Az Eszterházy Károly Tanárképző Főiskola Tudományos Közleményei. 2004. Sectio Biologiae. (Acta Academiae Paedagogicae Agriensis : Nova series ; Tom. 25)

Tuba, Z., Takács, Z., Juhász, A. and Lichtenthaler, H. K.: Pentose-phosphate pathway as the possible background of resaturation respiration in the desiccation-tolerant lichen Cladonia convoluta

Pentose-Phosphate Pathxay as the Possible Background. 155 replications with a ADC LCA2 (Hoddesdon, UK) infrared gas analyser in the first 30 minutes after rewetting. Results and Discussion The basic respiration rate of the continuously wet lichen C. convoluta was 2.6±0.29. However, the resaturation respiration rateof the wetted lichen was three times higher (Fig. 1.). The high intensity rehydration ('resaturation') respiration was terminated within 30 minutes and during the remaining 90 min of the experiment the respiration declined to a steady level (data not shown). Treatment with bromoxynil, an uncoupler of oxidative phosphorylation, increased this already high C0

2 emission by 66% indicating that the extraordinarily massive C0

2 efflux does not come entirely from the mitochondria, which has lost adenylate control due to uncoupled inner membranes. Nitrogen exposure (anaerobic conditions) and KCN treatment resulted in a surprising coincidence. They both decreased C0

2 emission rate by 30% in the lichen. This fact suggests that there is a component, which is non-sensitive to both cyanide and also oxygen deprivation. The only biochemical process, which can produce a significant amount of C0

2 in not senescing plant cells under anaerobic conditions, is the pentose-phosphate pathway. This pathway can play an essential part in the restoration of the plant's redox status by producing NADPH (Kranner & Grill, 1994). This observation also infers that the alternative mitochondrial pathway is not engaged after rehydration of the desiccated tissues, because C0

2 emission was not decreased more by the lacking of 0

2 than by cyanide, which clogs cytochrome pathway selectively. Due to the Bahr-Bonner model (Lambers, 1982), which considers the alternative oxidative pathway as an overflow, operating the alternative pathway would not make too much sense in desiccation tolerant plants spending its resources for recovery from the desiccated stage. Based on the above findings we would like to emphasise that the preponderance of resaturation respiration of the desiccated lichen thalli probably originates from the pentose-phosphate pathway. Acknowledgements The support to Zoltán Tuba by a DAAD (Bonn) professorial fellowship and a NATO senior fellowship at Botanical Institute II of the Karlsruhe University is gratefully acknowledged.