Taejun Han

Phenol toxicity to the aquatic macrophyte Lemna paucicostata

Phenol is a ubiquitous environmental pollutant and a widely used reference toxicant for many bioassays. However, little information is available regarding the toxic effects of phenol on aquatic macrophytes. Seventy-two hour bioassays, with different end-points, were carried out to assess phenol toxicity in Lemna paucicostata. A concentration-dependent decline in frond multiplication and colony disintegration was observed, with 11.38 and 22.76 μM phenol resulting in browning of fronds and colony disintegration, respectively. Growth of fronds, as measured by changes in surface area, was significantly inhibited with EC₅₀ value of 2.70 μM. When pulse amplitude modulated chlorophyll a (Chl a) fluorescence imaging (i-PAM) was employed, the maximum quantum yield of PS II (F(v)/F(m)) significantly declined with increasing phenol concentrations with resultant EC₅₀ of 1.91 μM and coefficients of variation (CVs) generated for the EC₅₀ values of less than 4.7%. A gradual increase in fluorescence emissions from chlorophylls a and b and pheophytin up to a concentration of 2.85 μM was found but declined markedly at higher concentrations. The significant correlation between the F(v)/F(m) and surface growth rate data implies that the former is an appropriate biomarker of whole plant toxicity. Using imaging Chl a fluorescence on L. paucicostata provides a rapid, sensitive and reliable method for assessing the toxic risks posed by phenol to aquatic ecosystems and has practical applications for municipal and industrial waste water management.

UV-B INDUCTION OF UV-B PROTECTION IN ULVA PERTUSA (CHLOROPHYTA)1

The green macroalga Ulva pertusa Kjellman produced UV‐B absorbing compounds with a prominent absorption maximum at 294 nm in response only to UV‐B, and the amounts induced were proportional to the UV‐B doses. Under a 12:12‐h light:dark regime, the production of UV‐absorbing compounds occurred only during the exposure periods with little turnover in the dark. There was significant reduction in growth in parallel with the production of UV‐B absorbing compounds. The polychromatic action spectrum for the induction of UV‐B absorbing compounds in U. pertusa exhibits a major peak at 292 nm with a smaller peak at 311.5 nm. No significant induction was detected above 354.5 nm, and radiation below 285 nm caused significant reduction in the levels of UV‐B absorbing compounds. After UV‐B irradiation at 1.0 W·m−2 for 9 h, the optimal photosynthetic quantum yield of the samples with UV‐B absorbing compounds slightly increased relative to the initial value, whereas that of thalli lacking the compounds declined to 30%–34% of the initial followed by subsequent recovery in dim light of up to 84%–85% of the initial value. There was a positive and significant relationship between the amount of UV‐B absorbing compounds with antioxidant activity as determined by the α,α‐diphenyl‐β‐picrylhydrazyl scavenging assay. In addition to mat‐forming characteristics and light‐driven photorepair, the existence and antioxidant capacity of UV‐B absorbing compounds may confer U. pertusa a greater selective advantage over other macroalgae, thereby enabling them to thrive in the presence of intense UV‐B radiation.

THALLUS DIFFERENTIATION OF PHOTOSYNTHESIS, GROWTH, REPRODUCTION, AND UV-B SENSITIVITY IN THE GREEN ALGA ULVA PERTUSA (CHLOROPHYCEAE)1

The chlorophyte Ulva is perceived as a simple and uniform algal form, with little functional differentiation within a thallus. We compared morphology, pigmentation, photosynthesis, growth, reproduction, and UV‐B sensitivity between different thallus regions of Ulva pertusa Kjellman. Thallus thickness and cell size were significantly greater, whereas cell number was less in the basal region than in other regions. Photosynthetic pigment contents were lowest in the basal region and increased toward the marginal region. Photosynthetic capacity and photosynthetic efficiency normalized to fresh weight, area, volume, and cell number showed a progressive increase from the basal to marginal parts; however, on a chl basis those values were equal regardless of thallus part. Values of light saturation point were not statistically different between regions. Growth rates increased from marginal to basal and to middle parts of the thallus, whereas sporulation was highest in marginal (100%) followed by middle (30%) and basal parts (0%). Daily observation over 9 days showed that 56% of the basal cells divided once and did not produce spores, whereas every marginal cell went through its first division and 89% of the primary daughter cells also divided, resulting in 100% sporulation. A 7‐day treatment with PAR and PAR + UV‐A caused a significant decrease in the effective quantum yield of all thallus regions, followed by a recovery toward the initial values, whereas PAR + UV‐A + UV‐B irradiation led to greater photoinhibition and less recovery. Marked differences in the UV‐B sensitivity were observed, with marginal parts being more sensitive and basal parts most resistant.

UV‐A/BLUE LIGHT–INDUCED REACTIVATION OF SPORE GERMINATION IN UV‐B IRRADIATED ULVA PERTUSA (CHLOROPHYTA)1

Recent reduction in the ozone shield due to manufactured chlorofluorocarbons raised considerable interest in the ecological and physiological consequences of UV‐B radiation (λ=280–315 nm) in macroalgae. However, early life stages of macroalgae have received little attention in regard to their UV‐B sensitivity and UV‐B defensive mechanisms. Germination of UV‐B irradiated spores of the intertidal green alga Ulva pertusa Kjellman was significantly lower than in unexposed controls, and the degree of reduction correlated with the UV doses. After exposure to moderate levels of UV‐B irradiation, subsequent exposure to visible light caused differential germination in an irradiance‐ and wavelength‐dependent manner. Significantly higher germination was found at higher photon irradiances and in blue light compared with white and red light. The action spectrum for photoreactivation of germination in UV‐B irradiated U. pertusa spores shows a major peak at 435 nm with a smaller but significant peak at 385 nm. When exposed to December sunlight, the germination percentage of U. pertusa spores exposed to 1 h of solar radiation reached 100% regardless of the irradiation treatment conditions. After a 2‐h exposure to sunlight, however, there was complete inhibition of germination in PAR+UV‐A+UV‐B in contrast to 100% germination in PAR or PAR+UV‐A. In addition to mat‐forming characteristics that would act as a selective UV‐B filter for settled spores under the parental canopy, light‐driven repair of germination after UV‐B exposure could explain successful continuation of U. pertusa spore germination in intertidal settings possibly affected by intense solar UV‐B radiation.

Influences of light and UV-B on growth and sporulation of the green alga Ulva pertusa Kjellman.

Abstract The cosmopolitan presence of Ulva spp. is partly due to its great reproductive ability, but relatively little information is available for the radiation conditions triggering reproduction. In the present study, we investigated the effect of photon irradiance, photoperiod, and spectral qualities of light on growth and reproduction of Ulva pertusa . During 8-day culture of discs cut from marginal parts of the thallus of U. pertusa , the size of the thallus discs was greatest at 10 μmol m −2 s −1 , while saturation of reproduction occurred at 30 μmol m −2 s −1 . The minimum photon irradiance allowing growth and reproduction was 5 and 10 μmol m −2 s −1 , respectively. Rapid increases in the size and subsequent initiation of sporulation were observed in samples transferred to saturating irradiance from 5 μmol m −2 s −1 or darkness for 9 days. When exposed to different photoperiods (8:16-, 12:12-, 16:8-h LD and continuous light regimes) combined with different photon irradiances (10 and 100 μmol m −2 s −1 ), U. pertusa thallus showed that the thallus size attained at the low irradiance was similar in daylengths longer than 12 h per day, while the surface area increased in parallel with increasing light duration at the high irradiance. The degree of sporulation at 10 μmol m −2 s −1 varied, ranging from no sporulation in 8:16-h LD to 80% in 16:8-h LD and continuous light. On the other hand, there was no remarkable difference in the degree of sporulation between the photoperiods except for slightly smaller percentage sporulation in 8:16-h LD at 100 μmol m −2 s −1 . At 5 μmol m −2 s −1 , the growth of U. pertusa was markedly lower in green than in blue or red light, but there was no sporulation in any spectral quality. The degree of sporulation at 20 μmol m −2 s −1 was almost twice as much in blue or red as in green light. The size of plants irradiated with 1.0 W m −2 of UV-B for 20–40 min increased by 18–21% relative to control, whereas higher UV irradiance caused inhibition of growth. There was a significantly lower incidence of sporulation in UV-B-irradiated plants with the degree of reduction being greater in those exposed to higher UV doses. The total biologically effective UV-B dose for 50% inhibition of sporulation was 0.085 Dose eff kJ m −2 . The time required to achieve 50% inhibition would be longer than 13 h at depths below 1 m in Ahnin coastal waters. The vertical attenuation coefficient of PAR ( λ =400–700 nm) and UV-B ( λ =300–320 nm) in April 1998 at Ahnin on the eastern coast of Korea was 0.21 m −1 for K PAR and 0.54 m −1 for K UV-B . A large reduction of light quantity and rapid disappearance of blue wavelength occurred by shading from overlying thalli. Percentage inhibition of sporulation was only 14–18% at 150–200 μmol m −2 s −1 compared with 70% at 10 μmol m −2 s −1 , when plants were incubated under different irradiances of PAR immediately after UV-B exposures. These different photoadaptive strategies for sporulation may in part account for the great ecological success of U. pertusa .

Physiological ecology and seasonality of Ulva pertusa on a temperate rocky shore

Abstract Green tides, i.e. blooms of Ulva species, occur on rocky intertidal shores over a wide geographic area in Korea. For the first time we report seasonal fluctuations in biomass, photosynthetic performance and chemical composition of the green-tide forming Ulva pertusa on the southern coast of Korea. Water temperature, salinity, inorganic nutrients and precipitation influencing Ulva mat dynamics were also monitored. There was a pronounced seasonality, not only in the biomass of U. pertusa, but also in photosynthetic performance and in variation in tissue pigments and nutrients. In addition to a primary seasonal response, significant variation in biomass was correlated in parts of the year with nutrient inputs from the surrounding watershed, heavy rain events and summer desiccation. There was a unimodal seasonal pattern in which biomass peaked in May (2.2 kg fw m−2) and dropped significantly from June to September. Recovery of Ulva mats, as indicated by recruitment of new plants, began during autumn. Photosynthetic rates, maximum photosynthesis (Pmax) and photosynthetic efficiency (α) were highest during the growth period and were lowest when biomass peaked or declined in May and July. Tissue pigments had a less clear seasonal pattern. Relative amounts of nitrogen and phosphorus bound in U. pertusa also displayed an obscure seasonal trend. Complex interactions among biological and environmental variables precluded strong correlations with any particular environmental factor. Stochastic events also played a major role in seasonality and can override normal physiological adaptations.

Physiological response ofLemna species to herbicides and its probable use in toxicity testing

Herbicides such as atrazine, diuron, simazine and glyphosate are of growing concern with respect to ecotoxicity as they are often encountered in outdoor water samples. The present study evaluates the potential damage caused by these xenobiotics on physiology of the aquatic plantLemna sp., thereby proposing its use as a probable bioindicator. Comparative study of a panel of classical endpoints (frond number and relative growth rate) and chlorophyll fluorescence parameters (Fo, Fm, NPQ, Fv/Fm and ETRmax) revealed that diuron caused maximum inhibition of increase in frond number. This coincided with the toxicity ranking obtained on the basis of RGRarea and RGRFW i.e. diuron>atrazine>simazine>glyphosate. The chlorophyll (chl)a fluorescence parameters revealed a concentration dependent decline in maximal fluorescence (Fm) in the plants exposed to diuron, atrazine and simazine; this decline was negligible in presence of glyphosate. Besides, an EC50 of 0.009 (0.008–0.010) mg/L was recorded in case of Fv/Fm of the diuron exposedLemna sp.; furthermore, the glyphosate exposed plant demonstrated EC50s>16 mg/L. ETRmax ofLemna sp. significantly (p<0.001) declined in presence of diuron, atrazine and simazine, whereas glyphosate did not cause any significant (p>0.05) reduction. A steady concentration-dependent decline in chl a fluorescence parameters ofLemna sp. (specifically Fv/Fm and ETRmax) as compared to the classical endpoints, demonstrated their superiority and sensitivity in detection of herbicides in the aquatic bodies. This study emphasizes on the probable use of chlorophyll fluorescence ofLemna sp. as a tool or bioindicator in evaluation of herbicides.

Effects of intense PAR and UV radiation on photosynthesis, growth and pigmentation in the rice-field cyanobacterium Anabaena sp.

The relative importance of photosynthetically active radiation and UV on photoinhibition has been studied in the cyanobacterium Anabaena sp. by measuring the effective quantum yield, growth, pigmentation and fluorescence emission.

Toxicity of single and combined herbicides on PSII maximum efficiency of an aquatic higher plant, Lemna sp.

The present study examined the effect of single and binary mixtures of four herbicides, namely, atrazine, diuron, simazine and hexazinone on the maximum quantum efficiency of photosynthesis (Fv/Fm) of Lemna sp. after 96 h of exposure. When applied singly, the toxicity ranking of the four herbicides was as follows: diuron>hexazinone>atrazine>simazine. Binary combinations of these toxicants revealed varying inhibition values; for example, the combination of low diuron concentration with both high and low concentrations of hexazinone resulted in a synergistic effect, with mean ratio of inhibition (RI) values ranging from 1.13±0.10 to 1.16±0.08. The combination of diuron with atrazine revealed an additive effect at low diuron levels (0.025 mg L−1) and high atrazine levels (0.1 mg L−1) with an RI value of 1.06±0.07. Our study emphasizes on the utility of combined toxicity models in predicting the toxicological impact of herbicide mixtures on aquatic ecosystems. Overall, this study provides valuable information on the chlorophyll fluorescence of Lemna sp. as a bioanalytical tool for the rapid and inexpensive assessment of photosystem II (PSII) inhibiting herbicide mixtures.

Aquatic toxicity tests of Ulva pertusa Kjellman (Ulvales, Chlorophyta) using spore germination and gametophyte growth

Aquatic toxicity tests using spore germination and gametophyte growth of the green alga, Ulva pertusa Kjellman, were developed and evaluated by assessing the toxicity of different organic and inorganic chemicals and elutriates of sewage or waste sludge. The toxic ranking of three metals was: Cu (EC50 of 0.017 mg l−1) > Zn (0.378 mg l−1) > Cd (0.789 mg l−1) for spore germination and Cu (0.023–0.027 mg l−1) > Cd (0.189–0.200 mg l−1) > Zn (0.307–0.317 mg l−1) for gametophyte growth. Spore germination (EC50 of 3.95 mg l−1) was more sensitive to formalin than gametophyte growth (6.92–7.18 mg l−1). The EC50 for tributyltin oxide differed between the endpoints, with values of 0.586 mg l−1 for germination and 0.391–0.396 mg l−1 for growth responses. After exposure to three different sludge elutriates the greatest and least toxic effects were found for urban sewage (7.6–8.3%) and filtration bed (>61%), respectively. The bioassays are simple, inexpensive, eco-relevant and have a potential application worldwide.