RELATION OF QUANTUM YIELD OF PHOTOSYSTEM II TO OXYGEN EVOLUTION RATE IN A LICHEN PHOTOBIONT TREBOUXIA ERICI
| Authors | |
|---|---|
| Year of publication | 2004 |
| Type | Article in Proceedings |
| Conference | Acta Physiologiae Plantarum |
| MU Faculty or unit | |
| Citation | |
| Web | http://psjc.icm.edu.pl |
| Field | Botany |
| Keywords | quantum yield; oxygen evolution; osmotic stress; lichen photobiont; Trebouxia |
| Description | Introduction: Lichen photosynthesis has been studied on a thalus level quite frequently (e.g. Kappen et al., 1998). Detailed photosynthetic studies on photobiont per se are not frequent. In the study the relation between oxygen evolution rate (OER) and quantum yield of photochemical reactions in photosystem II (ÖII) was examined in lichen symbiotic alga Trebouxia erici (axenic culture) exposed to different levels of photosynthetically active radiation (PAR) affected by osmotic dehydration. Material and Methods: Stock cultures cultivated in Petri dishes on agar BBM3N medium were transferred into liquid BBM3N medium (Ahmadjian, 1993). Cultures acclimated to liquid medium for 5 days were used for a simultaneous measurement of ÖII and OER in stepwise increasing PAR (37, 66, 135, 270, and 500 ľmol m-2 s-1). For measurement, double-modulated fluorometer FL-200 (PSI, CZ) was used equipped with a cuvette with an in-built oxygen electrode OC 223-B (THETA, CZ) connected to an O2-meter OxyCorder 401 (PSI, CZ). The effect of osmotic dehydration on the OER/ÖII relationship was evaluated for Trebouxia erici cells exposed to 2,0 M sucrose (Ř = -7.4 MPa) at 24 C for 60 hours. Results and Conclusions: OER and ÖII curvilinearly increased (OER) and decreased (ÖII) throughout all used irradiances. Under osmotic stress both parameters were significantly reduced. OER showed its maximum (1,2 ľmol l-1 s-1) at about 130 ľmol m-2 s -1. In non-stressed (control) culture, the ÖII to OER relation was linear. In osmotically-stressed culture, however, the relation was curvilinear due to reduced OER values in the irradiance above 200 ľmol m-2 s-1. The relation of ÖII and OER in increasing irradiance denote linear dependency in control, however, in an osmotically-stressed variant, the relation represents curvilinear dependency. In conclusion, under osmotic stress, photochemical linear electron transport chain is less limited than biochemical photosynthetic reactions of Trebouxia erici. References: Ahmadjian V. 1993. The Lichen Symbiosis. John Wiley & Sons, Inc., New York ed., 264 pp. Kappen L, Schroeter B, Green TGA and Seppelt RD. 1998. Chlorophyll a Fluorescence and CO2 Exchange of Umbilicaria Aprina Under Extreme Light Stress in the Cold. Oecologia 113(3): 325-331. |
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