PHYSIOLOGICAL RESPONSES OF ANABAENA VARIABILIS (CYANOPHYCEAE) TO INSTANTANEOUS EXPOSURE TO VARIOUS COMBINATIONS OF LIGHT INTENSITY AND TEMPERATURE1

Light intensity and temperature interactions have a complex effect on the physiological process rates of the filamentous bluegreen alga Anabaena variabilis Kütz. The optimum temperature for photosynthesis increased with increasing light intensity from 10°C at 42 μE·m^?2·s^?1 to 35°C at 562 μE·m^?2·s^?1. The light saturation parameter, I_K, increased with increasing temperatures. The maximum photosynthetic rate (2.0 g C·g dry wt.^?1·d^?1) occurred at 35°C and 564 μE·m^?2·s^?1. At 15°C, the maximum rate was 1.25 g C·g dry wt.^?1·d^?1 at 332 μE·m^?2·s^?1. The dark respiration rate increased exponentially with temperature. Under favorable conditions of light intensity and temperature the percent of extracellular release of dissolved organic carbon was less than 5% of the total C fixed. This release increased to nearly 40% under combinations of low light intensity and high temperature. A mathematical model was developed to simulate the interaction of light intensity and temperature on photosynthetic rate. The interactive effects were represented by making the light-saturation parameters a function of temperature.     

THE RELATIONSHIP OF LIPIDS WITH LIGHT AND CHLOROPHYLL MEASUREMENTS IN FRESHWATER ALGAE AND PERIPHYTON1

Lipid content and lipid class composition were determined in stream periphyton and the filamentous green algae Cladophora sp. and Spirogyra sp, Sterols and phospholipids were compared to chlorophyll a (chl a) as predictors of biomass for stream periphyton and algae. Chlorophyll a, phospholipids, and sterols were each highly correlated with ash-free dry mass (AFDM) (r² > 0.98). Stream periphyton exposed naturally to high light (HL) and low light (LL) had chl a concentrations (μg chl a-mg^?1AFDM) of 7.9± 0.7 and 12.4 ± 2.9, respectively, while the sterol concentrations of these HL and LL stream periphyton (1.6 ± 0.4) were not significantly different (P > 0.05). Periphyton exposed to an irradiance of 300 μmol photons·m^?2s^?1 in the laboratory for 60 h had 5.6 ± 0.55 μg chl a·mg^?1 AFDM, but the same periphyton exposed to 2% incident light for the same amount of time had 11.0 ± 0.56 μg chl a·mg^?1 AFDM. Sterol concentrations in these periphyton communities remained unchanged (1.5 ± 0.3 μg·mg^?1AFDM), Similar results (i.e. changes in chl a but stability of sterol concentrations in response to irradiance changes) were also found for Cladophora and Spirogyra in laboratory experiments. Sterols can be quantified rapidly from a few milligrams of algae and appear to be a useful predictor of eukaryote biomass, whereas cellular levels of chl a vary substantially with light conditions. Phospholipids (or phospholipid fatty acids) are considered to be a reliable measure of viable microbial biomass. Nevertheless, phospholipid content varied substantially and unpredictably among algae and periphyton under different light regimes. Irradiance also had a significant effect on storage lipids: HL Cladophora and HL periphyton had 2 × and 5 × greater concentrations of triacylglycerols, respectively, compared to their LL forms. HL and LL algae also differed in the concentration of several major fatty acids. These light-induced changes in algal lipids and fatty acids have important implications for grazers.     

EFFECTS OF HARVEST STAGE AND LIGHT ON THE BIOCHEMICAL COMPOSITION OF THE DIATOM THALASSIOSIRA PSEUDONANA1

The marine diatom Thalassiosira pseudonana (Hustedt, clone 3H) Hasle and Heimdal was cultured under three different light regimes: 100 μmol photon · m^?2· s^?1 on 12:12 h light : dark (L:D) cycles; 50 μmol photon · m^?2· s^?2 on 24:0 h L:D; and 100 μmol photon · m^?2· s^?1 on 24:0 h L:D. It was harvested during logarithmic and stationary phases for analysis of biochemical composition. Across the different light regimes, protein (as % of organic weight) was highest in cells during logarithmic phase, whereas carbohydrate and lipid were highest during stationary phase. Carbohydrate concentrations were most affected by the different light regimes; cells grown under 12:12 h L:D contained 37–44% of the carbohydrate of cells grown under 24:0 h L:D. Cells in logarithmic phase had high proportions of polar lipids (79 to 89% of total lipid) and low triacylglycerol (≤10% of total lipid). Cells in stationary phase contained less polar lipid (48 to 57% of total lipid) and more triacylglycerol (22 to 45% of total lipid). The fatty acid composition of logarithmic phase cells grown under 24:0 h L:D were similar, but the 100 μmol photon · m^?2· s^?1 (12:12 h L:D) cells at the same stage contained a higher proportion of polyunsaturated fatty acids (PUFAs) and a lower proportion of saturated and monounsaturated fatty acids due to different levels of 16:0, 16:1(n-7), 16:4(n-1), 18:4(n-3), and 20:5(n-3). With the onset of stationary phase, cells grown at 100 μmol photon · m^?2· s^?1 (both 12:12 and 24:0 h L:D) increased in proportions of saturated and monounsaturated fatty adds and decreased in PUFAs. Concentrations (% organic or dry weight) of 14:0, 16:0, 16:1(n-7), 20:5(n-3), and 22:6(n-3) increased in cells of all cultures during stationary phase. The amino acid compositions of cells were similar irrespective of harvest stage and light regime. For mariculture, the recommended light regime for culturing T. pseudonana will depend on the nutritional requirements of the animal to which the alga is fed. For rapidly growing bivalve mollusc larvae, stationary-phase cultures grown under a 24:0 h L:D regime may provide more energy by virtue of their higher percentage of carbohydrate and high proportions and concentrations of energy-rich saturated fatty acids.     

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.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

Effects of Indole-3-acetic Acid and Gibberellin on Synchronous Cultures of Chlorella fusca

The applicability of synchronous cultures of Chlorella fusca as a reproducible experimental system for the study of growth regulators has been investigated using indole-3-acetic acid (IAA) and gibberellin.

• 1 None of these compounds stimulated growth or sporulation.
• 2 IAA inhibited growth and sporulation at concentrations higher than 6 × 10^?5M, the effect increasing with increasing acidity. Gibberellin had no effect.

     

ADSORPTION AND UPTAKE OF COPPER BY THE GREEN ALGA SCENEDESMUS SUBSPICATUS (CHLOROPHYTA)1

Copper (II) accumulation has been investigated in the green alga Scenedesmus subspicatus G. Brinkmann considering both adsorption and uptake kinetics. Experiments were conducted in a Cu- and PH-buffered medium at different free Cu²⁺ concentrations that were neither growth limiting nor toxic. We distinguished between adsorption on the cell surface and intracellular uptake by extracting copper from the cells with EDTA. Data from short-term experiments were compared with data obtained from experiments under steady state conditions. The accumulation of Cu can be described by two processes, an initial fast adsorption occurring within a minute followed by a slower intracellular uptake. Metal uptake followed Michaelis-Menten kinetics and is mediated by two systems, one with low and the other with high affinity. The maximum uptake rates (1.30 × 10^?-¹⁰ mol·[g dry wt algae]^?1· min^?1, 3.67 × 10^?-⁹ mol·[g dry wt algae]^?1·min^?1), and the half-saturation constants (6.84 × 10^?-¹⁴ M, 2.82 × 10^?-¹² M) for the two uptake systems were determined using the Lineweaver-Burk plot. The calculated maximum concentration of binding sites on the surface of the algae is initially higher (9.0 × 10^?-⁶ mol Cu.[g dry wt algae]^?1) than under steady state conditions (2.9 × 10^?-⁶ mol Cu·[g dry wt algae]^?1). This suggests that the initial binding to the algal surface comprises the binding to specific transport ligands as well as to inert adsorption sites. The conditional stability constant of the Cu binding to surface ligands was calculated as log K_Cu= 11.0 at pH 7.9. This freshwater alga has a high ability to accumulate Cu, reflecting its adaptation to the bioavailable concentration of copper.     

THF INFLUENCE OF IRRADIANCE ON THF BIOCHEMICAL COMPOSITION OF THE PRYMNESIOPHYTE ISOCHRYSIS SP. (CLONE T-ISO)1

The effects of irradiance on the biochemical composition of the prymnesiophyte microalga, Isochrysis sp. (Parke; clone T-ISO), a popular species for mariculture, were examined. Cultures were grown under a 12:12 h light: dark (L:D) regime at five irradiances ranging from 50 to 1000 μE·m ²·s^?1 and harvested at late-logarithmic phase for analysis of biochemical composition. Gross composition varied aver the range of irradiances. The highest levels of protein were present in cells from cultures grown at 100 and 250 μE·m ³·s¹, and minimum levels of carbohydrate and lipid occurred at 50 μE·m^?2·s^?1. Because the cell dry weight was reduced at lower irradiances, different trends were evident when results were expressed as percentage of dry weights. Protein percentages were highest at Wand 100 μE·m^?2·s^?1 and carbohydrate at 100 μE·m^?2·s^?1. The composition of amino acids did not differ over the range of irradiances. Glutamate and aspartate were always present in high proportions (9.0–13.5%); histidine. methionine, tryptophan, cystine, and hydroxy-proline were minor constituents (0.0–2.6%). Glucose was the predominant sugar in all cultures, ranging from 23.0% (50 μE·m^?2·s^?1) to 45.0% (100 μE·m^?2·s^?1) of total polysaccharide. No correlation was found between the proportion of any of the sugars and irradiance. The proportions of the lipid class components and fatty acids showed little change with irradiance. The main fatty acids were 14:0, 16:0, 16:1(n-7), 18:1(n-9), 18:3(n-3). 18:4(n-3), 18:5(n-3), and 22:6(n-3). Proportions of 22: 6(n-3) increased, whereas l8:3(n-3). 18:3(n-6). and 18:4(n-3) decreased, with increasing irradiance. Pigment concentrations were highest in cultures grown at 50 μE·m^?2·s^?1, except for fucoxanthin and diadinoxanthin (100 μE·m^?2·s^?1). The concentrations of accessory pigments correlated with chlorophyll a, which decreased in concentration with increasing irradiance. On the basts of biochemical composition, an irradiance of 100 μE·m^?1·s^?1 (12:12 h L:D cycle)for the culture of Isochrysis sp. (clone T-ISO) may provide optimal nutritional value for maricultured animals, although feeding trials are now necessary to substantiate this.     

INFLUENCE OF IRRADIANCE ON VIRUS–ALGAL HOST INTERACTIONS1

The effect of different irradiance levels on the interactions between the algal host and its virus was investigated for two marine phytoplankton, Phaeocystis globosa Scherff. and Micromonas pusilla (Butcher) Manton et Parke. The algal cultures were acclimated at 25, 100, and 250 μmol photons · m^?2 · s^?1 (LL, ML, and HL, respectively), after which they were infected with a lytic virus (PgV‐07T and MpV‐02T) and monitored under the appropriate irradiance and in darkness. The effect of irradiance levels on the host–virus interactions differed for the two algal host–virus systems examined. For P. globosa, the LL‐acclimated cultures showed a 4 h prolonged latent period (11–16 h), which may be related to the subsaturated growth observed at this irradiance. The burst size was reduced by 50% at LL and HL compared to ML (525 PgV · cell^?1). The fraction of infectious viruses, however, remained unchanged. Viral replication was prevented when the LL P. globosa cultures were kept in darkness (up to 48 h) but recovered when placed back into the light. PgV‐07T still replicated in the dark for the ML‐ and HL‐acclimated cultures, but viral yield was reduced by 50%–85%. For M. pusilla, the burst size (285–360 MpV · cell^?1), the infectivity, and the latent period of MpV‐02T (7–11 h) remained unaffected by the incident light. Conversely, darkness not only inhibited MpV replication but also resulted in substantial cell lysis of the noninfected cultures. Our study implies that irradiance level is an important factor controlling algal host–virus interactions and hence the dynamics of phytoplankton populations.     

DETECTION OF DIATOM XANTHOPHYLL CYCLE USING SPECTRAL REFLECTANCE1

Analysis of reflectance spectra was used to monitor the conversion of diadinoxanthin (DD) into diatoxanthin (DT) in two benthic diatom species, Amphora coffeaeformis (C. Agardh) Kütz. and Cylindrotheca closterium (Ehrenb.) J. C. Lewin et Reiman, cultured at high light (HL, 400 μmol · m^?2 · s^?1 PAR) and low light (LL, 25 μmol · m^?2 · s^?1 PAR). Cultures were exposed to saturating light for 32 min. HL cultures of both species showed higher (DT + DD) content, whereas LL cultures exhibited higher chl a and fucoxanthin content. DD to DT conversion, measured by HPLC, occurred mainly in the first 2 min (LL) or 5 min (HL) after exposure to saturating light. Nonphotochemical quenching (NPQ), measured by PAM fluorescence, showed the same pattern as DT/(DD + DT), resulting in a linear relationship between these parameters. Addition of dithiothreitol (DTT) blocked the conversion of DD into DT and significantly reduced NPQ induction. Reflectance spectra showed no obvious change after light exposure. However, second derivative spectra (δδ) showed a shift in reflectance from 487 to 508 nm, which was not present for DTT‐treated samples. Changes in δδ₄₈₇ were strongly correlated with changes in DD (r = 0.76), while changes in δδ₅₀₈ were strongly correlated with changes in DT (r = 0.94). The best index to estimate DD to DT conversion was δδ₅₀₈/δδ₆₃₀ (r = 0.87). This index was very sensitive to minute changes that occurred immediately after exposure to light and was species insensitive. Good relationships were observed between indices for xanthophyll cycle activation (DD to DT conversion and NPQ induction) and the second derivative spectra. With further in situ validation, this index may prove to be highly useful for investigation into aquatic global photoregulation mechanisms in diatom‐dominated samples.     

EFFECT OF INDOLE-3-ACETIC ACID ON GROWTH OF CODIUM FRAGILE SUBSP. TOMENTOSOIDES (CHLOROPHYCEAE) IN CULTURE1

Growth of Codium fragile subsp. tomentosoides (van Goor) Silva in culture depends upon the season of seawater collection. One factor responsible for this variation in growth may be indole-3-acetic acid (IAA). When 10^?9 to 10^?4 M IAA is added to cultures of Codium fragile, optimum growth is at 10^?6 M. The response to exogenous IAA depends upon the time of year when the sea-water is collected. The growth in a range of known IAA concentrations allows the prediction of a seasonal cycle of IAA, or its physiological equivalent, in Rhode Island coastal waters. Such a compound may be an important ecological factor for some algal species.     

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.     

Effect of Light Intensity on Growth, CO2 Fixation, and Chlorophyll and Polar Lipid Production in Germinating Polytrichum commune Spores

The dry matter production in Polytrichum commune protonemata was increased when the light intensity was increased from 0 to 160 μE m^?2 s^?1, and at 160 μE m^?2 s^?1 production was about 200% of that found at 17 μE m^?2 s^?1. Production of chlorophyll (Chl) was increased by increasing light intensity from 0 to 17 μE m^?2 s^?1, but decreasing at light intensities above 17 μE m^?2 s^?1. At 160 μE m^?2 s^?1 the production of Chl was only about 50% of that at 17 μE m^?2 s^?1. The rate of CO₂ fixation was low (0.31 μg CO₂/mg Chi × h) at the light intensity of 17 μE m^?2 s^?1 as compared with that at 160 μE m^?2 s^?1 (0.83 μg CO₂/mg Chi × h). Production of mono- (MGDG) and diglycosyl diglycerides (DGDG) was closely associated with that of chlorophylls. At the higher light intensity (160 μE m^?2 s^?1) production of glycolipids was about 60% of that at 17 μE m^?2 s^?1. Production of more polar lipids was less affected by light intensity. Light intensity also affected the fatty acid pattern of the lipid fractions. The effect was most pronounced in the MGDG fraction, where the proportion of C 18: 3ω3 + C 16: 3ω3 was higher at the higher light intensity.     

Interaction of Kinetin and Indoleacetic Acid in the Avena Straight-Growth Test

Kinetin has a stimulating effect in the Avena straight-growth test. The action of different concentrations of kinetin, 2.5 × 10^?7, 2.5 × 10^?6 and 2.5 × 10^?5M, in combination with different concentrations of IAA was studied in this test. It was shown that the effect of low IAA concentrations, 0.25 × 10^?7 and 1 × 10^?7M, was strongly enhanced by the addition of all the kinetin concentrations investigated. The effect of the highest IAA concentrations, 25 × 10^?7 and 100 × 10^?7M, on the other hand, was inhibited relatively strongly by the highest employed concentration of kinetin. The results are explained as due to a kinetin-produced increase of auxin in the coleoptile segment, which in combination with low IAA concentrations can lead to a growth stimulation and with high IAA concentrations to a growth inhibition. Since kinetin in purification and chromatography of auxin can partly follow IAA, thereby affecting the quantitative yield, it is emphasized that, prior to the test, auxin extracts containing cytokinins should be freed from the latter by, for example, gel filtration or paper electrophoresis.     

Growth,biochemical and enzymatic responses of thermal cyanobacterium Gloeocapsa sp. (Cyanophyceae) to temperature and irradiance

The present study describes a strain of Gloeocapsa sp. designated as Gacheva 2007/R‐06/1, originally isolated from a geothermal flow located in Rupite, Bulgaria. To evaluate whether this cyanobacterium is locally adapted to hot environment or has the ability to tolerate lower temperatures, its growth, biochemical composition, enzyme isoforms and activity of the main antioxidant enzymes and proteases were characterized under various temperatures and two irradiance levels. The strain was able to grow over the whole temperature range (15–40°C) under two different photon fluence densities – 132 μmol photons m^?2 s^?1 (unilateral, low light, LL) and 2 × 132 μmol photons m^?2 s^?1 (bilateral, high light, HL). The best growth occurred at either 34°C and LL or at 36°C and HL, but significant growth inhibition was noted at 15°C and 40°C. Low temperature treatment (15°C) resulted in higher levels of total protein and an increased activity of manganese superoxide dismutase (MnSOD) and glutathione reductase, as compared to optimum growth temperatures. After simultaneous exposure to 15°C and HL, increases in lipid content and activity of iron superoxide dismutase and catalase (CAT) were also observed. Cultivation of cells at 40°C enhanced MnSOD, CAT and peroxidase activities, regardless of irradiance level. Increased total protein content and protease activity at 40°C was only associated with the HL treatment. Overall, these results indicate that Gloeocapsa sp. strain Gacheva 2007/R‐06/1 used different strategies to enable cells to efficiently acclimate and withstand adverse low or high temperatures. This strain obviously tolerates a wide range of temperatures below its natural habitat temperature, and does not seem to be locally adapted to its original thermal regime. It behaved as a thermotolerant rather than a thermophilic cyanobacterium, which suggests its wider distribution in nature.     

The benefits of foliar inoculation with <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> in soybean are explained by an auxin signaling model

Azospirillum sp. is one of the most studied genera of plant growth-promoting rhizobacteria (PGPR). The ability of Azospirillum sp. to promote plant growth has been associated with its ability to produce several phytohormones, such as auxins, gibberellins and cytokinins, but mainly indole-3-acetic acid (IAA). It has been propoosed that the production of IAA explains the positive effects of co-inoculation with Azospirillum sp. on the rhizobia-legume symbiosis. In this study, we constructed an IAA-deficient mutant of A. brasilense Az39 (ipdC ^? ) by using a restriction-free cloning method. We inoculated soybean seeds with 1·10⁶ cfu·seed^?1 of Bradyrhizobium japonicum E109 and co-inoculating leaves at the V3 stage with 1·10⁸ cfu.plant^?1 of A. brasilense Az39 wt or ipdC ^? or inoculated leaves with 20 μg.plant^?1 synthetic IAA. The results confirmed soybean growth promotion as there was increased total plant and root length, aerial and root dry weight, number of nodules on the primary root, and an increase in the symbiosis established with B. japonicum E109. Nodule weight also increased after foliar co-inoculation with the IAA- producer A. brasilense Az39. The exogenous application of IAA decreased aerial and root length, as well as the number of nodules on primary roots in comparison with the Az39 wt strain. These results allow us to propose a biological model of response to foliar co-inoculation of soybean with IAA-producing rhizobacteria. This model clearly shows that both the presence of microorganism as part of the colonization process and the production of IAA in situ are co-responsible, via plant signaling molecules, for the positive effects on plant growth and symbiosis establishment.     

Influence of light and temperature on photosynthesis and respiration by Pithophora oedogonia (Mont.) Wittr. (chlorophyceae)

Rates of net photosynthesis and respiration were determined for Pithophora oedogonia (Mont.) Wittr. acclimatized to 56 combinations of light (7–1200 μE m^?2 s^?1) and temperature (5–35°C). Conditions for maximum net photosynthesis were estimated to be 26°C and 970 μE m^?2 s^?1. The rate of net photosyntheses varied considerably with temperature, with the maximum measured value (9.67 mg O₂ h^?1 g dry wt.^?1) occurring at 25°C. Respiration rate increased with temperature and the light received just prior to measurement. The maximum respiration rate (7.05 mg O₂ g^?1 h^?1) occurred at 30°C and 1200 μE m^?2 s^?1. Exposure of Pithophora to light levels of 600 or 1200 μE m^?2 s^?1 prior to determination of the respiration rate resulted in significantly elevated levels of oxygen consumption at temperatures ≥ 15°C. The relationship between light, temperature and photosynthesis and respiration were summarized as three-dimensional response surfaces.     

Growth-Promoting Effects of Fatty Acids on Excised Wheat Roots and Oat Coleoptiles

The growth action of some fatty acids and alcohols with carbon number from 1 to 4 was tested on excised wheat roots in aseptic cultures. Growth, cell length, and dry weight were measured after seven days. The tested substances were: Formic acid, acetic acid, propionic acid, n-Butyric acid, isobutyric acid, acelaldehyde, propionaldohyde, ethanol, n-propanol, isopropanol, n-butanoL and isobutanol. The primary alcohols and all of the acids, except formic acid, promoted the cell elongation and the total growth, but the meristematic activity was inhibited in the higher concentrations. The concentrations with maximal growth-promoting activity were 10^?2M to 10^?3M for the alcohols and 10^?4M for the acids. Propionic acid was applied in darkness, red light, and white light and proved to increase the cell length from 215 μ, 180 μ, and 120 μ up to 240 μ in all three treatments. The growth rate was not affected, but the duration of the cell elongation was extended. The presence of iron proved to be necessary for the stimulation. The chlorophyll content in the light grown roots was relatively unaffected when the cell length was increased and the dry weight was not increased as long the cell number was normal. The growth of Avena coleoptile segments was slightly promoted by propionic acid in the presence of IAA.     

RELATIONSHIP BETWEEN PHOTOSYNTHESIS AND CELL SIZE OF MARINE DIATOMS12

Three photosynthetic parameters of 7 species of marine diatoms were studied using Na₂¹⁴CO₃ at 5–8 C using log phase axenic cultures. The cell volumes of the different species varied from 70 μm³ to 40 × 10⁵μm³. The present experiment is consistent with the interpretation that the initial slope α (mg C · [mg chl a]^?1· h^?1· w^?1· m²) of photosynthesis vs. light curves is controlled by self-shading of chlorophyll a in the cell. Pm, the rate of photosynthesis at light saturation (mg C · [mg cell, C]^?1· h^?1) and R, the intercept at zero light intensity (mg C · [mg cell C]^?1· H^?1) are both dependent on the ratio of surface area to volume of cell.     

Hernandulcin in hairy root cultures of Lippia dulcis

The hairy root culture of Lippia dulcis Trev., Verbenaceae, was established by transformation with Agrobacterium rhizogenes A4. The transformed roots grew well in Murashige and Skoog medium containing 2% sucrose. The roots turned light green when they were cultured under 16 h/day light. The green hairy roots produced the sweet sesquiterpene hernandulcin (ca. 0.25 mg/g dry wt) together with 20 other mono- and sesquiterpenes, while no terpenes were detected in the nontransformed root cultures. The growth and hernandulcin production in the hairy root cultures were influenced by the addition of auxins to the medium. The addition of a low concentration of chitosan (0.2 – 10.0 mg / l) enhanced the production of hernandulcin 5-fold.Abbreviations Cht chitosan - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - MS Murashige and Skoog(1962)