Effects of ultraviolet radiation and temperature on the ultrastructure of zoospores of the brown macroalga Laminaria hyperborea

Abstract

The interactive effects of an 8 h exposure to UV radiation and altered temperatures on the ultrastructure and germination of zoospores of the sublittoral brown alga Laminaria hyperborea (Gunn.) Foslie were investigated for the first time. Spores were exposed to four temperatures (2, 7, 12 and 17 degrees C) and three light regimes (PAR, PAR + UV-A, PAR + UV-A+UV-B). Freshly-released spores of L. hyperborea lack a cell wall and contain a nucleus with fine granular nucleoplasm and a nucleolus, one chloroplast, several mitochondria, dictyosomes and an endoplasmatic reticulum. Further, several kinds of so-called adhesive vesicles, lipid globuli and physodes containing UV-absorbing phlorotannins are embedded in the cytoplasm. No eye-spot is present. Physodes were found but they were rare and small. After an 8 h exposure to UV-B, the nucleoplasm had a mottled structure, chloroplasts contained plastoglobuli, the structure of the mitochondria changed from crista- to sacculus-type and germination was strongly inhibited at all temperatures. UV-A only had an impact on the ultrastructure at the highest temperature tested. The strongest effects were found at 17 degrees C, where germination was reduced to 35%, 32% and 9% after exposure to PAR, PAR+UV-A and PAR + UV-A + UV-B, respectively. This study indicates that UV-B radiation has strong damaging effects on the physiology and ultrastructure of zoospores of L. hyperborea. The results are important for developing scenarios for the effect of enhanced UV radiation and increasing temperatures caused by global climate changes.

Physiological, biochemical, and ultrastructural responses of the green macroalga Urospora penicilliformis from Arctic Spitsbergen to UV radiation

“…In the early life history stages of brown macroalgae, UVR-exposed zoospores of Laminaria hyperborea (Gunnerus) Foslie showed an enhanced formation of plastoglobuli in the chloroplast, mottling of the nucleoplasma, and transformation of the mitochondria structure from the tubulus to the sacculus type (Steinhoff et al 2008).…”

“…As a consequence, several physiological and metabolic processes such as photosynthesis, respiration, growth, and reproduction will be compromised (Caldwell et al 1998;Björn et al 1999;Roleda et al 2007). Under enhanced UVR, cellular development and ultrastructural integrity may also be at risk depending on the UV tolerance of the species (e.g., Meindl and Lütz 1996;Lütz et al 1997;Poppe et al 2002Poppe et al , 2003Steinhoff et al 2008).…”

The responses of brown macroalgae to environmental change from local to global scales: direct versus ecologically mediated effects

“…Wiencke et al (2006), for instance, showed detrimental UVR effects on germination rate in Laminaria species. Current depletion levels of stratospheric ozone suggest that Laminaria species dwelling from polar to temperate regions could be affected and that the detrimental UVR effects on zoospore structure and physiology, germination success, and growth may be intensified in a warmer ocean (Steinhoff et al 2008). According to the IPCC (2014), the intensity of storms and ultimately wave exposure will increase, in particular in the Arctic.…”

The vegetative arctic freshwater green alga Zygnema is insensitive to experimental UV exposure

“…Holzinger et al, 2004;Poppe et al, 2002Poppe et al, , 2003 and some brown algae (e.g. Roleda et al, 2006b;Steinhoff et al, 2008). This is not only related to their growth habit with different micro-climate at different depths but also related to their phylogeny with distinct biochemical pathways and physiological response and tolerance to different stress factors.…”