Structure and function of biological soil crusts from Antarctica with a special respect to their microtopography and UV-B sensitivity

Although an extensive professional literature exists on biological soil crusts (BSCs), especially on the species composition of hetero- and autotrophs forming the micro-biological comunity, micromorphological information on BSCs is extremely scarce. In our study, we focused on microstructure of the BSCs from the James Ross Island (Antarctica). We combined the approach of digital microscopy to study surface roughness of the BSCs with taxonomy of BSC-forming autotrophs and chlorophyll fluorescence study focused on the photosynthetic functioning of BSCs when exposed to controlled UV-B stress. Microprofiling of BSCs resulted in the finding that the examined BSCs might be classified as fine-grained surface with roughness characteristics: Ra (37.9 μm) and Rz (136.9 μm). The BSCs were rich in microautotrophs, both algae and cyanobacteria, however, Microcoleus sp. was found dominating species. It formed multifilament ropes on and inside the BSCs. Under UV-B stress, Microcoleus- and Nostoc-dominated BSC parts showed similar sensitivity and acclimatory response so long-term UV-B treatment, however, Microcoleus seemed to be slightly more sensitive to UV-B. Microcoleus-dominated parts of BSCs showed less pronounced acclimation to UV-B treatment than Nostoc-dominated parts. It was reflected in lower values of maximum (FV/FM) and effective (FPSII) quantum yields recorded after 6 d exposition.

Integration between ROS Regulatory Systems and Other Signals in the Regulation of Various Types of Heat Responses in Plants

Because of their sessile lifestyle, plants cannot escape from heat stress and are forced to alter their cellular state to prevent damage. Plants, therefore, evolved complex mechanisms to adapt to irregular increases in temperature in the natural environment. In addition to the ability to adapt to an abrupt increase in temperature, plants possess strategies to reprogram their cellular state during pre-exposure to sublethal heat stress so that they are able to survive under subsequent severe heat stress. Such an acclimatory response to heat, i.e., acquired thermotolerance, might depend on the maintenance of heat memory and propagation of long-distance signaling. In addition, plants are able to tailor their specific cellular state to adapt to heat stress combined with other abiotic stresses. Many studies revealed significant roles of reactive oxygen species (ROS) regulatory systems in the regulation of these various heat responses in plants. However, the mode of coordination between ROS regulatory systems and other pathways is still largely unknown. In this review, we address how ROS regulatory systems are integrated with other signaling networks to control various types of heat responses in plants. In addition, differences and similarities in heat response signals between different growth stages are also addressed.

Rapid cold-hardening of Drosophila melanogaster (Diptera: Drosophiladae) during ecologically based thermoperiodic cycles

In contrast to most studies of rapid cold-hardening, in which abrupt transfers to low temperatures are used to induce an acclimatory response, the primary objectives of this study were to determine (i) whether rapid cold-hardening was induced during the cooling phase of an ecologically based thermoperiod, (ii) whether the protection afforded was lost during warming or contributed to increased cold-tolerance during subsequent cycles and (iii) whether the major thermally inducible stress protein (Hsp70) or carbohydrate cryoprotectants contributed to the protection afforded by rapid cold-hardening. During the cooling phase of a single ecologically based thermoperiod, the tolerance of Drosophila melanogaster to 1 h at −7 degrees C increased from 5 +/− 5% survival to 62.5 +/− 7.3% (means +/− S.E.M., N=40-60), while their critical thermal minima (CTmin) decreased by 1.9 degrees C. Cold hardiness increased with the number of thermoperiods to which flies were exposed; i.e. flies exposed to six thermoperiods were more cold-tolerant than those exposed to two. Endogenous levels of Hsp70 and carbohydrate cryoprotectants were unchanged in rapidly cold-hardened adults compared with controls held at a constant 23 degrees C. In nature, rapid cold-hardening probably affords subtle benefits during short-term cooling, such as allowing D. melanogaster to remain active at lower temperatures than they otherwise could.

Variations in the stomatal density of salix herbacea L. under the changing atmospheric CO 2 concentrations of late- and post-glacial time

The rapidly rising CO 2 concentration of the past 200 years has been shown to be accompanied by a fall in stomatal density in the leaves of temperate trees. The present study attempts to investigate the relationship of atmospheric CO 2 change and stomatal density in the arctic-alpine shrub, Salix herbacea , over the longer time span of 11 500 years offered by fossil leaves from post-glacial deposits. Comparisons of fossil material from Scotland and Norway are made with leaves from living populations growing in Austria, Greenland and Scotland. The Austrian material, from an altitudinal gradient between 2000 and 2670 m above sea level, gives added comparison of contemporary differences of CO 2 partial pressure with altitude. The results of our investigation indicate, rather surprisingly, that the rising CO 2 concentration of the past 11 500 years has been accompanied by an increase in the stomatal density of S. herbacea in contrast to the shorter-term observations on the herbarium material of temperate trees. The most likely explanation appears to centre on the temperatures and water availability of the early postglacial environment overriding the effect of the lower CO 2 regime. However, the scale of the time interval involved may also be significant. Natural selection over the 11 500 year period concerned may have favoured a different response to what is, in effect, an acclimatory response observed in trees within the period of rapid CO 2 rise of the past 200 years.

Hypoxic Acclimation in the Lamprey, Lampetra Fluviatilis: Organismic and Erythrocytic Responses

Acute exposure of Lampetra fluviatilis to hypoxia (PO2 = 40–50 mmHg) resulted in a large increase in ventilation frequency and a significant increase in O2 consumption (from 40 to 60 mg kg−1h−1 at 8°C). After 1 week's hypoxia, the O2 consumption decreased (from 60 to 50 mg kg−1 h−1), indicating the existence of slow, acclimatory changes that remove some of the strain from the ventilatory response. The hypoxic animals had a higher blood O2 affinity than the normoxic controls. This acclimatory response is not the result of a decreased allosteric interaction between the haemoglobin and erythrocytic organic phosphates, as in teleost fish, but is attributable partly to dilution of haemoglobin within the red cells and partly to an increase in the intracellular pH. The intraerythrocytic pH of hypoxic animals, measured with a freeze-thaw method, was higher than the plasma pH, suggesting that protons are not passively distributed.