Benjamín Viñegla

Involvement of solar UV-B radiation in recovery of inhibited photosynthesis in the brown alga Dictyota dichotoma (Hudson) Lamouroux

Daily variations of photosynthetic performance of the brown alga Dictyota dichotoma (Hudson) Lamouroux (Dictyotales) (estimated by Fv/Fm ratio and net O2-based photosynthesis) have been determined under full-spectrum solar radiation (PAR+UV-A+UV-B), solar radiation depleted of ultraviolet-B (PAR+UV-A) and solar radiation depleted of total ultraviolet (photosynthetically active radiation, PAR). In the daily course, the photosynthetic response of the alga is inhibited by the three solar radiation conditions at midday, but recovers during the afternoon to those values measured in the early morning only under PAR + UV-A + UV-B, or PAR alone. Under solar radiation depleted of UV-B, the recovery of photosynthesis is significantly lower than in the other two solar radiation conditions. The relative electron transport rate (ETR) as a function of PAR is calculated for the three radiation treatments, at noon after 2 h exposure. The ETR is strongly inhibited under these conditions. In the PAR and PAR + UV-A + UV-B treatments, photosynthesis recovers after 1.5 h in low irradiance (< 10 μmol photons m−2 s−1) and attains values measured in the early morning. In the absence of UV-B, the inhibitory effect is persistent, visible as a low initial slope and lower ETR at higher levels of irradiance. These data suggest that UV-B may be involved both in the impairment and the recovery of photosynthesis of D. dichotoma.

Effects of solar radiation on photosynthesis, UV-absorbing compounds and enzyme activities of the green alga Dasycladus vermicularis from southern Spain

Abstract The effect of different wavebands of solar radiation (photosynthetically active radiation (PAR), ultraviolet A (UV-A) and ultraviolet B (UV-B)) produced by use of cut-off filters on chlorophyll fluorescence of the green alga Dasycladus vermicularis was assessed in summerautumn 1996 at a shallow site in Cabo de Gata-Nijar, southern Spain. Similar experiments were carried out under outdoor conditions at Malaga during summer and autumn 1997. In plants growing under in situ natural light conditions (2.5 m depth), the yield of variable chlorophyll fluorescence (ΔF/Fm′) decreases with increasing sunlight. The full solar spectrum (PAR + UV-A + UV-B) has more accentuated, long-lasting effects on fluorescence than irradiation deprived of UV-B. In general, decreases in ΔF/Fm′ do not exceed 30% in the three treatments. Under outdoor conditions, photoinhibition measured as a decrease in optimum quantum efficiency (Fv/Fm) varies between 40 and 75% with no obvious differences between treatments; however, recovery of photosynthesis after shade exposure is faster in plants treated with PAR + UV-A. Daily changes in nitrate reductase (NR) and carbonic anhydrase (CA) activities are antagonistic during the onset of natural radiation. The concentration of UV-absorbing compounds with maximum absorption at 348 and 332 nm is higher than that reported for other green algae. These compounds increase in plants exposed to the full solar spectrum (PAR + UV-A + UV-B) and decrease under PAR alone and PAR + UV-A conditions at noon. which underlines a possible photoprotective mechanism. Overall, data show that D. vermicularis is able to tolerate high solar radiation. Two physiological strategies seem to be basically active: dynamic photoinhibition at noon and an enhanced concentration of UV-screening substances.

Effects of UV Radiation and Temperature on Photosynthesis as Measured by PAM Fluorescence in the Red Alga Gelidium pulchellum (Turner) Kützing

Abstract Potosynthetic performance in response to UV radiation was measured in the red alga Gelidium pulchellumTurner (Kützing) from northern Portugal in the laboratory. The experiments basically consisted of exposures to three different UV radiation conditions (PAR + UV-A + UV-B; PAR + UV-A and PAR alone) using artificial lamps and cut off foils followed by incubations at low irradiance of white light to determine the recovery capacity. The effects of two different PAR backgrounds (105 and 480 μmol photon m−2 s−1) and two growth temperatures (15 and 25 °C) as additional factors were also assessed. The optimal quantum yield of fluorescence (Fv/Fm) decreased after 12 h exposure to PAR + UV (equivalent to a weighted UV dose closed to 150 kJ m−2; from photoinhibition of PSII electron transport action spectrum). The electron transport was also impaired by UV radiation. The PAR background was a key factor determining the UV responses in this species: thalli exposed to high PAR background (480 μmol m−2 s−1) exhibited a greater degree of photoinhibition and a slower recovery than plants irradiated by 105 μmol m−2 s−1. On the other hand, an incubation temperature of 15 °C exacerbated the effect of UV radiation on photosynthesis (increased photoinhibition) followed by a slowing down in the recovery kinetic compared to samples incubated at 25 °C. These results suggest that repair processes may be stimulated with increasing growth temperature.

EFFECTS OF SOLAR RADIATION ON PHOTOSYNTHESIS AND PHOTOINHIBITION IN RED MACROPHYTES FROM AN INTERTIDAL SYSTEM OF SOUTHERN SPAIN

The effects of solar radiation on photosynthesis, chlorophyll content and photoinhibition of the red macrophytes Asparagopsis armata, Gelidium sesquipedale, Plocamium cartilagineum and Feldmannophycus rayssiae from an intertidal system of southern Spain were estimated by means of pulse amplitude modulated fluorometer (PAM), by measurement of the O2 exchange, and by quantification of the chlorophyll content of the thalli. The effective quantum yield ( / ^) decreased in all the experimental organisms after 60 min of exposure to solar radiation; moreover, photoinhibition seemed to be more pronounced and long-lasting in shade-type plants. Secondly, all macrophytes from this study suffered more or less pronounced photoinhibition during some hours of the day at their natural living site. Photoinhibition was maximal around noon and the early afternoon, but almost complete recovery of photosynthesis was achieved by dusk. Similarly, oxygen production and chlorophyll a content were minimal around noon. The ratio (l-qP)/qN was lower in shade than in sun algae indicating a lower electron flow rate, and a lower rate of protective energy dissipation in shade than in sun-grown algae. This ratio is suggested as a good indicator of light stress, to compare different algal species with different pigment content, i. e. sunand shade-type algae.

Effects of solar UV radiation on photosynthesis and enzyme activities (carbonic anhydrase and nitrate reductase) in marine macroalgae from southern Spain

En este trabajo se presenta el efecto de la radiacion solar ultravioleta (UV) durante el ciclo diario de luz sobre la actividad fotosintetica y la de dos enzimas claves en la incorporacion de carbono, la anhidrasa carbonica, y en la reduccion de nitrogeno inorganico, la nitrato reductasa, en macroalgas del sur de Espana. Durante el ciclo diario de luz, la fotoinhibicion, expresada como porcentaje de disminucion del rendimiento cuantico efectivo desde la manana al mediodia, estuvo linear y negativamente correlacionada con la irradiancia integrada diaria. Sin embargo, la recuperacion, expresada como porcentaje de incremento del rendimiento cuantico efectivo desde el mediodia hasta el atardecer siguio un patron diferente. Se observo recuperacion completa a irradiancias integradas diarias menores a 1.0 x 104 kJ m-2. Sin embargo, a irradiancias diarias mayores, la recuperacion fue solo del 50 %. La existencia de fotoinhibicion y de una recuperacion diaria completa en macroalgas hace pensar que la fotoinhibicion esta funcionado como un mecanismo de fotoproteccion contra radiaciones solares altas como ocurre en plantas terrestres. Ademas, los patrones de fotoinhicion y recuperacion tienen relacion con la dosis acumulada diaria. Las actividades enzimaticas (anhidrasa carbonica y nitrato reductasa) fueron determinadas en tres macroalgas marinas (Plocamium cartilagineum, Ulva rigida y Fucus spiralis) bajo radiacion solar completa (PAR + UV-A + UV-B) y excluyendo la radiacion UV (PAR). Bajo PAR + UV-A + UV-B se observo un maximo en la actividad de ambas enzimas en P. cartilagineum por la tarde, lo que concuerda con datos publicados en otras algas rojas. La situacion fue modificada en ausencia de UV ya que el incremento de ambas actividades fue retrasado en el tiempo (varias horas). En las tres macroalgas bajo radiacion solar completa se encontro una correlacion significativa y negativa solo cuando los datos de la actividad nitrato reductasa fueron desplazados al menos 4 horas respecto a los de la anhidrasa carbonica. Esta correlacion se pierde en Ulva rigida cunado se excluye la radiacion UV. La existencia de variaciones diarias y la correlacion negativa entre la actividad de ambas enzimas podria reflejar una compleja regulacion conjunta entre el metabolismo del carbono y del nitrogeno bajo radiacion solar. Debido a que esta correlacion se pierde en ausencia de UV en Ulva o los maximos se retrasan en Plocamium, se sugiere que la radiacion UV podria ser una senal medioambiental implicada en el control de los ciclos enzimaticos. Se sugiere la existencia de procesos de retroalimentacion que controlan el metabolismo del nitrogeno en funcion del contenido de carbono

Photoinhibition in Mediterranean macroalgae by solar radiation measured on site by PAM fluorescence

Photoinhibition under solar radiation was measured in several green, red, and brown macroalgae harvested from different depths using pulse amplitude modulation (PAM) fluorescence on site in Cabo de Gata (South East Spain). Photosynthetic quantum yield decreased after exposure to unfiltered solar radiation and recovered during subsequent shade exposure. Surface algae were inhibited but recovery was fast and complete within a few hours. In contrast, inhibition in deep water algae were even more pronounced, and recovery was incomplete or non-existent. Photosynthetic quantum yield was determined from dawn to dusk at 1 h intervals in algae immediately after harvest. Photoinhibition occurs in all algae even at their natural habitat when the sun is at high angles. Similarly, photoinhibition was found during noon hours in algae harvested from deep water and exposed at 2 m depth. # 1998 Elsevier Science B.V. All rights reserved

Effect of artificial UV radiation on carbon and nitrogen metabolism in the macroalgae Fucus spiralis L. and Ulva olivascens Dangeard

Thalli of the intertidal Phaeophyte Fucus spiralis L. and the subtidal Chlorophyte Ulva olivascens Dangeard were exposed to artificial UV-A, UV-B and photosynthetically active radiation (PAR) by combination of PAR + UV-A + UV-B (PAB), PAR + UV-A (PA) and PAR (P) treatments. UV-A enhanced photosynthesis and stimulated carbonic anhydrase (CA) and nitrate reductase (NR) in F. spiralis whilst PAR only had an inhibitory effect in this species. U. olivascens suffered chronic photoinhibition in all the treatments as evidenced by reduced maxima photosynthesis (Pmax) and photosynthetic efficiency (α). Non stimulatory effect was observed upon CA and NR in this species. Our results showed that artificial UV radiation triggered opposite responses in both species. We suggest that differences shown by both species might be related to their location in the rocky shore and their ability to sense UV. We propose that the ratio UV:PAR acts as an environmental signal involved in the control of photosynthesis as shown by pronounced inhibition in samples exposed to only PAR. We also suggest that UV-regulated photosynthesis would be related to carbon (C) and nitrogen (N) cycles, regulating feedback processes that control C and N assimilation.

Pulse amplitude modulated fluorescence in the green macrophytes, Codium adherens, Enteromorpha muscoides, Ulva gigantea and Ulva rigida, from the Atlantic coast of Southern Spain

Abstract The effect of ambient and enhanced solar radiation on the photosynthetic apparatus in four marine green macroalgae on the Southern coast of Spain (Strait of Gibraltar) was investigated using pulse amplitude modulation (PAM) fluorescence. The dependence of the fluorescence parameters on the irradiance of the actinic light was determined for all four species. It showed that maximal fluorescence after light adaptation ( F m ′), photochemical quenching ( q P ) and the photosynthetic quantum yield decreased in Enteromorpha muscoides with irradiance while non-photochemical quenching ( q N ) rose continuously. In Ulva rigida the photosynthetic quantum yield dropped at irradiances above 4 W m −2 but q P did not decrease with increasing light. q N quenching rose sharply above 37 W m −2 , and maximal fluorescence dropped above 1 W m −2 . In Ulva gigantea the yield dropped to zero at irradiances of 37 W m −2 , as did q P at 53 W m −2 . q N started from an intermediate level and increased to a maximum at the highest irradiances. In Codium adherens , the yield and q P behaved similarly as in U. rigida , while q N rose at much lower irradiances. All investigated algae suffered from photoinhibition even at their natural sites of growth when the sun is at high angles. The hypothesis that algae with flat thalli suffer more than those with massive ones was confirmed. Photoinhibition was less pronounced in U. rigida and C. adherens than in the other two species. After 1 h of exposure to solar radiation at the surface, the photosynthetic quantum yield decreased substantially in the surface algae E. muscoides and U. rigida . In both macroalgae, recovery of the photosynthetic quantum yield was almost complete after 2–3 h in the shade. Two other green algae from shaded habitats ( U. gigantea and C. adherens ) did not show complete recovery of the yield from photoinhibition. This confirms the second hypothesis that sun-adapted algae recover faster from photoinhibition than those adapted to shaded sites.