A SMALLER AND IMPAIRED XANTHOPHYLL CYCLE MAKES THE DEEP SEA MACROALGAE LAMINARIA ABYSSALIS (PHAEOPHYCEAE) HIGHLY SENSITIVE TO DAYLIGHT WHEN COMPARED WITH SHALLOW WATER LAMINARIA DIGITATA¹

Abstract

Pigment composition, fluorescence parameters, and oxygen evolution of the deep water Laminaria abyssalis Oliveira and of the shallow water L. digitata Lamoroux were determined in response to high irradiances. This was performed in the presence and absence of an inhibitor of violaxanthin de‐epoxidase (dithiothreitol) or an inhibitor of the chloroplast‐encoded protein synthesis (chloramphenicol). Photochemical quenching in L. digitata was almost 3‐fold that seen in L. abyssalis, whereas both nonphotochemical quenching and PSII photochemical yield were doubled. Laminaria digitata possessed a xanthophyll‐cycle pool nearly double that of L. abyssalis. After photoinhibitory treatment, L. digitata displayed substantial violaxanthin de‐epoxidation, whereas in L. abyssalis de‐epoxidation only took place in limited amounts. Both species were able to fully recover their epoxidation status after transfer back to dim light. Overnight incubation with dithiothreitol fully blocked de‐epoxidation in both species, and both displayed similar fluorescence properties. Chloramphenicol caused no change in their fluorescence parameters. With high light treatment, L. abyssalis was completely and irreversibly inhibited both in the presence and absence of inhibitors, whereas L. digitata showed 60% inhibition of its photosynthetic activity and full recovery in the absence of inhibitors. In the presence of dithiothreitol, L. digitata did not recover to the preillumination conditions and chloramphenicol delayed the recovery of the oxygen evolution activity. We suggest that the xanthophyll cycle is the main mechanism of photoprotection of these Laminaria species and that the higher susceptibility of L. abyssalis to photoinhibition may be due to its limited de‐epoxidation capacity and reduced xanthophyll‐cycle pool size.

Regulation and function of xanthophyll cycle-dependent photoprotection in algae

“…Much less is known about the biochemistry of the Vx cycle enzymes of the brown algae. However, the Phaeophyceae show deepoxidation and epoxidation kinetics comparable to the vascular plants and green algae, and Vx conversion is stimulated under high light conditions, whereas Zx epoxidation takes place under conditions of low light illumination or darkness (Gevaert et al 2003;Rodrigues et al 2002;García-Mendoza and Colombo-Pallotta 2007). This indicates that the biochemical characteristics of the brown algal enzymes with respect to the pH dependence of enzyme activation and the co-substrates are comparable to those of vascular plants and green algae.…”

“…Like the Vx cycle of vascular plants and green algae, the Vx cycle of brown algae is involved in photoprotection and leads to increased dissipation of excessively absorbed excitation energy detectable as NPQ (Gevaert et al 2003;Rodrigues et al 2002;García-Mendoza and ColomboPallotta 2007). However, with respect to the mechanism of NPQ, there is a significant difference compared to vascular plants and green algae.…”

Effects of light intensity and nitrogen starvation on growth, total fatty acids and arachidonic acid in the green microalga Parietochloris incisa

“…The lower proportions of AA under these conditions may result from the discrepancy between the rates of carbon fixation and the terminal steps of PUFA synthesis (desaturation) (Rodrigues et al 2002). Under extremely high PFDs (2500 μE m −2 s −1 ), when culture growth was even faster, a further decrease in the proportion of AA was recorded (ChengWu et al 2002).…”

Macroalgal responses to ocean acidification depend on nutrient and light levels

“…Thermal dissipation measured as non-photochemical PSII fluorescence quenching (NPQ) is triggered by the trans-thylakoidal proton gradient ( pH) and zeaxanthin (ZEA) synthesis through the xanthophyll cycle (Gilmore et al, 1994) and is recognized as the most important photoprotective mechanisms in higher plants and several algal divisions (Rodrigues et al, 2002). Fucoxanthin and violaxanthin levels were not affected in C. compressa whereas in P. pavonica fucoxanthin and violaxanthin increased under 70% PAB conditions, nutrient enrichment and medium CO 2 levels.…”