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

154 Tuba, Z. et al. emission can be observed in the very first minutes after re-wetting, which is considered to be a physical process; i.e. water replaces C0

2 molecules absorbed on the cell walls (Brown et al., 1983). However, this wetting burst is followed for a few hours by a respiration which has been termed resaturation respiration and which has a higher intensity than that of constantly metabolically active lichens (Smith & Molesworth, 1973). This elevated respiration does not serve the replenishment of the ATP pool because the latter is already completed within 5-10 minutes after rewetting (Krochko et al., 1979). Gordy and Hendrix (1982) considered the resaturation respiration of mitochondrial origin because they could eliminate completely the 0

2 uptake during this phase with the simultaneous usage of cyanide and salicylhydroxamic acid. The increasing evidence of membrane destruction in desiccated lichens led to the conclusion that resaturation respiration is a result of the uncoupled inner mitochondrial membrane (Farrar & Smith, 1976). The initially high rehydration respiration rate is also occurring in the higher/flower desiccation-tolerant higher flowering plants, like in the monocot Xerophyta scabrida where it lasts up to 30 hours (Tuba et al., 1994). In the lichens and mosses the resaturation respiration lasts only from few minutes up to 5 h (e.g. Smith & Molesworth 1973; Bewley et al. 1978). In order to reveal the biochemical background of the resaturation respiration, we treated a highly desiccation tolerant cryptogamic species, the lichen Cladonia convoluta (see: Tuba et al., 1996) with uncouplers, with potassium cyanide (KCN) and bromoxynil (Kerr and Wain, 1964 and Hock et al., 1995) or we deprived them of oxygen by applying inert N

2 gas. Our aim was to identify the possible cause of the boosted C0

2 efflux during the rehydration of the desiccated C. convoluta lichen thallus. Materials and Methods The foliose green algae lichen thallus Cladonia convoluta (Lam.) P. Cout. were used in the experiment after being collected from a semi-desert sand grassland (Fekete at al., 1997) near Fülöpháza (Hungary, Great Plain). The samples were cleaned by rinsing in deionized water and placed on wet filter paper. The upper green part of the moss and the separated healthy lobes of lichen thallus were used. Prior to desiccation plants spent 24 hours in a metabolically active state (20 °C, 100% Rh, 200 jiM m"

2 sec 1 PhAR for 14 hours). Slow desiccation was carried out on the next day when Rh was lowered to 70%. For rehydration deionized water (control, N

2-treatment), 10" 3 M KCN, and 10~

3 M bromoxynil (4-hydroxy-3

,5 dibromo benzonitrile) were applied. Rehydration was conducted in small Plexiglas chambers (20 °C, 100% Rh, 200 pM m"

2 sec"

1 PhAR). C0

2 gas exchange measurements were carried out according to Tuba et al. (1996) in five