Physiological, morphological and ultrastructural responses to exposure to ultraviolet radiation in the red alga Aglaothamnion uruguayense (W.R. Taylor)

Abstract

In this study, we examined the effect of ultraviolet radiation (UV) at the thalli of Aglaothamnion uruguayense (W.R. Taylor) N.E. Aponte, D.L. Ballantine & J.N. Norris exposed to two different conditions of radiation: PAR (control) and PAR + UVA + UVB for 3 h per day during 7 days. The effects of radiation on growth rates, photosynthetic pigments, cell viability, phenolic compounds and total soluble sugar and starch were analyzed. The morphology and the ultrastructure were also assessed. Algae were cultivated and then exposed to photosynthetically active radiation (PAR) at 14 W m−2 and PAR + UVA (0.70 W m−2) + UVB (0.35 W m−2) 3 h per day for 7 days. After exposure to PAR + UVA + UVB, A. uruguayense exhibited a 75% reduction in growth. Photosynthetic pigments, in particular, phycobiliproteins (allophycocyanin, phycocyanin and phycoerythrin), increased after exposure to PAR + UVA + UVB. UVR exposure changed the synthesis of carotenoids, including decreased of lutein by 67.1% and increased of β-carotene by 64.3% and of zeaxanthin by 23%. Phenolic compounds were reduced while flavonoids decreased by approximately 12.9% compared with samples exposed to PAR (control). Moreover, as determined by PAS, TEM and total starch extraction, the amount of starch grains decreased in algae exposed to UV. When observed under confocal microscopy, treated samples showed a significant reduction in the number and shape alteration of chloroplasts. TEM revealed changes in ultrastructure, including increased cell wall thickening and disorganization of cellulose microfibrils. Chloroplasts showed disrupted thylakoid membranes, damage to envelope membranes, and increased number of plastoglobuli. From these results, it can be concluded that UVB is a factor that negatively affects the growth and development of the macroalga A. uruguayense.