The pyrenoid ultrastructure in Oocystis lacustris CHODAT ... - Fottea

Fottea 9(1): 149–154, 2009 149 

The pyrenoid ultrastructure in Oocystis lacustris Ch o d at (Chlorophyta, 

Trebouxiophyceae) 

Maya P. St o y n e va 1 , Elisabeth In g o l I ć 2 , Georg Gä rt n e r 3* & Wim vy v e r m a n 4 

1 Sofia University “St Kliment Ohridski”, Faculty of Biology, Department of Botany, 8 bld. Dragan Zankov, BG– 

1164 Sofia, Bulgaria 

2 Forschungsinstitut für Elektronenmikroskopie und Feinstrukturforschung, Steyrergasse 17, A–8010 Graz, 

Austria 

3* Leopold-Franzens-Universität Innsbruck, Institut für Botanik, Sternwartestr. 15, A–6020 Innsbruck, Austria; 

corresponding author: e-mail: georg.gaertner@uibk.ac.at 

4 Ghent University, Department Biology, Laboratory of Protistology and Aquatic Ecology, Krijgslaan 281–S8, 

B–9000 Gent, Belgium 

Dedicated to Dr. Pe t r ma rva n on the occasion of his 80 th birthday 

Abstract: The fine structure of vegetative cells of Oocystis lacustris has been studied with special attention to 

the ultrastructure of the pyrenoid and its starch sheath. The TEM-investigation showed that the pyrenoid matrix 

is homogenous, not traversed by thylakoids and the surrounding starch sheath is continuous, horseshoe-shaped or 

fragmented in 2 starch plates. This starch sheath structure is regarded as a common feature within Oocystis and 

closely related genera Eremosphaera and Neglectella. 

Key words: Oocystis lacustris, ultrastructure, pyrenoids, starch sheath 

Introduction 

Photosynthetic pigments, storage products and 

structure of plastids are some of the important 

features in the taxonomy of eukaryotic algae. In 

many types of algae within the chloroplast occurs 

a dense proteinaceous body, visible with light 

microscope and designated as a pyrenoid. The 

term “pyrenoid” was created by Sc h m i t z (1882) 

who was the first to associate this structure with an 

effect on the accumulation of starch grains in the 

chloroplasts of green algae. Nowadays it is well 

known that pyrenoids contain the carbon fixing 

enzyme Rubisco and are commonly associated 

with formation of storage products (e.g. Gr a h a m 

& Wi l c o x 2000, le e 2008). A remarkable number 

of morphological types of pyrenoids exists (e.g. 

Do D G e 1973, et t l 1980, Wh at l e y 1993). The 

absence or presence of pyrenoids in vegetative 

cells was already used as a taxonomic criterion 

on the generic level of algae (Sta r r 1955, hi n D a k 

1977-1990) whereas the morphology of the starch 

sheath itself, its structure, and location can assist 

in the identification of green algal species (Br o W n 

& mcle a n 1969, et t l 1976, ko m á r e k & Fo t t 

1983, et t l & Gä rt n e r 1988a). The starch sheath 

of green algal pyrenoids is normally visible with 

light microscopе (et t l 1980) especially when 

stained with reagents such as Lugol’s iodine 

solution. The main structure of the pyrenoid 

matrix (homogenous, perforated, lamellate or 

traversed by thylakoids) is also visible in LM with 

extraordinary optical equipment and when stained 

with reagents such as azocarmine-G solution 

(et t l 1976, 1983, Gä rt n e r 1985). The electron 

microscopy only cleared characteristic internal 

details of the pyrenoid matrix (Gi B B S 1962, Do D G e 

1973, PI c k e t t-He a P s 1975, Fr I e d l 1989, In g o l I ć & 

Gä rt n e r 2003). Among the members of the genus 

Oocystis A. Br. the ultrastructure of a pyrenoid 

with horseshoe-shaped starch sheath was first 

shown by Sc h n e P F, ko c h & De i c h G r ä B e r (1966, 

p. 165, fig. 33) in a schematic graph of Oocystis 

solitaria Wi t t r o c k f. maior Wi l l e. Later on, 

ro B i n S o n & Wh i t e (1972, p. 112, fig. 5) presented 

a pyrenoid in one TEM-micrograph of Oocystis 

apiculata W. We S t, and recently So l D o et al. 

(2005, p. 314, fig. 2 A) documented the pyrenoid 

of Oocystis nephrocytioides Fo t t et Ča d o in a 

micrograph of an ultra thin cell section. 

In this paper the ultrastructural details of 

the pyrenoid in cells of Oocystis lacustris ch o D at 

are described for first time and comparison with 

the related genera Neglectella Vo d e n I Č a r o V

150 St o y n e va et al.: The pyrenoid ultrastructure 

et Be n D e r l i e v, Eremosphaera De Ba ry and 

Siderocelis Fo t t is done. 

Material and methods 

Oocystis lacustris material was obtained from selected 

phytoplankton samples from Lake Tanganyika dated 

June–July 2003 when it formed dense populations 

(St o y n e va et al. 2007) and fixed in acid Lugol’s 

solution. For detailed description of localities, sampling 

and methods refer to St o y n e va et al. (2007). For TEM 

study cells were fixed a) in 3% glutaraldehyd in 0,1 M 

cacodylate buffer and b) in 1% aqueous O s O 4 in 0,1 M 

cacodylatbuffer, dehydrated in acetone and embedded 

in Spurr’s resine¸ ultrathin sections were stained with 

uranyl acetate and lead citrate (re y n o l D S 1963). 

Electron micrographs were taken with a Tecnai 12 

(FEI) microscope equipped with a Gatan ccd camera. 

Results 

In ultra thin sections most of the vegetative cells of 

Oocystis lacustris contain one parietal chloroplast 

filling more than half of the cell size (Figs 1c, 

3c). However, sometimes also two chloroplasts, 

and, occasionally, four or more of them have been 

observed. Their thylakoids occur in pairs. In each 

chloroplast one pyrenoid with a homogenous matrix 

is situated and surrounded by a thick starch sheath 

(Figs 1p, 2p, 3p). The diameter of the pyrenoid 

body is between 1 and 1.5 µm; the thickness of 

the starch sheath is about 0.25 µm. Thylakoids 

are not traversing the pyrenoid matrix. The starch 

sheath around the pyrenoid appears like a closed 

ring (Fig. 2) or as a horseshoe-shaped starch plate 

(Fig. 3). There can also be a sheath consisting of 

two starch plates, more or less regular in thickness 

(Fig. 1 st). Additionally, single lenticular starch 

grains, which are not in close association with 

the pyrenoid, are visible inside the chloroplast 

(Fig. 2s). These stroma starch grains may reach 

Fig. 1 Vegetative cell of Oocystis lacustris with 1 chloroplast 

(c) and a starch sheath (st) consisting of two starch plates 

around the homogenous matrix of the pyrenoid (p). n = 

nucleus. Scale bar 1 µm. 

Fig. 2 Pyrenoid (p) with homogenous starch sheath and 

additional stroma starch grains (s) in the chloroplast. n = 

nucleus. Scale bar 1µm. 

Fig. 3 Chloroplast (c) with pyrenoid (p) and homogenous 

horseshoe-shaped starch sheath. Scale bar 1µm.


considerable dimensions (up to 0.25–0.75 µm). A 

single nucleus is embedded in the cell lumen (Figs 

1n, 2n). The cell wall is multilayered (Figs 1–3). 

Its appearance in wavy structure, most probably, 

is a result of fixation and dehydration during 

preparation. 

Discussion 

The finding of the multilayered cell wall during 

this study is in conformity with all previous data, 

which showed that the cell walls in Oocystaceae 

Bo h l i n are composed of several layers and this 

diacritic criterion is in accordance with the 

molecular data (ko m á r e k 1979, he P P e r l e et al. 

2000). 

The pyrenoids and their starch components 

are of great value among the main diagnostic 

features for identifying coccal green algae with 

light microscope. Their structure can be cleared 

up by using staining procedures and squashingmethod 

(et t l & Gä rt n e r 1988b, 1995). For 

further taxonomic investigations of unicellular 

green algae on species level TEM studies of 

ultrastructural details of cell components are 

important. Among them the pyrenoid matrix 

(homogenous, with invaginations or traversing 

thylakoids) combined with details of the starch 

sheath composition are significant. Br o W n & Bo l D 

(1964) and Br o W n & mcle a n (1969) were the 

first who used the ultrastructure of the pyrenoid 

and number and position of starch grains to 

classify various species of the green algal genera 

Chlorococcum me n e G h i n i and Tetracystis Br o W n 

et Bo l D. In the genus Trebouxia Pu y m a ly tubular 

or ramified invaginations into the pyrenoid matrix 

and thylakoids traversing through the matrix were 

shown to be species-specific (Fr I e d l 1989, In g o l I ć 

& Gä rt n e r 2003). 

Profound light microscopical investigations 

of some genera of the Oocystaceae family have 

been published previously (e.g. Pl ay Fa i r 1916, 

Sk u j a 1956, Fo t t & ka l i n a 1962, Fo t t & 

Ře H á k o V á 1963, sm It H & Bo l d 1966, Ře H á k o V á 

1969, hi n D á k 1977–1990, ko m á r e k & Fo t t 

1983) and recently LM observations on Oocystis 

lacustris from tropical Lake Tanganyika have been 

documented by St o y n e va et al. (2007). However, 

for a comprehensive cytomorphological and 

taxonomic study of the whole group (subfamilies 

Oocystoideae and Eremosphaeroideae in ko m a r e k 

& Fo t t 1983) still more investigations of cell 

ultrastructure and the pyrenoid construction would 

be necessary. 

The genus Siderocelis Fo t t was also 

placed into the Oocystoideae (Fo t t 1976) based 

on detailed light microscopy (Fo t t 1976, hi n D á k 

1977-1990) but yet the fine structure of its cells 

in most of the species is unknown. Identical 

cell wall structures of Amphikrikos nanus (Fot t 

et hey n i G) hi n D á k = Siderocelis nana Fo t t et 

he y n i G to Oocystis species were documented by 

cr aW F o r D & he a P (1978). Recent TEM-studies 

of Siderocelis irregularis hi n D á k from Lake 

Tanganyika revealed its pyrenoid organization: 

matrix traversed by single undulating thylakoids 

and starch sheath consisting of 2–10 plates 

(St o y n e va et al. 2008, p. 798, figs. 21, 22). This 

structure is clearly different from the pyrenoids of 

Oocystis and Eremosphaera, as they are discussed 

below. This could be accepted as additional prove 

for the exclusion of Siderocelis from Oocystaceae 

(et t l & ko m á r e k 1982, ko m á r e k & Fo t t 1983). 

Nevertheless, the degree of relationship of 

Siderocelis to the Oocystaceae and its inclusion 

in the trebouxiophycean lineage (tS a r e n k o et al. 

2006) need support of molecular investigations, 

which still are lacking. 

In the genus Neglectella Vo d e n I Č a r o V 

et BenDer l i e v, generally regarded as close 

to Oocystis, a pyrenoid with massive, thick 

continuous and homogenous starch sheath is 

described (Be n D e r l i e v 1971, Vo d e n I Č a r o V & 

Be n D e r l i e v 1971). According to the comparative 

studies of Be n D e r l i e v (1971) and the text in 

Vo d e n I Č a r o V & Ben d e r l I e V (1971) the pyrenoid 

of Neglectella is of the same type as the pyrenoid 

of Eremosphaera viridis De Ba ry. This coincides 

extensively with the descriptions given by Fo t t 

& ka l i n a (1962) but is in opposition to Sm i t h 

& Bo l D (1966, p. 25) where in E. viridis “a 

number of polygonal starch grains often surround 

the pyrenoids, especially in aging or nitrogendeficient 

cells”. Such discrepancies could be 

based on different cultivation conditions. Recently 

in the description of Eremosphaera tanganyikae 

St o y n e va, Gä rt n e r, co c q u y t et vyver m a n 

(St o y n e va et al. 2006) some diagnostic features 

of pyrenoid and starch sheath - visible with light 

microscope - were included. The starch sheath was 

shown to contain two plates (St o y n e va et al. 2006, 

figs. 37, 39). These results generally coincide with 

our LM observations on Oocystis lacustris, where 

continuous starch sheath was detected (St o y n e va 

et al. 2007, p. 587) and with our recent TEM


investigations, showing that starch plates do not 

exceed two in number. 

The presence or absence of a pyrenoid is 

documented for most species of Oocystis (e.g. 

Sk u j a 1956, Bo u r r e l ly 1966, Ph i l i P o S e 1967, 

hi n D á k 1977–1990, ko m á r e k 1983, ko m á r e k 

& Fo t t 1983, jo h n & tS a r e n k o 2002), but 

the organization of the starch sheath was often 

neglected. A special note about the continuous 

starch sheath was provided by Fo t t & Ča d o (1966) 

in their LM diagnosis of Oocystis nephrocytioides. 

The TEM photo in So l D o et al. (2005) reveals 

a pyrenoid with homogenous matrix and bipartite 

starch sheath. Observations with TEM of Oocystis 

apiculata showed a “bilenticular” pyrenoid type 

(ch a D e Fa u D 1941, ho r i & ue D a 1967) traversed 

by thylakoids and enclosed by a starch sheath 

fragmented in two parts (ro B i n S o n & Wh i t e 

1972). 

Our results on Oocystis lacustris coincide 

partially with the observations on O. apiculata. 

In O. apiculata, as well as in O. lacustris, the 

starch envelope around the pyrenoid appears 

continuous or fragmented in two parts. But O. 

apiculata pyrenoids are traversed by a simple 

(single) tubular thylakoid system as it is shown by 

ro B i n S o n & Wh i t e (1972, p.112, fig. 5). This was 

never observed in cells of O. lacustris where the 

pyrenoid matrix appeared homogenous and was 

not traversed by thylakoids (Figs 1–3). Therefore 

it is clear that the type of pyrenoid matrix 

(homogenous or traversed by thylakoids) still 

needs further studies and, most probably, is not a 

diacritic feature in Oocystis and in Oocystaceae. 

However, it seems that continuous or slightly 

fragmented starch sheath with at most two starch 

plates is a common diagnostic feature in members 

of the genus Oocystis and its closely related genera 

Neglectella and Eremosphaera, but this still has to 

be verified by further observations with TEM on 

more species. 

Acknowledgements 

The work was partially supported in the frame of a 

research fellowship for the first author (M. P. St.) by the 

Belgian Science Policy Office (CLIMLAKE project) 

and by a research fellowship for the third author (G. 

Gä.) financed by the Austrian Research Association 

(MOEL-project nr. 118). 

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© Czech Phycological Society 

Received November 3, 2008 

Accepted January 10, 2009

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