Photosynthetic fluorescence emission spectra measurement at the temperature of 77 K (-196°C) is an often-used technique in photosynthesis research. At low temperature, biochemical and physiological processes that modulate fluorescence are mostly abolished, and the fluorescence emission of both PSI and PSII become easily distinguishable. Here we briefly review the history of low-temperature chlorophyll fluorescence methods and the characteristics of the acquired emission spectra in oxygen-producing organisms. We discuss the contribution of different photosynthetic complexes and physiological processes to fluorescence emission at 77 K in cyanobacteria, green algae, heterokont algae, and plants. Furthermore, we describe practical aspects for obtaining and presenting 77 K fluorescence spectra., J. J. Lamb, G. Røkke, M. F. Hohmann-Marriott., and Obsahuje bibliografické odkazy
A practical four-point probe for measurement of electrical resistivity of thin layers at temperatures from 4.2 K to 300 K was designed and built. The probe is cooled by inserting in the neck of a commercial Dewar vessel. Uncertainties of measured resistivity and temperature are of about 5 % and less than 0.1 K, respectively. and Realizovali jsme praktickou čtyřbodovou sondu pro měření měrného odporu tenkých kovových vrstev při teplotách 4,2 K až 300 K. Sonda se prochlazuje zasunutím do hrdla komerční heliové Dewarovy nádoby. Požadovaná teplota vzorku se dosahuje kombinací polohy v hrdle a termostatování. Neurčitost měření měrného odporu činí přibližně 5 % při neurčitosti teploty vzorku maximálně 0,1 K. Sonda byla použita i k měření kritické teploty a strmosti přechodu do supravodivého stavu nízkoteplotních supravodičů.
Fruit of two almond, Prunus amygdalus Linnaeus, cultivars (Retsou and Truoito) containing diapausing larvae of Eurytoma amygdali Enderlein, were collected in early August from coastal areas in northern Greece. Some larvae were removed from the fruit and maintained singly in open plastic vials and others left in the fruit until the end of the low-temperature period. They were kept at a low temperature of 10°C from the beginning, or after 8 weeks at 20°C. The larvae were subsequently maintained at 20°C and whether they completed the two diapause stages was recorded for 60 more weeks. When the larvae in vials, were kept initially for 8 weeks at 20°C, most of those from Retsou and all of those Truoito almonds completed the first stage of diapause. Of the larvae in the fruits, most of those in Truoito but less than 50% of those in Retsou almonds completed the first stage of diapause after 8 weeks at 20°C. Larvae from different orchards and different almond cultivars differed in diapause intensity. When the larvae were kept at a low temperature of 10°C from the beginning for 4, 8 or 16 weeks and then at 20°C they completed the second diapause stage synchronously, but the time of completion was delayed, and depended on the duration of the low temperature treatment. In several cases the time to diapause completion was bimodally distributed and the relative size of peak depended on the duration of the early exposure to low temperature.
Chilocorus kuwanae Silvestri is an effective predator of Unaspis euonymi (Comstock), a scale insect harmful to spindle trees (Euonymus europeus L. and E. japonicus Thumb). The feeding behaviour was studied on wild adults, collected from spindle trees in the Botanic Garden of Perugia University, and fed on overwintering U. euonymi females. The insects were exposed to gradually changing constant temperatures (13°-->10°-->8°-->6°-->4°-->2°-->13°-->15°C) for a ten day period at each temperature. C. kuwanae adults preyed on the scale also at low temperatures. The number of scales eaten decreased with decreasing temperatures from the initial 13°C to 4°C, and at 2°C the trophic activity of C. kuwanae adults almost stopped although they made brief walks in the petri dishes. At all tested temperatures the ladybirds made holes in or lifted the scale cover and preyed on the female. Sometimes they lifted the scale cover , but did not prey on these U. euonymi females which were destined to die from cold. As the temperature dropped from 13°C to 4°C, the number of females eaten by ladybird males and females did not differ statistically. When the temperature was raised to 13°C and 15°C, the ladybirds resumed feeding. Large differences were recorded between sexes, with females showing a much higher feeding activity than males. Scale cover lifting was most frequent at the beginning of the experiment and then decreased with diminishing temperatures, although no significant difference was recorded among temperatures within the range from 10°C to 4°C. The threshold for trophic activity can be taken as 2°C since we noted that a few (12%) individuals on one day showed predatory activity. At 13°C and 15°C lifting activity rose again but remained at a lower level than at the initial exposure to 13°C. There was no significant difference in activity at 13 and 15°C upon raising the temperature. As for total number of U. euonymi damaged by C. kuwanae the trend in damage revealed the same pattern as for number of scales eaten. At the final exposure to 15°C, 60% of C. kuwanae females laid eggs. Our data demonstrate that C. kuwanae can reduce U. euonymi populations in a submediterranean environment even in winter when the range of temperatures is similar to that tested in this experiment.
In plants, hydrogen peroxide (H2O2) acts as a signalling molecule that facilitates various biochemical and physiological processes. H2O2 is a versatile molecule, involved in several cellular processes both under stress and stress-free conditions. In regulating plant metabolism under stress conditions, exogenous application of H2O2 also plays a pivotal role which is manifested in improved growth, photosynthetic capacity, and antioxidant protection. Abiotic stress is an inevitable environmental factor that extensively affects and reduces growth, quality, yield, and productivity of plants. Several signalling pathways involved in H2O2-mediated stress and defense responses have been extensively studied and there is ample scope of additional research that could further clarify the mechanism and modulating factors which regulate these pathways. An attempt has been made to dissect the role of H2O2 under low temperature stress and how it affects plant growth and development, photosynthetic capacity, regulation of antioxidant system, and signalling., T. A. Khan, M. Yusuf, Q. Fariduddin., and Obsahuje bibliografii
Abiotic and biotic factors determine success or failure of individual organisms, populations and species. The early life stages are often the most vulnerable to heavy mortality due to environmental conditions. The deer ked (Lipoptena cervi Linnaeus, 1758) is an invasive insect ectoparasite of cervids that spends an important period of the life cycle outside host as immobile pupa. During winter, dark-coloured pupae drop off the host onto the snow, where they are exposed to environmental temperature variation and predation as long as the new snowfall provides shelter against these mortality factors. The other possible option is to passively sink into the snow, which is aided by morphology of pupae. Here, we experimentally studied passive snow sinking capacity of pupae of L. cervi. We show that pupae have a notable passive snow sinking capacity, which is the most likely explained by pupal morphology enabling solar energy absorption and pupal weight. The present results can be used when planning future studies and when evaluating possible predation risk and overall survival of this invasive ectoparasite species in changing environmental conditions., Sirpa Kaunisto, Hannu Ylönen, Raine Kortet., and Obsahuje bibliografii
In this paper we present the effect of low temperatures on the size of the thermal lensin the active medium ofsolid-state lasers. Thermal effects are the main limiting factor of high-power laser systems. One possibility of minimizing thermal effects is the cooling of the active medium at cryogenic temperatures, which has a major impact on material properties - thermal conductivity, coefficient of thermal expansion and thermo-optic coefficient, which determine their nature. In addition to temperature, these parameters depend on the concentration of active ions. By measuring the optical power of the thermal lens we can determine the effect of the temperature of the crystal and the concentration of active ions to the magnitude of these parameters. In the article we compare experimentally dependence of the thermal lens on the temperature of active medium for crystals Yb: YAG and Yb new material: LuAG at low temperatures and the results are compared with a simple physical model. and V tomto článku je prezentován vliv nízkých teplot na velikost tepelné čočky v aktivním prostředí pevnolátkových laserů. Tepelné efekty jsou hlavním omezujícím faktorem vysokovýkonných laserových systémů. Jednou z možností jejich minimalizování je ochlazení aktivního prostředí na kryogenní teploty, což má zásadní vliv na materiálové parametry - tepelnou vodivost, koeficient teplotní roztažnosti a termooptický koeficient, které určují jejich povahu. Kromě teploty jsou tyto parametry závislé i na koncentraci aktivních iontů. Měřením optické mohutnosti tepelné čočky lze stanovit vliv teploty krystalu a koncentrace aktivních iontů na velikost těchto parametrů. V článku jsou experimentálně porovnány závislosti tepelné čočky na teplotě aktivního prostředí pro krystaly Yb:YAG a nový materiál Yb:LuAG při nízkých teplotách a výsledky jsou porovnány s jednoduchým fyzikálním modelem.