Although B has been implicated in the cross-linking of RGII monomers in higher plant cell walls, there is increasing evidence that this micronutrient also plays a role in organisms without cell walls. The results presented here support the hypothesis that boron interacts with surface glycolipids, reinforcing the structure of the heterocyst envelope in cyanobacteria. However, the involvement of this micronutrient in regulatory mechanisms cannot be ruled out. The up-regulation of genes involved in the transport of glycolipids and polysaccharides to the heterocyst surface in response to B deficiency might indicate a sensing mechanism, dependent on the integrity of the heterocyst envelope.