Over last decades, several studies have been focused on
short-term high light stress in lichens under laboratory conditions. Such studies reported a strong photoinhibition of photosynthesis accompanied by a partial photodestruction of PSII, involvement of photoprotective mechanisms, and resynthetic processes into gradual recovery. In our paper, we applied medium [800 μmol(photon) m-2 s-1] light stress to induce negative changes in PSII funcioning as well as pigment and glutathione (GSH) content in two Antarctic fruticose lichen species. Chlorophyll (Chl) fluorescence parameters, such as potential and effective quantum yield of photosynthetic processes and fast transients (OJIP) recorded during high light exposition and recovery, revealed that Usnea antarctica was less susceptible to photoinhibition than U. aurantiaco-atra. This might be supported by a more pronounced high light-induced reduction in Chl a and b contents in U. aurantiaco-atra compared with U. antarctica. In both experimental species, total GSH showed an initial increase during the first 30-40 min of high light treatment followed by a decrease (60 min) and an increase during dark recovery. Full GSH recovery, however, was not finished in U. aurantiaco-atra even after 5 h indicating lower capacity of photoprotective mechanisms in the species. OJIP curves showed high light-induced decrease in both species, however, the recovery of the OJIPs shape to pre-photoinhibitory values was faster and more apparent in U. antarctica than in U. aurantiaco-atra. The results are discussed in terms of sensitivity of the two species to photoinhibition and their photosynthetic performance in natural environment., K. Balarinová, M. Barták, J. Hazdrová, J. Hájek, J. Jílková., and Obsahuje bibliografii
Květnová schůzka členů Kosmologické sekce České astronomické společnosti se nesla ve slavnostním duchu. Důvodem byl avizovaný křest Gravitačního atlasu Antarktidy, významné vědecké monografie nakladatelství Springer Verlag autorů J. Klokočníka, J. Kosteleckého a A. Bezděka. Modrá posluchárna Matematického ústavu AV se tak stala svědkem znamenité akce, kde dobré šampaňské pocelovalo jednu z vynikajících současných vědeckých publikací. Okuste tedy, milí čtenáři, prostřednictvím Československého časopisu pro fyziku trošku z té slávy a milé nálady, která z fotografií našeho kolegy Františka Lomoze doslova dýchá. and Jana Žďárská.
Desiccation resistance of adult males and females of the midge, Belgica antarctica (Diptera: Chironomidae) was evaluated to determine how this short-lived stage maintains water balance in the dry Antarctic environment. Both sexes had slightly lower water content (≈60%) and a higher dehydration tolerance (>30% water loss) than most other insects. Water loss rates were high and increased rapidly at temperatures above 15°C, indicating that the adult midges are more hygric than many other polar terrestrial arthropods. Water gain was accomplished by free water uptake with minimal or no contribution from absorption of water vapor or metabolic water production. Parameters related to water balance did not differ among populations from different islands. Overall, the high water requirements of the adult midge appear to be a significant challenge and presumably dictate that the adult midges must emerge during the brief period when free water is readily available and seek protected microhabitats that facilitate water retention.
The possibility to study quantitatively the diet of the Antarctic shag Phalacrocorax bransfieldensis by the analysis of pellets, applying correction factors to compensate for the digestion and loss through the gastrointestinal tract of fish otoliths represented in pellets, was evaluated at two localities of the South Shetland Islands. For such purpose, the results from the analysis of 566 pellets (= regurgitated casts) collected at Harmony Point, and 296 at Duthoit Point, throughout the 1995/96 and 1996/97 breeding seasons, were corrected with the mentioned factors and the shag daily consumption rate was estimated. The estimations indicated that, except for Duthoit Point in 1996/97, the daily food intake increased from November to January (pre-laying to late-rearing) and slightly decreased in February when chicks start to fledge, thus reflecting the energy requirements at the nest. These estimations, in general, are in line with those previously obtained for other colonies and/or shag species by different methods, which suggests that after correction the use of pellets is an acceptable method to quantify the diet of the Antarctic Shag.
Cystacanths of Corynosoma pseudohamanni Zdzitowiecki, 1984 (Palaeacanthocephala: Polymorphidae) are redescribed on the basis of specimens recovered from three species of Antarctic notothenioid fish, Trematomus bernacchii Boulenger, Gobionotothen gibberifrons (Lönnberg) and Notothenia coriiceps Richardson, collected from the Prince Gustav Channel, Antarctica. The cystacanths' morphometry and their internal anatomy including trunk muscles were studied using light and scanning electron microscopy (SEM). The characteristic features of this species such as the length of proboscis and the number of hooks (i.e. 260 hooks arranged in 20 rows with 13 hooks each, including two basal hooks) were confirmed and the intraspecific variability was evaluated. Sexual dimorphism was manifested in the shape of the hindtrunk, and the distribution and extent of the somatic armature only. SEM observations of internal anatomy revealed the detailed organization of trunk musculature.
Ultrastructural and physiological effects of exposure to 1 ppm and 5 ppm of cadmium (Cd) on cultured cells of Koliella antarctica, a green microalga from Antarctica, were investigated. The amount of Cd in the alga rose with the increase of the metal concentration in the growth medium and most Cd remained outside the cells, bound to the components of the cell walls. The increase of Cd in the microalga was concomitant with the decrease of other elements, mainly calcium (Ca). Exposure to 1 ppm Cd slowed culture growth by inhibiting cell division and also caused the development of some misshapen cells with chloroplast showing disordered thylakoids. However, this concentration did not substantially affect the chlorophyll (Chl) content or photosystem (PS) activity. At 5 ppm, Cd cell growth suddenly stopped and some cells lysed. After a week of Cd contamination, the cells were enlarged and severely damaged. The chloroplasts showed great ultrastructural alterations and a reduced Chl content. Cd exposure negatively affected PSII, whose activity was almost completely lost after four days. and N. La Rocca ... [et al.].