Changes in ultrastructure and histochemistry of two red macroalgae strains of Kappaphycus alvarezii (Rhodophyta, Gigartinales), as a consequence of ultraviolet B radiation exposure E ´ der Carlos Schmidt a, *, Lidiane Angela Scariot a , Ticiane Rover a , Zenilda Laurita Bouzon a,b a Department of Cell Biology, Embryology and Genetics, Federal University of Santa Catarina 88049-900, CP 476, SC Floriano ´polis, SC, Brazil b Central Laboratory of Electron Microscopy, Federal University of Santa Catarina 88049-900, CP 476, SC Floriano ´polis, SC, Brazil 1. Introduction The stratospheric ozone provides a natural layer that protects the world’s biological organisms from ultraviolet radiation (UVR) exposure (Madronich, 1992). Its depletion occurs mainly by atmospheric pollutants, such as chlorofluorocarbons (CFCs), halocarbons, carbon dioxide (CO 2 ) and methyl chloroform (MCF) (Kerr and McElroy, 1993). Increasingly, ultraviolet B radiation (UVBR) (280–320 nm) reaches the earth’s surface as a result of ozone layer depletion (Mitchell et al., 1992; Lubin and Jensen, 1995). As a result, UV energy induces photodamage in proteins, nucleic acids and other compounds in biological tissues (Mitchell et al., 1992). Similar to other places in middle and high latitudes in the northern and southern hemispheres (Santee et al., 1995; Kirchhoff et al., 1996, 2000; Rousseaux et al., 1999), southern Brazil has been exposed to a gradual increase in the levels of UVR. According to the Brazilian Institute for Space Research (INPE), this region receives natural solar radiation from 225 mW cm 2 to 350 mW cm 2 , based on a daily UV index that varies from 9 to 14 during a typical summer. Ultraviolet radiation affects all biological organisms, especially those in the aquatic ecosystem, in many important ways. Several studies have shown effects, such as decreased macroalgae growth rate (Wood, 1987), reduced primary productivity (Worrest, 1983), DNA damage (Karentz et al., 1991), and many alterations in biochemical metabolism of marine microalgae (Premkumar et al., 1993). The photosynthetic process is also potentially affected, inhibiting the activity of the 1,5-di-phosphate carboxylase/ oxygenase (Rubisco) and D1 polypeptides of the photosystem II reaction center (Lesser and Shick, 1994), as well as altering the thylakoid membrane composition of chloroplasts (Grossman et al., 1993). One of the strategies used by macroalgae to survive exposure to high levels of UVR is the synthesis and accumulation of photoprotective compounds, such as mycosporine-like amino acids (MAAs) and carotenoids, which directly or indirectly absorb UVR energy (Karsten and Wiencke, 1999; Karsten et al., 1999; Sommaruga, 2001; Sonntag et al., 2007). Only a few papers have reported changes in the ultrastructure and cell biology of macroalgae exposed to UVBR (Poppe et al., 2002, 2003; Holzinger et al., 2004, 2006; Holzinger and Lu ¨ tz, 2006; Steinhoff et al., 2008). These changes mainly occur in the chloroplasts, modifying the quantity, size, organization, as well as the number of thylakoids (Talarico and Maranzana, 2000). While the species Kappaphycus Micron 40 (2009) 860–869 ARTICLE INFO Article history: Received 11 May 2009 Received in revised form 12 June 2009 Accepted 12 June 2009 Keywords: Ultraviolet radiation Kappaphycus alvarezii Ultrastructure Cell wall Chloroplast ABSTRACT Ultraviolet radiation (UVR) affects macroalgae in many important ways, including reduced growth rate, reduction of primary productivity and changes in cell biology and ultrastructure. Among red macroalgae, Kappaphycus alvarezii is of economic interest by its production of kappa carrageenan. Only a few reports have examined the changes in macroalgae ultrastructure and cell biology resulting from UVB radiation exposure. Therefore, we examined two strains of K. alvarezii (green and red) exposed to UVB for 3 h per day during 28 days and then processed them for histochemical and electron microscopy analysis. Reaction with Toluidine Blue showed an increase in the thickness of the cell wall and Periodic Acid-Schiff stain showed a decrease in the number of starch grains. UVBR also caused changes in the ultrastructure of cortical and subcortical cells, which included increased thickness of the cell wall and number of free ribosomes and plastoglobuli, reduced intracellular spaces, changes in the cell contour, and destruction of chloroplast internal organization. Based on these lines of evidence, it was evident by the ultrastructural changes observed that UVBR negatively affects intertidal macroalgae and, by extension, their economic viability. Crown Copyright ß 2009 Published by Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +55 48 3721 5149. E-mail address: edcash@terra.com.br (&.C. Schmidt). Contents lists available at ScienceDirect Micron journal homepage: www.elsevier.com/locate/micron 0968-4328/$ – see front matter . Crown Copyright ß 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2009.06.003