Heat stress and the photosynthetic electron transport chain of the lichen <Emphasis Type="Italic">Parmelina tiliacea</Emphasis> (Hoffm.) Ach. in the dry and the wet state: differences and similarities with the heat stress response of higher plants |
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Authors: | Email author" target="_blank">Abdallah?OukarroumEmail author Reto?J?Strasser Gert?Schansker |
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Institution: | 1.Laboratories of Bioenergetics and Microbiology, Department of Botany and Plant Biology,University of Geneva,Jussy, Geneva,Switzerland;2.Department of Chemistry and Biochemistry,University of Quebec in Montreal,Montreal,Canada;3.Institute of Plant Biology,Biological Research Center of the Hungarian Academy of Sciences,Szeged,Hungary |
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Abstract: | Thalli of the foliose lichen species Parmelina tiliacea were studied to determine responses of the photosynthetic apparatus to high temperatures in the dry and wet state. The speed
with which dry thalli were activated by water following a 24 h exposure at different temperatures decreased as the temperature
was increased. But even following a 24 h exposure to 50°C the fluorescence induction kinetics OJIP reflecting the reduction
kinetics of the photosynthetic electron transport chain had completely recovered within 128 min. Exposure of dry thalli to
50°C for 24 h did not induce a K-peak in the fluorescence rise suggesting that the oxygen evolving complex had remained intact.
This contrasted strongly with wet thalli were submergence for 40 s in water of 45°C inactivated most of the photosystem II
reaction centres. In wet thalli, following the destruction of the Mn-cluster, the donation rate to photosystem II by alternative
donors (e.g. ascorbate) was lower than in higher plants. This is associated with the near absence of a secondary rise peak
(~1 s) normally observed in higher plants. Analysing the 820 nm and prompt fluorescence transients suggested that the M-peak
(occurs around 2–5 s) in heat-treated wet lichen thalli is related to cyclic electron transport around photosystem I. Normally,
heat stress in lichen thalli leads to desiccation and as consequence lichens may lack the heat-stress-tolerance-increasing
mechanisms observed in higher plants. Wet lichen thalli may, therefore, represent an attractive reference system for the evaluation
of processes related with heat stress in higher plants. |
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