Antonio Flores-Moya

An inventory of UV-absorbing mycosporine-like amino acids in macroalgae from polar to warm-temperate regions

A qualitative and quantitative survey of 11 green, 27 brown and 30 red macroalgal species collected from polar (Spitsbergen), cold-temperate (Helgoland) and warm-temperate (southern Spain) regions revealed that all Rhodophyceae from the eulittoral zone contained several UV-absorbing mycosporine-like amino acid compounds (MAAs), which are assumed to function as natural UV-sunscreens. In contrast, deep-water red algae, as well as the Chlorophyceae and Phaeophyceae did not contain MAAs or exhibited only trace concentrations. Within all species investigated 9 distinct compounds were found, of which 7 were identified as mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol and palythene. The remaining two substances are unknown; they had different retention times under the Chromatographie conditions used, but identical absorption spectra with a maximum at 357 nm. Both compounds are restricted to a few polar red algae. In Polysiphonia arctica J. Agardh (Rhodophyta) from Spitsbergen the concentrations of MAAs decreased from depths of 1 to 7 m. Shallow-water isolates contained > 5-fold higher total MAA amounts compared to deep-water samples. In addition, the contents of all MAAs correlated with the biogeographic region indicating that the lower the natural solar irradiance in the respective habitat the less MAAs are synthesised and accumulated. The red algal samples from Spain exhibited up to 2-fold higher MAA contents compared to species from cold-temperate and polar waters supporting the idea of a UV-dose-dependent induction and/or concentration. The data support the idea that MAAs represent a least for red macroalgae a natural defense system against exposure to biologically harmful UV-radiation.

Long-Term Effects of Natural Sunlight under Various Ultraviolet Radiation Conditions on Growth and Photosynthesis of Intertidal Ulva rigida (Chlorophyceae) Cultivated In Situ

Abstract Long-term effects of full-spectrum solar radiation, solar radiation without UVB, and solar radiation without total UV (UVA + UVB) radiation were studied in intertidal Ulva rigida C. Agardh (Chlorophyta). The experiment was carried out under natural conditions and at prevailing winter levels of UV radiation. Changes in relative growth rate, photosynthesis and pigment content were studied after 7 and 20 d of cultivation under the three solar radiation conditions. Relative growth rate was enhanced (50 %) in the absence of UVB radiation after one week, but no difference was found after 20 d. Pigment content (chlorophyll a, chlorophyll b and carotenoids) was significantly higher in the presence of UVB, suggesting an efficient protective-pigment mechanism. When UVB was removed, photosynthetic performance measured as oxygen exchange and fluorescence parameters exhibited higher values than under the other treatments after 7 d of incubation. When samples were cultivated under PAR alone, photosynthetic performance was always negatively affected compared to in the presence of UV radiation. On the whole, intertidal U. rigida exhibited a remarkable capacity to cope with fluctuating light conditions.

Involvement of solar UV-B radiation in recovery of inhibited photosynthesis in the brown alga Dictyota dichotoma (Hudson) Lamouroux

Daily variations of photosynthetic performance of the brown alga Dictyota dichotoma (Hudson) Lamouroux (Dictyotales) (estimated by Fv/Fm ratio and net O2-based photosynthesis) have been determined under full-spectrum solar radiation (PAR+UV-A+UV-B), solar radiation depleted of ultraviolet-B (PAR+UV-A) and solar radiation depleted of total ultraviolet (photosynthetically active radiation, PAR). In the daily course, the photosynthetic response of the alga is inhibited by the three solar radiation conditions at midday, but recovers during the afternoon to those values measured in the early morning only under PAR + UV-A + UV-B, or PAR alone. Under solar radiation depleted of UV-B, the recovery of photosynthesis is significantly lower than in the other two solar radiation conditions. The relative electron transport rate (ETR) as a function of PAR is calculated for the three radiation treatments, at noon after 2 h exposure. The ETR is strongly inhibited under these conditions. In the PAR and PAR + UV-A + UV-B treatments, photosynthesis recovers after 1.5 h in low irradiance (< 10 μmol photons m−2 s−1) and attains values measured in the early morning. In the absence of UV-B, the inhibitory effect is persistent, visible as a low initial slope and lower ETR at higher levels of irradiance. These data suggest that UV-B may be involved both in the impairment and the recovery of photosynthesis of D. dichotoma.

Effects of UV radiation and temperature on growth of germlings of three species of Fucus (Phaeophyceae)

Measurements of relative growth rates (RGR) of germlings of three species of Fucus (Fucales, Phaeophyceae) collected in Helgoland (North Sea, Germany) were carried out in the laboratory in order to determine the effects of different ultraviolet radiation (UVR, λ = 280–400 nm) conditions, UVR doses and temperatures. High ultraviolet-B radiation (UVBR, λ = 280–315 nm) levels and low temperature, as independent factors, led to a species-specific reduction in RGR which appears to be related to the vertical distribution of the species in the intertidal zone. The inhibition of RGR ranged from 10% to even death of the germling. For the most sensitive species, high temperature in combination with a high dose of UVBR caused the death of the germlings, whereas at low temperature germlings were able to survive. This suggest growth-related temperature dependence of sensitivity to UVBR.

Growth seasonality, photosynthetic pigments, and carbon and nitrogen content in relation to environmental factors: a field study of Ulva olivascens (Ulvales, Chlorophyta)

Abstract Relative growth rate, photosynthetic pigment content, and internal carbon and nitrogen levels of Ulva olivascens P.A. Dangeard, were examined on a seasonal basis under natural conditions from December 1994 to February 1996. Biotic variables were correlated with abiotic factors, including phosphate and nitrate/nitrite [(NO3− + NO2−)] concentrations in the seawater, temperature, photosynthetically active radiation (PAR), and UV-A and UV-B radiation. The relative growth rate of the alga was 68% higher in spring and early summer than in mid summer. In the same spring-to-summer period, photosynthetic pigment concentrations (chlorophyll a, chlorophyll b, and carotenoids) decreased by 70–80%. From March to July, nitrogen and carbon content declined by 62% and 11%, respectively, which yielded a change in the carbon: nitrogen mass ratio from 12.9 to 39.4. In late summer, the alga disappeared from the field site. Seasonal variations in relative growth rate of U. olivascens were governed by changes in primary ecological factors, i.e., [NO3− + NO2−] concentration (70%), PAR (15%), UV-B (5%), and temperature (4%). UV-B and UV-A radiations and PAR, were primarily responsible for the seasonal changes in chlorophyll a and b and carotenoid contents. More than 78% of the changes in internal carbon and nitrogen levels could be explained by seasonal changes in UV-B radiation. These results suggest that the metabolic stress due to UV-B radiation has little impact on the seasonal growth cycle of U. olivascens but has significant impact on pigments and internal carbon and nitrogen content.

Evolution of microalgae in highly stressing environments: An experimental model analyzing the rapid adaptation of Dictyosphaerium chlorelloides (chlorophyceae) from sensitivity to resistance against 2,4,6-trinitrotoluene by rare preselective mutations

The increasing rates of global extinction due to human activities necessitate studies of the ability of organisms to adapt to the new environmental conditions resulting from human disturbances. We investigated the evolutionary adaptation of a microalga to sudden environmental change resulting from exposure to novel toxic chemical residues. A laboratory strain of Dictyosphaerium chlorelloides (Naum.) Kom. and Perm. (Chlorophyceae) was exposed to increasing concentrations of the modern contaminant 2,4,6‐trinitrotoluene (TNT). When algal cultures were exposed to 30 mg·L− 1 TNT, massive lysis of microalgal cells was observed. The key to understanding the evolution of microalgae in such a contaminated environment is to characterize the TNT‐resistant variants that appear after the massive lysis of the TNT‐sensitive cells. A fluctuation analysis demonstrated unequivocally that TNT did not facilitate the appearance of TNT‐resistant cells; rather it was found that TNT‐resistant cells appeared spontaneously by rare mutations under nonselective conditions, before exposure to TNT. The estimated mutation rate was 1.4 × 10−5 mutants per cell division. Isolated resistant mutants exhibited a diminished fitness in the absence of TNT. Moreover, the gross photosynthetic rate of TNT‐resistant mutants was significantly lower than that of wild‐type cells. Competition experiments between resistant mutants and wild‐type cells showed that in small populations, the resistant mutants were driven to extinction. The balance between mutation rate and the rate of selective elimination determines the occurrence of about 36 TNT‐resistant mutants per million cells in each generation. These scarce resistant mutants are the guarantee of potential for adaptation.

Photosynthetic oxygen production and PAM fluorescence in the brown algaPadina pavonica measured in the field under solar radiation

The effects of solar radiation on photosynthetic oxygen production, pulse amplitude-modulated (PAM) fluorescence and pigmentation were measured in the Mediterranean brown macroalgaPadina pavonica (Linnaeus) Lamouroux under field conditions and natural sunlight. Exposure of thalli to solar radiation for 1 h caused a dramatic decrease of their photosynthetic quantum yield, which recovered to initial levels after they had been placed in the shade for 3 h. Photoinhibition also occurred at the natural growth site ofP. pavonica during the hours of maximal solar irradiance. Photosynthetic oxygen production was also affected by high levels of solar radiation both in algae harvested from the surface and from 6 m depth; oxygen production started to decrease after a few minutes of exposure, and negative values were found after 1 h of solar exposure. Chlorophylla content inP. pavonica also decreased during the hours of maximal solar irradiation. These results suggest that photoinhibition ofP. pavonica occurs during part of a typical summer day on Mediterranean coasts.

EFFECTS OF SOLAR RADIATION ON PHOTOSYNTHESIS AND PHOTOINHIBITION IN RED MACROPHYTES FROM AN INTERTIDAL SYSTEM OF SOUTHERN SPAIN

The effects of solar radiation on photosynthesis, chlorophyll content and photoinhibition of the red macrophytes Asparagopsis armata, Gelidium sesquipedale, Plocamium cartilagineum and Feldmannophycus rayssiae from an intertidal system of southern Spain were estimated by means of pulse amplitude modulated fluorometer (PAM), by measurement of the O2 exchange, and by quantification of the chlorophyll content of the thalli. The effective quantum yield ( / ^) decreased in all the experimental organisms after 60 min of exposure to solar radiation; moreover, photoinhibition seemed to be more pronounced and long-lasting in shade-type plants. Secondly, all macrophytes from this study suffered more or less pronounced photoinhibition during some hours of the day at their natural living site. Photoinhibition was maximal around noon and the early afternoon, but almost complete recovery of photosynthesis was achieved by dusk. Similarly, oxygen production and chlorophyll a content were minimal around noon. The ratio (l-qP)/qN was lower in shade than in sun algae indicating a lower electron flow rate, and a lower rate of protective energy dissipation in shade than in sun-grown algae. This ratio is suggested as a good indicator of light stress, to compare different algal species with different pigment content, i. e. sunand shade-type algae.

Adaptation of the chlorophycean Dictyosphaerium chlorelloides to stressful acidic, mine metal-rich waters as result of pre-selective mutations

Several species of microalgae, closely related to mesophilic lineages, inhabit the extreme environment (pH 2.5, high levels of metals) of the Spains Aguas Agrias Stream water (AASW). Consequently, AASW constitutes an interesting natural laboratory for analysis of adaptation by microalgae to extremely stressful conditions. To distinguish between the pre-selective or post-selective origin of adaptation processes allowing the existence of microalgae in AASW, a Luria-Delbrück fluctuation analysis was performed with the chlorophycean Dictyosphaerium chlorelloides isolated from non-acidic waters. In the analysis, AASW was used as selective factor. Preselective, resistant D. chlorelloides cells appeared with a frequency of 1.1 x 10(-6) per cell per generation. AASW-resistant mutants, with a diminished Malthusian fitness, are maintained in non-extreme waters as the result of a balance between new AASW-resistant cells arising by mutation and AASW-resistant mutants eliminated by natural selection (equilibrium at c. 12 AASW-resistants per 10(7) wild-type cells). We propose that the microalgae inhabiting this stressful environment could be the descendents of chance mutants that arrived in the past or are even arriving at the present.

Adaptation of green microalgae to the herbicides simazine and diquat as result of pre-selective mutations.

Aquatic ecosystems located close to agricultural areas are increasingly polluted by herbicides. We evaluated the capacity for adaptation of green microalgae to lethal concentrations of the herbicide simazine in one strain of Dictyosphaerium chlorelloides and two strains of Scenedesmus intermedius, as well as adaptation to the herbicide diquat in one of the strains of S. intermedius. A Luria-Delbrück fluctuation analysis was carried out in order to distinguish between resistant cells arising from physiological adaptation (acclimatization) or post-adaptive mutation (both events occurring after the exposure to the herbicides), and adaptation due to mutations before the exposure to the herbicides. Simazine-resistant cells arose by rare spontaneous mutations before the exposure to simazine, with a rate of 3.0 x 10(-6) mutants per cell per generation in both strains of S. intermedius, and of 9.2 x 10(-6) mutants per cell per generation in D. chlorelloides. Diquat-resistant cells in S. intermedius arose by pre-selective mutations with a rate of 17.9 x 10(-6) per cell per generation. Rare, pre-selective mutations may allow the survival of green microalgae in simazine- or diquat-polluted waters, via herbicide-resistant selection. Therefore, human-synthesized pollutants, such as the herbicides simazine and diquat, could cause the emergence of evolutionary novelties in aquatic environments.