Nitrogen fixation by Baltic cyanobacteria is adapted to the prevailing photon flux density

N₂ fixation, measured as acetylene reduction, was studied in laboratory cultures and in natural assemblages (both as a mixed population and as individually picked colonies) of the heterocystous cyanobacteria Aphanizomenon sp. and Nodularia spp. from the Baltic Sea. During a diurnal cycle of alternating light and darkness, these organisms reduced acetylene predominantly during the period of illumination, although considerable activity was also observed during the dark period. In both laboratory cultures and natural populations N₂ fixation was saturated below a photon flux density of 600 μm⁻² s⁻¹. In cyanobacterial blooms in the Baltic Sea, nitrogenase activity was mostly confined to the surface layers. Samples collected from greater depths did not possess the same capacity for acetylene reduction as samples from the surface itself, even when incubated at the photon flux density prevailing in surface waters. This suggests that, with respect to N₂ fixation, Baltic cyanobacteria are adapted to the intensity of illumination that they are currently experiencing.     

Effect of ultraviolet radiation on accumulation and leakage of 86Rb+ in guard cells of Vicia faba

The effects of UV-C (254 nm), UV-A (365 nm) and broad-band UV (280–380 nm) on guard cells of Vicia faba L. cv. Long Pod were investigated in the presence of white light (450 μmol m⁻² s⁻¹). UV-C (7 μmol m⁻² s⁻¹) was found to cause leakage of ⁸⁶Rb⁺ from guard cells, while UV-A (0.3 μmol m⁻² s⁻¹) stimulated increased uptake in these cells. A relatively small stimulatory effect was observed by broad-band UV (3 μmol m⁻² s⁻¹) during the first 30 min of irradiation with an apparent equilibration of influx and efflux thereafter. Leakage of ⁸⁶Rb⁺ from guard cells continued despite the removal of UV-C and an increase in the amount of white light from 450 to 1500 μmol m⁻² s⁻¹, suggesting that membranes were irreversibly damaged. Irradiation of guard cells with UV-C for 30, 45 and 90 min indicated that these cells began to be affected already by 30 min UV-C irradiation.     

A relationship between irradiation, carbohydrates and rooting in cuttings of Pisum sativum

Rooting ability was studied for cuttings derived from pea plants ( Pisum sativum , L. cv. Alaska) grown in controlled environment rooms. When the cuttings were rooted at 70 μmol m⁻² s⁻, ¹ (photosynthetic photon flux density) or more, a stock plant irradiance at 100 μmol m⁻² s⁻¹ decreased rooting ability in cuttings compared to 5 μmol m⁻², s⁻¹, However, cuttings rooted at 160 μmol m⁻² s⁻¹ formed more roots compared to 5 (μmol m⁻² s⁻¹. Although a high irradiance increased the number of roots formed, it could not overcome a decreased potential for root formation in stock plants grown at high irradiance. Light compensation point and dark respiration of cuttings decreased by 70% during the rooting period, and the final levels were strongly influenced by the irradiance to the cuttings. Respiratory O₂ uptake decreased in the apex and the base of the cutting from day 2 onwards, whereas a constant level was found in the leaves. Only the content of extractable fructose, glucose, sucrose and starch varied during the early part of the rooting period. We conclude that the observed changes in the cuttings are initiated by excision of the root system, and are not involved in the initiation of adventitious roots.     

Sublittoral abundance and food consumption of Baltic gobies

Two small demersal fishes, the sand goby Pomatoschistus minutus and the common goby Pomatoschistus microps , were quantified on soft bottoms at 20–40 m depth in the Baltic Sea, using a camera placed above the bottom. The largest numbers of gobies were seen following the settlement of young in late summer and autumn. Most recorded fishes were sand gobies. An annual average of 4·7 individuals m⁻²(0·24 g dry mass m⁻²) was recorded in 1983–1985 and 2·5 individuals m⁻²(0·13 g m⁻²) in 1997–1998. Using these densities, the annual goby food consumption was estimated to 100 kJ m⁻² in 1983–1985 and 50 kJ m⁻² in 1997–1998, corresponding to most of the annual macrobenthos production available to the gobies. The resulting goby production, assumed equal to 25% of the food consumed, must have been an important food source for the larger fishes occasionally recorded in the photographs.     

CIRCADIAN GROWTH IN PORPHYRA UMBILICALIS (RHODOPHYTA): SPECTRAL SENSITIVITY OF THE CIRCADIAN SYSTEM

The circadian rhythm in growth of the red macroalga Porphyra umbilicalis (Linnaeus) J. Agardh was investigated under different spectral light conditions in laboratory-grown thalli. A free-running rhythm was observed in constant green or red light at irradiances of 2.5 to 20 μmol photons·m⁻²·s⁻¹, whereas arhythmicity occurred in constant blue light at 6–20 μmol photons·m⁻²·s⁻¹. The circadian oscillator controlling growth rhythmicity in Porphyra uses most of the visible sunlight spectrum and possibly multiple photoreceptors with a high sensitivity for blue light and a lower sensitivity for red light. This was inferred from three experimental results: (1) The free-running period, τ, of the growth rhythm decreased with increasing irradiance, from approximately 25 h at 2.5 μmol photons·m⁻²·s⁻¹ to 22 h at 20 μmol photons·m⁻²·s⁻¹ in red or green light, (2) Dark pulses of 3 h duration, interrupting otherwise continuous green or red light, caused advances during the subjective day and delays during the subjective night; the circadian oscillator in Porphyra can discriminate darkness from green or red light, and (3) Low-irradiance blue light pulses (2.5 μmol photons·m⁻²·s⁻¹) shifted the growth rhythm in red light of higher irradiance (e.g. 10 μmol photons·m⁻²·s⁻¹), and a strong, high amplitude, type 0 phase response curve was obtained that is usually observed with light pulses shifting a circadian rhythm in otherwise continuous darkness.     

Light effects on in vitro adventitious root formation in axillary shoots of mature Prunus serotina

Light effects on in vitro adventitious root formation in axillary shoots of a 95-year-old black cherry ( Prunus serotina Ehrh.) were examined using microcuttings derived from cultured vegetative buds. Three studies were performed: 1) complete darkness and 4 levels of continuous white light irradiance were tested at 70, 278, 555 and 833 μmol m⁻² s⁻¹; 2) white, red, yellow and blue light were tested to assess the importance of spectral quality; and 3) the effect of blue light at intensities of 7,15, 22 and 30 μmol m⁻² s⁻¹ was also studied, Measurements included rooting percentage, total number of roots per shoot, and shoot and root dry weight. There was a strong negative effect of white light intensity upon root formation. Blue light between 15 and 22 μmol m⁻²: s⁻¹ significantly retarded root formation and completely inhibited it at 36 μmol m⁻² s⁻¹. Shoots treated with yellow light exhibited the highest rooting percentage, mean number of roots per shoot, and root dry weight.     

Influence of irradiance on in vitro growth and proliferation of Vaccinium corymbosum (highbush blueberry) and subsequent rooting in vivo

The effects of light on in vitro proliferation and subsequent in vivo rooting and acclimatisation of Vaccinium corymbosum were investigated. The shoots were exposed in vitro to different irradiances (total radiation ranging from 55 to 240 μmol m⁻² s⁻¹) for 7 to 60 days. In vitro growth and proliferation and the possible consequences on in vivo rooting were observed.
As compared to the control treatment (55 μmol m⁻² s⁻¹), higher irradiances improved proliferation and rooting ratios only with short applications (7 days). Short but high (210 μmol m⁻² s⁻¹) exposures applied at the end of the proliferation phase increased in vivo growth and rooting of the shoots. The shoots treated with strong light for longer times (14 and 28 days) showed both inhibition of growth and red colour of leaves and sprouts, and were less vigorous when transferred in vivo.     

Photophobic stop-response in a dinoflagellate: Modulation by preirradiation

Gyrodinium dorsum Kofoid responds photophobically to flashes of blue light. The photophobic response consists of a cessation of movement (stop-response). Without background light and after a flash fluence above 10 J m⁻², 75–85% of the cells show a stop-response, while only 50% of the cells show this response at 5 J m⁻². With a flash fluence of 5 J m⁻², background light of different wavelengths either increases (614 nm. 5.5–18.2 μmol m⁻² s⁻¹) or decreases (700 nm, 18.4–36.0 μmol m⁻² s⁻¹) the stop-response. Two hypotheses for the mechanism of the modulation by background light of the photophobic response are discussed: an effect of light on the balance of the photosynthetic system (PS I/PS II) or an effect on a phytochrome-like pigment (P_r/P_fr). This study supports the idea that a phytochrome-like pigment works in combination with a blue light-absorbing pigment. It was also found that cells of Gyrodinium dorsum cultured in red light (39.8 μmol m⁻²) had a higher absorption in the red region of the absorption spectra than those cultured in white light (92.7 μmol m⁻²).     

PHOTOSYNTHETIC RESPONSE OF STREAM PERIPHYTON TO FLUCTUATING LIGHT REGIMES

  An experiment was conducted on intact algal assemblages of stream periphyton to test their response to fluctuating and constant light regimes having the same mean intensity. The light regimes (in μmol·m⁻²·s⁻¹) were constant light at 100, light fluctuating between 50 and 150 with a period of 5 min, and light fluctuating between 10 and 460 with periods of either 4:1 or 8:2 min. Compared to the rates measured under 100 in μmol·m⁻²·s⁻¹ constant light conditions, fluctuations ranging between 50 and 150 in μmol·m⁻²·s⁻¹ with a 5-min period produced a 23% greater rate of photosynthesis. Conversely, fluctuations between 10 and 460 in μmol·m⁻²·s⁻¹ led to a 59%–74% decrease in photosynthetic activity. Detailed examination of periphytic algal responses to fluctuating light revealed that higher light intensities produced steeper photosynthesis/time slopes, but it was the combined interaction with lower light intensity that ultimately determined overall photosynthetic rate for a given light regime. This study offers compelling evidence that variable light regimes have important consequences for algal photosynthesis in natural streams.     

PHYSIOLOGICAL RESPONSES TO TEMPERATURE AND IRRADIANCE IN SPIROGYRA (ZYGNEMATALES, CHAROPHYCEAE)1

Spirogyra Link (1820) is an anabranched filamentous green alga that forms free-floating mats in shallow waters. It occurs widely in static waters such as ponds and ditches, sheltered littoral areas of lakes, and stow-flowing streams. Field observations of its seasonal distribution suggest that the 70-μm-wide filament form of Spirogyra should have a cool temperature and high irradiance optimum for net photosynthesis. Measurements of net photosynthesis and respiration were marie at 58 combinations of tight and temperature in a controlled environment facility. Optimum conditions were 25°C and 1500 μmol photons m⁻² s⁻¹, at which net photosynthesis averaged 75.7 mg O₂ gdm⁻¹ h⁻¹. Net photosynthesis was positive at temperatures from 5° to 35°C at most irradiances except at combinations of extremely low irradiances and high temperatures (7 and 23 μmol photons m⁻² s⁻¹ at 30°C and 7, 23, and 35 μmol photons m⁻² s⁻¹ at 35°C). Respiration rates increased with both temperature and prior irradiance. Light-enhanced respiration rates were significantly greater than dark respiration rates following irradiances of 750 μmol photons m⁻² s⁻¹ or greater. Polynomials were fitted to the data to generate response surfaces; such response surfaces can be used to represent net photosynthesis and respiration in ecological models. The data indicate that the alga can tolerate the cool water and high irradiances characteristic of early spring but cannot maintain positive net photosynthesis under conditions of high temperature and low light (e.g. when exposed to self-shading ).     

Photosynthesis and transpiration by young Larix kaempferi trees: C3 responses to light and temperature

The effects of photon flux density and temperature on net photosynthesis and transpiration rates of mature and immature leaves of three-year-old Japanese larch Larix kaempferi (Lamb.) Sarg. trees were determined with an infrared, differential open gas analysis system. Net photosynthetic response to increasing photon flux densities was similar for different foliage positions and stage of maturity. Light compensation was between 25 and 50 μmol m⁻² s⁻¹. Rates of photosynthesis increased rapidly at photon flux densities above the compensation level and became saturated between 800 and 1000 μmol m⁻² s⁻¹. Transpiration rates at constant temperature likewise increased with increasing photon flux density, and leveled off between 800 and 1000 μmol m⁻² s⁻¹. Photosynthetic response to temperature was determined in saturating light and was similar for all foliage positions; it increased steadily from low temperatures to an optimum range betweeen 15 and 21°C and then decreased rapidly above 21°C. Transpiration rate, however, increased continuously with rising temperature up to the experimental maximum. CO₂ compensation concentrations for mature foliage varied between 58 and 59 μl l⁻¹; however, foliage borne at the apex of the terminal leader compensated at 75 μl l⁻¹. None of these data support the claim that Japanese larch possesses C₄ photosynthetic characteristics.     

Spectacular abundance of ciliates in anoxic pond water: contribution of symbiont photosynthesis to host respiratory oxygen requirements

Abstract: Very large numbers (3466 ml⁻¹) of ciliated protozoa were found living beneath the oxic-anoxic boundary in a stratified freshwater pond. Most ciliates (96%) contained symbiotic algae ( Chlorella spp.). Peak abundance was in anoxic water with almost 1 mol free CO₂ m⁻³ and a midday irradiance of 6 μmol photon m⁻² s⁻¹. Photosynthetic rate measurements of metalimnetic water indicated a light compensation point of 1.7 μmol photon m⁻² s⁻¹ which represents 0.6% of sub-surface light. We calculate that photosynthetic evolution of O₂ by symbionts is sufficient to meet the demand of the host ciliates for 13 to 14 hours each day. Each 'photosynthetic ciliate' may therefore become an aerobic island surrounded by anoxic water.     

Influence of red light on the activity of phosphofructokinase in Chlorella kessleri

In crude extracts of the unicellular green alga Chlorella kessleri Fott et Novákóva grown in red light the activity of the glycolytic enzyme phosphofructokinase (PFK, EC 2.7.1.11) is about 40% higher compared to white light conditions giving the same dry matter production. Application of cycloheximide and density labelling with D₂O indicate that this increase depends on the de novo synthesis of the enzyme: Twelve h of illumination at a fluence rate of 7 × 10¹⁸ quanta m⁻² s⁻¹ (11.6 μmol m⁻² s⁻¹) suffice to saturate the effect. In autotrophically grown algae maximal increase in enzyme saturate the effect. In autotrophically grown algae maximal increase in enzyme activity is reached in light of 680 nm, while in 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU)-poisoned, glucose-fed cells, light of wavelengths around 727 nm is most effective. Involvement of a phytochrome-like photoreceptor is discussed.     

Laboratory models of diel vertical migration in the dinoflagellate Ceratium hirundinella

SUMMARY. Diel vertical migrations of a dinoflagellate, Ceratium hirundinella , were induced in a laboratory tube (1.63 × 0.15 m) under a light-dark cycle. The timing of vertical migrations differed between cultures in the exponential and stationary phases of growth; the latter showed a greater coincidence with the light regime.
Migration of cells into the surface layers occurred at low values of surface irradiance (<550 μeinsteins m⁻² s⁻¹). At irradiances more closely approaching summer sunshine (> 1300 μE m⁻² s⁻¹) there was a marked avoidance of surface waters, and population maxima were found at depths associated with a relative irradiance level of 10% or c. 150 μE m⁻² s⁻¹). Thermal stratification restricted downward movement of cells into the cooler layers. The combination of high surface irradiance and thermal stratification resulted in large, stable, sub-surface maxima of Ceratium , similar to those observed in natural waters under comparable environmental conditions.     

The effect of turbidity and illumination on the reaction distance and search time of the marine planktivore Gobiusculus flavescens

Both reduced illumination and increased turbidity caused a significant reduction in reaction distance of Gobiusculus flavescens . The longest reaction distance, 18.9 cm for larger prey (Calanus finmarchicus) , occurred at a light level of 80 μmol m ⁻² s ⁻¹ compared to 12.9 cm for a smaller prey (Acartia clausi) at 8 μmol m⁻² s⁻¹. Above a light saturation level of 10 μmol m⁻² s⁻¹, additional light had little influence on reaction distance. In the turbidity experiments, the longest reaction distances were measured at turbidity levels of 10–20 JTU. Prey size influenced reaction distance at all tested light levels. Search time was influenced by prey size only at low illumination. With increasing turbidity, reaction distance to a group of prey was longer than to one prey.     

The role of light and CO2 in optimising the conditions for shoot proliferation of Actinidia deliciosa in vitro

Proliferating cultures of Actinidia deliciosa A. Chev., C. F. Liang and A. R. Ferguson cv. Tomuri (♂) were grown under photosynthetic photon flux density (PPFD) rates ranging from 30 to 250 μmol m⁻² s⁻¹ in order to determine certain physiological parameters in vitro: CO₂ evolution, photosynthesis at three CO₂ atmospheric concentrations (330, 1450 and 4500 μl l⁻¹), fresh and dry matter accumulation and proliferation rate.
A proportional response in dry weight, dry/fresh weight ratios and PPFD was found. The proliferation rate increased up to 120 μmol m⁻² s⁻¹ but decreased at higher rates. At the highest PPFD, the CO² released from cultures and accumulated in the vessels reached 200 μl l⁻¹ of; at the lowest rate the CO₂ concentration reached 10500 μl l⁻¹ after 28 days of culture. The photosynthetic rate at 1450 and 4500 μl l⁻¹ of CO₂ was nearly 4 times higher than at the lowest concentration tested.     

Inhibition of hypocotyl elongation by ultraviolet-B radiation in de-etiolating tomato seedlings. I. The photoreceptor

Broad-band UV-B radiation inhibited hypocotyl elongation in etiolated tomato ( Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by < 3 μmol m⁻² s⁻¹ of UV-B radiation provided against a background of white light (> 620 μmol m⁻² s⁻¹ between 320 and 800 nm), and was similar in wild-type and phytochrome-1-deficient aurea mutant seedlings. These observations suggest that the effect of UV-B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 μmol m⁻² s⁻¹ of monochromatic UV radiation against a while light background (63 μmol m⁻² s⁻¹ showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV-B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN, and phenylacetic acid) largely abolished the inhibitor) effect of broad-hand UV-B radiation when applied to the root zone before irradiation. KI was effective at concentrations < 10⁻⁴ M , which have been shown in vitro to be effective in quenching the triplet excited stales of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV-A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation evened by UV-B. Kl applied after UV-B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system invoked in UV-B perception by tomato seedlings during de-etiolation may be a flavin.     

Photoinhibition of photosynthesis in Lemna gibba as induced by the interaction between light and temperature. I. Photosynthesis in vivo

The floating angiosperm Lemna gibba L. was exposed for 2 h to various combinations of photosynthetic photon flux densities and temperature. The extent of photoinhibition of photosynthesis was assayed by measuring the net CO₂ uptake before and after a photoinhibitory treatment, and the time course for photoinhibition was studied. It was found that the maximum quantum yield and the light-saturated rate of CO₂ uptake were affected by the interaction between light and temperature during the photoinhibitory treatment. At a constant photon flux density of 650 μmol m⁻² s⁻¹ the extent of photoinhibition increased with decreasing temperature showing that even a chilling-resistant plant like L. gibba is much more susceptible to photoinhibition at chilling temperatures. About 60% photoinhibition of the quantum yield for CO₂ uptake could be obtained either by a high photon flux density of 1 750 μmol m⁻² s⁻¹ and 25°C or by a moderate photon flux density of 650 μmol m⁻² s⁻¹ and 3°C. The time courses of recovery from 60% photoinhibition produced by either of these two treatments were similar, indicating that the nature of the photoinhibition was intrinsically similar. The extent of photoinhibition was related to the amount of light absorbed in excess to what could be handled by photosynthesis at that temperature. The vital importance of photosynthesis in alleviating photoinhibition is discussed.     

Energy balance and temperature relations of Azorella compacta, a high-elevation cushion plant of the central Andes

The environmental relationships and ecophysiology of Azorella compacta, a giant cushion plant, were investigated in Parque Nacional Lauca, Chile (18°10'–18°25' S and 69°16' W, 4400 m asl). The diurnal temperature range can reach 42 °C on some days of the year. The surface temperature of A. compacta was 13 °C below that of the air temperature of −7 °C at dawn, but from midmorning to late afternoon, the plant surface temperature remained within a few degrees of the air temperature. Soil surface temperatures did not differ between north- and south-facing slopes, but a model showed an increase in radiation reception by north-facing slopes throughout most of the year. Gas exchange measurements of A. compacta measured at the onset of the wet season ranged from −0.6662 to 11.4 μmol·m⁻²·s⁻¹, and maximum stomatal conductance (Gs) was 410 mmol·m⁻²·s⁻¹. The estimated light compensation point was 89 μmol·m⁻²·s⁻¹ and estimated light saturation occurred at about 1280 μmol·m⁻²·s⁻¹. Diurnal water potential measurements for A. compacta ranged from −1.67 to −2.65 MPa. This is one of the first ecophysiological studies of a tropical alpine cushion plant.     

Benzyladenine-induced stimulation of 5-aminolevulinic acid accumulation under various light intensities in levulinic acid-treated cotyledons of etiolated cucumber

Benzyladenine (BA) stimulated 5-aminolevulinic acid (ALA) accumulation in the presence of levulinic acid during illumination with 43 μmol m⁻² s⁻¹ light in excised etiolated cotyledons of cucumber ( Cucumis sativus L. cv. Aonagajibai). A short dark-pretreatment (6 h) with BA eliminated the lag phase of ALA accumulation. The rate of ALA accumulation during the steady-state phase in cotyledons pretreated with BA for a long period (14 h) was considerably accelerated compared to that in cotyledons pretreated with BA for 6 h. The rate of ALA accumulation during the lag phase was saturated at a very low light fluence (<1.4 μmol m⁻² s⁻¹) in both BA-pretreated and water-control cotyledons. The steady-state rate of ALA accumulation increased with increasing light fluence up to 43 μmol m⁻² s⁻¹ (parallel to that of Chl formation) in water-control cotyledons. In contrast, in cotyledons pretreated with BA for either 6 or 14 h, the steady-state rate reached a plateau at a very low light fluence. Based on the above results together with our finding that there are two components of Chl formation (M. Dei, 1984. Physiol. Plant. 62: 521–526) possible intermediate steps of Chl biosynthesis pathway affected by BA and light intensity are discussed.