Oospore Germination in Two Species of Chara

Abstract

Germination of the oospores of Chara contraria Kutzing and C. zeylanica Willd. was investigated with respect to the effect of a variety of environmental factors, among them, photoperiod, presence or absence of oxygen, culture medium, and temperature. The results indicated that the oospores of the species investigated require a period of dormancy before germination. This period may be shortened by treatment at low temperature (5° to 7℃), but if t his is omitted, germination follows ultimately, but is delayed. Germination occurs under both aerobic and anaerobic conditions, contrary to reports in the literature. The ontogeny of the protonema and of the primary axis in early germination has been described for Chara contraria and is essentially similar to the general pattern described by earlier investigators for other species of the genus. Studies of the organism in culture indicated clearly the important role of the rhizoids in generating secondary protonemata and, thus, in the colonization of a given substrate.The species of Chara are submerged aquatics attached to the substrate by rhizoids. They are colonial plants and form dense patches on the bottom of fresh and brackish bodies of water. Some grow in deep water, some in shallow, some in still water and some in rapidly running streams; perennial species grow intermingled with annual ones. They prefer oligotrophic waters and never grow in water which is polluted.In nature, as streams and ditches containing Chara become dry, the oospores remain as agents of survival during dormancy. When the rain again fills dry stream beds, the oospores germinate and start a new generation. Oospores in nature, however, also germinate in habitats where they are not subjected to desiccation.The writer has been interested in studying the early morphogenesis of Chara, and undertook experiments to germinate the oospores of Chara contraria and C. zeylanica.Ross (1959), Proctor (1960), Carr and Ross (1963) and Forsberg (1965) have reported some of their experiments on germination of the oospores of different species of Chara. Carr and Ross, and Forsberg all emphasize the requirement of anaerobic condition for the germination of the oospore of Chara.The writer devised an agar-plate method as a convenient way of germinating Chara oospores. With this method, the development and morphogenesis of the sporelings of Chara contraria were studied.The materials used were oospores of Chara contraria collected from the dried plants and from mud, and oospores collected from the living plants of C. zeylanica. The method of selection and sterilization of the oospores for germination is described as follows: Oospores were separated from the soil particles and debris layer by means of a series of soil-sieves, and were retained in the finest U. S. standard sieve number 70 with nominal openings of 0.21 mm. The oospores were then picked out with a small forceps under the stereoscopic binocular microscope, and were washed and sterilized as follows. The oospores were immersed in detergent solution, sonicated mechanically for 10 sec., washed, and then rinsed with sterilized water ten times. The oospores were then sterilized by adding 3 drops of Clorox to the tube containing 6 ml of water, and oospores were left in Clorox for 1 min. and then washed with sonication, five times.The clean, sterilized oospores were introduced into Petri dishes with sterilized 2% plain agar. The oospores were then picked up from the agar surface with flamed needles or small forceps and arranged separately on Petri dishes containing proteose yeast-extract agar. These plates were then stored in an incubator of 37℃ three days for testing the presence of bacteria. If any bacteria were present, the bacterial colonies were obvious around the Chara oospores. Only sterile oospores were picked out and planted.