Photosynthesis and growth of red and green morphotypes ... - Biblioteca

8 downloads 60 Views 192KB Size Report
(Doty) Doty under controlled conditions. Chlorophyll a and phycoerythrin (PE) levels were similar in the red and green morphotypes cultured under the same ...
Marine Biology (2001) 138: 679±686

Ó Springer-Verlag 2001

E. Aguirre-von-Wobeser á F. L. Figueroa A. Cabello-Pasini

Photosynthesis and growth of red and green morphotypes of Kappaphycus alvarezii (Rhodophyta) from the Philippines

Received: 19 June 2000 / Accepted: 28 November 2000

Abstract The e€ect of photosynthetic available radiation (PAR) levels, light quality, ultraviolet (UV) radiation, and temperature on photosynthesis, growth, and chlorophyll ¯uorescence was evaluated in red and green morphotypes of the rhodophyte Kappaphycus alvarezii (Doty) Doty under controlled conditions. Chlorophyll a and phycoerythrin (PE) levels were similar in the red and green morphotypes cultured under the same conditions, but phycocyanin (PC) and allophycocyanin (APC) levels were 2-fold greater in the green than in the red morphotype. Pigment characterization indicated that the overexpression of PC and APC masked the red pigmentation in the green morphotype. Maximum photosynthesis and photosynthetic eciency were similar between the two morphotypes assayed at a wide temperature range, which was re¯ected in the similar growth rates observed in outdoor culture systems. In the green morphotype, photosynthetic eciency increased 2-fold relative to the red morphotype when assayed with red light (k > 600 nm), indicating that photosynthetic characteristics are modi®ed as a result of pigment variation in these morphotypes. Such increase in photosynthetic eciency in the green morphotype, however, did not result in greater growth rates when cultured under

Communicated by M. Horn, Fullerton/ O. Kinne, Oldendorf/Luhe E. Aguirre-von-Wobeser Facultad de Ciencias Marinas, Universidad AutoÂnoma de Baja California, A.P. 453, Ensenada, Baja California 22800, Mexico F. L. Figueroa Departamento de EcologõÂ a, Facultad de Ciencias, Universidad de MaÂlaga, Campus Universitario Teatinos, 29071 MaÂlaga, Spain A. Cabello-Pasini (&) Instituto de Investigaciones OceanoloÂgicas, Universidad AutoÂnoma de Baja California, A.P. 453, Ensenada, Baja California 22800, Mexico e-mail: [email protected] Tel.: +52-6-1744601; Fax: +52-6-1745303

white light. Short exposure to high levels of solar radiation (UV-A + UV-B + PAR), and ®ltered solar radiation (UV-A + PAR or PAR) decreased e€ective quantum yield (DF/Fm¢) in both morphotypes. The reduction of DF/Fm¢ values in the red and green morphotypes was accounted for by high levels of PAR and not by the UV-A + UV-B + PAR and UV-A + PAR treatments. Photoinhibition caused by UV-A, UV-B, or PAR was completely reversed within 30 h after incubations. Recovery rates from photoinhibition, however, were signi®cantly reduced in the green morphotype when incubated with UV-B radiation. The results here suggest that the overexpression of pigments do not necessarily increase photosynthesis and growth in these morphotypes.

Introduction Kappaphycus alvarezii has been exploited in Asia for several decades and is one of the most important sources of carrageenan in the world (Doty and Norris 1985; Doty et al. 1987). Natural populations of K. alvarezii, however, have decreased drastically as a result of overharvesting (Doty et al. 1987). Presently, most of the K. alvarezii harvested in the Philippines comes from small private farms, which produce more than 30,000 tons annually (Doty et al. 1987). Despite the great economic importance of this species as a carrageenan source, there are few studies that relate its physiology to the wide ¯uctuations of irradiance and temperature observed in the culture systems (Wu et al. 1989; Ganzon-Fortes et al. 1993; Hurtado-Ponce 1995). The existence of morphotypes of K. alvarezii with varied pigmentation in the ®eld and culture systems has been reported in the literature for decades (Doty et al. 1987; Hurtado-Ponce 1995). These morphotypes generally show di€erences in their photosynthetic characteristics and levels of carrageenan. Similarly, it has been shown that growth rates of green morphotypes are slightly lower than growth rates of red and brown

680

morphotypes (Dawes et al. 1994; Hurtado-Ponce 1995). Such di€erences in photosynthetic characteristics and growth rates could be critical for the selection of morphotypes of K. alvarezii with rapid growth rates in commercial seaweed cultures. Despite these important physiological di€erences, there are no studies that relate the percentage and frequency of the red and green morphotypes of K. alvarezii in the ®eld. Light is absorbed di€erentially by the di€erent photosynthetic pigments of algae and vascular plants (Kursar et al. 1983). As a consequence, the photosynthetic and growth response to di€erent light qualities can vary in algae with di€erent pigment composition (Dawes 1992). Although phycoerythrin (PE) levels can be lower in the green morphotype than in the red morphotype of K. alvarezii (Dawes 1992), little is known about the in¯uence of pigment variations on photosynthesis and growth of either morphotype. It would be expected that the photosynthetic and growth eciency would be reduced in morphotypes with lower pigment levels per unit biomass and as a consequence be selected against in nature. It has been demonstrated that a reduction of PE and phycocyanin (PC) levels, as a consequence of exposure to ultraviolet (UV) radiation, is correlated to a decrease of optimal quantum yield in red algae (Figueroa et al. 1997). The e€ect of UV radiation on morphotypes of K. alvarezii with low biliprotein levels, however, is not known. In this study we have examined growth and photosynthesis of red and green morphotypes of K. alvarezii as a function of light levels and temperature under both natural and controlled laboratory conditions. We also investigated the e€ect of UV and photosynthetically available radiation (PAR) on the photoinhibition of photosynthesis of this species. These experiments will further our understanding of the impact of environmental factors such as temperature and increasing UV radiation on the physiology of natural and cultured populations of marine algae.

Materials and methods Plant material Red-pigmented and green-pigmented morphotypes of Kappaphycus alvarezii were collected in seaweed farms from the Philippines and transported at ambient temperature in dark containers to a laboratory facility in Ensenada, Baja California, MeÂxico. Prior to the experiments, approximately 30 individuals of the red and green morphotypes were maintained in the laboratory for approximately 1 year in 30-l containers at approximately 25 °C. Individuals were kept on a 16:8 light:dark photoperiod with approximately 100 lmol photons á m)2 s)1 from wide-spectrum cool ¯uorescent bulbs. Water was changed once weekly, enriched with 250 lM NaNO3, and kept under constant aeration. All experiments were conducted on morphotypes maintained under laboratory conditions. Growth Growth experiments were conducted from April to July 1997 using 100-l outdoor tanks under natural irradiance and temperature.

Incident irradiance reached approximately 2,000 lmol photons á m)2 s)1 at midday throughout the experiment, and water temperature averaged 24 °C initially and increased to approximately 29 °C at the end of the experimental period. Seawater was changed twice weekly and NaNO3 supplied to a ®nal concentration of 100 lM. Ten individuals of the red and green morphotypes of K. alvarezii of approximately 5 g FW were tagged individually and the increase in fresh weight was determined twice weekly. Plants were gently blotted with paper towels and fresh weight determined with an electronic balance. Daily growth rates (G; % á day)1) were determined using the following equation: G…%  day)1) =  1=t  …Wt =W0 †  100, where Wt is tissue weight after an incubation period (t) and W0 is the initial tissue weight. Pigment and protein analysis Chlorophyll was extracted from approximately 0.1 g of tissue in 5 ml of 90% acetone (v/v) using a glass tissue homogenizer. The homogenate was centrifuged at approximately 2,000 g for 15 min and chlorophyll a levels were determined following the equations described by Je€rey and Humphrey (1975). PE, PC and allophycocyanin (APC) were extracted in 5 ml of 0.1-M phosphate bu€er (pH 6.9), 1 mM EDTA, and 1 mM dithiothreitol (DTT) using a glass tissue homogenizer. The homogenate was centrifuged at approximately 2,000 g for 15 min and biliprotein levels were determined using the equations described by Kursar et al. (1983). Total protein levels were evaluated by disrupting approximately 0.1 g of tissue with 3 ml of extraction bu€er (0.1-M phosphate bu€er (pH 6.9), 1 mM EDTA, 1% (w/v) PVP, and 1 mM DTT) in a glass tissue homogenizer. Protein concentration of the extracts was estimated as described by Bradford (1976) and standardized against bovine serum albumin. Photosynthesis versus irradiance relationships Photosynthetic response and dark respiration were evaluated in the red and green morphotypes of K. alvarezii maintained under laboratory conditions. Photosynthetic and respiratory rates were evaluated polarographically on tissue segments. Lamps with halogen bulbs (500 W, quartzline) were used as light sources and photosynthetic photon ¯ux (PPF) was varied using neutral-density ®lters from 0 to 650 lmol photons á m)2 s)1. All measurements were conducted in 5-ml jacketed chambers at speci®c temperatures between 8 °C and 37 °C using a temperature-controlled water bath. Maximum oxygenic photosynthesis (Pmax), respiration (R), photosynthetic eciency (a), and the threshold for irradiance-saturated photosynthesis (Ik) were determined by a non-linear direct ®tting algorithm (Sigma Plot, Jandel Scienti®c) of the data to the exponential equation described by Webb et al. (1974). The e€ect of red light (k > 600 nm) on photosynthesis was evaluated at 25 °C on the red and green morphotypes of K. alvarezii. The photosynthetic response to increasing red light was evaluated by placing a red ®lter (HT026, Lee Filter, England) directly in front of the light path so that only k > 600 nm reached the incubation chambers. Lamps with halogen bulbs (500 W, quartzline) were used as light sources and PPF was varied using neutral-density ®lters from 0 to 650 lmol photons á m)2 s)1. Controls were evaluated using white light (without red ®lters) and photosynthesis was evaluated as described above. In vivo ¯uorescence Photoinhibition of photosynthesis was determined by evaluating in vivo chlorophyll ¯uorescence with a pulse amplitude-modulated ¯uorometer (PAM 2000, Waltz, E€eltrich, Germany) as described by Schreiber and Neubauer (1990). E€ective quantum yield (DF/Fm¢ ) from tissue exposed to di€erent light treatments is a measurement of the actual quantum yield for photosynthesis at the experimental irradiance, and its decrease at high experimental irradiances can be used as a measure of photoinhibition (Genty et al. 1989; Krause

681 and Weis 1991). Values of e€ective quantum yield were calculated as DF/Fm0 where DF ˆ Fm0 ) Ft0 , Fm0 is the maximal ¯uorescence and Ft0 is the basal steady-state ¯uorescence. Values of Ft0 and Fm0 in the tissue were determined at very low-intensity pulse of red light (650 nm, 0.3 lmol photons á m)2 s)1), and Fm0 was induced with a saturating white light pulses (0.4 s, approx. 9,000 lmol photons á m)2 s)1). E€ective quantum yield was determined in the algae submerged in seawater under white ¯uorescent light (Osram DL, 20W) at an irradiance of 50 lmol photons á m)2 s)1. Tissue from K. alvarezii was placed horizontally in a seawater cuvette with a cooling jacket (Walz, Germany) and fastened at a distance of 2 mm from the ®ber optic of the ¯uorometer. E€ect of UV light on photoinhibition of photosynthesis The e€ect of UV radiation on photoinhibition of the red and green morphotypes was determined by evaluating chlorophyll ¯uorescence. Values of DF/Fm0 were determined in both morphotypes prior to the experiments and then after a 1-h incubation period at noon under PAR + UV-A + UV-B (Ultraphan, Digrefa GmbH, Germany, k > 295 nm), PAR + UV-A (Folex 320 nm, Folex GmbH, Germany), and PAR alone (Ultraphan k > 395). The transmission spectra of the ®lters have been previously reported by Figueroa et al. (1997). After the experimental treatment, the algae were transported in a black container with seawater (17 °C) to the laboratory nearby and chlorophyll ¯uorescence was determined within 2 min of collection. It has been demonstrated that DF/Fm0 values do not vary within 10 min of collection of the algae from the ®eld (VinÄegla 2000). Levels of PAR were approximately 2,000 lmol photons á m)2 s)1, 53 W á m)2 UV-A, and approximately 1.5 W á m)2 UV-B during the incubation period. Incident PAR levels were determined with a LI±190SA 2p quantum sensor attached to a LI-COR data logger. Ultraviolet A and B radiation levels were determined using UV sensors connected to a RM-11 radiometer (Grobel Instruments, Germany). Values of UV radiation were corrected against an Optronic 752 double monochromator spectroradiometer (Optronic Labs, Florida, USA). After the incubation period, the individuals were placed in an incubator at approximately 10 lmol photons á m)2 s)1 PAR and 17 °C, and the recovery of DF/Fm0 was followed for 30 h in both morphotypes. Measurements were conducted on a minimum of six individuals. Statistical analysis Statistical di€erences in the pigment and protein levels between the red and green morphotypes of K. alvarezii were evaluated using Student t-tests. The statistical di€erence of growth rates and the e€ect of UV radiation in both morphotypes was evaluated with one-way analysis of variance (ANOVA) after testing for homoscedasticity and normality of the data (Sokal and Rohlf 1981). Speci®c di€erences were determined using Tukey's multiple comparison test. Slope di€erences were evaluated through an analysis of covariance (ANCOVA). Minimum signi®cance level was established at P < 0.05.

Results Pigments and protein The absorption spectra of some pigments varied in the red and green morphotypes of Kappaphycus alvarezii (Fig. 1). The chlorophyll and PE spectra showed similar absorbance patterns in the red and green morphotypes; the absorbance from PC and APC in the green morphotype, however, was approximately 2-fold greater than that of the red morphotype. As expected, PE peaks were

Fig. 1 Absorbance spectra of chlorophyll a (Chl a), organic soluble pigments, phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC) in the red and green morphotypes of Kappaphycus alvarezii

2- to 3-fold greater than PC and APC peaks in the red morphotype. However, absorbance peaks of PE, PC, and APC were relatively similar in the green morphotype. Biomass-normalized pigment levels also varied between the red and green morphotypes of K. alvarezii (Table 1). Chlorophyll a levels were statistically similar in the two morphotypes, which is inconsistent with observations by Dawes (1992). In general, the levels of PE were approximately 2-fold greater (P < 0.05) than PC and APC levels in the red morphotype, which is consistent with observations made in other rhodophytes. In contrast, the levels of PE, PC, and APC were similar in the green morphotype (P > 0.05). Levels of PE were statistically similar in the red and green morphotypes of K. alvarezii. However, PC levels were approximately 3fold greater in the green morphotype than in the red morphotype. Similarly, APC levels were 2-fold greater in the green morphotype than in the red morphotype. Protein levels were signi®cantly greater in the green than in the red morphotype of K. alvarezii. Biliprotein levels Table 1 Chlorophyll a, phycoerythrin, phycocyanin, allophycocyanin, and protein concentration and statistical signi®cance in the red and green morphotypes of Kappaphycus alvarezii. Values in parentheses indicate 1 SD. Degrees of freedom (df), statistical t value (t), probability value (P) Pigment level mg gFW)1

Morphotype

Chlorophyll a Phycoerythrin Phycocyanin Allophycocyanin

0.061 0.238 0.077 0.103

Total proteins

0.66 (0.11)

Red

df

t

P

Green (0.010) (0.037) (0.012) (0.015)

0.062 0.203 0.195 0.213

(0.009) (0.019) (0.016) (0.046)

0.76 (0.11)

5 0.91 n.s. 6 1.62 n.s. 6 11.99 600 nm) and white light controls. Bars represent average (n ˆ 6) and error bars one standard deviation

the green morphotype were 2-fold greater (P < 0.05) when incubated under red light, relative to the white light control (Fig. 5B). Values of a did not vary (P > 0.05) in the red morphotype when incubated in red light, relative to the white light control. E€ect of UV light on photoinhibition Values of DF/Fm0 decreased in the red and green morphotypes when exposed to high levels of UV-A, UV-B, or PAR. Values of DF/Fm0 in both morphotypes signi®cantly declined (P < 0.05) to approximately 30% of pretreatment levels after treatments with UV-A + UV-B + PAR, UV-A + PAR and to approximately 40% after treatments with PAR (Fig. 6). However, the decrease of DF/Fm0 was not signi®cantly di€erent (P > 0.05) among treatments. Complete recovery of DF/Fm0 was observed in the red and green morphotypes and all treatments after a 30-h incubation under no UV

Fig. 6A±C Relative values DF/Fm0 in the red and green morphotypes of K. alvarezii incubated under UV-A + UV-B + PAR, UV-A + PAR, and PAR. First data point represents pretreatment values followed by a 1-h light quality treatment (second data point). Photoinhibition recovery was determined after individuals were transferred to a low PAR and no UV radiation environment. Symbols represent average (n ˆ 6) and error bars one standard deviation

684

radiation and low photosynthetic photon ¯ux. Initial recovery slope of DF/Fm0 under all treatments was similar (P > 0.05) in the red morphotype, but the recovery of DF/Fm0 in the green morphotype treated with UV-B radiation showed signi®cantly lower (P < 0.05) values than those treated under UV-A or PAR (Fig. 7).

Discussion The evaluation of the physiological characteristics among mutants from algae and vascular plants has proved critical for understanding photosynthesis, pigment synthesis, and other autotrophic metabolic pathways (Schmidt and Lyman 1974; Russell and Dra€an 1978; Lam et al. 1995). Marine algae lacking chlorophyll or with varied concentrations of biliproteins are known to occur in nature or have been mutagenized by chemical treatments (Russell and Dra€an 1978; Kursar et al. 1983; Hurtado-Ponce 1995). Kappaphycus alvarezii is one of the most important sources of carrageenan in the world and the presence of green-pigmented morphotypes has been reported. It is not known, however, if such pigmentation provides a physiological advantage/ disadvantage relative to the red-pigmented morphotype (Doty et al. 1987; Dawes 1992; Hurtado-Ponce 1995). Here we characterized the photosynthetic response of red and green morphotypes of K. alvarezii under laboratory conditions. Our results clearly show that the pigment composition di€ers in the red and green morphotypes of K. alvarezii, but photosynthesis and growth are relatively similar in the two morphotypes when

Fig. 7 Recovery rates of DF/Fm0 values in the red and green morphotypes of K. alvarezii after a 1-h treatment under UV-A + UV-B + PAR, UV-A + PAR, and PAR. Bars represent average (n ˆ 6) and error bars one standard deviation

incubated under white light. Furthermore, there is a greater photoinhibition of the green morphotype when exposed to UV-B radiation compared to the red morphotype. The green pigmentation in the green morphotype of K. alvarezii has been assumed to be the result of low PE levels (Doty et al. 1987). Our results indicate rather, that the green pigmentation is the result of an overexpression of PC and APC in the green morphotype. Such elevated concentrations of PC and APC in the green morphotype mask the characteristic red coloration of this rhodophyte. Since proteins can be an important nitrogen reserve, it has been suggested that low levels of PE and other biliproteins are responsible for the lower ability of the green morphotype of K. alvarezii to store nitrogen, relative to the red morphotype (Dawes 1992). The increase in protein levels in the green morphotype here was accounted for by the increase in PC and APC levels, suggesting an increase of nitrogen reserves in the green morphotype relative to the red morphotype. The lack of expression or the overexpression of some pigments in some species has been shown to be metabolically disadvantageous for the mutant morphotypes when compared to the wild-natural morphotypes (Russell and Dra€an 1978; Kursar et al. 1983; Dawes 1992). Although there was a lag response in growth rates for approximately 1±2 weeks as a result of transferring the individuals to the outdoor culture system, growth rates increased rapidly afterwards and maintained similar values in both the green and red morphotypes throughout the study period. Similarly to growth, Pmax and a values showed comparable responses in the green and red morphotypes of K. alvarezii exposed to white light. This is in agreement with results observed by Hurtado-Ponce (1995) and Dawes (1992) and suggests that in culture systems or in the wild, the light requirements for maximum photosynthesis are ful®lled by the light-harvesting scheme of the red morphotype. In contrast to this study, relative growth rates under laboratory conditions have been reported to be generally greater in the red than in the green morphotype (Dawes et al. 1994); however, the pigment compositions of the morphotypes were not reported and are dicult to compare with results here. The results here also show that the overexpression of PC and APC does not impart a photosynthetic advantage to the green K. alvarezii morphotype when incubated in white light. This is consistent with results from other studies that demonstrate that an increase in pigment levels in rhodophytes does not always result in an increase of photosynthetic activity (Talarico 1996). Phycobilisomes are structured with an internal core of APC, several intermediate packets of PC, and an external layer of PE (Talarico 1996). As a consequence, the energy transfer in phycobilisomes is from PE to PC to APC. The lack of an increase in photosynthetic eciency (a) in the green morphotype, compared to the red one, suggests that PC and APC energy absorbance is much lower than that of PE and chlorophyll.

685

Values of Pmax in both morphotypes were maximal at approximately 30 °C, which is consistent with the observed optimum growth rate temperature for K. alvarezii in culture systems (Wu et al. 1989; Ohno et al. 1994). Maximum growth rates, however, were not maintained for prolonged periods in the culture systems here once temperature approached 30 °C. In contrast to Pmax, a values were optimal at lower incubation temperatures here. Such ¯uctuations in photosynthetic characteristics are consistent with results observed in other species (Davison 1987) and probably contribute to the ability of K. alvarezii to maximize growth rates over a wide temperature range. Additionally, temperature in culture systems where K. alvarezii is grown ¯uctuates from approximately 15 °C to above 30 °C (Wu et al. 1989; Ohno et al. 1994), indicating that seasonal temperature changes might regulate the photosynthetic and growth metabolism of this species. Morphological and physiological changes, including pigment levels and composition, have been observed in red algae incubated under red and blue light (Talarico 1996). Relative to white light controls, light-saturated photosynthesis decreased in the red morphotype when incubated under long wavelength light. At k > 600 nm, light absorbance by PS II is absorbed mainly by PC and APC (Kursar et al. 1983). As a consequence, the decrease in Pmax in the red morphotype is probably the result of insucient levels of PC and APC to harvest the incident red light. The greater a values observed in the green K. alvarezii morphotype incubated under red light (>600 nm) here are consistent with its greater levels of APC and PC compared to the red morphotype. As PE absorbs at wavelengths lower than 600 nm (Kursar et al. 1983; Lorenz et al. 1997), the overexpression of PC and APC (absorbance >600 nm) in the green morphotype probably results in an increase of photosynthetic eciency when incubated with k > 600 nm. However, the decrease of Pmax values of the red morphotype incubated with red light, relative to those incubated in white light, indicates that short wavelengths are more eciently used during photosynthesis, as observed in other species (Forster and Dring 1994). In the red treatment where PE is not absorbing, the increase of Pmax values in the green morphotype is explained by the overexpression of PC and APC, and the increased capacity for the absorbance of photons relative to the red morphotype. It is clear that photosynthetic characteristics vary as a function of pigment composition in K. alvarezii, but PE absorbance appears to saturate growth in both morphotypes grown under white light in the ®eld or culture systems. This might explain why the green morphotype of K. alvarezii has not been selected for/against in nature. The comparable photosynthetic response between the red and green morphotypes throughout the experimental temperatures is consistent with the similar growth rates observed in the culture tanks. These results suggest that the survival of the green morphotype in the ®eld is the result of similar photosynthetic and growth patterns

throughout the year as observed in other studies (Dawes et al. 1994). The low Pmax and a values observed for both morphotypes at 8 °C and 37 °C are probably the result of extreme experimental temperatures that would not be observed in the ®eld under normal conditions. The similar photoinhibitory e€ect of UV-A, UV-B, and PAR irradiance on DF/Fm0 of photosystem II in both morphotypes suggests that high levels of PAR account for most of the photoinhibition in K. alvarezii under the experimental conditions used here. These results are consistent with those observed in the red alga Palmaria palmata and other species where PAR, and not UV radiation, accounted for most of the photoinhibition (Lorenz et al. 1997; Aguirre-von-Wobeser et al. 2000). Photoinhibition in marine algae generally follows a diurnal pattern, with high DF/Fm0 values in the morning and afternoon and low photosynthetic activity at noon (HaÈder et al. 1996, 1997; Cabello-Pasini et al. 2000). As K. alvarezii grows or is cultured in shallow water columns (Doty et al. 1987), it is likely that both morphotypes exhibit photoinhibition, particularly during maximum irradiance levels at noon. The relatively high inhibition observed here after 1-h incubation at natural irradiance levels suggests that K. alvarezii might grow better at depths where elevated photon ¯ux is reduced, as observed for other species (Figueroa et al. 1997). However, the complete recovery of DF/Fm0 values after a few hours at low irradiances suggests an e€ective mechanism of photosystem repair that might provide an advantage over other species to inhabit environments with elevated UV and PAR levels. The ability to recover from photoinhibition was lowered when individuals were treated with UV-B, as observed for other rhodophytes (Figueroa et al. 1997; Lorenz et al. 1997). Hanelt et al. (1992) found that red seaweeds exposed to full solar radiation could have permanent photodamage after photoinhibition. Our results suggest that K. alvarezii has a high rate of photosystem repair that is critical for maintaining rapid growth rates in environments with elevated irradiance levels, such as those experienced in natural populations or culture systems. These experiments provide the ®rst evidence of the e€ect of light quality on the physiology and pigment composition of the red and green morphotypes of K. alvarezii from the Philippines. The results here suggest that photosynthesis and growth are not a€ected by an overexpression of PC and APC in red algae if PE levels remain constant. Although marked physiological di€erences between the two morphotypes are described here, there are no studies describing the frequency of these morphotypes in the wild. More investigations are also necessary to determine the possible advantage and the subsistence of the green morphotype of K. alvarezii in the natural environment. Acknowledgements We thank Dr. Jose Zertuche for providing the red and green morphotypes of Kappaphycus alvarezii, and Dr. David Chapman and Dr. Alejandro Buschmann for reviewing

686 the original manuscript. We thank Dr. D.-P. HaÈder for the calibration of the UV sensors. This work was supported by grants from the University of Baja California (UABC/IIO 4023, UABC 4078-30) and Consejo Nacional de Ciencia y TecnologõÂ a (I26655N). All experiments conducted within this study comply with the current laws of Mexico.

References Aguirre-von-Wobeser E, Figueroa FL, Cabello-Pasini A (2000) E€ect of UV radiation on photoinhibition of marine macrophytes in culture systems. J Appl Phycol 12: 159±168 Bradford MM (1976) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 72: 248±254 Cabello-Pasini A, Aguirre-von-Wobeser E, Figueroa FL (2000) E€ect of solar radiation on photoinhibition of marine macrophytes in culture systems. J Photochem Photobiol 57: 167±178 Davison IR (1987) Adaptation of photosynthesis in Laminaria saccharina (Phaeophyta) to changes in growth temperature. J Phycol 23: 273±283 Dawes CJ (1992) Irradiance acclimation of the cultured Philippine seaweeds, Kappaphycus alvarezii and Eucheuma denticulatum. Bot Mar 35: 189±195 Dawes CJ, Lluisma AO, Trono GC (1994) Laboratory and ®eld growth of commercial morphotypes of Eucheuma denticulatum and Kappaphycus alvarezii in the Philippines. J Appl Phycol 6: 21±24 Doty MS, Norris JN (1985) Eucheuma species (Soliriaceae, Rhodophyta) that are major sources of carrageenan. In: Abbott IA, Norris JN (eds) Taxonomy of economic seaweeds. California Sea Grant College, San Diego, pp 47±63 Doty MS, Caddy JF, Santelises B (1987) The production and use of Eucheuma. In: Doty MS, Caddy JF, Santelices B (eds) Case studies of seven commercial seaweed resources. FAO, Rome, pp 124±164 Figueroa FL, Salles S, Aguilera J, Jimenez C, Mercado J, VinÄegla B, Flores-Moya A, Altamirano M (1997) E€ects of solar radiation on photoinhibition and pigmentation in the red alga Porphyra leucosticta. Mar Ecol Prog Ser 151: 81±90 Forster RM, Dring MJ (1994) In¯uence of blue light on the photosynthetic capacity of marine plants from di€erent taxonomic, ecological and morphological groups. Eur J Phycol 29: 21±27 Ganzon-Fortes ET, Azanza-Corrales R, Aliaza T (1993) Comparison of photosynthetic responses of healthy and ``diseased'' Kappaphycus alvarezii (Doty) Doty using P vs. I curve. Bot Mar 36: 503±506 Genty B, Briantais JM, Baker NR (1989) The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll ¯uorescence. Biochem Biophys Acta 990: 87±92 HaÈder DP, Lebert M, Mercado J, Aguilera J, Salles S, Flores-Moya A, Jimenez C, Figueroa FL (1996) Photosynthetic oxygen production and PAM ¯uorescence in the brown alga Padina pavonica measured in the ®eld under solar radiation. Mar Biol 127: 61±66

HaÈder DP, Lebert M, Flores-Moya A, Jimenez C, Mercado J, Salles S, Aguilera J, Figueroa FL (1997) E€ects of solar radiation on the photosynthetic activity of the red alga Corallina elongata Ellis et Soland. J Photochem Photobiol 37: 196± 202 Hanelt D (1992) Photoinhibition of photosynthesis in marine macrophytes of the south Chinese Sea. Mar Ecol Prog Ser 82: 199±206 Hurtado-Ponce AQ (1995) Carrageenan properties and proximate composition of three morphotypes of Kappaphycus alvarezii Doty (Gigartinales, Rhodophyta) grown at two depths. Bot Mar 38: 215±219 Je€rey SW, Humphrey GF (1975) New spectrophotometric equations for determining chlorophylls a, b, c1 and c2 in higher plants, algae and natural phytoplankton. Biochem Physiol P¯anz167: 191±194 Krause GH, Weis E (1991) Chlorophyll ¯uorescence and photosynthesis: the basics. Annu Rev Plant Physiol Plant Mol Biol 42: 313±349 Kursar TA, Van der Meer J, Alberte RS (1983) Light-harvesting system of the red alga Gracilaria tikvahiae. I. Biochemical analyses of pigment mutations. Plant Physiol 73: 353±360 Lam HM, Coschigano K, Schultz C, Melo-Oliveira R, Tjaden G, Oliveira I, Ngal N, Hsieh MH, Coruzzi G (1995) Use of Arabidopsis mutants and genes to study amides amino acid biosynthesis. Plant Cell 7: 887±898 Lorenz M, Schubert H, Forster RM (1997) In vitro- and in vivoe€ects of ultraviolet-B radiation on the energy transfer in phycobilisomes. Photosynthetica 33: 517±527 Ohno M, Largo DB, Ikumoto T (1994) Growth rate, carrageenan yield and gel properties of cultured kappa-carrageenan producing red alga Kappaphycus alvarezii (Doty) Doty in the subtropical waters of Shikoku, Japan. J Appl Phycol 6: 1±5 Russell GK, Dra€an AG (1978) Light-induced enzyme formation in a chlorophyll-less mutant of Euglena gracilis. Plant Physiol 62: 678±682 Schmidt GW, Lyman H (1974) Photocontrol of chloroplast enzyme synthesis in mutant and wild-type Euglena gracilis. In: Weizmann Institute of Science (ed) Proceedings of the Third International Congress on Photosynthesis. Elsevier, Amsterdam, pp 1755±1764 Schreiber U, Neubauer C (1990) O2 dependent electron ¯ow, membrane energization and mechanism of non-photochemical quenching of chlorophyll ¯uorescence. Photosynth Res 25: 279± 293 Sokal RR, Rohlf FJ (1981) Biometry. Freeman, New York Talarico L (1996) Phycobiliproteins and phycobilisomes in red algae: adaptive responses to light. Sci Mar 60: 205±222 VinÄegla B (2000) Efecto de la radiacion UV sobre actividades enzimaticas relacionadas con el metabolismo del carbono y nitrogeno en macroalgas y fanerogamas marinas. Ph.D. dissertation, Universidad de Malaga, Spain Webb WL, Newton M, Starr D (1974) Carbon dioxide exchange of Alnus rubra. A mathematical model. Oecologia 17: 281±291 Wu C, Li J, Xia E, Peng Z, Tan S, Li J, Wen Z, Huang X, Cai Z, Chen G (1989) On the transplantation and cultivation of Kappaphycus alvarezii in China. Chin J Oceanol Limnol 7: 327± 334