Effect of aluminum on cellular division and photosynthetic electron transport in Euglena gracilis and Chlamydomonas acidophila

Environmental Toxicology and Chemistry, Vol. 29, No. 4, pp. 887–892, 2010# 2009 SETAC

Printed in the USADOI: 10.1002/etc.109

EFFECT OF ALUMINUM ON CELLULAR DIVISION AND PHOTOSYNTHETIC ELECTRON

FRANCOIS PERREAULT,y DAVID DEWEZ,y CLAUDE FORTIN,z PHILIPPE JUNEAU,§ AMIROU DIALLO,k and RADOVAN POPOVIC*yyDepartment of Chemistry, Universite du Quebec a Montreal, C.P. 8888, Succ. Centre-Ville, Montreal, Quebec, H3C 3P8 Canada

zInstitut National de Recherche Scientifique, Eau Terre et Environnement, Universite du Quebec, 490 rue de la Couronne, Quebec, Quebec, G1K 9A9 Canada

§Department of Biological Sciences-Centre de Recherche en Toxicologie de l’environnement, Universite du Quebec a Montreal, C.P. 8888,Succ. Centre-Ville, Montreal, Quebec, H3C 3P8 Canada

kDepartement de Biodiversite et Amenagement du territoire, Centre d’Etude et de Recherche en Environnement, Universite de Conakry,Conakry, BP 1147 Guinea

(Submitted 14 April 2009; Returned for Revision 26 July 2009; Accepted 19 October 2009)

* T(popov

Pub(www.

Abstract—The present study investigated aluminum’s effect on cellular division and the photosynthetic processes in Euglena gracilisand Chlamydomonas acidophila at pH 3.0, at which Al is present mostly as Al3þ, AlSO4

þ, and Al(SO4)2�. These algal species were

exposed to 100, 188, and 740mM Al, and after 24 h cell-bound Al was significantly different from control only for the highestconcentration tested. However, very different effects of Al on algal cellular division, biomass per cell, and photosynthetic activity werefound. Aluminum stimulated cell division but decreased at some level biomass per cell in C. acidophila. Primary photochemistry ofphotosynthesis, as Photosystem II quantum yield, and energy dissipation via nonphotochemical activity were slightly affected. However,for E. gracilis, under the same conditions, Al did not show a stimulating effect on cellular division or photosynthetic activity. Primaryphotochemical activity was diminished, and energy dissipation via nonphotochemical pathways was strongly increased. Therefore,when Al is highly available in aquatic ecosystems, these effects may indicate very different response mechanisms that are dependent onalgal species. Environ. Toxicol. Chem. 2010;29:887–892. # 2009 SETAC

Keywords—Aluminum Photosynthesis Algae Acid environment

INTRODUCTION

Acid rain may result in acidification of the aquatic environ-

ment, increasing the solubility of metals [1], and it has been

shown that such ecosystems, under some conditions, can reach

high concentrations of soluble aluminum [2,3]. Solubility of Al

is dependent on pH, and, at neutral pH, this metal is present

mostly as insoluble complexes that are less bioavailable to

aquatic organisms [4]. At low pH, below 5.0, because of the

increased Al3þ concentration, toxicity will be more pronounced

[5,6]. However, at low pH, competition between Hþ and Al3þ

ions for binding sites on the cell surface may at some level

reduce this toxicity [7]. Aluminum appeared to have different

effects on growth of aquatic species, in that, for some algae and

bacteria species, it was found to induce inhibition [5,8,9],

whereas, for other microorganisms, growth rate was increased

[10–12]. Therefore, Al interactions with unicellular algae are

dependent on algal species, metal concentration and bioavail-

ability, which may result in complex interactions.

When Euglena gracilis has been exposed to Al for either

short or long durations, photosynthetic efficiency was shown to

be decreased [13]. A strong decrease of oxygen evolution and

variable fluorescence as photosynthetic parameters has been

reported for Caulerpa taxifolia when exposed to 1 mM Al [14].

Therefore, when photosynthetic processes are altered, it can be

expected that algal growth will also be affected. The primary

o whom correspondence may be [email protected]).lished online 31 December 2009 in Wiley InterScienceinterscience.wiley.com).

887

target of metal inhibition in photosynthesis was shown to be

photosystem II (PSII). Different sites of such interaction

have been noted; the PSII electron donor side, associated with

oxygen-evolving complex and, at QB, PSII electron acceptor

side [15,16]. However, the sites of Al inhibition of electron

transport in some unicellular algae are still the subject of debate

[5,9,13]. When photosynthetic electron transport is altered, it is

known that alternative pathways of energy dissipation will

develop to prevent photoinhibition by excess light energy

absorbed via chlorophyll in the light-harvesting complex but

not used for electron transport [17]. It is important to mention

that metal inhibition of photosynthetic electron transport may

consequently increase the sensitivity of PSII to photoinhibition,

as has been reported for Cu [18,19].

When Al is highly available, the mechanism of Al inter-

action with photosynthesis and its effect on cellular division of

unicellular algae are still mostly unclear. By providing high

availability of Al to Euglena gracilis and Chlamydomonasacidophila, the present study investigated the specificity of

Al interaction with cellular division and photosynthetic proc-

esses concerning primary photochemistry, electron transport

efficiency, and distribution of light energy dissipation via PSII.

MATERIALS AND METHODS

Algal culture

Euglena gracilis (UTCC 95) and Chlamydomonas acido-phila (UTCC 121) were obtained from the University of

Toronto Culture Collection (UTCC, Canada) and cultivated

888 Environ. Toxicol. Chem. 29, 2010 F. Perreault et al.

in 1-L batch cultures in growth medium [20]. Cultures were

grown under continuous illumination (100� 5mE m�2 s�1)

provided by white fluorescent lamps (Grolux F 36 W; Osram

Sylvania) with continuous aeration at 25� 18C. Algal cells for

Al exposure were taken from cultures during exponential

growth. Aluminum stock solution (0.25 mM) was prepared with

Al2(SO4)3 � 18 H2O (Thermo Fisher Scientific) in acidified

nanopure water. Medium used for Al exposure was the same

as growth medium with the exception that ethylenediaminete-

traacetic acid (EDTA) was omitted. Chlorophyll concentration

in exposed cultures was 0.25mg/ml in a total volume of 50 ml,

in which pH was adjusted to 3.0. Aluminum speciation in the

treatment medium was calculated with MINEQLþ v 4.5 soft-

ware [21]. For all treatment conditions, Al speciation was

constant; the main Al forms were Al3þ (27%), AlSOþ4

(45%), and Al(SO4)�2 (24%). Under these conditions, free

Al3þ was highly available for algal cells. It is important to

mention that, at this pH, growth of both species has been shown

to be in the optimal range [22,23]. Concentrations of measured

total dissolved Al (mM) used for treatments were 100� 11,

185� 5, and 840� 80 for E. gracilis and 99� 1, 191� 6, and

640� 50 for C. acidophila (n¼ 3). For brevity, these concen-

trations are referred to hereafter as 100, 188, and 740mM.

Samples with no addition of Al were considered as controls, in

which measured Al concentration was below the detection limit

(<0.08mM).

To determine the change in dry weight when algal cultures

had been exposed for 24 h to Al, algal cells culture was filtered

on No. 1 Whatman filter paper and dried at 1058C during 48 h

before weight measurement. The change in cell density was

measured by flow cytometry (FacScan; Becton Dickinson

Instruments) by using fluorescent microbead (Microspheres)

suspensions of a known concentration, according to Robins and

Bedo [24]. Size threshold of the cytometer was fixed just below

the size of the microbeads. To discriminate among algal cells,

microbeads, and noncellular particles, all measurements were

separated by using a relationship between particle size and red

fluorescence level. Algal cells (large particles with a high level

of red fluorescence resulting from the chlorophyll fluorescence)

and microbeads (small size and low fluorescence level) permit-

ted correct cell counts and discrimination of others events.

Algae cell count was made using the algae/microbeads ratio:

cell density¼ (% algal cell/% microbeads)microbeads den-

sity. Total chlorophyll (a þ b) was extracted in 100% methanol

at 658C, and quantitative determination was done according

to Lichtenthaler [25]. Before determination of cell-bound Al,

aliquots of exposed algal cells (25 ml) were harvested on

cellulose nitrate filter membranes (Millipore HAWP02500)

placed in filter holders. Cells were washed with 30 ml

of 20 mM EDTA to remove adsorbed Al on cell surface.

Aluminum concentration was determined by inductively

coupled plasma atomic emission spectrometry (ICP-AES; Vista

AX; Varian). Algal samples were mineralized by with concen-

trated HNO3 (600ml) and hydrogen peroxide (75ml) for 24 h at

room temperature. Prior to measurement, samples were diluted

to 6% HNO3 by addition of 10 ml nanopure water. Values were

then normalized per mass unit (mg Al/g algal dry weight).

Before fluorescence measurements, exposed cells were dark

adapted for 30 min to obtain equilibrium of PSII oxido-reduction

state. An aliquot of algal cells (5mg chlorophyll) was placed on a

13-mm glass fiber filter (Millipore No. AP20 01300) by low-

pressure filtration to obtain a humidified, uniform layer of algal

cells on the surface. This approach did not induce physiological

stress to algal cells, which might affect fluorescence measure-

ments [26]. The rapid, polyphasic rise of chlorophyll a fluore-

scence was measured with a plant efficiency analyzer (PEA)

fluorimeter (Hansatech) by using a 2-s saturating flash

(2,500mE m�2 s�1). The fluorescence yield at 50ms was con-

sidered to be the FO value, noted as F50ms. Maximum fluores-

cence yield P was considered as the maximal value of

fluorescence yield under saturating illumination. The variable

fluorescence yields for J and I transients were determined at 2 ms

(F2ms) and 30 ms (F30ms), respectively. The ratio of total antenna

size per active reaction center (ABS/RC) was determined

as ([Mo/Vj]/[Fv/FM]), where Mo¼ (4[F300ms � F50ms]/[FM �F50ms]) and Vj¼ ([F2ms � F50ms]/[FM � F50ms]). This measure-

ment and analytical approach was used according to Strasser

et al. [27]. According to Rohacek and Bartak [28], modulated Chl

a fluorescence kinetics were measured by using pulse amplitude

modulated fluorescence (PAM; FMS/2S; Hansatech). The

fluorescence, FO, was evaluated by using a modulated light with

a low intensity (1mE m�2 s�1) to avoid the reduction of PSII

primary electron acceptor, QA. The maximal fluorescence

yield, FM, was induced by a short, saturating pulse of white

light (2,000mE m�2 s�1, 0.7 s duration), which triggered

the maximal reduction state of PSII. The value of FS was

determined at the steady state of variable fluorescence obtained

when algal samples were exposed continuously (15 min) to

100mE m�2 s�1 of actinic light. The maximal fluorescence

yield, F0M, was determined by application of a saturating

pulse (2,000mE m�2 s�1, 0.7 s duration) at steady state of

fluorescence when algal cells were exposed to continuous actinic

light illumination. To measure F0O at a steady state of electron

transport, actinic light was turned off, and far-red light was

applied to induce maximal oxidation of all PSII primary electron

acceptor QA. Therefore, fluorescence F0O obtained under this

condition represents the fluorescence yield when most PSII

reaction centers are in the open state. The maximal PSII quantum

yield, indicating efficiency of light energy transfer to primary

acceptor QA, was the ratio at which FMII¼ (FM � FO)/FM [29].

According to Genty et al. [30], at steady state of fluorescence

yield (15 min under continuous actinic light), the operational

quantum yield was determined as the ratio F0MII¼ (F0

M � FS)/F0

M, and the photochemical quenching value was evaluated as

qP¼ (F0M � FS)/(F0

M � F0O) representing the photochemical

energy conversion at PSII reaction centers when the primary

acceptor QA has been oxidized [31]. The fluorescence quenching

that was not related to photochemistry of PSII was measured

as qN¼ 1 � ([F0M � F0

O]/[FM � FO]) [32]. Parameters that

represent nonphotochemical energy fluxes of PSII were deter-

mined according to Kramer et al. [33]: the yield of nonphoto-

chemical energy dissipation via PSII nonregulated pathways was

FNO¼ 1/(([FM � F0

M]/F0

M) þ 1 þ (qP[FO0/F])(FM/FO � 1)); the

yield of PSII nonphotochemical energy dissipation via regulated

pathways was FNPQ¼ 1 � F0MII � FNO. The sum of F0

MII þFNO þ FNPQ¼ 1 was the total energy dissipation via PSII.

Data analysis and statistical analysis

The treatments were done in three replicates, and three

samples were analyzed for each replicate. Means and standard

Aluminum’s effect on algal growth and photosynthesis Environ. Toxicol. Chem. 29, 2010 889

deviations were calculated for each treatment. Significant dif-

ferences between control samples and Al-exposed algal samples

were determined by analysis of variance and Tukey honestly

significant differences test, and a p value less than 0.05 was

considered to be significant.

RESULTS AND DISCUSSION

Cell-bound Al has been investigated in two different algal

species, E. gracilis and C. acidophila, when they were exposed

during 24 h to 100, 188, and 740mM of Al. Aluminum content

for both species, when exposed to 100 and 188mM of Al,

was less than or equal to 0.02mg Al/mg dry weight, and no

significant differences were found when Al treatments were

compared with control samples ( p> 0.05; see Fig. 1). However,

at the highest concentration tested, Al uptake increased up to

approximately 4mg/mg for both species. This may be inter-

preted as a large increase of cell-bound Al resulting from

adherence of polymeric Al complexes within the intracellular

space or at the cell surface resisting the EDTA wash because of

its slow complexation kinetics. It has been shown earlier that

Chara corallina binds high amounts of nonexchangable Al on

the algal cell wall at pH 3.7. This has been hypothesised to be a

consequence of Al precipitation or polymerization into the cell

wall [34]. The present study shows no significant differences in

cell-bound concentrations of Al when the two algal species

were compared (Fig. 1). Because E. gracilis and C. acidophilahave different sensitivities to metals effects, it was of interest to

compare their specific toxic responses to Al.

The evaluation of Al’s effect on algal culture growth

was done by measuring both cellular division and biomass

production as dry weight. Growth of C. acidophila cultures

was evidently affected after 24 h exposure to Al. For

C. acidophila, cellular growth was shown to be dependent

on Al concentration, and at 740mM Al cellular division was

increased by 140%, whereas for E. gracilis, such a change was

not found. The increases in cell density and chlorophyll con-

centration in C. acidophila were very similar at 100 and 188mM

of Al, but, at 740mM Al for this algal species, the increase in

chlorophyll concentration was diminished compared with the

Fig. 1. Total cell-boundaluminumper dry weightofalgalbiomass inEuglenagracilis (white bars) and Chlamydomonas acidophila (gray bars) after 24 h ofexposure. A and B indicate significantly different results (p< 0.05).

increase in cell density. This difference indicated that, at this

concentration of Al, chlorophyll synthesis per cell was

decreased (Fig. 2). It should be mentioned that similar concen-

trations of cell-bound Al found for E. gracilis and C. acidophila(�4mg/mg), exposed to 740mM Al, did not induce a similar

effect on cell density and chlorophyll synthesis. Therefore,

the increase in cell density and chlorophyll synthesis in

C. acidophila is due to different mechanisms of acclimation

to high Al concentration. Compared with E. gracilis,

C. acidophila appeared to be highly adapted to maintain cellular

physiology at a low pH and a high concentration of Al. The

effect of Al on cellular division might have a different effect

that is dependent on pH conditions and algal species adaptation

to these conditions. In earlier reports, it was found that, at

neutral pH, Al may have an opposite effect, insofar as cellular

division of Dunaliella parva was decreased [10], whereas for

Scenedesmus obtusiusculus it was increased [11]. In the present

study, in which a low pH value (3.0) was used, Al induced very

different effects on E. gracilis compared with C. acidophila.

Moreover, it was observed that. for C. acidophila, cellular

division was not correlated with the change in dry weight. It

appeared that, after Al exposure, cellular synthetic processes

were affected, because dry weight per cell was decreased by

half. Indeed, it was evident that Al decreased cellular biomass

regardless of the increase in cellular division. It should be noted

that such an Al effect was seen for the first time. In earlier

studies, it has been reported that Al decreases total ATP cellular

Fig. 2. Changes in cell density, dry weight, and total chlorophyll permilliliter of culture in Euglena gracilis (white bars) and Chlamydomonasacidophila (gray bars) after 24 h of exposure to aluminum. The letters A–Dindicate significantly different results (p< 0.05).

890 Environ. Toxicol. Chem. 29, 2010 F. Perreault et al.

content, probably because of its synthesis inhibition [5,35].

Therefore, it is expected that, when ATP content is decreased,

biosynthetic processes will be affected. Indeed, in the present

study, the decrease of dry weight per cell when E. gracilis and

C. acidophila were exposed to Al may be caused by diminished

cellular metabolism that will require ATP synthesis. It was

evident that chlorophyll levels determine the capacity of the

photosynthetic light-harvesting complex [36] responsible for

photosynthetic efficiency and, consequently, ATP synthesis

necessary for cellular synthetic processes. The present study

shows that Al induced a decrease of photosynthetic capacity of

the cell by decreasing PSII capacity for charge separation at the

PSII reaction center. Indeed, in the presence of 740mM Al,

PSII primary photochemistry was decreased. Interestingly, PSII

photochemistry appeared to be more affected in E. graciliscompared with C. acidophila. It appeared that PSII electron

transport dependent on reduction of plastoquinones (PQ) was

decrease by 50 and 20% in E. gracilis and C. acidophila,

respectively. This comparison was made on the basis of fluo-

rescence yield at P transient (Fig. 3). For both cases, the present

study found that Al has no altering effects on the presence of

O-J-I-P fluorescence transients, regardless of change in fluo-

rescence yield. Such an Al effect may be interpreted similarly to

that observed in a study of copper and mercury effects on

the water-splitting system. When Dunaliella tertiolecta and

Scenedesmus obliquus were inhibited by Cu and Hg, causing

water-splitting system inhibition, the yield of variable fluore-

scence was decreased but without any change in rapid fluo-

rescence transients [26,37]. This indicates that Al’s inhibitory

effect may be associated with the water-splitting system. Based

on this interpretation, it appeared that Al induces inactivation of

some PSII reaction centers and consequently diminishes total

PSII electron transport capacity toward PSI (see the rapid

fluorescence transient). This interpretation is in agreement with

some earlier findings based on Al’s effect on reconstructed

chloroplast electron transport in Chlorella vulgaris. By using

Fig. 3. Changes in the rapid polyphasic chlorophyll a fluorescence rise in Euglena gof aluminum for 24 h. Numbers represent micromolar Al concentrations.

exogenous electron acceptors, acting before the PQ pool, Al was

found to induce inhibition of electron transport from the water-

splitting system toward PQ [5].

To date, Al’s effects on functioning properties of photo-

synthetic apparatus in unicellular algae under light-adapted

conditions are not well known. Therefore, to obtain more

information, the present study examined the change in different

photosynthetic fluorescence parameters indicating distribution

of energy dissipation in photosynthesis when Al effect takes

place (Table 1). The change in PSII maximal quantum

yield may indicate how much of the absorbed light energy is

converted by the primary photochemical act responsible for

photosynthetic electron transport. It appeared that maximal PSII

quantum yield, FMII, of E. gracilis was decreased from 0.66 to

0.25, whereas for C. acidophila the decrease was only from

0.70 to 0.62. These results are in agreement with the change in

variable fluorescence observed at the O-J-I-P rapid fluorescence

rise in E. gracilis and C. acidophila affected by Al (Fig. 3).

However, the change in PSII operational quantum yield, F0MII,

may show an integrated Al effect on total PSII–PSI electron

transport. Here, the strong susceptibility of E. gracilis to the Al

effect compared with C. acidophila is evident, in that the PSII

operational quantum yield measured at steady state of fluore-

scence, F0MII, was found to decrease in E. gracilis from 0.27 to

0.07 and in C. acidophila from 0.62 to 0.48. At this point,

there is no adequate explanation for why C. acidophila was

more resistant when high levels of cell-bound Al were found

(see Fig. 1). Growth resistance of C. acidophila to Cd, Co, Cu,

and Zn was noted earlier [38]. However, the resistance of algae

to Al has still not been fully investigated, especially with

respect to photosynthetic processes. The present study may

advance some interpretations of how Al affects energy distri-

bution in photosynthesis of E. gracilis and C. acidophila. It was

important to find out how Al may change ther photochemical

quenching value qP, a parameter that indicates the capacity for

PSII reaction centers to convert absorbed light energy into

racilis and Chlamydomonas acidophila exposed to increasing concentrations

Table 1. Changes in chlorophyll a fluorescence parameters in Euglena gracilis and Chlamydomonas acidophila exposed to different aluminum concentrations

Fluorescence parameter

Aluminum concentration (mM)

Control 188 740

E. gracilis FMIIa 0.66� 0.04 A 0.39� 0.04 B 0.25� 0.04 CF0MIIb 0.27� 0.02 A 0.19� 0.03 B 0.07� 0.02 C

qPc 0.55� 0.551 A 0.41� 0.07 B 0.21� 0.08 CqNd 0.24� 0.16 A 0.40� 0.21 A 0.80� 0.03 B

ABS/RCe 5.32� 0.43 A 5.37� 0.24 A 9.51� 0.72 BFNPQf 0.10� 0.06 A 0.14� 0.06 AB 0.22� 0.01 BFNOg 0.63� 0.02 A 0.67� 0.03 AB 0.71� 0.04 B

C. acidophila FMII 0.70� 0.04 A 0.64� 0.02 A 0.62� 0.02 AF0MII 0.62� 0.05 A 0.55� 0.03 AB 0.48� 0.05 B

qP 0.74� 0.01 A 0.70� 0.02 A 0.61� 0.04 BqN 0.63� 0.08 A 0.70� 0.09 A 0.80� 0.06 A

ABS/RC 1.06� 0.05 A 1.46� 0.01 B 1.39� 0.01 BFNPQ 0.09� 0.03 A 0.09� 0.01 A 0.13� 0.02 AFNO 0.29� 0.04 A 0.36� 0.02 AB 0.39� 0.03 B

Letters A–C indicate significantly different results (p< 0.05). For further details on parameter definitions see Materials and Methods.a Photosystem II maximal quantum yield.b Photosystem II operational quantum yield.c Photochemical quenching of fluorescence.d Nonphotochemical quenching of fluorescence.e Effective antenna size per active reaction center.f Yield of regulated nonphotochemical energy dissipation of Photosystem II.g Yield of nonregulated nonphotochemical energy dissipation of Photosystem II.

Aluminum’s effect on algal growth and photosynthesis Environ. Toxicol. Chem. 29, 2010 891

charge separation and photosynthetic electron transport. After

24 h of exposure, qP was decreased from 0.55 to 0.21 for

E. gracilis, whereas this decrease was only from 0.74 to 0.61

for C. acidophila. When conversion of absorbed light energy

into electron transport has deteriorated, it is known that the

dissipation of energy will take place via thermal pathways [39].

This was indicative that nonphotochemical quenching of

fluorescence qN, a parameter indicating thermal dissipation,

was rapidly increased when E. gracilis was exposed to Al in

comparison with C. acidophila (see Table 1). In this study, the

change found for PSII energy dissipation in E. gracilis may

indicate that Al causes inactivation of some active PSII reaction

centers, causing the increase of thermal dissipation. High

amounts of inactive reaction centers should consequently

increase energy dissipation via nonphotochemical pathways.

Such an interpretation is supported by data showing that the

ABS/RC ratio, reflecting the total light-harvesting antenna

complex available per active reaction center, increased

from 5.05 to 8.42 in E. gracilis. This indicated that, after

the Al-induced inactivation of some PSII reaction centers,

more antenna chlorophyll was available per remaining active

PSII reaction center (Table 1). For the Al-resistant alga

C. acidophila, there were small changes of energy dissipation

via a nonphotochemical pathway, which may indicate that

fewer inactive PSII reaction centers were induced by Al.

Consequently, chlorophyll antenna per active reaction center

did not change drastically; the variation in ABS/RC ratio was

from 1.06 to 1.39. According to Kramer et al. [33], the increase

in energy dissipation via nonphotochemical pathways can be

the result of regulated (light-induced increase of thermal

energy dissipation, FNPQ) or nonregulated processes, called

basal thermal energy dissipation (FNO). For E. gracilis, FNPQ

and FNO were increased, whereas F0MII was remarkably

decreased. For the same effect, a smaller increase was found

for C. acidophila. It appeared that the change in those para-

meters when E. gracilis and C. acidophila were exposed to Al

showed the same tendency as qN and qP [31]. Differences in

PSII energy dissipation with exposure to Al may also be the

result of incapacity of the cell to regulate its intracellular pH,

resulting in acidification of the lumen, which consequently

may change transthylakoidal pH-dependent energy dissipation

processes. This interpretation is supported by earlier reports

concerning Al’s effect on proton transfer through the cell

membrane [40]. The present study tested how pH affects

energy dissipation processes in both algal species. By

using pH 3 and pH 7 control cultures, for C. acidophila, no

difference was found in PSII energy dissipation pathways

between pH 3 and pH7 control cultures, indicating that this

algal species has a good capacity to regulate its intracellular pH

(data not shown). For E. gracilis, at pH 7 compared with pH 3,

F0MII was decreased from 0.27 to 0.16 and FNPQ from 0.10 to

0.05, whereas FNO was increased from 0.63 to 0.79 (data not

shown). However, when the pH effect was compared with the

Al effect, which increased both regulated and nonregulated

nonphotochemical energy dissipation, it was evident that

intracellular pH change cannot explain Al toxicity.

CONCLUSIONS

The present study concluded that, when Al was highly

bioavailable, the effect of this metal on cell division and

photosynthesis was highly dependent on algal species. It

appeared that C. acidophila was well adapted to those con-

ditions, insofar as Al stimulated cell division but at some

level decreased biomass per cell. In this alga, photosynthetic

processes were slightly affected, because fluorescence para-

meters showed efficient primary photochemical activity and

electron transport capacity, even in the presence of high levels

of cell-bound Al. However, for E. gracilis, under the same

conditions, Al did not have a stimulating effect on cellular

892 Environ. Toxicol. Chem. 29, 2010 F. Perreault et al.

division. Moreover, in this alga species, Al induced strong

alteration of photosynthesis, indicated by diminished photo-

synthetic electron transport and increased energy dissipation via

heat. When Al is highly available in aquatic ecosystems, these

effects may indicate very different response mechanisms of

algal species to Al exposure.

Acknowledgement—This research was financially supported by a FondQuebecois de la Recherche sur la Nature et les Technologies team researchproject grant awarded to R. Popovic and C. Fortin. F. Perreault was supportedby a Natural Sciences and Engineering Research Council PhD fellowship. A.Diallo was supported by the Canadian International Development Agency.The authors thank Michel Lavoie for his technical assistance with ICP-AES.

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