Algal-fungal mutualism: cell recognition and maintenance of the symbiotic status of lichens

Lichens are specific symbiotic associations between photosynthetic algae or cyanobacteria and heterotrophic fungi forming a double entity in which both components coexist. Specificity required for the lichen establishment can be defined in this context as the preferential, but not exclusive, association of a biont with another, since the algal factor susceptible to be recognized is an inducible protein. Recognition of compatible algal cells is performed by specific lectins produced and secreted by the potential mycobiont. Some lectins from phycolichens and cyanolichens are glycosylated arginases which bind to an algal cell wall receptor, identified as a a-1, 4-polygalactosylated urease. However, other ligands exist which bind other lectins specific for mannose or glucose. This implies that, after recognition of a potential, compatible partner, other fungal lectins could determine the final success of the association. Since the fungus can parasitize non - recognized partners during the development of the association, the success after the first contact needs of a set of algal cells, the number of which was sufficient to prevent that the death of a certain number of them makes fail the symbiosis. Fungal lectins act as chemo tactic factors in such a way that algae and cyanobacteria move towards the hyphae, to acquire that critical size of the colony, by means of successive contractions and relaxation of the actomyosin cytoskeleton in absence of any motile appendages

Biologically-active compounds from Brazilian lichens and their affinity with ether

It can be obtained from lichens biologically-active extracts and pure substances, many of them of phenolic nature. They are usually obtained by using organic solvents, such as diethyl ether. In this paper the usefulness of ether for the obtainment of crude extracts and the subsequent purification of pure substances from Brazilian lichen is reviewed, as well as alternatives to their production through cells or thallus immobilization in bioreactors and their entrapment in inert matrix

Putrescine accumulation does not affect RNA metabolism in the lichen Evernia prunastri.

Evernia prunastri thaiIi are able to accumulate exogenous putrescine from the media. This accumulation is optimal at pH 9.15 although the highest uptake rate is achieved at pH 5.0 in parallel to the highest production of endogenous diamine. The lowest values of RNase activity seems to be related to alkaline pH values rather than accumulation of free putrescine.Peer Reviewe

High Performance Liquid Chromatography of the Dansyl Derivatives of Putrescine, Spermidine, and Spermine

A high performance liquid chromatographic (HPLC) method, based on dansylation and fluorescence detection, is described for the estimation of putrescine, spermidine, and spermine in lichen (Evernia prunastri [L.]) samples. Because of the high concentrations of phenols and salts, dansylation was followed by a pre-HPLC purification step. Both flow rate and mobile phase (methanol:water) followed a gradient for optimum resolution on a reverse-phase column. Amounts as small as 0.3 picomole of standard polyamines could be detected. In applying the method to lichens, it was found that 5.45% (w/w) of the exogenous putrescine taken up by the thallus was unbound in the algal partner and that 60% (w/w) was conjugated in the thallus, perhaps to lichen phenolics

Effects of light and growth regulators on the reversibility of the senescence in attached leaves of barley.

Senescence of intact barley seedlings (Hordeum vulgare) judged by the loss of chlorophyll, was induced by putting them in the dark. Reversal of senescence by application of light was also observed. The chlorophyll content recovered after two days in the light, but seedlings were unable to recover their initial level of pigment after four days in the dark, This suggests the onset of an irreversible stage in senescence from the fourth day. Supply of kinetin to the leaf after two or four days in the dark induces a slight increase in chlorophyll content. Whereas reversion of the senescence is obtained immediately after the dark period, the same treatment with abscisic acid accelerates the loss of chlorophylls and retards the reversion by light treatment.Peer Reviewe

L-ornithine decarboxylase from Evernia prunastri.

L-ornithine decarboxylase (EC 4.1.1.17) was 88-fold purified from E. prunastri thallus with an overall yield of 14.5%. The enzyme developed maximum activity when lichen thalli were floated on 40 mML-ornithine. Addition of cycloheximide to the ornithine-containing medium did not nullify activity. However, when chloramphenicol was added to the same medium, the loss of activity was about 90%. Two cellular sites of enzyme synthesis are postulated.Peer Reviewe

Uptake and accumulation of putrescine in the lichen Evernia prunastri

Putrescine uptake and accumulation by Evernia prunastri thallus was studied. Putrescine is effectively taken by lichen cells in the mono-protonated form and then accumulated whithout significant enzymatic degradation of diamine. However, the diprotonated form, which is produced at pH 5.0, is trapped on the cell walls and a high proportion of it can be degraded before uptake by a secretable diamine oxidase, which is produced at acidic pH values.This work was supported by a grant from the CAICYT (Spain) Nº 328/84.Peer reviewe

The effect of spermidine, spermine and putrescine analogues on the uptake and adsorption of putrescine by the lichen Evernia prunastri

Competition for putrescine uptake among polyamines and between polyamines and their analogues has been studied in thalli of the lichen Evernia prunastri. Uptake experiments included measurements of both transport and adsorption of putrescine. Spermidine and spermine behaved as competitive inhibitors of putrescine transport, with K-i values of 1.55 mM and 1.34 mM, respectively. Basic amino acids, such as arginine, ornithine and lysine did not seem to compete for the same site of transport. Furthermore, putrescine uptake was slowly enhanced by Na+, K+, Ca-2+ and Mg-2+, and diminished by Mn-2+, Ni-2+ and La-3+. About 64% of putrescine taken up by lichen thalli was located in mycobiont cells. No metabolism of putrescine to other polyamines, such as spermidine and spermine, occurred after its uptake.Peer Reviewe

Putrescine affects mannitol metabolism in the lichen Evernia prunastri.

Peer Reviewe