International Journal of Molecular Sciences / Subcellular sequestration and impact of heavy metals on the ultrastructure and physiology of the multicellular freshwater alga Desmidium swartzii

Due to modern life with increasing traffic, industrial production and agricultural practices, high amounts of heavy metals enter ecosystems and pollute soil and water. As a result, metals can be accumulated in plants and particularly in algae inhabiting peat bogs of low pH and high air humidity. In the present study, we investigated the impact and intracellular targets of aluminum, copper, cadmium, chromium VI and zinc on the filamentous green alga Desmidium swartzii, which is an important biomass producer in acid peat bogs. By means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) it is shown that all metals examined are taken up into Desmidium readily, where they are sequestered in cell walls and/or intracellular compartments. They cause effects on cell ultrastructure to different degrees and additionally disturb photosynthetic activity and biomass production. Our study shows a clear correlation between toxicity of a metal and the ability of the algae to compartmentalize it intracellularly. Cadmium and chromium, which are not compartmentalized, exert the most toxic effects. In addition, this study shows that the filamentous alga Desmidium reacts more sensitively to aluminum and zinc when compared to its unicellular relative Micrasterias, indicating a severe threat to the ecosystem.(VLID)156767

A novel blue fluorescent chlorophyll catabolite accumulates in senescent leaves of the peace lily and indicates a split path of chlorophyll breakdown

AbstractColorless, non-fluorescent Chl-catabolites (NCCs) are the typical, ubiquitous products of chlorophyll (Chl)-breakdown in senescent leaves. However, a fluorescent Chl-catabolite (FCC) accumulated in de-greened leaves of Spathiphyllum wallisii (Peace Lily), which showed a weak blue luminescence. The FCC, named Sw-FCC-62, was ‘hypermodified’ with an unprecedented 6-(2-[3,4-dihydroxy-phenyl]-ethyl)-β-glucopyranosidyl ester at the propionyl group. Such esters stabilize FCCs against their typical and rapid, spontaneous isomerization to NCCs. Chl-breakdown in Sp. wallisii thus branches off from the ‘common’ path in leaves, and furnishes unique and ‘persistent’ FCCs. Our findings on ‘hypermodified’ FCCs also call for attention as to possible physiological roles of Chl-catabolites in plants

Hyposaline conditions affect UV susceptibility in the Arctic kelp Alaria esculenta (Phaeophyceae) - results of laboratory experiments at Kongsfjorden, June/July 2014

The kelp Alaria esculenta represents a key species in high Arctic marine fjord ecosystems. However, the European Arctic is currently experiencing extensive environmental change. Glacial fjord systems, such as Kongsfjorden (Spitsbergen, Svalbard), are subjected to rising temperature, increased freshwater inflow from glaciers and melting snow and a changing ultraviolet (UV) radiation regime related to stratospheric ozone depletion. Thus, in addition to natural seasonality, sessile organisms require acclimation in order to adapt to an environment in transition. We examined the physiological and ultrastructural responses of A. esculenta to the combined exposure to hyposalinity and UV radiation. Photosynthetic quantum yield slightly decreased during a low-salinity treatment of 7 d. Exposure to UV radiation also lowered quantum yield, but specimens previously treated with hyposalinity were significantly less susceptible to UV than nontreated individuals. Concomitant with a loss of chlorophyll during the hyposaline treatment, phlorotannin and antioxidant contents were maintained, and samples treated with low salinities exhibited higher UV-screening characteristics as demonstrated by significantly higher absorption ratios at 300/680 nm. Ultrastructural analyses revealed a treatment-dependent swelling of cell walls and accumulations of phlorotannin-containing vesicles. Our findings point to a strategy by which kelps apply a fast and cost-efficient redistribution of phlorotannins rather than increased synthesis as a general stress response to different environmental drivers in contrast to stress-specific responses. The notion that acclimation to one stressor (low salinity) reflects increased tolerance towards a second stressor (UV radiation) supports the concept of 'cross-acclimation' as established for higher plants but not yet for seaweeds

Sample characteristics and pigment concentration of arctic snow and permafrost algal strains

Ten algal strains from snow and permafrost substrates were tested for their ability to produce secondary carotenoids and a-tocopherol in response to high light and decreased nitrogen levels. The Culture Collection of Cryophilic Algae at Fraunhofer IBMT in Potsdam served as the bioresource for this study. Eight of the strains belong to the Chlorophyceae and two strains are affiliated to the Trebouxiophyceae. While under low light, all 10 strains produced the normal spectrum of primary pigments known to be present in Chlorophyta, only the eight chlorophyceaen strains were able to synthesize secondary carotenoids under stress conditions, namely canthaxanthin, echinenone and astaxanthin; seven of them were also able to synthesize minor amounts of adonixanthin and an unidentified hydroxyechinenone. The two trebouxiophyceaen species of Raphidonema exhibited an unusually high pool of primary xanthophyll cycle pigments, possibly serving as a buffering reservoir against excessive irradiation. They also proved to be good alpha-tocopherol producers, which might also support the deactivation of reactive oxygen species. This study showed that some strains might be interesting novel candidates for biotechnological applications. Cold-adapted, snow and permafrost algae might serve as valuable production strains still exhibiting acceptable growth rates during the cold season in temperate regions

Rescue of heavy metal effects on cell physiology of the algal model system Micrasterias by divalent ions

AbstractRecent studies have shown that metals such as copper, zinc, aluminum, cadmium, chromium, iron and lead cause severe dose-dependent disturbances in growth, morphogenesis, photosynthetic and respiratory activity as well as on ultrastructure and function of organelles in the algal model system Micrasterias denticulata (Volland et al., 2011, 2012; Andosch et al., 2012). In the present investigation we focus on amelioration of these adverse effects of cadmium, chromium and lead by supplying the cells with different antioxidants and essential micronutrients to obtain insight into metal uptake mechanisms and subcellular metal targets. This seems particularly interesting as Micrasterias is adapted to extremely low-concentrated, oligotrophic conditions in its natural bog environment.The divalent ions of iron, zinc and calcium were able to diminish the effects of the metals cadmium, chromium and lead on Micrasterias. Iron showed most ameliorating effects on cadmium and chromium in short- and long-term treatments and improved cell morphogenesis, ultrastructure, cell division rates and photosynthesis. Analytical transmission electron microscopic (TEM) methods (electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI)) revealed that chromium uptake was decreased when Micrasterias cells were pre-treated with iron, which resulted in no longer detectable intracellular chromium accumulations. Zinc rescued the detrimental effects of chromium on net-photosynthesis, respiration rates and electron transport in PS II. Calcium and gadolinium were able to almost completely compensate the inhibiting effects of lead and cadmium on cell morphogenesis after mitosis, respectively. These results indicate that cadmium is taken up by calcium and iron transporters, whereas chromium appears to enter the algae cells via iron and zinc carriers. It was shown that lead is not taken up into Micrasterias at all but exerts its adverse effects on cell growth by substituting cell wall bound calcium. The antioxidants salicylic acid, ascorbic acid and glutathione were not able to ameliorate any of the investigated metal effects on the green alga Micrasterias when added to the culture medium

Physiological, biochemical and ultrastructural responses of the green macroalga Urospora penicilliformis from Arctic Spitsbergen to UV radiation

Exposure of the filamentous turf green alga Urospora penicilliformis to ambient and artificial ultraviolet radiation (UVR) revealed a considerable resilient species. This explains the ability of this alga to thrive in the middleupper intertidal zones of the Arctic sea where it is periodically exposed to environmental extremes. A transient UVR effect on photosynthesis under photosynthetically active radiation (PAR) + UV-A and PAR + UV-A + UV-B was found, but dynamic recovery of photoinhibition was observed immediately after reduction of the photon fluence rate of PAR in the absence or presence of background UVR under laboratory and natural solar radiation, respectively. Chlorophylls, carotenoids, and xanthophyll cycle pigments (violaxanthin, antheraxanthin, and zeaxanthin) concentrations were not significantly different between freshly collected samples and filaments exposed to additional laboratory radiation treatment. The ultrastructure of the U. penicilliformis gametophytes showed that the cells are well adapted to UVR. No significant ultrastructural alterations were observed in filaments exposed to different spectral irradiance in the laboratory compared to in situ acclimated specimen. The antioxidant α-tocopherol was detected in minute quantity while the search for flavonoid-like compounds was negative. Other UV screening strategies or certain genetically fixed physiological protective mechanism could be operating in this species responsible for their occurrence in higher shoreline and ecological success. Further molecular and biochemical studies are needed to elucidate the stress resistance in this turf alga. There is an indication that the extremely thick cell wall of U. penicilliformis gametophytes covered with mucilage sheath and dense layer of mineral depositions may provide a shield against unfavorable environmental conditions in general and against UVR in particular