Rikunomizu（Limnology in Tokai Region of Japan）60 : 35 - 39（2013）

Regional Report
Formation process of conjugation and zygospores of a filamentous green alga,Spirogyra species collected from a lowland marsh, Naka-ikemi, Tsuruga, Fukui, Japan
Kentaro NOZAKI 1), 2)

Abstract
The formation process of conjugation and zygospores of a Spirogyra species collected from a Japanese lowland marsh on
12 March 2012 is described using microscopic photographs of the Spirogyra filaments, and physical and chemical conditionsof their sampling site were shown in order to consider the factor inducing conjugation. Single cell of the Spirogyra was 40-50
μm wide and 60-100μm long with plane end cell walls. One chloroplast was making 2-5 turns in each cell. Conjugationof the Spirogyra was scalariform-type, and tubes elongated both sides of the filaments. Fertile and sterile cells were mostly
cylindrical, sometimes enlarged or inflated. Characteristics of fully-ripened zygospores were ellipsoidal, with a smoothmedium spore wall and brownish color. The Spirogyra in this report was identified as S. variformis TRANSEAU. Changes inNO3--N concentration and water temperature seem to be factors inducing conjugation.
Key words: conjugation, Naka-ikemi, Spirogyra variformis TRANSEAU, zygospore(Received: 12 October 2012, Accepted: 6 December 2012)

Route 8, Bypass

Introduction

NGenus Spirogyra (Zygnemataceae) is a common group of�Stationfilamentous green algae observed in many freshwater environments.

Outflow

Their formation process of conjugation and zygospores are
generally introduced in sexual reproduction in biology textbook.
PondAlthough conjugation of Spirogyra is a well-known phenomenon,0

little is understood about its detailed processes and mechanism,

300 m

because of difficulty in reproducible induction of conjugation in thelaboratory (Ikegaya et al., 2012). Because the Spirogyra species
has been classified by the shape and color of conjugation and fully-Fig. 1. Map of the sampling site, Naka-ikemi marsh.

ripened zygospores formed in sexual reproduction (Yamagishi,1966; Yamagishi, 1977), determination of the exact species isvery difficult. Many studies of Spirogyra classification have been

Spirogyra filaments, and physical and chemical conditions of theircarried out using samples collected from natural environments.

sampling site were shown in order to consider the factor inducing

However, only a few studies have showed the water environmental

conjugation.

condition of the sampling site (e.g. Nozaki, 2010). In the present
report, the formation process of conjugation and zygospores of aMethods

Spirogyra species collected from a Japanese lowland marsh in early
spring of 2012 is described using microscopic photographs of the1)

This study was carried out in a Japanese lowland marsh, Naka-School of Education, Sugiyama Jogakuen University and 2) Environmental Education Project, Sugiyama Human Research Centre, Motomachi 17-3,Hoshigaoka, Chikusa, Nagoya 464-8662, Japan (E-mail: ken@sugiyama-u.ac.jp)

35Kentaro NOZAKI
Spirogyra cell measured 40-50 μm wide and 60-100 μm longwith plane end cell walls. One chloroplast was making 2-5 turns
in each cell (Fig. 3a, b). Sexual reproduction of the Spirogyra
was started by formation of papilla on cells opposite each other(Fig. 3b). After elongation of the papilla, 2 filaments aligned andconjugation tubes were formed between cells. Conjugation of theSpirogyra was scalariform-type and tubes elongated both sidesof the filaments (Fig. 3d). Fertile and sterile cells were mostly
cylindrical, sometimes enlarged or inflated. Zygospores matured byapproximately 40-50 days after sampling. Characteristics of fullyripened zygospores were ellipsoidal, smooth medium spore walland brownish color (Fig. 3e, f). The Spirogyra in this report is
identified to be S. variformis TRANSEAU according to monographs

Fig. 2. Sampling station.

(Transeau, 1938; Yamagishi, 1966; Yamagishi, 1977).
Physical and chemical conditions of the water sample collectedikemi, Tsuruga, Fukui Prefecture, located at latitude 35°
39’N andfrom sampling station are shown in Table 1. Electric conductivity

longitude 136 °06’E near the center of Tsuruga City. The marsh(25.9 mS m-1) and NO3--N concentration (1383 μg L-1) in theis in a hilly district with an elevation of 50-60 m and extends

station were relatively higher than those of other areas in this

1.3 km from east to west and 0.5 km from north to south, with amarsh (Nozaki and Tuji, 1999; Tuji et al., 1999). In this study,2total area of approximately 0.25 km (Fig. 1). More information

the Spirogyra filaments were incubated using tap water of ourabout the location of the study site was provided in Nozaki et al.

laboratory (Nagoya City, Aichi Prefecture), and its NO 3--N(2009). Samples of Spirogyra filaments and water were collectedconcentration was only about 500μg L-1 (Nozaki, 2009). The rolefrom a small pool within a reed zone on 12 March 2012 (Fig. 2).

of nitrogen depletion and light intensity were suggested as key

Water temperature, pH (WAK-pH, Kyoritsurika Co.) and electric

factors for inducing conjugation (Yamashita and Sasaki, 1979).

conductivity (CM21P, TOA-DDK Co.) were measured at theThus, the decline of dissolved nitrogen concentration seems to besampling station. Samples were stored in a box with ice and werea factor inducing conjugation in this study. Although the water

returned to the laboratory within 8 hours after sampling.

temperature at the sampling station was 9.3 ℃ , the temperature

Turbidity of water samples was measured with a water analyzer

condition of our laboratory where the Spirogyra filaments were(WA1, Nippon Denshoku Co.) using pre-filtered water. Water

incubated was clearly higher than that of the station. Thus, thesample was transferred to a glass fiber filter (GF-75, Advantec

rise in water temperature is regarded as another factor controllingCo.) in preparation for the analysis of water color and nutrient

conjugation of the Spirogyra. To understand in more detail theconcentrations. Water color was also measured with a water

factors affecting the conjugation and zygospore formation of theanalyzer (WA1, Nippon Denshoku Co.). Nutrients analyses were

Spirogyra, further field and laboratory studies are warranted.

as follows: NH4+-N (Solorzano, 1969), NO2--N (Bendschneiderand Robinson, 1952), NO3--N (Kalff and Bentzen, 1984) and PO43Table 1. Characteristics of water quality in sampling station on 12March 2012.

-P (Murphy and Riley, 1962).
Spirogyra filaments were placed in a 100-mL glass beaker filled

Sampling timewith tap water in our laboratory was kept on a shelf in front of awindow facing south. Spirogyra filaments were observed underan optical microscope (BX 51, Olympus Co.), and microscopicphotographs of conjugation and zygospores were taken by digital

13:17

Water temperature（℃）

9.3

pH

6.5

Turbidity (degree)

1.6

Water color (degree)

camera (Camedia C-5060, Olympus Co.).

4.0-1

Results and Discussion

Electric conductivity (mS m )25.9

NH4+-N (μg L-1)

5.6--1

0.8--1NO3 -N (μg L )1383.0PO43--P (μg L-1)

4.5

NO2 -N (μg L )The formation process of conjugation and zygospores of
the Spirogyra filaments is illustrated in Figure 3a-f. A single

36

Conjugation and zygospores of a filamentous green alga, Spirogyraa)�400
March,12b)�400
March,26c)�400
March,260

37

50�m

Kentaro NOZAKId)�400
March,28e)�400
May,3f)�400
May,3Fig. 3a-f. Microscopic photographs of formation process of conjugation and zygospores of theSpirogyra collected from Naka-ikemi marsh on 12 March 2012.

38

Conjugation and zygospores of a filamentous green alga, Spirogyra
ikemi marsh, Tsuruga, Fukui, Japan-Importance of water quality

Acknowledgementson the conservation of marsh vegetation. Japanese Journal ofThe author is grateful to Yuki MORI of the School of Education,Limnology, 60 : 201-213 (in Japanese with English Abstract).

Sugiyama Jogakuen University, for her generous assistance in theYamagishi, T. (1966): Studies on the Genus Spirogyra collected

field sampling. The author wishes to thank Dr. Takashi TASHIRO

in Japan. Scientific Report of Tokyo Kyoiku Daigaku, Section

and Tomohiro YOSHIIKE of the Nagoya University for their help

Biology, 12 : 73-105.

in this study. This research was supported by a Grant-in-Aid for

Yamagishi, T. (1977): Illustrations of the Japanese fresh-water

Scientific Research (C) from Japan Society for the Promotion ofalgae. In: Hirose H. and T. Yamagishi (eds.): 416-461. Uchida
Roukakuho Publishing Co., Ltd., Tokyo (in Japanese).

Science (No. 24501114) to Kentaro NOZAKI.

Yamashita, T. and K. Sasaki (1979): Conditions for the inductionof the mating process and changes in contents of carbohydrates

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