Effects of salinity stress on cellular location of elements and photosynthesis in Ramalina canariensis Steiner

Abstract

AbstractThe impact of incubation in saline solutions of different concentrations on the uptake and cellular location of essential elements (Na+, K+, Mg2+ and Ca2+), and its effects on membrane integrity and on the photosynthetic apparatus, were investigated in the lichen Ramalina canariensis Steiner. Saline incubation resulted in a rapid uptake of Na+ and Mg2+ in the cell wall fraction, whereas in the intracellular fraction the accumulation of Na+ was slower. No changes were observed for intracellular Mg2+, suggesting that no generalized membrane damage occurred. Concomitantly with the increase in intracellular Na+, there was a specific loss of K+ from the cell interior, indicating that membrane permeability may have been compromised. Incubation in a 100% artificial sea water solution reduced the maximum photochemical efficiency of Photosystem II (Fv/Fm) by 17% after 5 min, and this inhibition increased with incubation time. In samples incubated in 100% artificial sea water solution for 2 h followed by 2 h incubation in deionized water, ion distribution and Fv/Fm did not recover to control values. The present findings show the importance of determining the cellular location of elements when assessing their physiological impact. Results indicate that saline stress may irreversibly impair photosynthesis, thus compromising lichen vitality.