Lectins are glycoproteins of 60-100 kDa produced by plants, fungi and animals.   Lectins seem to be involved in the recognition between cells. In lichens, the fungal partner produces lectins that are secreted and they selectively bind to some specific receptors in the cell wall of a compatible algal partner. This binding implies an affinity mechanism between some specific amino acid residues of the lectin and spercific sugar residues of the glycosidic moieties of receptor (the lectin ligand). This last retains the fungal lectin on the surface of the compatible algal cell wall and, then, the holobiont could be constructed.            Algal incompatibility against a particular fungal species is done by the lack of the adequate lectin receptor. Then, the lectin, which also develops an enzymatic activity related to the production of polyamines, enters the algal cell and there produces chloroplast disorganization, hydrolysis of the cell wall and, finally, cell death.