Peltigera Rufescens Research Articles

Water Status of Green and Blue‐green Phycobionts in Lichen Thalli after Hydration by Water Vapor Uptake: Do They Become Turgid?

AbstractIt is known from previous investigations that dry lichens with green algae are able to recover net photosynthesis through rehydration with water vapor, whereas all blue‐green lichens tested so far lack this ability. The REM micrographs of the present study show that the green phycobionts (Trebouxia spec.) of Ramalina maciformis become turgid only after water vapor uptake. In contrast, the blue‐green phycobionts (Nostoc spec.) of Peltigera rufescens do not differ in appearance from the dry state, even when the thallus has reached equilibrium with the water vapor‐saturated air; they require liquid water for turgidity. It is hypothesized that, after humidity hydration, water content is not sufficient for reestablishment of a functioning osmotic cell system in the blue‐green phycobiont.

Chlorophyll Fluorescence of Lichens Containing Green and Blue‐Green Algae During Hydration by Water Vapor Uptake and by Addition of Liquid Water*

AbstractThe fluorescence yield at room temperature of the lichens Ramalina maciformis and Peltigera rufescens, containing either green or blue‐green algae (Cyanobacteria) as phycobionts, has been investigated during rehydration of the dry lichens by water vapor uptake or by wetting with liquid water. In the dry state the fluorescence yield with all reaction centers open, Fo, was low and no variable fluorescence could be induced with both species. Whereas R. maciformis, containing green algae, regained normal fluorescence behavior during water vapor uptake, the photosynthetic apparatus of the blue‐green algae‐containing P. rufescens stayed inhibited and could be reactivated only by addition of liquid water. During stepwise rehydration at increasing air humidities, a pattern was established for the recovery of the different fluorescence parameters in R. maciformis. At a dry‐weight related water content between 30 and 40%, Fo rose sharply. Maximal variable fluorescence yield expressed as (Fv)m/Fo, strongly increased in the same range of water content and remained constant above a water content of 50%. Non‐photochemical fluorescence quenching, qNP, determined at the end of a period of actinic illumination, decreased with increasing water vapor uptake. While spraying the lichen with liquid water did not induce a further decrease of qNP, slow dehydration at lowered air humidity led to a minimal value of qNP at a water content of 65 % indicating optimal photosynthetic rate under these conditions. These results extend the conclusions drawn from earlier gas exchange experiments that blue‐green algae‐containing lichens are unable to reactivate photosynthesis by water vapor uptake. During a re‐ and de‐hydration cycle, no hysteresis in the hydration dependence of the fluorescence parameters was found. From this and the presence of a stable and low Fo value at prolonged incubation in nearly water vapor saturated air, we conclude that the reactivation of photosynthesis in blue‐green algae‐containing lichens is not prevented through high diffusion resistances for water.

Electrophoretic variation in a population of the lichen Peltigera rufescens (Weis.) Mudd.

Isoelectric focusing was used to investigate the distribution of enzymes exhibiting phosphoglucose isomerase, phosphoglucose mutase, malate dehydrogenase, esterase, hexokinase, glucose-6-phosphate dehydrogenase, peroxidase and fructose-1,6-bisphosphatase activities in a central Ontario population of the lichen Peltigera rufescens (Weis) Mudd. Samples of thalli were collected in order to estimate enzymatic variation in thalli collected within a site (separated by distances of 1-10 m) and between sites (separated by 5-15 km). A total of 85 different enzyme bands were identified in the 27 samples analysed. The results indicated that, at some locations, within site variation was as large as between site variation. The importance of this variation in the design of physiological studies of lichens is discussed.

Inhibition of Energy-Transfer to Photosystem II in Lichens by Dehydration: Different Properties of Reversibility with Green and Blue-green Phycobionts

Dry lichens with green algal phycobionts are able to recover net photosynthesis through rehydration with water vapor, whereas lichens with blue-green algae lack this ability (Lange, Kilian and Ziegler, Oecologia 71, 104–110, 1986). By measurements of 77 K fluorescence emission and excitation spectra, it is investigated whether this basic difference in rehydration properties of green and blue-green lichens is due to the different organization of the antenna pigments. Emission spectra obtained from a lichen with a blue-green alga (Peltigera rufescens) and from a free-living blue-green alga (Nostoc cf. commune) were essentially identical after normalization at 710 nm and revealed the following major features: Equilibration of a dry organism with air of 99 % r.h. resulted in a pronounced increase of fluorescence emission at 650 nm when excited at 580 nm (i.e. at maximal absorbance for the phycobilin pigments). Additional spraying with liquid water led to a strong fluorescence increase around 690 nm. With excitation of chlorophyll at 430 nm no such changes could be observed with both procedures. Excitation spectra for emission at 695 nm revealed that the efficiency for fluorescence excitation at 565 nm compared to that at 435 nm was minimal after equilibration at 99 % r.h., whereas spraying with liquid water resulted in a strong enhancement. It is concluded that desiccation induces a functional detachment of the phycobilisomes (PBS) from photosystem II (PS II). Energy transfer from PBS to PS II is restored only when rehydration occurs with liquid water. Similar experiments with the lichen Ramalina maciformis, which contains a green phycobiont (Trebouxia spec.) yielded distinctly different responses. The desiccation induced lowering of fluorescence emission was almost totaly reversed by equilibration with air of 93 % r.h. Excitation spectra of 695 nm emission showed a large reduction of the emission ratio with 480 nm excitation over that with 435 nm induced by desiccation. Rehydration by increasing air humidity resulted in a gradual increase of this ratio until it was almost maximal at about 99 % r.h. It is concluded that with green algal symbionts desiccation induces a functional interruption of energy transfer between the light harvesting chl a/b pigment complex and PS II and that this can be largely restored by rehydration with humidified air, in contrast to the situation with blue-green algal symbionts.

Seasonal Changes in the Kinetic Parameters of a Photosynthetic Fructose-1,6-Bisphosphatase Isolated from Peltigera rufescens

The kinetic parameters of the photosynthetic fructose-1,6-bisphosphatase isolated from Peltigera rufescens (Weis) Mudd. were measured on a seasonal basis and during a laboratory-induced temperature acclimation. Both the substrate affinity and Ea changed on a seasonal basis. During the summer, the Ea decreased from 91.8 to 62.3 kilojoules per mole. The K(m) fructose-1,6-bisphosphate measured at temperatures above 25 degrees C was also found to decrease by 50%. This seasonal change in K(m) can be induced by growing the lichen under appropriate conditions for 2 weeks, and is correlated to a change in the net photosynthetic rates. It is hypothesized that this change in fructose-1,6-bisphosphatase is related to the seasonal temperature acclimation process that has been previously reported in this species.

Isolation and Characterization of Two Enzymes Capable of Hydrolyzing Fructose-1,6-Bisphosphatase from the Lichen Peltigera rufescens

Two enzymes capable of hydrolyzing fructose-1,6-bisphosphate (FBP) have been isolated from the foliose lichen Peltigera rufescens (Weis) Mudd. These enzymes can be separated using Sephadex G-100 and DEAE Sephacel chromatography. One enzyme has a pH optimum of 6.5, and a substrate affinity of 228 micromolar FBP. This enzyme does not require MgCl(2) for activity, and is inhibited by AMP. The second enzyme has a pH optimum of 9.0, with no activity below pH 7.5. This enzyme responds sigmoidally to Mg(2+), with half-saturation concentration of 2.0 millimolar MgCl(2), and demonstrates hyperbolic kinetics for FBP (K(m) = 39 micromolar). This enzyme is activated by 20 millimolar dithiothreitol, is inhibited by AMP, but is not affected by fructose-2-6-bisphosphate. It is hypothesized that the latter enzyme is involved in the photosynthetic process, while the former enzyme is a nonspecific acid phosphatase.

PHOTOSYNTHETIC CAPACITY CHANGES IN PELTIGERA

SummaryThe seasonal net photosynthetic response matrix to moisture, temperature and light has been examined in two populations of Peltigera rufescens (Weis) Mudd, geographically widely separated and representative of arctic and temperate climates, respectively. The arctic population shows a seasonally constant net photosynthetic rate whereas the temperate population exhibits a marked summer increase of photosynthetic capacity under high temperatures and levels of illumination. This change in capacity is shown by use of photosynthetic‐illumination curves to be due to temperature acclimation, presumably involving a seasonal enzymatic change in the Calvin cycle. Experimental induction of the summer or winter response can be achieved by storage of air‐dry thalli under an appropriate combination of ambient temperature and day length. The data are discussed both in relation to the ecology of the two contrasting populations and to seasonal changes in the photosynthetic capacity of other lichen species.

PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS

SUMMARYThe potential control by temperature and moisture of the movement of glucose from the phycobiont in Collema furfuraceum, Peltigera polydactyla and Peltigera rufescens is examined. The ratio of labelled mannitol to labelled glucose after exposure to 14CO2 is used as a measure of the amount of glucose transported and converted to mannitol in the lichen thallus over a range of experimental temperatures and levels of thallus hydration. The results show that temperature has little effect on the proportion of the total label appearing in mannitol except at 5°C. This is interpreted as a minimum temperature requirement for the conversion of glucose to mannitol within the mycobiont. The effect of thallus hydration, however, shows that in Peltigera polydactyla the major movement of fixed carbon from the phycobiont to the fungal partner occurs at, or close to, full thallus saturation. Below 300% thallus moisture by weight the amount of label appearing in mannitol declines sharply. Conversely, in Collema furfuraceum and Peltigera rufescens, transport of glucose continues at a constant rate down to very low levels of thallus hydration.These results are discussed in relation to our previous findings using Peltigera praetextata, and in relation to the balance of total photosynthate between the lichen symbionts during a drying cycle. It is evident that the rate of transport of glucose is closely controlled by the level of thallus hydration which in turn correlates with the xeric or mesic preference of each species. Alternate wetting and drying cycles effectively ensure that each biont obtains an adequate supply of the fixed carbon resources, thus maintaining the integrity of the lichen.

METAL UPTAKE IN TERRICOLOUS LICHENS

SummaryThe observed modifications of the morphology and histology of Peltigera canina and Peltigera rufescens in metal‐polluted environments are: reduction in thallial size and rhizinal length, and dense rhizinal growth, profusely‐branched veins and hypertrophy of the medulla. The value of terricolous lichens as bioindicators of metal‐enriched substrata is related to the biologically‐available metal concentrations in the associated soils and the nature of the substratum.

Preliminary Studies of the Gross Photosynthetic Response of Lichens to Peroxyacetylnitrate Fumigations

Samples of Collema nigrescens (Huds.) DC., Hypogymnia enter- omorpha (Ach.) Nyl. and Parmelia sulcata Tayl. were fumigated with peroxy- acetylnitrate (PAN) daily for 4 h periods over 7-8 days at concentrations of 100 and 50 ppb. All of these species as well as Peltigera rufescens (Weis.) Humb. were fumigated for 1 h at 200 ppb PAN. Injury was evaluated as reduction in gross photosynthesis during the fumigation periods. Results of the long term, low concentration fumigations show that P. sulcata is more sensitive to PAN than H. enteromorpha and that C. nigrescens is apparently unaffected under the experimental conditions. Results of the acute high dose fumigation show slight enhancement of photosynthesis in all species except H. enteromorpha. With the exception of C. nigrescens, laboratory results are generally consistent with unpublished observations of distribution and vital- ity of the species in the field. Deleterious effects of air pollution to lichens are well documented (Nash, 1976a; Ferry et al., 1973), but have centered on sulfur dioxide, hydrogen fluoride and trace metals as pollutants. Investigations of the effects of photochemical oxidants on lichens have only recently been initiated and have yielded varied results. Fumigations with relatively high concentrations of nitrogen dioxide (Nash, 1976b) resulted in significant reduction in the chlorophyll concentrations of Anaptychia neoleucomelaena, Leca- nora chrysoleuca, Parmelia praesignis and Usnea cavernosa. In more recent experi- ments with ozone, Brown and Smirnoff(1978) found no effect on photosynthetic 14CO2- fixation in Cladonia rangiformis after a 2 h fumigation treatment, and Rosentreter and Ahmadjian (1977) reported essentially no change in chlorophyll concentrations of Cladonia arbuscula nor in the phycobiont isolated from Cladina stellaris. In contrast, Nash and Sigal (1979) found significant reductions in gross photosynthesis of Parmelia sulcata and Hypogymnia enteromorpha during the course of 12 h ozone fumigations, with P. sulcata exhibiting greater sensitivity to ozone than H. enteromorpha. The present study extends experimentation with photochemical oxidants and li- chens to include peroxyacetylnitrate (PAN), an oxidant air pollutant implicated as a cause of considerable injury to vegetation in southern California (Taylor, 1968, 1969).

The Role of Desert Cryptogams in Nitrogen Fixation

Several desert cryptogams and associated microorganisms were tested for potential nitrogen fixation using the acetylene-reduction method. Ethylene accumulation was very low for most plants with values between 1.26 and 3.17 n moles ethylene/g/ml/15 days. The highest ethylene assays were obtained for Peltigera rufescens (3720 n moles/g/ml/ 10 days), Grimmia sp. (52.3 n moles/g/ml/15 days) and Dermatocarpon lachneum mixed with free-living Nostoc spp (162 n moles/g/ml/15 days. Free-living blue-green algae, the Nostoc sp. phycobiont of P. rufescens and Azotobacter-like organisms, were implicated as the nitrogen fixers. However, the role of these organisms as the major providers of nitrogen to the desert ecosystem was questioned.

NITROGEN FIXATION BY LICHENS IN SCOTLAND

SUMMARYOf thirty‐six species of metabolically active lichens taken mainly from Scottish coastal habitats, eight showed a capacity to reduce acetylene to ethylene. These were species of Collema Web., Lichina C. Ag., Peltigera Willd. and Placopsis Nyl. and all contained a blue‐green alga as the primary or secondary phycobiont. Acetylene reduction rates were sometimes high in the field and showed marked diurnal and seasonal variations. Nitrogenase activity was higher in vegetative than in fruiting thalli of Peltigera rufescens, and in P. canina was higher nearer the apices of the thalli than in older parts. Of the environmental factors affecting fixation, desiccation was the most important, temperature was less important and the lichens, while requiring light, could continue to fix nitrogen in the dark for up to 18 hours (Lichina confinis) and 26 hours (Peltigera rufescens). The average percentage nitrogen contents of nitrogen‐fixing lichens (2·20%) was significantly higher than the non‐nitrogen‐fixing lichens (0·83%). The maximum and mean rates of nitrogen fixation by P. rufescens were 38·1 and 4·1 μg N (mg N)‐1 day‐1 respectively. The corresponding values for Lichina confinis were 29·4 and 0·4.

Le Thalle, Les Apothecies Et Les Asques Du Peltigera Rufescens (Weis)Humb. (Discolichen, Peltigeracee)

SummaryThe thallus of Peltigera rufescens has a cladomian structure. It is developed from axial filaments which are lodged in the veins and from which are developed several, short, ventral pleuridia and numerous well-developed, which are developed, dorsal ramifications.The latter form the remainder of the thallus.The ascocarps develop directly from a small number of marginal, dorsal pleuridia which form a well-delimited primordium from which is built up a primary corpus, similar to the type formed in graphidian and lecanorian species. To this is added a parathecial apparatus. Although this development is to be qualified lecanorian, certain peculiarities may be noted; these are a very long angiocarpic stadium in the course of which are built up a parathecioid envelope and a marginal crown, the characters of which are intermediate between those of primary and secondary elements.The asci are bitunicate and ‘archaeascé’.