Photoacclimation Responses of the Brown MacroalgaSargassum Cymosumto the Combined Influence ofUVRadiation and Salinity: Cytochemical and Ultrastructural Organization and Photosynthetic Performance

Abstract

The photoacclimation responses of the brown macroalga Sargassum cymosum were studied to determine its cytochemical and ultrastructural organization, as well as photosynthetic pigments and performance. S. cymosum was cultivated in three salinities (30, 35 and 40 psu) under four irradiation treatments: PAR-only, PAR + UVA, PAR + UVB and PAR + UVA + UVB. Plants were exposed to PAR at 70 μmol photons m(-2) s(-1), PAR + UVB at 0.35 W m(-2) and PAR +UVA at 0.70 W m(-2) for 3 h per day during 7 days in vitro. Growth rate was not significantly affected by any type of radiation or salinity. The amount of pigments in S. cymosum was significantly influenced by the interaction of salinity and radiation treatments. Compared with PAR-only, UVR treatments modified the kinetics patterns of the photosynthesis/irradiance curve. After exposure to UVR, S. cymosum increased cell wall thickness and the presence of phenolic compounds. The number of mitochondria increased, whereas the number of chloroplasts showed few changes. Although S. cymosum showed insensitivity to changes in salinity, it can be concluded that samples treated under four irradiation regimes showed structural changes, which were more evident, but not severe, under PAR + UVB treatment.

The brown seaweed Sargassum cymosum: changes in metabolism and cellular organization after long-term exposure to cadmium

“…An important work involving S. cymosum and UV radiation as a stressor factor was developed by Polo et al (2014)., These authors found that, as defence mechanisms, samples exposed to UV radiation developed thickening of cell walls with an increasing amount of polysaccharides, as well as exudation of physode contents rich in phenolic compounds and vesicles migrating to cortical cells. In the present study, after 7 days of exposure to Cd, TEM analysis showed that S. cymosum fibrils were disrupted close to cell walls, with regions of plasmodesmata connections.…”

“…Macroepiphytes were eliminated by cleaning with a brush and washed with filtered and UVC sterilized seawater. In accordance with Polo et al (2014), acclimation parameters and period were defined for this species by using similar culture conditions. Apical portions of approximately 5 cm were maintained in sterilized seawater enriched with von Stosch enrichment solution at half strength (VSES/2 without EDTA; Edwards 1972).…”

“…They are primary producers and, as such, they are also responsible for nutrient cycling and the production of organic matter based on the food chain (Worm et al 2000;Polo et al 2014). Seaweeds can also bioamplify toxic impacts in that the retention and accumulation of chemicals, such as heavy metals, in thalli could transfer the toxic effects to grazers and other macroinvertebrates (Riosmena-Rodríguez et al 2010).…”

Physiological responses of macroalga Gracilaria lemaneiformis (Rhodophyta) to UV-B radiation exposure

“…Further, UVBR was found to alter the phycobiliprotein content in the macroalgae such as Gracilaria edulis (Eswaran et al, 2002), Gracilaria domingensis (Schmidt et al, 2010c) and Hypnea musciformis (Schmidt et al, 2012b). The decrease in photosynthetic activity during or after UV stress might result from the direct impairment to key components of the primary and secondary photosynthetic reactions, loss of photosynthetic pigments, as well as due to the reduced expression of genes involved in photosynthesis (Bischof et al, 2002;Bouzon et al, 2012;Polo et al, 2014).…”

Cumulative Effects of Ultraviolet Radiation and Photosyntheically Active Radiation on Phycobiliproteins of A Hot-Spring Cyanobacatrium Nostoc sp. strain HKAR-2

“…The fraction of solar radiation consists of reduced energy UV-A (95 %) that reaches to the Earth's surface (Santos et al, 2013). About 5% UV-B radiation which is not completely absorbed by stratospheric ozone layer reaches to the Earth's surface and is harmful to all living organisms (Polo et al, 2014).…”