A siphonous morphology affects light-harvesting modulation in the intertidal green macroalga Bryopsis corticulans (Ulvophyceae)

Maxwell A Ware,Guangye Han,Xiaochun Qin,Alexander V Ruban,Petra Ungerer,Vasco Giovagnetti,Wen-Da Wang,Jian-Ren Shen,Tingyun Kuang

doi:10.1007/s00425-018-2854-5

Abstract

Main conclusionThe macroalga Bryopsis corticulans relies on a sustained protective NPQ and a peculiar body architecture to efficiently adapt to the extreme light changes of intertidal shores.During low tides, intertidal algae experience prolonged high light stress. Efficient dissipation of excess light energy, measured as non-photochemical quenching (NPQ) of chlorophyll fluorescence, is therefore required to avoid photodamage. Light-harvesting regulation was studied in the intertidal macroalga Bryopsis corticulans, during high light and air exposure. Photosynthetic capacity and NPQ kinetics were assessed in different filament layers of the algal tufts and in intact chloroplasts to unravel the nature of NPQ in this siphonous green alga. We found that the morphology and pigment composition of the B. corticulans body provides functional segregation between surface sunlit filaments (protective state) and those that are underneath and undergo severe light attenuation (light-harvesting state). In the surface filaments, very high and sustained NPQ gradually formed. NPQ induction was triggered by the formation of transthylakoid proton gradient and independent of the xanthophyll cycle. PsbS and LHCSR proteins seem not to be active in the NPQ mechanism activated by this alga. Our results show that B. corticulans endures excess light energy pressure through a sustained protective NPQ, not related to photodamage, as revealed by the unusually quick restoration of photosystem II (PSII) function in the dark. This might suggest either the occurrence of transient PSII photoinactivation or a fast rate of PSII repair cycle.

Highlights

Oxygenic photosynthesis uses sunlight energy to convert carbon dioxide and water into carbohydrates and molecular oxygen, through the transfer of electrons between photosystems II and I (PSII and PSI) (Blankenship 2014)
A photosystem II (PSII) maximum quantum yield in the dark (Fv/Fm) of 0.76 ± 0.01 was measured. This is in agreement with values previously reported for other green macroalgae belonging to the order of Ulvales (Franklin et al 1992; Henley et al 1991; Henley 1992; Yamazaki et al 2005) and Bryopsidales (Yamazaki et al 2005; Cruz et al 2014), as well as for several different species of Bryopsidales cultured in the laboratory under constant low light (i.e. 25 μmol photons m−2 s−1 with a 12 h light/12 h dark photoperiod; Christa et al 2017)
Given the morphology and absorption properties of the filament clusters of B. corticulans, we investigated if the ‘algal body architecture’ could itself function in the photoprotective strategy adopted against excess light exposure

Summary

Introduction

Oxygenic photosynthesis uses sunlight energy to convert carbon dioxide and water into carbohydrates and molecular oxygen, through the transfer of electrons between photosystems II and I (PSII and PSI) (Blankenship 2014). This process generates an electrochemical proton gradient across the thylakoid membranes that is used for the synthesis of adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH), and feedback modulation of light harvesting (Cardol et al 2011). These systems display marked differences in pigment–protein composition/organisation and size to match the diversity in light intensity and quality of different habitats (Falkowski and Raven 2007; Ruban et al 2011; Ballottari et al 2012; Blankenship 2014)

Methods

Results

Conclusion