Growth kinetics related to physiological parameters in young Saccorhiza dermatodea and Alaria esculenta sporophytes exposed to UV radiation

Abstract

Young sporophytes of Saccorhiza dermatodea and Alaria esculenta cultured from Spitsbergen isolates were exposed in the laboratory to either only photosynthetically active radiation (PAR) or to a spectrum including UV-radiation (PAR+UVA+UVB) by use of cutoff glass filters. The plants were grown at 8±2°C and 16:8 h light-dark cycles with 6 h additional UV exposure in the middle of the light period. Growth was measured every 10 min using growth chambers with online video measuring technique for 18-21 days. Tissue morphology and absorption spectra were measured in untreated young sporophytes while tissue chlorophyll-a content and DNA damage were measured from treated thalli at the end of the experiment. Under UVR, growth rates of S. dermatodea were significantly reduced while A. esculenta have a potential to acclimate. Tissue chlorophyll-a contents in both species were not significantly different between treatments suggesting that these algae may acclimate to moderate UVR fluence. Higher DNA damage in S. dermatodea effectively diverted photosynthetic products for repair constraining growth. Tissue optics (opacity and translucence) was correlated to the tissue absorbance in the UVR region characteristics of phlorotannin, an important UV-absorbing compound in brown macroalgae. Growth rates of sporophytes of both species exposed to PAR without UV was similar during day and night. The results showed that both species can recruit and inhabit a similar coastal zone when appropriate strategies are expressed to minimize damage in response to the stress factor.

Thallus morphology and optical characteristics affect growth and DNA damage by UV radiation in juvenile Arctic Laminaria sporophytes

“…Three growth chambers (ISITEC GmbH, Bremerhaven, Germany) with circulating water system and online video measuring technique were operated simultaneously in the experiment as described by Roleda et al (2004bRoleda et al ( , 2005b. Each growth chamber contained 2 basal pieces of thalli (average size=30 mm 2 , ±6 mm of the phylloid including the meristem), positioned 20 mm apart from each other.…”

“…They were individually fitted to an exponential equation N t =N 0 e rt , where N t is growth at time t, N 0 is initial size and r is the intrinsic rate of increase (Roleda et al 2004b(Roleda et al , 2005b. To determine circadian growth rates of the sporophytes exposed to P and PAB treatments, three days average (% h À1 ) were computed during the start of the light phase without UVR (0500-0900 hours), in the middle of the light phase with UVR supplement (0900-1500 hours), at the end of the light phase without UVR (1500-2100 hours), and during the dark phase (2100-0500 hours).…”

“…To determine thallus thickness, wet weight: surface area (mg: mm 2 ) ratio was measured as described by Roleda et al (2004aRoleda et al ( , 2005b. Surface area of sporophytes taken directly from the unialgal cultures was measured using a scanner and WinFolia 5.0 image analysis software (Regent Instrument, Quebec City, Canada) and the corresponding wet weight of the blotted tissue was weighed using Sartorius (CP225D, Germany) weighing scale (n=10).…”

“…In L. solidungula, photosynthetic efficiency of sporophytes collected at 15 m and transplanted to 1 and 3 m depths were significantly affected, but no longer at 4 m depth, under full solar radiation (Karsten et al 2001). Growth rates of Laminaria species are higher compared to other Laminariales such as Saccorhiza dermatodea (0.42±0.12% h À1 ) and Alaria esculenta (0.31±0.02% h À1 , measured during the dark phase) (Roleda et al 2005b). The pioneering work of Lu¨ning (1992) on online growth measurements within three days showed an increasing growth rate throughout the light phase and a subsequent continuous decrease in growth at the onset of darkness.…”

Transient sediment load on blades of Arctic Saccharina latissima can mitigate UV radiation effect on photosynthesis

“…In this study, the decrease in F v /F m was attributed to UVR because the PAR Xuence used was low (maximum 30 mol photon m ¡2 s ¡1 ) and does not cause photoinhibition (Roleda et al 2004). Repeated exposure of juvenile sporophytes to ultraviolet radiation in the laboratory did not only aVect photosynthetic performance of kelps but also growth, pigments and DNA (Roleda et al 2004(Roleda et al , 2005. Morphological damage such as bleaching, tissue blisters, lesions and deformation, and thickening of the meristematic lamina has been reported in Laminaria ochroleuca Bachelot de la Pylaie exposed to UVR (Roleda et al 2004).…”