Photosynthetic responses to Cu2+ exposure are independent of light acclimation and uncoupled from growth inhibition in Fucus serratus (Phaeophyceae)

We have studied the effect of light acclimation on photosynthetic responses and growth during Cu²⁺ exposure (0–0.84 μM) in the brown seaweed Fucus serratus. Measurements of chlorophyll fluorescence parameters showed that Cu²⁺ exposure amplified ETR, reduced the chlorophyll content at the cellular level and that there was no effect of light adaptation on the Cu²⁺ resistance of the algae. In contrast to the inhibitory effects of Cu²⁺ on chlorophyll fluorescence, O₂ evolution and the total content of chlorophyll and carotenoid of the algae was unaffected by Cu²⁺. We conclude that photoinhibition and perhaps pigment degradation in the meristoderm was compensated for by cells deeper in the thallus with the result that the overall photosynthetic fitness of the algae was maintained. The pronounced inhibitory effects of Cu²⁺ on algae growth was not a consequence of photoinhibition and could be attributed to direct inhibitory effects on the growth process.     

Short-term photoacclimation effects on photoinhibition of phytoplankton in the Drake Passage (Southern Ocean)

We assessed whether short-term photoacclimation responses of natural phytoplankton populations in the Drake Passage (Southern Ocean) were affecting protection from photodamage as cells are mixed up to the surface from depth. To this end, we measured phytoplankton fluorescence characteristics and their ratio of xanthophyll cycle pigment to photosynthetic pigments within the upper mixed layer (UML) and in short-term deck incubation experiments. Phytoplankton within the UML photoacclimated by increasing their ratio of xanthophyll cycle (diadinoxanthin [dd] and diatoxanthin [dt]) pigments to chlorophyll a. The photoacclimation processes observed within the UML did, however, not influence the protection of phytoplankton from photodamage during short-term near-surface irradiance experiments. Exposure to near-surface irradiance resulted in photodamage in all experiments, regardless of the phytoplankton community composition and irradiance levels. Incubating phytoplankton for six hours at either 2% or 50% of surface irradiance prior to exposure to near-surface irradiance did not alter the photodamage characteristics. This suggests that short-term photoacclimation processes within the UML are not adequate to protect phytoplankton from photodamage when cells are mixed up to the surface from depth, and that repair of damaged photosystems is crucial for maintaining photosynthesis under fluctuating irradiance conditions, even at very low mean irradiance levels. Likely, continuously operating photoacclimation processes offset to some extent the negative effects of photodamage on photosynthetic performance, albeit with increased metabolic costs.     

Photosynthetic responses to Cu exposure are independent of light acclimation and uncoupled from growth inhibition in Fucus serratus (Phaeophyceae)

We have studied the effect of light acclimation on photosynthetic responses and growth during Cu²⁺ exposure (0–0.84 μM) in the brown seaweed Fucus serratus. Measurements of chlorophyll fluorescence parameters showed that Cu²⁺ exposure amplified ETR, reduced the chlorophyll content at the cellular level and that there was no effect of light adaptation on the Cu²⁺ resistance of the algae. In contrast to the inhibitory effects of Cu²⁺ on chlorophyll fluorescence, O₂ evolution and the total content of chlorophyll and carotenoid of the algae was unaffected by Cu²⁺. We conclude that photoinhibition and perhaps pigment degradation in the meristoderm was compensated for by cells deeper in the thallus with the result that the overall photosynthetic fitness of the algae was maintained. The pronounced inhibitory effects of Cu²⁺ on algae growth was not a consequence of photoinhibition and could be attributed to direct inhibitory effects on the growth process.