Photoinhibition and photosynthetic pigment reorganisation dynamics in light/darkness cycles as photoprotective mechanisms of Porphyra umbilicalis against damaging effects of UV radiation

  • Aguilera J
  • Figueroa F
  • Häder D
 et al. 
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summArY: Porphyra umbilicalis l. Kutzing collected from the upper intertidal zone at Helgoland, north sea, was ex-posed to different spectral ranges of uV radiation under both 12/12 h light/dark cycles and continuous irradiation. in light/ dark cycles, oscillations of the optimal quantum yield (F v /F m) were observed during the experiments, reaching maximal values at the end of the light phase followed by lower values during the dark phase. Decreased F v /F m was observed in thalli illuminated with photosynthetic active radiation (PAr) plus uV-A and PAr+uV-A+uV-B, compared with the PAr control, indicating a certain degree of uV-induced photoinhibition. in addition, a decrease in the percentage of change of the linear initial slope and maximum electron transport rate (etr) estimated from etr vs. irradiance curves was induced by uV radia-tion during the light phase. recovery during the 12 h dark phase was almost completed in uV-A treated plants. PAr+uV-A seemed not to affect the photosynthesis, measured as o 2 production. However, a decrease in o 2 production was observed in the PAr+uV-A+uV-B treatment, but it recovered to initial values after 48 h of culture. no changes in total content of photosynthetic pigments were observed. However, thallus absorptance and the in vivo absorption cross-section in the PAr range (400-700 nm) normalised to Chl a (a* parameter) fluctuated during light/dark cycles and were positively correlated with changes in the optimum quantum yield, thus indicating that daily pigment reorganisation in the light-harvesting com-plex may play a key role in the photosynthetic performance of the algae. Both uV-A and uV-B treatments under continuous irradiation induced a significant reduction in the optimal quantum yield, ETR efficiency and photosynthetic oxygen produc-tion during the first 36 h to values around 30% of the initial ones. Thus, different protective mechanisms against UV stress can be observed in P. umbilicalis: dynamic photoinhibition when uVA is combined with PAr, followed by full recovery of photosynthesis during the dark phase, and a more pronounced photoinhibition under uV-B, with only partial recovery after longer time periods, in which photosynthetic pigment reorganisation plays an important role. resumen: Dinámicas De fotoinhibición y reorganización pigmentaria bajo ciclos De luz/oscuriDaD como mecanismos De fotoprotección en PorPhyra umbilicalis frente a los efectos Dañinos De la raDiación ultravioleta. – talos del alga roja Porphyra umbilicalis l. Kutzing fueron cultivados bajo diferentes condiciones espectrales de radiación ultravioleta en condiciones de ciclos de luz/oscuridad de 12 horas y bajo luz continua. el rendimiento cuántico óptimo (F v /F m), estimado a través de la fluorescencia de la clorofila a del fotosistema ii, evolucionó con oscilaciones en los ciclos de luz/oscuridad, con valores máximos al final de cada fase de luz seguida de valores bajos a lo largo de la fase de oscuridad. Los cultivos ilumi-nados bajo radiación fotosintéticamente activa (PAr)+uV-A y la PAr+uV-A+uV-B disminuyeron los valores de la relación (F v /F m) respecto a los cultivos bajo PAr. los cultivos bajo radiación uV provocaron además una caída, durante la fase de luz, tanto de la pendiente inicial como de los valores máximos de la tasa de transporte electrónico (etr) estimados a partir de las curvas etr vs. irradiancia. en el caso de los cultivos bajo PAr + uV-A la recuperación de los valores fotosintéticos fue casi completa durante la fase de oscuridad. Dicho tratamiento no afectó a la producción fotosintética de o 2 mientras que el cultivo bajo PAR+UV-A+UV-B disminuyó significativamente dicha tasa, la cual recuperó los valores iniciales tras 48 h de cultivo. no se observaron cambios en el contenido total de los pigmentos fotosintéticos. no obstante, los ciclos de luz/oscuri-dad afectaron tanto a la absorptancia de los talos como a los valores de corte transversal in vivo en el rango del PAr (400-700 Scientia Marina 72(1) march 2008, 87-97, Barcelona (spain) ISSN: 0214-8358 88 • J. AguilerA et al.

Author-supplied keywords

  • UV-radiation
  • chlorophyll fluorescence
  • light/dark cycles
  • photosynthesis
  • stress tolerance
  • thallus absorptance

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  • José Aguilera

  • Félix L Figueroa

  • Donat-P Häder

  • Carlos Jiménez

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