Adaptações de cianobactérias filamentosas e seus efeitos nas estratégias reprodutivas de Pistia stratiotes

Abstract

With an estimated origin of 3.5 billion years, cyanobacteria have acted, since then, in the modification of the terrestrial atmosphere and in association with several organisms. They are fundamental in several ecosystems, participating as primary producers and playing an important role in biogeochemical cycles, in addition to forming complex networks of biotic associations. Among ecosystem services, it is worth mentioning the high rate of oxygen production through photosynthesis, especially in marine environments, the sequestration of atmospheric carbon, also related to photosynthesis, but also the biological nitrogen fixation, which in turn is responsible for make atmospheric nitrogen available so that, among other functions, photosynthesis and carbon sequestration take place. Of the many biotic associations with cyanobacteria, we highlight those that occur with photosynthetic beings, in these cases, the main benefit to the "hosts" is the nitrogen compounds made available by the associated cyanobacteria. Cyanobacteria of the genus Nostoc are associated with mosses, gymnosperms (Cycas) and angiosperms (Gunneraceae) in an endophytic manner. However, there are also epiphytic and peripheral associations, as with the macrophy Pistia stratiotes, which has characteristics that guarantee adaptive advantages resulting in its cosmopolitan distribution. The root system of this floating macrophyte is noteworthy, as it has many secondary roots that enable interactions with microorganisms. Based on these premises, we set out to study the relationship between filamentous cyanobacteria and P. stratiotes. Thus, we evaluated the adaptive strategies of filamentous cyanobacteria and the vegetative and reproductive allocation in this macrophyte depending on the supply of nutrients (carbon and nitrogen) and the availability of light. We saw that depending on the nutritional supply, both the cyanobacteria and the macrophyte showed plasticity. in behavior. With the nitrogen supply, we found a high production of necrids in cyanobacteria, and a greater investment in the vegetative growth of the macrophyte. With the contribution of carbon, cyanobacteria modified cells into heterocytes and macrophytes invested in sexual reproduction. We conclude, then, that in case of excess of nutrients there will be cellular changes in the cyanobacteria that will provide the maintenance of the community epiphytically associated with the macrophyte, and with alternation in the dominance of certain strains.