Detection of photochemical processes in Antarctic lichen <i>Xanthoria elegans</i> using chlorophyll fluorescence imaging.
| Authors | |
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| Year of publication | 2004 |
| Type | Article in Proceedings |
| Conference | Book of Abstracts. Xth Days of Plant Physiology. |
| MU Faculty or unit | |
| Citation | |
| Field | Botany |
| Keywords | photosynthesis; dehydration; Antarctica; lichen; physiological activity |
| Description | Introduction: Within last two decades, chlorophyll fluorescence imaging has met increasing number of applications in photosynthesis research. Using the technique, heterogeneity of photochemical processes of photosynthesis might be visualized at various levels ranging from a single cell to a plant community. In lichens, the technique has been used several times in anatomic[1] and photosynthetic studies made under controlled laboratory conditions[2]. In the presented study, we used the technique in the field in order to quantify photosynthetic processes in an epilithic crustose lichen species (Xanthoria elegans) as dependent on daily courses of in situ temperature, water availability and resulting hydration/dehydration of lichen thallus. Material and Methods: Heterogeneity of several photosynthetic chlorophyll (Chl) fluorescence parameters was measured on thalli of X. elegans attached to stone surfaces. Study plot was located at permanently deglaciated coastal areas of Galindez Island (64 W, 65 S, maritime Antarctica) in the vicinity of Ukrainian antarctic station Vernadsky (former Faraday). In March 2004, potential yield of photochemical reactions in photosystem II (Fv/Fm) and quantum yield of photosystem II (FII) were measured using a portable fluorometer HFC-010 (Photon Systems Instruments, Czech Republic) equipped with a CCD camera and image analysis system. The set up allowed to record 512 x 512 pixel grey scale images of X. elegans thalli with maximum recording rate of 20 ms. To visualize time courses of Chl fluorescence parameters, the grey scale images were converted to false colour images. The images of Fv/Fm and FII distribution over a thallus were taken repeatedly during a daytime and analyzed in relation to daily courses of temperature and thallus hydration. Aditionally, photosynthetic gas exchange and water potential measurements of thalli were made using a portable IR gas analyzer EGM-3 (PP Sytems, United Kingdom) and water potential meter WP4-T (Decagon, USA). Results and discussion: Field measurements revealed that hydration status of thallus is main limiting factor of photosynthetic processes in X. elegans. Maximum daily values of Fv/Fm and FII were found after rainfall and/or snowfall episodes when thalli reached optimum hydration. With ongoing desiccation of thalli caused by above-zero thallus temperature and wind velocity, gradual decrease of Fv/Fm and FII was recorded. Dehydration-dependent reduction and loss of photosynthetic activity was related to thallus age and structure. Intrathalline differences of Fv/Fm and FII in drying thallus caused heterogeneity of photosynthetic processes within a single thallus. Critical water potential for primary photosynthetic processes was about -30 MPa. Chl fluorescence imaging and water potential measurements documented that X. elegans is capable to maintain some detectable photosynthetic activity even at extremely low water potential of its thallus. This gives the species an advantage to prolong positive carbon balance during periods with suboptimal hydration. |
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