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The presence of RNase activity has been detected in the two saxicolous lichen species, Lasallia hispanica (Frey) Sancho & Crespo and Cornicularia normoerica (Gunn.) DR. Activity was localized in the soluble fraction and had an acid optimum pH in both species. When proteins from the soluble fraction of the two lichens were separated by isoelectric focusing, multiple electromorphs with RNase activity were detected. L. hispanica RNase was separated into seven bands, characterized by pis 7, 6.28, 4.58, 4.45, 4.25, 3.95, and 3.47. In C. normoerica four bands were detected, with pis of 6.28, 3.98, 3.57, and 3.39. The molecular mass of the main RNase of L. hispanica estimated by SDS-PAGE was 31.86 kDa, which corresponds to the 33 kDa estimated for the undenatured RNase by gel chromatography. Proteins from C. normoerica were resolved by SDS-PAGE in three bands, with estimated molecular mass of 36.07 kDa, 31.86 kDa and 17.13 kDa. In order to improve the detection of RNase activity, gels were incubated after the run (electrophoresis or isoelectric focusing) in a RNA solution, instead of including the substrate in the gel. In both species, RNase activity increased during hydration and decreased during desiccation. This pattern of activity resembles that of other enzyme activities in lichens, which decrease in response to water deficits, and is different from the response of other poikilohydrous organisms such as bryophytes. These results are discussed in relation to the mechanisms that lichens have to withstand dehydration.

The r2 isolate of Fusarium oxysporum f.sp. radicis-lycopersici produced several pectic enzymes that differ in substrate preference, reaction mechanism, and action pattern. We detected three forms that have lyase activity, four forms with polygalacturonase activity and one form with pectinesterase activity. Lyases had an absolute requirement for calcium and pIs of 9.20, 9.00, and 8.65. The two more alkaline forms had a weak preference for pectin, whereas the other was more active on polygalacturonate. Polygalacturonases had pIs of 9.30, 7.35, 6.85, and 6.55 and were inhibited by calcium ions. Lyases and polygalacturonases were induced by galacturonic acid and were subject to catabolite repression. Induced synthesis occurred at pHs 5.5 and 8.0 and no increase in lyase activities were promoted by alkalinization of cultures. Pectin lyase had an endo mode of action, whereas pectate lyase and polygalacturonase behaved more as exoenzymes. These results are discussed in relation to the appearance of the different pectic enzymes when the fungus is confronted with a pectic polymer.Key words: Fusarium oxysporum f.sp. radicis-lycopersici, Lycopersicon esculentum, pectate lyase, pectin lyase, polygalacturonase.

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