Two components of onset and recovery during photoinhibition of Ulva rotundata

Abstract

Short-term (up to 5 h) transfers of shade-adapted (100 μmol · m(-2) · s(-1)) clonal tissue of the marine macroalga Ulva rotundata Blid. (Chlorophyta) to higher irradiances (1700, 850, and 350 μmol · m(-2) · s(-1)) led to photoinhibition of room-temperature chlorophyll fluorescence and O2 evolution. The ratio of variable to maximum (Fv/Fm) and variable (Fv) fluorescence, and quantum yield (ϕ) declined with increasing irradiance and duration of exposure. This decline could be resolved into two components, consistent with the separation of photoinhibition into energy-dissipative processes (photoprotection) and damage to photosystem II (PSII) by excess excitation. The first component, a rapid decrease in Fv/Fm and in Fv, corresponds to an increase in initial (Fo) fluorescence and is highly sensitive to 1 mM chloramphenicol. This component is rapidly reversible under dim (40 μmol · m(-2) · s(-1)) light, but is less reversible with increasing duration of exposure, and may reflect damage to PSII. The second (after 1 h exposure) component, a slower decline in Fv/Fm and Fv with declining Fo, appears to be associated with the photoprotective interconversion of violaxanthin to zeaxanthin and is sensitive to dithiothreitol. The accumulation of zeaxanthin in U. rotundata is very slow, and may account for the predominance of increases in Fo at high irradiances.

Photosystem II Excitation Pressure and Development of Resistance to Photoinhibition (I. Light-Harvesting Complex II Abundance and Zeaxanthin Content in Chlorella vulgaris)

“…Increased levels of Z in the light-harvesting antenna have been implicated to protect PSII upon exposure to excessive light by dissipating excess absorbed light energy as heat in higher plants (Demmig-Adams, 1990) and algae (Franklin et al, 1992). This energy dissipation is often reflected in a quenching of the F, leve1 (Weis and Berry, 1987;DemmigAdams et al, 1988).…”

Novel amplification of non‐photochemical chlorophyll fluorescence quenching following viral infection in Chlorella

“…The absence of xanthophyll related NPQ in green algae has been previously noted and constitutes a major difference between algae and land plants [1,20]. Of the green algae only Ulva rotundata has been intensively studied with regard to photoinhibition.…”

Microstructures and photosynthetic diurnal changes in the different types of lichen soil crusts

“…It was just because of the different photosynthetic taxa, the different types of LSCs in our experiment released different chlorophyll fluorescence information, which had long been used as a proxy for photosynthetic efficiency in plant ecophysiological studies [31,32]. Among the chlorophyll fluorescence parameters, Fv/Fm is the maximum quantum yield of photosystem (PS) II, reflecting the largest photochemical efficiency when all the PSII reaction centers are open [22,33]. This value is relatively stable and generally remains at 0.4e0.5 in cyanobacteria [34] and about 0.65 in algae [35] under unstressed conditions; while decreases under stress conditions [22].…”