Response of chlorophyll d-containing cyanobacterium Acaryochloris marina to UV and visible irradiations

Abstract

We have previously investigated the response mechanisms of photosystem II complexes from spinach to strong UV and visible irradiations (Wei et al J Photochem Photobiol B 104:118-125, 2011). In this work, we extend our study to the effects of strong light on the unusual cyanobacterium Acaryochloris marina, which is able to use chlorophyll d (Chl d) to harvest solar energy at a longer wavelength (740 nm). We found that ultraviolet (UV) or high level of visible and near-far red light is harmful to A. marina. Treatment with strong white light (1,200 μmol quanta m(-2) s(-1)) caused a parallel decrease in PSII oxygen evolution of intact cells and in extracted pigments Chl d, zeaxanthin, and α-carotene analyzed by high-performance liquid chromatography, with severe loss after 6 h. When cells were irradiated with 700 nm of light (100 μmol quanta m(-2) s(-1)) there was also bleaching of Chl d and loss of photosynthetic activity. Interestingly, UVB radiation (138 μmol quanta m(-2) s(-1)) caused a loss of photosynthetic activity without reduction in Chl d. Excess absorption of light by Chl d (visible or 700 nm) causes a reduction in photosynthesis and loss of pigments in light harvesting and photoprotection, likely by photoinhibition and inactivation of photosystem II, while inhibition of photosynthesis by UVB radiation may occur by release of Mn ion(s) in Mn4CaO5 center in photosystem II.

Optimization and effects of different culture conditions on growth of Halomicronema hongdechloris – a filamentous cyanobacterium containing chlorophyll f

“…Recently, additional chlorophylls have been found in some cyanobacteria and the function of these novel chlorophylls in photosynthesis challenges the traditional belief of oxygenic photosynthesis: Chl a is the only chlorophyll that can involve the charge separation in the photosynthetic reaction centers (Miyashita et al, 1996; Chen et al, 2010). Cyanobacteria take advantage of having different compositions of photopigments to capture the available sunlight present in a particular ecological niche (Chen and Scheer, 2013; Hou et al, 2013). For example, Acaryochloris marina synthesizes chlorophyll d (Chl d ) to capture far-red light that is the leftover light from phototrophs using Chl a existing in the upper stacked biolayers (Kühl et al, 2005; Loughlin et al, 2013).…”

Photosynthesis at the far-red region of the spectrum in Acaryochloris marina

“…Similarly as like normal oxygenic photosystem II, UV-B irradiation resulted into fall of manganese from the Mn 4 CaO 5 cluster of PSII [58]. …”

Unidirectional photodamage of pheophytin in photosynthesis

“…Multiple photoprotective hypotheses have been established including Mn-mediated UV photoinactivation (Hakala et al, 2005; Ohnishi et al, 2005; Wei et al, 2011; Hou et al, 2013), cytochrome b-559 cyclic electron flow or cytochrome b-559 reversible interconvertion between the two redox forms (Thompson and Brudvig, 1988; Barber and De Las Rivas, 1993; Shinopoulos and Brudvig, 2012), and a β-carotene photooxidation (Telfer et al, 2003; Alric, 2005; Shinopoulos et al, 2014). The unidirectional photodamage of pheophytin in photosynthesis is discovered.…”