STRUCTURE AND GERMINATION OF BLASTOCLADIELLA EMERSONII RESISTANT SPORANGIA

Resistant sporangia of Blastocladiella emerson?i were induced by the addition of bicarbonate, potassium chloride, sodium chloride, or ammonium chloride to the medium and by the exposure of the zoospores to ultraviolet irradiation. Mature resistant sporangia induced by all of these conditions exhibit similar areolate wall pitting. Under suitable conditions resistant sporangia in all cases examined germinated with the cracking of the outer sporangial wall, with the formation of exit tubes by the inner sporangial wall, and with the cleavage and release of zoospores through discharge papillae formed in the tips of the exit tubes. BLASTOCLADIELLA EMERSONII Cant. & Hyatt, a non-filamentous water mold in the order Blastocladiales, has been the object of many morphogenetic and biochemical studies (Cantino and Lovett, 1964). The zoospores grow into thalli, each producing a single sporangium of either of two types. The resistant sporangia (RS) have thick, pitted walls and are orange-brown in color. The ordinary colorless sporangia (OC) have thin, non-pitted walls and no pigmentation. Under suitable conditions both types of sporangia germinate, cleaving their protoplasts into many tiny zoospores which escape through discharge papillae formed in the sporangial wall. Cantino (1951) showed that the addition of bicarbonate to a medium which otherwise supports the development of OC causes RS to develop instead. Griffin (1965a) showed that potassium chloride in suitable concentrations would also induce the formation of resistant sporangia. In a preliminary report (Griffin, 1965b) it was further shown that sodium and ammonium chlorides are equally as effective as potassium chloride in the induction of RS formation. These data are presented here in full for the first time. Lovett (personal communication) discovered that if a suspension of zoospores is exposed to ultraviolet light and then allowed to develop on an agar medium, a large percentage of the first-generation thalli will form resistant sporangia. This study shows that the effect of potassium chloride in inducing the formation of resistant sporangia is not specific and that sodium and ammonium chlorides are equally effective. The effect of these salts is not purely an osmotic phenomenon, since sucrose added in concentra1 Received for publication 13 May 1968. Supported in part by National Science Foundation Grant GB4747 to the junior author. 2 Present address: Department of Forest Botany, State University College of Forestry, Syracuse, N. Y. 13210. tions up to the point w-here the spores can no. longer grow does not cause the formation of RS. Resistant sporangia formed under all known conditions of induction, bicarbonate, chlorides of potassium, sodium and ammonium, and ultraviolet irradiation of the zoospores are essentially alike in wall sculpturing and germination behavior. MATERIALS AND METHODS-Cultures of B. emersonii (Berkeley Culture Collection strain 49-1) were used throughout this study. This is a subculture of the original isolate (Cantino and Hyatt, 1953). Stock cultures were maintained on PYG agar containing peptone (Difco), 1.25 g;yeast extract (Difco), 1.25 g; glucose (Fisher), 3.0 g; and agar (Difco), 15 g per liter of water. Experiments to test the specificity of salts in inducing RS formation were performned usinga medium consisting of yeast extract (Difco), 1.25 g; glucose (Fisher), 3.0 g; and agar (Difco), 15 g per liter of water, and salts as specified in the text. RS grown for photography and germination were grown on medium PYG supplemented with either KC1 3.5 X 10-2M, NaCl 7.5 X 102-m, NH4Cl 7.5 X 10-2M, or KHCO3 1.0 X 10-2M before autoclaving. For obtaining ultraviolet-induced RS a suspension of zoospores, was spread evenly over the surface of a PYG agarplate and irradiated for 10 sec at a distance of 15 cm with a UVS-11 short wave ultraviolet lamp (Ultraviolet Products, Inc., San Gabriel, Calif.). Individual RS thalli were removed from theagar with a fine needle and water mounts weremade for observation and photography. To obtain Fig. 1-6.-Fig. 1-3. Mature RS showing areolate pitting. -Fig. 1. HCO3-grown.-Fig. 2. KCl-grown.-Fig. 3. U1traviolet-induced.-Fig. 4-6. Germinating RS showing cracked wall.-Fig. 4. HCO3-grown.-Fig. 5. KCI-grown. -Fig. 6. Ultraviolet-induced.--Magnification of all, X560.-