MATURATION OF THE MEIOSPORANGIA OF EUALLOMYCES. II. PRELIMINARY OBSERVATIONS ON THE EFFECT OF AUXINS

Abstract

THE SPOROPHYTIC GENERATION of the water molds in the subgenus Euallomyces bears thick-walled, pitted, brown meiosporangia which ultimately give rise to an independent gametophytic generation. When the sporophyte is grown on nutrient agar slants, the sporangia develop immediately behind the growing front so that the slant appears brown. An individual sporangium acquires its characteristic morphology and color in 48-72 hr. after initiation. At this time each meiosporangium contains about a dozen diploid nuclei and numerous spherical, orceinstaining bodies called chromospheres. They are, however, immature because they will not germinate when placed in water. If the slants are stored at room temperature in the laboratory for 2 weeks to two or more months, depending on the strain, a process of maturation takes place within the sporangia. If then, the mature structures are placed in water they germinate with the discharge of approximately 4 dozen motile, haploid, uninucleate meiospores each of which develops directlv into a gametophytic plant (see Emerson, 1941 or Sparrow, 1943 for the detailed life cycle, and Emerson and Wilson, 1949 and Wilson, 1952 for the nuclear cycle). The purposes of this study and the preceding one (Machlis and Ossia, 1953) were to find methods for shortening the period of maturation and to learn what is involved in the process of maturation. Emerson and Wilson (Wilson, 1952) made the important observation that a mature sporangium was characterized by the absence of chromospheres and the presence of nuclei in an advanced prophase of meiosis I. They postulated that the attainment of maturity, i.e., germinability, was equivalent to the disappearance of the chromospheres and the concomitant appearance of late prophase nuclei. Such mature meiosporangia can be stored dry for many years. Upon immersion in water, meiosis resumes, the content swells with a consequent cracking of the thick, outer wall, cleavage takes place, and the meiospores are discharged. Machlis and Ossia (1953) confirmed the fact that no sporangia become mature until the chromospheres disappear. They showed that the digestion of the chromospheres occurs rapidly. For example, in one series of observations of sporangia developed and matured on agar, chromospheres were evident for 23 days in over 90 per cent of the sporangia; 24 hr. later over 90 per cent of the sporangia were without chromospheres. Simultaneous with the disappearance of the chromospheres, germinability also abruptly increases