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A new light microscope–temperature-controlled chamber (LM–TCC) has been constructed. The special feature of the light microscope–temperature-controlled chamber is the Peltier-element temperature control of a specimen holder for biological samples, with a volume capacity of 1 mL. This system has marked advantages when compared to other approaches for temperature-controlled microscopy. It works in a temperature range of −10°C to +95°C with an accuracy of ±0.1°C in the stationary phase. The light microscope–temperature-controlled chamber allows rapid temperature shift rates. A maximum heating rate of 12.9°C min−1 and a maximum cooling rate of 6.0°C min−1 are achieved with minimized overshoots (≤1.9°C). This machinery operates at low cost and external coolants are not required. Especially with samples absorbing irradiation strongly, temperature control during microscopy is necessary to avoid overheating of samples. For example, leaf segments of Ficaria verna exposed to 4500 μmol photons m−2 s−1 in a standard microscopic preparation show a temperature increase (δT) of 18.0°C, whereas in the light microscope–temperature-controlled chamber this is reduced to 4°C. The kinetics of microscope-light induced δT are described and infrared thermography demonstrates the dissipation of the temperature. Chloroplasts of the cold adapted plant Ranunculus glacialis show the tendency to form stroma-filled protrusions in relation to the exposure temperature. The relative number of chloroplasts with protrusions is reduced at 5°C when compared to 25°C. This effect is reversible. The new light microscope–temperature-controlled chamber will be useful in a wide range of biological applications where a rapid change of temperature during microscopic observations is necessary or has to be avoided allowing a simulation of ecologically relevant temperature scenarios. [ABSTRACT FROM AUTHOR]

Aeroterrestrial green algae are exposed to desiccation in their natural habitat, but their actual volume changes have not been investigated. Here, we measure the relative volume reduction (RVRED) in Klebsormidium crenulatum and Zygnema sp. under different preset relative air humidities (RH). A new chamber allows monitoring RH during light microscopic observation of the desiccation process. The RHs were set in the range of ∼4 % to ∼95% in 10 steps. RVRED caused by the desiccation process was determined after full acclimation to the respective RHs. In K. crenulatum, RVRED (mean ± SE) was 46.4 ± 1.9%, in Zygnema sp. RVRED was only 34.3 ± 2.4% at the highest RH (∼95%) tested. This indicates a more pronounced water loss at higher RHs in K. crenulatum versus Zygnema sp. By contrast, at the lowest RH (∼4%) tested, RVRED ranged from 75.9 ± 2.7% in K. crenulatum to 83.9 ± 2.2% in Zygnema sp. The final volume reduction is therefore more drastic in Zygnema sp. These data contribute to our understanding of the desiccation process in streptophytic green algae, which are considered the closest ancestors of land plants. [ABSTRACT FROM AUTHOR]

ABSTRACTThe significance of leaf rosette closure for survival of drought and heat under high irradiation on alpine rock sites was investigated in the cushion forming rosette plant, Saxifraga paniculata Mill. With decreasing water content the leaves fold over the rosette centre reducing reversibly the evaporative leaf surface area by 80%. Internal water redistribution driven by an osmotic gradient from older to younger leaves occurs. The oldest leaves dry out to promote the survival of the individual. Leaf temperatures above 45 °C (which match heat tolerance limits 45–57 °C; LT50) co-occurred with low substrate water potentials (less than – 0·5 MPa) on 11·3% of summer days. Shading by leaves can be crucial to surviving high temperatures as it keeps the rosette centre up to 10 °C colder. Mutual shading prevented sustained drought-induced photoinhibition in upper leaf surfaces at relative water contents below 60%. In exposed lower leaf surfaces restoration of photosystem II took several days. Leaf temperatures above 40 °C (21·3% of summer days) induced photoinhibition in situ. Periods with sufficient water supply can be fully utilized as rehydration is fast (< 12 h) and exposes the upper leaf surfaces that showed only minor photoinhibition. By reversible leaf rosette closure environmental extremes that otherwise could exceed tolerance are efficiently avoided. [ABSTRACT FROM AUTHOR]