Murray T. Brown

Spatiotemporal Patterning of Reactive Oxygen Production and Ca2+ Wave Propagation in Fucus Rhizoid Cells

Both Ca2+ and reactive oxygen species (ROS) play critical signaling roles in plant responses to biotic and abiotic stress. However, the positioning of Ca2+ and ROS (in particular H2O2) after a stress stimulus and their subcellular interactions are poorly understood. Moreover, although information can be encoded in different patterns of cellular Ca2+ signals, little is known about the subcellular spatiotemporal patterns of ROS production or their significance for downstream responses. Here, we show that ROS production in response to hyperosmotic stress in embryonic cells of the alga Fucus serratus consists of two distinct components. The first ROS component coincides closely with the origin of a Ca2+ wave in the peripheral cytosol at the growing cell apex, has an extracellular origin, and is necessary for the Ca2+ wave. Patch-clamp experiments show that a nonselective cation channel is stimulated by H2O2 and may underlie the initial cytosolic Ca2+ increase. Thus, the spatiotemporal pattern of the Ca2+ wave is determined by peripheral ROS production. The second, later ROS component localizes to the mitochondria and is a direct consequence of the Ca2+ wave. The first component, but not the second, is required for short-term adaptation to hyperosmotic stress. Our results highlight the role of ROS in the patterning of a Ca2+ signal in addition to its function in regulating cell wall strength in the Fucus embryo.

The toxicity of copper(II) species to marine algae, with particular reference to macroalgae

Ambient concentrations of dissolved copper(II) in seawater are very low. However, levels can increase as a result of natural and anthropogenic sources. Such increase can have profound effects on organisms in the vicinity resulting in inhibition of growth, reduced fecundity, and even death. This paper highlights the importance of pecieation when considering the toxic effects of cooper, with particular reference to macroalgae in a marine environment, and to encourage more biologists to take account of this in their studies of metal pollution. 104 refs., 2 figs., 4 tabs.

Impacts of anthropogenic stresses on the early development stages of seaweeds

Seaweeds are important primary producers, and as such contributesignificantly to nearshore ecosystems. Studies on the effects ofanthropogenic stresses on these organisms have largely been concernedwith the vegetative adult stages of the life cycle. Here we review thelimited information on the sensitivity of early stages in the life cycleof seaweeds to global change (UV increase; global warming;increased storm frequencies) and pollution (eutrophication, trace metalsand oil). Impacts on fertility, substrate attachment, development,photosynthesis, growth and mortality are highlighted. In their naturalhabitats, early stages are shade-adapted, as they live shel tered underadult canopies and in pores of the substrata. Although some acclimationunder increased moderate irradiance is seen, higher solar irradiance,and especially ultraviolet-B, inhibits early development. Global warmingmay decrease the fertility and shorten the fertile period of somespecies. With the increasing likelihood of storms associated with globalwarming, gamete release may be inhibited while scouring by suspendedsediments may detach newly settled stages. Succession and localdistribution patterns are likely to be affected. Eutrophication canresult in accelerated development of the early stages of some algalspecies but sewage discharges have a negative impact on sperm motility,fertilisation and can cause increased mortality in germlings. Impacts ofother, indirect effects of eutrophication, including increased sedimentcover of substrata, scouring caused by wind-induced resuspension ofsediments, and grazing, are also expected to be negative. Toxic tracemetals affect gamete viability, inhibit fertilisation and development,and reduce growth rates. Gametes are particularly susceptible to oilpollution and interactions between hydrocarbons and the adhesive mucussurrounding the embryonic stages seem to inhibit settlement.Recommendations for future studies are provided that are aimed atgaining greater insight into the effects of anthropogenic stress on theweakest links in the development cycle of seaweeds.

Trace metal concentrations in marine macroalgae from different biotopes in the Aegean Sea

The commonest species of red, brown, and green macroalgae were sampled from a range of biotopes in the Aegean Sea and analysed for five different trace metals. Significant differences in metal concentrations were found among different seaweed species from the same biotope. The concentrations of metals in the various seaweed species may reflect their morphology, with those having a larger surface area having a greater internal content. Different species of seaweed have different affinities for different heavy metals. This may reflect competition between metals for binding or uptake sites in the seaweed. Comparing metal concentrations in algae among the studied sampling stations clearly indicates that the degree of accumulation depends not only on human activities but also on the geology of the specific area. While seaweed can be used successfully to assess the levels of heavy metals in the marine environment, not all elevated concentrations of heavy metals necessarily reflect increased levels of pollution. Indeed, the high concentrations of certain metals, e.g., Ni, found in our seaweed samples reflected the metaliferrous nature of the rock. It is therefore important to take account of a regions geology before attempting to interpret the data.

Copper, copper mine tailings and their effect on marine algae in Northern Chile

Results are presented of a long-term research programme on the effect of copper contamination on biota in Chilean coastal waters. In spite of the magnitude of the copper mining tailings that affected Caleta Palito and surroundings in northern Chile, the effects on the intertidal assemblages remain restricted to a small geographic area. Even within the affected area, the effects are not homogeneous and there is evidence of active recovery in biological diversity in recent few years. Experimental evidence suggests that the current low algal diversity and abundance is strongly influenced by herbivory, although chronic effects of the discharges cannot be ruled out. Cellular changes in Enteromorpha compressa from the impacted area were characterised by abnormal granules in the cytoplasm, though these granules did not contain detectable levels of copper or other heavy metals.

Evaluating environmental contamination in Ria Formosa (Portugal) using stress indexes of Spartina maritima

Species of Spartina are potentially useful for biomonitoring coastal systems because they are abundant in the intertidal and have a wide geographic distribution in temperate zones. In this study, three indexes of physiological stress, thiolic protein concentration, adenylic energy charge (AEC) index [AEC = ATP + 0.5ADP/(ATP + ADP + AMP)] and photosynthetic efficiency (Fv/Fm), are measured in Spartina maritima plants collected at four sites and compared with metal concentrations in the sediments and Spartina tissues. Two sites were close to urban centers and two were located further away, in less contaminated areas. Concentrations of copper, cadmium, lead and zinc were determined by atomic absorption spectrophotometry, thiolic proteins were determined by polarography and adenilic nucleotides were determined by high performance liquid chromatography. Photosynthetic efficiencies were measured with a fluorometer. The sediments of sites closer to urban centers had higher concentrations of metals than the sites located further away. Metal concentration within plants did not follow this spatial pattern, probably due to spatial differences in metal bioavailability, uptake rates, internal transport and excretion processes. Concentrations of all metals studied were higher in underground plant structures than aerial, except cadmium whose levels were not significantly different. On the other hand, the stress indexes followed the spatial pattern of metals in the sediment. Thiolic protein concentrations were higher in plants from polluted sites, and were three to four times higher in aerial than in underground plant structures. Leaf AEC ratios and photosynthetic efficiencies were lower in plants from polluted sites indicating that they were growing under stressful conditions. We conclude that the use of these indexes in S. maritima represent a useful tool to monitor contamination in Ria Formosa lagoon as they provide an integrated measure of the toxicological burden of contamination.

THE RELEASE OF COPPER-COMPLEXING LIGANDS BY THE BROWN ALGA FUCUS VESICULOSUS (PHAEOPHYCEAE) IN RESPONSE TO INCREASING TOTAL COPPER LEVELS

The growth of Fucus vesiculosus L. germlings in chemically defined culture media containing a range of Cu concentrations (20–1000 nM) was monitored simultaneously with measurement of the Cu speciation in the media by competitive equilibrium‐adsorptive cathodic stripping voltammetry. Fucus vesiculosus germlings were found to exude Cu‐complexing ligands with conditional stability constants of the order of 1.6 × 1011. Ligand concentrations increased with increasing total dissolved Cu concentrations (CuT) until a concentration of 500–800 neq Cu·L−1 was reached. Concentrations of the ligand exceeded CuT in treatments containing 20 and 100 nM Cu, were similar to CuT in the 500‐nM Cu treatment, but were less than CuT in the 1000‐nM treatment. Therefore, [Cu2+] were calculated to be at concentrations of 10−11− 10−10 M in the 20‐ and 100‐nM treatments, 10−9 M in the 500‐nM treatment, and 10−7 M in the 1000‐nM treatment. Growth rates were lowest at Cu2+ concentration > 10−9. These results are discussed within the context of the potential roles for exuded copper‐complexing ligands.

Spatial and temporal variations in the copper and zinc concentrations of two green seaweeds from Otago Harbour, New Zealand.

Copper and zinc concentrations of the cosmopolitan green seaweeds Enteromorpha intestinalis and Ulva lactuca were obtained for the first time from various sites within Otago Harbour, southern New Zealand. Spatial variation in the concentrations of both metals was found, with increasing levels at stations in the upper harbour basin. While temporal fluctuations were apparent, a significant seasonal trend was evident only for zinc in U. lactuca; concentrations varied from approximately 10 μg g−1 dry weight in winter to 2 μg g−1 in summer. Over four consecutive years of sampling there was little change in metal concentrations of either species. Concentrations of both metals were invariably higher in E. intestinalis than U. lactuca, at all sampling stations and at all sampling times. These results are compared with those from other studies employing the same two green seaweed genera and are discussed in the context of the value of seaweeds as biomonitors of trace metal pollution. The levels of copper and zinc recorded in both species indicate that Otago Harbour is relatively free of trace metal contamination. This conclusion concurs with that reached in previous studies of dissolved copper and zinc concentrations in the surface waters of the harbour.

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.

Ultraviolet radiation and cyanobacteria.

Cyanobacteria are the dominant photosynthetic prokaryotes from an ecological, economical, or evolutionary perspective, and depend on solar energy to conduct their normal life processes. However, the marked increase in solar ultraviolet radiation (UVR) caused by the continuous depletion of the stratospheric ozone shield has fueled serious concerns about the ecological consequences for all living organisms, including cyanobacteria. UV-B radiation can damage cellular DNA and several physiological and biochemical processes in cyanobacterial cells, either directly, through its interaction with certain biomolecules that absorb in the UV range, or indirectly, with the oxidative stress exerted by reactive oxygen species. However, cyanobacteria have a long history of survival on Earth, and they predate the existence of the present ozone shield. To withstand the detrimental effects of solar UVR, these prokaryotes have evolved several lines of defense and various tolerance mechanisms, including avoidance, antioxidant production, DNA repair, protein resynthesis, programmed cell death, and the synthesis of UV-absorbing/screening compounds, such as mycosporine-like amino acids (MAAs) and scytonemin. This study critically reviews the current information on the effects of UVR on several physiological and biochemical processes of cyanobacteria and the various tolerance mechanisms they have developed. Genomic insights into the biosynthesis of MAAs and scytonemin and recent advances in our understanding of the roles of exopolysaccharides and heat shock proteins in photoprotection are also discussed.