The effect of heat on photosynthesis, dark respiration and cellular ultrastructure of the arctic-alpine psychrophyte Ranunculus glacialis |
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Institution: | (1) Institut für Botanik, Universit?t Innsbruck, Sternwartestraβe 15, A-6020, Innsbruck, Austria;(2) GSF Forschungszentrum für Umwelt und Gesundheit, Expositionskammern, Ingolst?dter Landstra?e 1, D-85764, Neuherberg, Germany |
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Abstract: | Effects of high temperatures on the leaves of Ranunculus glacialis were studied in plants taken from sites located between
2400-2550 m in the Central Alps. Changes in CO2 exchange rates, in vivo chlorophyll fluorescence, and cellular ultrastructure
were investigated during and after an experimental heat exposure. The earliest heat stress effect was inactivation of the
net photosynthetic rate at 38-39 °C. Between 40-42 °C, disorders appeared in the photosynthetic apparatus and in the tonoplast.
Heat shock granules were observed at 42 °C in chloroplasts, and at 44 °C also in mitochondria. In this temperature range,
the dark respiration rate was reversibly enhanced, and an increased number of polyribosomes indicated repair after the primary
injury. Above 44 °C, the degradation progress entered the phase of chronic impairment leading to irreversible damage at 45-46
°C. An unusually wide temperature range from the start of reversible photosynthetic inhibition to incipient necrosis indicated
a pronounced heat sensitivity, particularly in cellular functions, of this arctic-alpine species.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | CO2 exchange chlorophyll fluorescence in vivo chloroplasts heat shock granules stress criteria thermosensitivity |
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