The sensitive period for light and temperature regulation of sporangiophore development inPhycomyces

Light and temperature markedly influence sporangiophore development inPhycomyces blakesleeanus. Under normal conditions in the dark, low temperature drastically stimulates the production of dwarf sporangiophores (microphorogenesis) and inhibits that of giant sporangiophores (macrophorogenesis). These effects of low temperature could still be observed if applied only for a short period before sporangiophore initiation. Continuous white illumination strongly inhibits microphorogenesis and slightly stimulates macrophorogenesis. Short exposures to white light noticeably inhibit microphorogenesis and stimulate macrophorogenesis when given to mycelia grown for between 90 and 160 h at 14° C or 150 h or more at 10° C. These results indicate the existence in the mycelium of developmental stages for the regulation of sporangiophorogenesis by environmental signals.     

The effects of temperature acclimation on the photoinhibitory responses of Ulva rotundata Blid.

The effect of acclimation to 25, 18, or 10° C on the relationship between photoprotection and photodamage was tested in low-light-grown (80 mol · m^–2 · s^–1) Ulva rotundata Blid. exposed to several higher irradiances at the acclimation temperature. Changes in chlorophyll fluorescence parameters (minimum fluorescence, F₀, and the ratio of variable to maximum fluorescence, F_v/F_m, measured after 5 min darkness) were monitored during 5 h transfers to 350, 850, and 1700 mol · m^–2 · s^–1, and during recovery after 1- or 5-h treatments. At all temperatures, rate of onset and final extent of photoinhibition, measured by a decrease in F_v/F_m, increased with increasing irradiance. At a given photoinhibitory irradiance, rate of onset was most rapid at 10 ° C, but the extent was temperature-independent. Recovery rates from mild light stress were similar at all temperatures, but recovery from the most extreme photoinhibitory treatment lagged 2 h at 10° C. De-epoxidation of xanthophyll-cycle components proceeded faster and to a lower epoxidation status at 25° C, but there was little difference in the pool size among the three growth conditions. Using chloramphenicol to inhibit chloroplast protein synthesis and dithiothreitol to inhibit violaxanthin de-epoxidation, it was shown that at the lowest light treatment given, the extent of photoinhibition could be attributed both to greater amounts of photodamage and to greater zeaxanthin-related photoprotection at 25 than at 10° C. While these two mechanisms for high-light-induced loss of photosynthetic efficiency were operating at 10° C, there was evidence for a relatively greater proportion of zeaxanthin-unrelated photoprotection at the low temperature. This photoprotective mechanism is related to a rapidly reversible increase in F₀ and is insentivite to both chloramphenicol and dithiothreitol.Abbreviations and Symbol CAP chloramphenicol - DTT dihiothreitol - F₀, F_m, F_v minimum, maximum, and variable fluorescence - quantum yield This research was conducted in partial fulfillment of the requirements for the Ph. D. degree in the Department of Botany, Duke University. The author wishes to thank E.-M. Aro, W.J. Henley, G. Levavasseur, C.B. Osmond, and J. Ramus for helpful discussions, and C. Lovelock for pigment standards. Funding was provided by Grants-in-Aid of Research from Sigma Xi and the Phycological Society of America, and a Lynde and Harry Bradley Foundation Fellowship to L.A.F., and National Science Foundation grant OCE-8812157 to C.B.O. and J.R.     

Effect of temperature and light on the toxicity and growth of the blue-green alga Microcystis aeruginosa (UV-006)

The toxicity and growth of Microcystis aeruginosa (UV-006) from the Hartbeespoort Dam, South Africa were investigated at different temperatures and photon fluence rates under laboratory conditions. Cells harvested in late logarithmic growth phase were most toxic when grown at 20°C (LD₅₀) median lethal dose [IP, mouse]=25.4 mg kg^-1). Toxicity was markedly reduced at growth temperatures above 28° C. Fluence rate had a smaller effect on the toxicity of the cells, but toxicity tended to be less at the very low and high light fluences. Optimal conditions for growth did not coincide with those for toxin production. Well-aerated cultures of this isolate kept at pH 9.5 by CO₂ addition, a temperature of 20–24° C, a fluence rate of 145 mol photons m^-2 s^-1 and harvested in the late logarithmic growth phase yielded the maximum quantity of toxin.Abbreviation LD₅₀ median lethal dose An abstract of this work, presented as a poster at the IUBS symposium on toxins and lectins, held at the CSIR, Pretoria, South Africa during 1982 was published in S. Afr. J. Sci. 78, 375 (1982)     

Dependence of CO2 gas exchange and acid metabolism of the alpine CAM plant Sempervivum montanum on temperature and light

Summary The influence of light intensity and temperature on the diurnal course and magnitude of CO₂ gas exchange and on acid metabolism was studied in the laboratory with rooted rosettes of Sempervivum montanum collected at 2,200 m above sea level in the Central Alps. Under a temperature regime having a cool dark period and warm light period, S. montanum exhibited the time course of CO₂ gas exchange typical of a CAM plant; the response was very distinct even when the plants were well-watered. At day temperatures of less than 10° C and at night temperatures greater than 35° C, S. montanum behaved like a C₃ plant. Characteristic for S. montanum are a broad temperature optimum and a wide range of temperatures in which CO₂ uptake in light is possible (-2° to 45° C). Dark fixation of CO₂ is evident between-2° and 35° C, an apparent uptake of external CO₂, on the other hand, only as high as 20° C. Light saturation of CO₂ uptake is reached at 60–80 W m^-2 while the rate of deacidification is nearly maximal at 40 W m^-2. These results show that, due to their specific metabolism, CAM plants can be favored not only in xeric habitats, but also in heat stressed mountain habitats where the daily variation in temperature may be extreme.Dedicated with appreciation to Dr. K.F. Springer     

Photosystem II reaction centres stay intact during low temperature photoinhibition

Photoinhibition of photosynthesis was studied in intact barley leaves at 5 and 20°C, to reveal if Photosystem II becomes predisposed to photoinhibition at low temperature by 1) creation of excessive excitation of Photosystem II or, 2) inhibition of the repair process of Photosystem II. The light and temperature dependence of the reduction state of Q_A was measured by modulated fluorescence. Photon flux densities giving 60% of Q_A in a reduced state at steady-state photosynthesis (300 mol m^–2s^–1 at 5°C and 1200 mol m^–2s^–1 at 20°C) resulted in a depression of the photochemical efficiency of Photosystem II (F_v/F_m) at both 5 and 20°C. Inhibition of F_v/F_m occurred with initially similar kinetics at the two temperatures. After 6h, F_v/F_m was inhibited by 30% and had reached steady-state at 20°C. However, at 5°C, F_v/F_m continued to decrease and after 10h, F_v/F_m was depressed to 55% of control. The light response of the reduction state of Q_A did not change during photoinhibition at 20°C, whereas after photoinhibition at 5°C, the proportion of closed reaction centres at a given photon flux density was 10–20% lower than before photoinhibition.Changes in the D1-content were measured by immunoblotting and by the atrazine binding capacity during photoinhibition at high and low temperatures, with and without the addition of chloramphenicol to block chloroplast encoded protein synthesis. At 20°C, there was a close correlation between the amount of D1-protein and the photochemical efficiency of photosystem II, both in the presence or in the absence of an active repair cycle. At 5°C, an accumulation of inactive reaction centres occurred, since the photochemical efficiency of Photosystem II was much more depressed than the loss of D1-protein. Furthermore, at 5°C the repair cycle was largely inhibited as concluded from the finding that blockage of chloroplast encoded protein synthesis did not enhance the susceptibility to photoinhibition at 5°C.It is concluded that, the kinetics of the initial decrease of F_v/F_m was determined by the reduction state of the primary electron acceptor Q_A, at both temperatures. However, the further suppression of F_v/F_m at 5°C after several hours of photoinhibition implies that the inhibited repair cycle started to have an effect in determining the photochemical efficiency of Photosystem II.Abbreviations CAP D-threochloramphenicol - F₀ and F ₀ fluorescence when all Photosystem II reaction centres are open in dark- and light-acclimated leaves, respectively - F_m and F _m fluorescence when all Photosystem II reaction centres are closed in dark- and light-acclimated leaves, respectively - F_s fluorescence at steady state - Q_A the primary, stable quinone acceptor of Photosystem II - q_N non-photochemical quenching of fluorescence - q_P photochemical quenching of fluorescence     

Temperature and irradiance and the total daily photosynthetic production of the crown of a Pinus radiata tree

Summary Carbon dioxide exchange rates were recorded for different ages and positions of foliage and parts of the main stem of a 7-m tall Pinus radiata D. Don tree growing in a large, artificially lit, controlled-environment room. Irradiance levels were varied from dark to approximately full sunlight, and air temperatures from 10° to 35°C in 5°C steps. Leaf temperatures within the cuvettes used for CO₂ exchange measurements, however, were up to 5°C higher than the room air temperature set but this varied with position in the tree crown, the shaded lower crown being at approximately room temperature. A balance sheet was prepared to show the photosynthetic gains and respiratory losses of different parts of the crown over 24 h at each air temperature and at irradiances of 400, 270, and 135 W m^-2 during the 8-h photosynthetic period. The greatest daily photosynthetic gain was at 10° C, although this temperature is considered sub-optimal for growth. At temperatures greater than 25° C, even at the greatest irradiance level for 8 h, total respiration was greater than photosynthesis.     

Temperature dependence of violaxanthin de-epoxidation and non-photochemical fluorescence quenching in intact leaves ofGossypium hirsutum L. andMalva parviflora L.

The temperature dependence of the rate of de-epoxidation of violaxanthin to zeaxanthin was determined in leaves of chilling-sensitive Gossypium hirsutum L. (cotton) and chilling-resistant Malva parviflora L. by measurements of the increase in absorbance at 505 nm (A ₅₀₅) and in the contents of antheraxanthin and zeaxanthin that occur upon exposure of predarkened leaves to excessive light. A linear relationship between A ₅₀₅ and the decrease in the epoxidation state of the xanthophyll-cycle pigment pool was obtained over the range 10–40° C. The maximal rate of de-epoxidation was strongly temperature dependent; Q₁₀ measured around the temperature at which the leaf had developed was 2.1–2.3 in both species. In field-grown Malva the rate of de-epoxidation at any given measurement temperature was two to three times higher in leaves developed at a relatively low temperature in the early spring than in those developed in summer. Q₁₀ measured around 15° C was in the range 2.2–2.6 in both kinds of Malva leaves, whereas it was as high as 4.6 in cotton leaves developed at a daytime temperature of 30° C. Whereas the maximum (initial) rate of de-epoxidation showed a strong decrease with decreased temperature the degree of de-epoxidation reached in cotton leaves after a 1–2 · h exposure to a constant photon flux density increased with decreased temperature as the rate of photosynthesis decrease. The zeaxanthin content rose from 2 mmol · (mol chlorophyll)^–1 at 30° C to 61 mmol · (mol Chl)^–1 at 10° C, corresponding to a de-epoxidation of 70% of the violaxanthin pool at 10° C. The degree of de-epoxidation at each temperature was clearly related to the amount of excessive light present at that temperature. The relationship between non-photochemical quenching of chlorophyll fluorescence and zeaxanthin formation at different temperatures was determined for both untreated control leaves and for leaves in which zeaxanthin formation was prevented by dithiothreitol treatment. The rate of development of that portion of non-photochemical quenching which was inhibited by dithiothreitol decreased with decreasing temperature and was linearly related to the rate of zeaxanthin formation over a wide temperature range. In contrast, the rate of development of the dithiothreitol-resistant portion of non-photochemical quenching was remarkably little affected by temperature. Evidently, the kinetics of the development of non-photochemical quenching upon exposure of leaves to excessive light is therefore in large part determined by the rate of zeaxanthin formation. For reasons that remain to be determined the relaxation of dithiothreitolsensitive quenching that is normally observed upon darkening of illuminated leaves was strongly inhibited at low temperatures.Abbreviations and Symbols Chl chlorophyll - DTT dithiothreitol - EPS epoxidation state - NPQ non-photochemical chlorophyll fluorescence quenching - PFD photon flux density - PSII photosystem II - F, F_m fluorescence emission at the actual, full closure of the PSII centers C.I.W.-D.P.B. Publication No. 1092We thank Connie Shih for skillful assistance in growing the plants, for conducting the HPLC analyses, and for preparing the figures. A Carnegie Institution Fellowship and a Feodor-Lynen-Fellowship by the Alexander von Humboldt-Foundation to W.B. is gratefully acknowledged. This work was supported by Grant No. 89-37-280-4902 of the Competitive Grants Program of the U.S. Department of Agriculture to O.B.     

The role of temperature in the regulation of the circadian rhythm of CO2 fixation in Bryophyllum fedtschenkoi

Detached leaves of Bryophyllum fedtschenkoi Hamet et Perrier kept in normal air show a single period of net CO₂ fixation on transfer to constant darkness at temperatures in the range 0–25 °C. The duration of this initial fixation period is largely independent of temperature in the range 5–20 °C, but lengthens very markedly at temperatures below 4 °C, and is reduced at temperatures above 25 °C. The onset of net fixation of CO₂ on transfer of leaves to constant darkness is immediate at low temperatures, but is delayed as the temperature is increased. The ambient temperature also determines whether or not a circadian rhythm of CO₂ exchange occurs. The rhythm begins to appear at about 20 °C, is most evident at 30 °C and becomes less distinct at 35 °C. The occurrence of a distinct circadian rhythm in CO₂ output at 30° C in the absence of a detectable rhythm in PEPCase kinase activity shows that the kinase rhythm is not a mandatory requirement for the rhythm of PEPCase activity. However, when it occurs, the kinase rhythm undoubtedly amplifies the PEPCase rhythm.Abbreviation PEPCase phosphoenolpyruvate carboxylase We thank the Agricultural and Food Research Council for financial support for this work.     

Heat-Induced Increase in the Tolerance of the Wheat Photosynthetic Apparatus to Combined Action of High Temperature and Visible Light: CO2 Fixation,Photosynthetic Pigments,and Chloroplast Ultrastructure

Heating of the leaves of 15-day-old wheat (Triticum aestivum L.) plants at 42°C in the light (370 W/m² PAR) suppressed their ability to fix CO₂ twice stronger than heating in darkness. Heat hardening (3 h at 38–39°C) improved the tolerance of photosynthesis to combined action of high light and temperature but did not affect the tolerance to photoinhibition at 30°C. Hardening did not induce changes in the levels of photosynthetic pigments and their ratios. De-epoxidation of violaxanthin turned out to be more tolerant to photoinhibition at 42°C than CO₂ fixation. Protective effect of hardening was not related to the accumulation of zeaxanthin and activation of the xanthophyll cycle. Hardening protected the most sensitive population of chloroplasts against heat-induced photodamage and simultaneously increased the number and length of thylakoids. An increase in the volume of the thylakoid system was also induced by heating at 42°C and exposure to high light at 30°C. The formation of additional thylakoids and grana of shade type was not associated with improved tolerance of photosynthesis to heat and light stresses.     

Volatile Metabolites and External CO2Exchange of Wheat Cenoses under Optimal Conditions and Thermal Stress

The effects of elevated temperature (35 and 45°C) on photosynthesis, respiration, and both the qualitative and quantitative compositions of volatile emissions (VE) of wheat (Triticum aestuvumL. cultivar 232) cenoses at light intensities of 70, 150, or 240 W/m²of photosynthetically available radiation (PAR) were studied. At a PAR of 240 W/m², the thermal stabilities of photosynthesis and respiration increased at 35°C and decreased at 45°C. Elevated temperatures nonuniformly changed the rates and direction of VE syntheses. In this process, the highest increase in VE evolution was observed at 70 W/m²and 35°C; the lowest, at 240 W/m². In addition, the concentrations and composition of VE during the repair period differed from the initial values.     

Photosynthetic responses of cassava cultivars (Manihot esculenta Crantz) from different habitats to temperature

Maximum photosynthetic CO₂ exchange rates (P_n) of single attached leaves were determined for several cassava cultivars selected from different habitats and grown in pots outdoors at CIAT, Colombia, S.A. P_n rates were in a narrow range of 22 to 26 mol CO₂ m^–2s^–1 for all cultivars tested when measured at high photon flux density, normal air, optimum temperature and with low leaf-air vapor pressure differences. For all tested cultivars (9 cvs.), there was a broad optimum temperature for P_n between 25 to 35°C. At temperatures below and above this range P_n declined in all cultivars with P_n rates reaching 80% of maximum at 20 and 40°C. P_n temperature coefficient (Q₁₀) from 15–25°C was 1.6±0.2 across cultivars. No consistent relation existed between P_n, optimum temperature, and the original habitat.     

Circadian rhythms in Kalanchoë: effects of irradiance and temperature on gas exchange and carbon metabolism

Gas exchange in K. blossfeldiana shows a circadian rhythm in net CO₂ uptake and transpiration when measured under low and medium irradiances. The period length varies between 21.4 h at 60 W m^-2 and 24.0 h at 10 W m^-2. In bright light (80 W m^-2) or darkness there are no rhythms. High leaf temperatures result in a fast dampening of the CO₂-uptake rhythm at moderate irradiances, but low leaf temperatures can not overcome the dampening in bright light. The rhythm in CO₂ uptake is accompanied by a less pronounced and more rapidly damped rhythm in transpiration and by oscillations in malate levels with the amplitude being highly reduced. The oscillations in starch content, usually observed to oscillate inversely to the acidification in light-dark cycles, disappear after the first cycle in continuous light. The balance between starch and malate levels depends in continuous light on the irradiance applied. Leaves show high malate and low starch content at low irradiance and high starch and low malate in bright light. During the first 12 h in continuous light replacing the usual dark period, malate synthesis decreases with the increasing irradiance. Up to 50 W m^-2 starch content decreases; at higher irradiances it increases above the values usually measured at the end of the light period of the 12:12 h light-dark cycle.Abbreviations CAM Crassulacean acid metabolism - FW fresh weight - PEP phosphoenolpyruvate     

Influence of temperature and ambient oxygen on the swimming energetics of cyprinid larvae and juveniles

Synopsis The relationship between respiration and swimming speed of larvae and juveniles (2–100 mg fresh mass) of Danube bleak, Chalcalburnus chalcoides (Cyprinidae), was measured at 15° and 20° C under hypoxic (50% air saturation), normoxic, and hyperoxic (140% air saturation) conditions. In a flow-tunnel equipped with a flow-through respirometer the animals swam at speeds of up to 8 lengths · s^-1; speeds were sustained for at least two minutes. The mass specific standard, routine, and active respiration rates declined with increasing body mass at both temperatures. Metabolic intensity increased with temperature, but also the critical swimming speed (at which oxygen uptake reached its maximum) was higher at 20° than at 15° C by about 30%. Nevertheless, the oxygen debt incurred by the fish at the highest speeds was about 40%, and the net cost of swimming about 32%, lower at 20° than at 15°C. The standard metabolic rate was more strongly dependent on temperature (Q₁₀ around 2.5) than the maximum active rate (Q₁₀ below 2). Whereas standard and routine respiration rates were well regulated over the pO₂-range investigated (8.5–25.8 kPa), the active rates showed a conformer-like pattern, resulting in factorial scopes for activity between 2 and 4. Under hypoxia, the critical swimming speed was lower than under normoxia by about 1.51 · s^-1, but the net cost of swimming was also lower by about 30%. On the other hand, hyperoxia neither increased the swimming performance nor did it lead to a further increase of the metabolic cost of swimming. The hypoxia experiments suggest that in response to lowered tensions of ambient oxygen maintenance functions of metabolism not directly related to swimming may be temporarily reduced, leading to increased apparent swimming efficiency under these conditions. The responses of the larvae of Danube bleak to low temperature and low ambient oxygen are discussed in terms of the metabolic strategies by which energy-limited animals meet the challenge of environmental deterioration.     

The effect of temperature on glycollate decarboxylation in leaf peroxisomes

[1-¹⁴C]glycollate was oxidised to¹⁴CO₂ by peroxisomes isolated from leaves of spinach beet about 3 times as rapidly at 35°C as at 25°C; the rate was further increased with rise in temperature to a maximum at 55°C. These increases are shown to be mainly due to the increased H₂O₂ available to oxidise glyoxylate non-enzymically as a result of the higher temperature coefficient of glycollate oxidase activity relative to that of catalase. These results are compared with similar increases in the rate of¹⁴CO₂ release between 25°C and 35°C when [1-¹⁴C]glycollate was supplied to leaf discs in light or darkness. The role of these reactions in accounting for the temperature effect on the release of photorespiratory CO₂ is discussed.Abbreviations PHMS Pyrid-2-yl--hydroxymethane sulphonate - FMN flavin mononucleotide     

Respiration of individual honeybee larvae in relation to age and ambient temperature

The CO₂ production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO₂ produced appeared to fall only moderately from 3.89±1.57 µl mg^–1 h^–1 in 0.5-day-old larvae to 2.98±0.57 µl mg^–1 h^–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg^–1 h^–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO₂ production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg^–1 h^–1 CO₂ at 18 °C, and 3.97±0.50 µl mg^–1 h^–1 CO₂ at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q₁₀ was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - T_I inflexion point of a logistic (sigmoid) curve - T_L lethal temperature - T_O temperature of optimum (maximum) developmentCommunicated by G. Heldmaier     

Photoinhibition of photosynthesis in intact bean leaves: role of light and temperature,and requirement for chloroplast-protein synthesis during recovery

Photoinhibition of photosynthesis was induced in intact leaves of Phaseolus vulgaris L. grown at a photon flux density (PFD; photon fluence rate) of 300 mol·m^-2·s^-1, by exposure to a PFD of 1400 mol·m^-2·s^-1. Subsequent recovery from photoinhibition was followed at temperatures ranging from 5 to 35°C and at a PFD of either 20 or 140 mol·m^-2·s^-1 or in complete darkness. Photoinhibition and recovery were monitored mainly by chlorophyll fluorescence emission at 77K but also by photosynthetic O₂ evolution. The effects of the protein-synthesis inhibitors, cycloheximide and chloramphenicol, on photoinhibition and recovery were also determined. The results demonstrate that recovery was temperature-dependent with rates slow below 15°C and optimal at 30°C. Light was required for maximum recovery but the process was light-saturated at a PFD of 20 mol·m^-2·s^-1. Chloramphenicol, but not cycloheximide, inactivated the repair process, indicating that recovery involved the synthesis of one or more chloroplast-encoded proteins. With chloramphenicol, it was shown that photoinhibition and recovery occurred concomitantly. The temperature-dependency of the photoinhibition process was, therefore, in part determined by the effect of temperature on the recovery process. Consequently, photoinhibition is the net difference between the rate of damage and the rate of repair. The susceptibility of chilling-sensitive plant species to photoinhibition at low temperatures is proposed to result from the low rates of recovery in this temperature range.Abbreviations and symbols Da Dalton - Fo, Fm, Fv instantaneous, maximum, variable fluorescence emission - PFD photon flux density - PSII photosystem II - photon yield C.I.W.-D.P.B. Publication No. 871     

Phytoplankton primary production in a eutrophic cooling water pond

The seasonal variation of phytoplankton photosynthesis was measured with ¹⁴C-method in a warmed ice-free pond in central Finland. Simultaneously with in situ measurements the photosynthesis was also measured in an incubator with different water temperatures and constant light (ca. 16 W m^–2). The total annual photosynthesis was 57.2 C m^–2 a^–1. The portion of the winter and spring production of the annual photosynthesis was 18.4%, that of the autumn production ws 17.4%. Thus 64.3% of the total annual phytoplankton photosynthesis occurred in the three summer months. The range of the daily integrated photosynthesis per unit area was 1.9—563 mg C m^–2d^–1. The photosynthetic rate per unit chlorophyll a varied in situ from 0.94 to 33.1 mg C (mg chl. a)^–1 d^–1. The highest value was measured in the beginning of July and the lowest in mid-January. The photosynthetic rate increased in situ exponentially with increasing water temperature. In the incubator the highest photosynthetic rate values were also found in July and August (at+20 °C) when the phytoplankton population was increasing and the minimum values occurred after every diatom maximum both in spring and autumn. Light was a limiting factor for photosynthesis from September to Mid-January, low water temperature was a limiting factor from late January through May. The efficiency of the photosynthesis varied between 0.1 and 0.7% of P.A.R. According to the incubator experiments the Q₁₀ values for the photosynthesis were 2.45 and 2.44 for the winter population between 1 and 10° C and for the summer population between 5 and 15° C, respectively, but the Q₁₀ values decrease at the higher temperatures. The main effect of the warm effluents on the yearly photosynthesis was the increase of production in spring months due to the lack of ice cover. However, the increase of total annual phytoplankton photosynthesis was only ca. 10–15%, because the water temperature was during the spring months below 10° C.     

Long-Term Temperature Acclimation of Photosynthesis in Steady-State Cultures of the Polar Diatom <Emphasis Type="Italic">Fragilariopsis cylindrus</Emphasis>

Cultures of the obligate psychrophilic diatom Fragilariopsis cylindrus (Grunow) were grown for 4 months under steady-state conditions at −1 °C and +7 °C (50 μmol photons m⁻² s⁻¹) prior to measurements in order to investigate long-term acclimation of photosynthesis to both temperatures. No differences in maximum intrinsic quantum yield of PS II (F_V/F_M) and relative electron transport rates could be detected at either temperature after 4 months of acclimation. Measurements of photosynthesis (relative electron transport rates) vs. irradiance (P vs. E curves) revealed similar values for relative light utilization efficiency (α = 0.57 at −1 °C, α = 0.60 at +7 °C) but higher values for irradiance levels at which photosynthesis saturates (E_K) at −1 °C and, therefore, higher maximum photosynthesis (P_MAX = 54 (relative units) at −1 °C, P_MAX = 49 at +7 °C). Nonphotochemical quenching (NPQ) measurements at 385 μmol photons m⁻² s⁻¹ indicated higher (37%) NPQ for diatoms grown at −1 °C compared to +7 °C, which was possibly related to a 2-fold increase in the concentration of the pigment diatoxanthin and a 9-fold up-regulation of a gene encoding a fucoxanthin chlorophyll a,c-binding protein. Expression of the D1 protein encoding gene psbA was ca. 1.5-fold up-regulated at −1 °C, whereas expression levels of other genes from Photosystem II (psbC, psbU, psbO), as well as rbcL, the gene encoding the Rubisco large subunit were similar at both temperatures. However, a 2-fold up-regulation of a plastid glyceraldehyde-P dehydrogenase at −1 °C indicated enhanced Calvin cycle activity. This study revealed for the first time that a polar diatom could efficiently acclimate photosynthesis over a wide range of polar temperatures given enough time. Acclimation of photosynthesis at −1 °C was probably regulated similarly to high light acclimation.     

Effects of temperature and solar radiation interactions on the survival of quiescent conidia of the entomopathogenic hyphomycetePaecilomyces fumosoroseus (Wize) Brown and Smith

The detrimental effect of solar radiation on the survival of conidia of the entomopathogenic fungusPaecilomyces fumoroseus was studied by monitoring germinability and ability to form colonies (CFU) of conidia irradiated at two temperatures, 25 and 35 °C, harmless to shaded conidia. There was no apparent effect when spores were exposed to a high level of artificial radiation (0.66 W m^–2 UVB). However, at a lower level of irradiance (0.33 W m^–2), effects of radiation occurred more quickly at 35 °C than at 25 °C. Under natural solar radiation, the rate of decrease in germinability or viability was doubled at 35 °C as compared to 25 °C, indicating an interaction between temperature and radiation effects under natural conditions. This interaction was not detected in indoor experiments, indicating that the spectral distribution of UV radiation has to be taken in account as well as its irradiance when studying its effects.Abbreviations CFU Colony Forming Units - UTC Universal Time Coordinates - UVB Ultra Violet B radiation (280–320 nm)