1. However, this critical quantum dose was higher (0.4 E·m^?2·d^?1) when instantaneous irradiances were less than 5 μE·m^?2·s^?1. The saturation quantum dose was also affected by the rate at which the quantum dose was received and varied from 0.4 to 0.8 E·m^?2·d^?1. Gametophytes in all three photoperiods reached 100% fertility at quantum irradiances above 5 μE·m^?2·s^?1. Photoperiod effects were small and could be accounted for by quantum dosage effects.     

PAR modulation of the UV-dependent levels of flavonoid metabolites in Arabidopsis thaliana (L.) Heynh. leaf rosettes: cumulative effects after a whole vegetative growth period

Long-term effects of ultraviolet (UV) radiation on flavonoid biosynthesis were investigated in Arabidopsis thaliana using the sun simulators of the Helmholtz Zentrum München. The plants, which are widely used as a model system, were grown (1) at high photosynthetically active radiation (PAR; 1,310 µmol m^?2?s^?1) and high biologically effective UV irradiation (UV-B_BE 180 mW m^?2) during a whole vegetative growth period. Under this irradiation regime, the levels of quercetin products were distinctively elevated with increasing UV-B irradiance. (2) Cultivation at high PAR (1,270 µmol m^?2?s^?1) and low UV-B (UV-B_BE 25 mW m^?2) resulted in somewhat lower levels of quercetin products compared to the high-UV-B_BE conditions, and only a slight increase with increasing UV-B irradiance was observed. On the other hand, when the plants were grown (3) at low PAR (540 µmol m^?2?s^?1) and high UV-B (UV-B_BE 180 mW m^?2), the accumulation of quercetin products strongly increased from very low levels with increasing amounts of UV-B but the accumulation of kaempferol derivatives and sinapoyl glucose was less pronounced. We conclude (4) that the accumulation of quercetin products triggered by PAR leads to a basic UV protection that is further increased by UV-B radiation. Based on our data, (5) a combined effect of PAR and different spectral sections of UV radiation is satisfactorily described by a biological weighting function, which again emphasizes the additional role of UV-A (315–400 nm) in UV action on A. thaliana.     

EFFECTS OF EXTERNAL INORGANIC NITROGEN CONCENTRATION ON METABOLISM,GROWTH AND ACTIVITIES OF KEY CARBON AND NITROGEN ASSIMILATORY ENZYMES OF LAMINARIA SACCHARINA (PHAEOPHYCEAE) IN CULTURE1

The growth rate of Laminaria saccharina (L.) Lamour. is dependent on inorganic nitrogen in culture. Growth rates were saturated between 5 and 10 μmol · L^?1 nitrate. The activities of ribulose-1,5 bisphosphate carboxylase, phosphoenolpyruvate carboxykinase, mannitol-1-phosphate dehydrogenase, nitrate reductase and glutamine synthetase also varied with the concentration of inorganic nitrogen in the medium. All enzyme activities were lowest at 2.5 μmol · L^?1 nitrate (the lowest concentration used) increasing to a maximum activity between 10 and 30 μmol · L^?1 nitrate. Most enzyme activities followed a hyperbolic curve resembling those described by the Michaelis-Menten equation, with different half-saturation constants.