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Photoinhibition of photosynthesis in marine macroalgae
D. Hanelt

Photoinhibition should be considered as a mechanism that protects the photosynthetic apparatus. In algae exposed to high fluence rates dynamic photoinhibition converts excess light energy into heat and prevents photodamage. As a result radiationless energy dissipation increases and variable fluorescence of photosystem 11 (photosynthetic efficiency) and photosynthetic capacity decrease. The decrease of the photosynthetic parameters showed a linear correlation with the increase in zeaxanthin content in photosystem 11 antenna of marine brown algae. Field measurements of variable fluorescence and oxygen production rate indicate that the depression caused by dynamic photoinhibition follows a diurnal pattern with the lowest photosynthetic activity occurring usually between noon and the early afternoon. In the afternoon photosynthesis commences to recover, and is almost complete by the evening. However, the diurnal pattern depends on the tidal level because the water column above the algal beds protects the algae from high fluence rates. Desiccation of benthic marine algae during low tide showed different effects on the photoinhibitory level in different species. Photosynthetic measurements made in the natural habitat of different latitudes clearly showed that dynamic photoinhibition occurs regardless of water temperature. The Antarctic brown alga Adenocystis utricularis regulated photosynthesis by dynamic photoinhibition even faster than brown macroalgae of the tropic or temperate zones. However, algal zonation is thought to depend in part on the capability for dynamic photoinhibition. Investigations of photoinhibition of photosynthesis usually use both fluorescence and oxygen measurements. However, recent studies indicate that the two methods can give different results if the rate of saturated oxygen production is compared to the variable fluorescence of photosystem 11 in red algae.

Keywords: Fluorescence, marine algae, oxygen production, photoinhibition, photosynthesis, temperature adaptation, zeaxanthin.
Contents of this volume Sci. Mar. 60(Suppl.1) : 243-248 Back PDF
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