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Temperature sensing and cold acclimation.

Abstract

The fundamental question in cold acclimation is how do plants perceive the low but nonfreezing temperatures that activate cold acclimation responses. New findings in the past year suggest that changes in membrane fluidity, cytoskeleton rearrangement, and calcium influxes are among the earliest events taking place in plants upon exposure to low nonfreezing temperatures. In the cyanobacterium Synechocystis PCC6803, temperature change is detected by at least two separate sensors. One of these measures membrane fluidity using a classical two-component system involving histidine kinases and a response regulator in a His-to-Asp phosphorelay. Although these Synechocystis results may not be directly relevant to cold acclimation, they can guide our thinking as we search for biological thermometers in higher plants.

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J Browse, Z Xin. 2001. Temperature sensing and cold acclimation.. https://doi.org/10.1016/s1369-5266(00)00167-9

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Cold acclimation induces proliferation of sarcoplasmic reticulum without increase in Ca2+-ATPase activity in white axial muscle of striped bass (Morone saxatilis).

The effects of acclimation of striped bass to cold (5 degrees C) and warm (25 degrees C) temperatures upon ultrastructural features of white axial skeletal muscle are quantified. Surface density of sarcoplasmic reticulum (SR) increased by almost 30%, and SR volume density increased by about 20% during cold acclimation. Proliferation of SR suggests an increase in available SR surface for re-sequestration of Ca2+ and a decrease in diffusion path length for Ca2+ during cold acclimation. Average cross-sectional areas and cross-sectional perimeters of myofibrils situated in the center of muscle fibers decreased during cold acclimation by approximately 20% and 11%, respectively. Additionally, average major and minor axes of ellipses fit to central myofibrillar cross-sections decreased by approximately 12% and 8%, respectively, during cold acclimation. These measurements define a decrease in average myofibrillar diameter and suggest a decrease in diffusion path length for Ca2+ to and from myofibrillar activation sites. Measurements of peripheral myofibrils that had elongated profiles in cross-sections indicate that maximum profile length of these myofibrils decreases by about 17%. Peripheral myofibrils may break up into smaller myofibrils with more rounded cross-sectional profiles during cold acclimation. SR Ca2+-ATPase of white axial muscle was also measured in unfractionated homogenates and in crude SR-enriched subcellular fractions from cold- and warm-acclimated striped bass. No difference in SR Ca2+-ATPase activity per g wet weight was observed between cold- and warm-acclimated animals. Lack of increase in SR Ca2+-ATPase per g wet weight, despite a significant proliferation of SR, probably results in a decrease in average Ca2+-ATPase pump density within the SR membrane during cold acclimation. Thus, compensation for decreased diffusion coefficient of Ca2+ during cold acclimation appears due to the combined effects of proliferation of SR surface density and a decrease in average myofibrillar diameter.

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HtpG plays a role in cold acclimation in cyanobacteria.

Abstracts. The heat shock protein HtpG is homologous to members of the Hsp90 protein family of eukaryotes and is essential for basal and acquired thermotolerances in cyanobacteria. In this study we have examined the role of HtpG in the cyanobacterium, Synechococcus sp. PCC 7942, in the acclimation to low temperatures. The inactivation of the htpG gene resulted in severe inhibition of cell growth and of the photosynthetic activity when the htpG mutant was shifted to 16 degrees C from 30 degrees C. Wild-type cells were able to resume growth without a lag period when shifted to 30 degrees C after 5 days at 16 degrees C, while the mutant displayed a detectable lag. The HtpG protein was induced in the wild-type cells at 16 degrees C. Electrophoresis in the absence of sodium dodecyl sulfate (SDS) showed that a novel, high-molecular-weight complex containing GroEL and DnaK accumulated at 16 degrees C, but the accumulation was strongly inhibited in the htpG mutant. Our results demonstrate that the HtpG protein contributes significantly to the ability of cyanobacteria to acclimate to low temperatures.

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