RNase inLasallia hispanicaandCornicularia normoerica: multiplicity of electromorphs and activity changes during a hydration-dehydration cycle

Abstract

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.

Variability of Ribonuclease Activity in Lichen Thalli

“…However, the present study has not revealed a pattern of variation that could be related exclusively to the habitat or seasonal differences. RNase activity of these lichen species is dependent on the water status of the thalli, as has previously been shown (de los Rios et al 1996;de los Rios 1997). The microclimatic characterization of the habitats where the lichens were collected during the sampling period, has revealed frequent changes in relative humidity in the proximity of the thalli (de los Rios 1997).…”

“…In the saxicolous lichens referred to above, L. hispanica, P. omphalodes and C. normoerica, the changing pattern of RNase activity in the course of a hydration-dehydration cycle has been studied. RNase activity increased markedly in three species when the thalli were maintained in a relative humidity of 100% and decreased again when the thalli were dehydrated, down to values similar to those of untreated thalli (de los Rios et al 1996). RNase activity in these lichens does not increase during desiccation, as has been shown in bryophytes and other organisms that can withstand dehydration (Bewley & Krochko 1982;Gniazdowska-Skocek & Bandurska 1994).…”

“…Four main types of RNases have been distinguished in higher plants according to biochemical features (mode of action, molecular mass, normoerica, the activity of a soluble RNase with an acidic optimum pH, low molecular mass and insensitivity to EDTA has been detected. These characteristics suggest that this RNase belongs to type I (de los Rios et al 1996). Type I are soluble endoribonucleases with a optimum pH of 5-0-5-5 and a molecular mass of 20-25 KDa; they produce 3' nucleotides and are not sensitive to EDTA (Green 1994).…”

Rehydration conditions for isolation of high quality RNA from the lichen Lobaria pulmonaria

“…One of the early activities of metabolism upon restoration of cell function after desiccation is thought to be transcript formation [ 1 ], in part because synthesis of antioxidant proteins protects cells from the rapid intracellular release of reactive oxygen species after rehydration [ 12 ]. However, RNA-degrading endonucleases released during rehydration [ 13 ], may reduce RNA quantity and quality [ 14 ]. After the effects of rehydration reach a steady-state condition representative of the natural lichen, further experimentation provides the opportunity to investigate a variety of questions such as the ecological plasticity of the lichen by monitoring phenotypic, physiological or transcriptional metrics in response to different rehydration conditions.…”

Ribonuclease activity in roots of soybean seedlings subjected to chilling stress and recovery

“…Changes in RNase activity are commonly observed in response to abiotic environmental stressors such as heat shock (Chang and Gallie 1997), salinity (Gomes Filho and Sodek 1988), hydration -dehydration (de los Rios et al 1996), O2-deprivation (Fennoy et al 1997). Also, ribonuclease activity is influenced by plant hormones such as abscisic acid (Panavas et al 1998), auxin (Vetter 1974), gibberellic acid (Brown and Ho 1986). In plants low temperature stress causes a number of physiological and developmental changes resulting from disturbances in fundamental cellular functions.…”