Chlorophyll a fluorescence and ultrastructural changes in chloroplast of water hyacinth as indicators of environmental stress

Chlorophyll a fluorescence parameters and transmission electron microscopy (TEM) were used to assess the stress conditions in water hyacinth along the Paraíba do Sul River (PSR), an important River in southeastern Brazil. The data were obtained at the end of the dry season of 2005 and at the end of the wet season of 2006. Changes in F0 and Fm parameters were observed as differentiated responses, depending on the season. Non-photochemical dissipation (qN and NPQ) from plants was greater in the most industrialized region of the PSR in both seasons. However, Fv/Fm for all samples ranged between 0.77 and 0.81, showing that high maximum quantum yield was maintained. Although the Fv/Fm suggests that the plants were exhibiting normal photochemical activities, ultrastructural changes in chloroplasts showed thylakoids disorganization. Plants from the most industrialized region showed non-stacking grana thylakoids disposition. In spite of these alterations, the membrane integrity was maintained, suggesting an adaptation to adjustment to adverse environmental conditions.