| Popis: |
Gametophytes of Pteridium aquilinum can be maintained in red light as either 1or 2-dimensional structures. The mode of growth realized in red light is dependent upon the activity of the meristem. An active meristem in a 2-dimensional structure will permit a continued development of that structure. A breakdown in meristematic activity results in filament formation. It is suggested that a group of actively dividing cells in some manner inhibits cell elongation and thus prevents filament formation in red light. THE OBSERVATION (Sobota, 1966) that a 2-dimensional (2-D) gametophyte of P. aquilinum could be maintained in red light, after an initial period of development in white light, constituted the basis for the present investigation. This type of development is in contrast to the germination of spores in red light which always results in filament formation. If these filaments are transferred to white or blue light transition occurs, resulting in the formation of a 2-D structure. Mohr and Ohlenroth (1962) have suggested that this transitional development is under the control of a photoreactive system dependent upon blue light. It has been demonstrated however, that a wide variety of treatments will influence transition. On this basis Sobota and P'artanen (1966) have suggested that transition occurs as a consequence of the interaction of cell division and cell elongation. M\iiller (1968) also has concluded that the initiation of a 2-D mode of growth can be explained ". . . in terms of the various mechanisms operating in the control of cell division and cell elongation." The present study examines the role of red light in bringing about a reversal of 2-D growth previously established in white light. 1\IATERIALS AND METHODS-Gametophytes of P. aquilinum were cultured under sterile conditions according to methods previously described (Sobota and Partanen, 1966). Spores were collected in the fall of 1968 near Youngstown, Ohio. The medium contained a modified Knudson's salt solution plus trace elements and 0.25 % sucrose. The pH was adjusted to 5.5 and the medium was solidified with 8 g/liter of Difco bacto-agar. Spores were sterilized for 5 min in a 5 % calcium hypochlorite solution and placed in suspension at a density of 4 mg per 100 ml I Received for publication 19 September 1969. Supported, in part, by grant 23 from the University Research Council, Youngstown State University, Youngstown, Ohio. of sterile water. Inoculations were made into petri plates containing about 20 ml of medium by placing 1 ml of the spore suspension on the surface of the medium with a Pasteur pipette. The plates were taped to prevent loss of water from the cultures. In some cases, after germination in white light, specific metabolites were added to the plates following filtration through a M\iillipore filter having a pore size of 0.45 M. The cultures were maintained under Sylvania "Gro-Lux" fluorescent lamps at 24 ?t 2 C with a light period of 12 hr light and 12 hr darkness. Cinemoid filters (No. 14 and 46, Kliegl Corporation) were used to isolate the red portion of the spectrum. Light intensity was measured with a YSI model 65 radiometer with a wave length response of 0.25 to 3.301A. The development of the gametophytes was followed by photographing the cultures at specific intervals under a Wild dissecting scope at a magnification of 25 X. Cell numbers and the initiation of 1-dimensional (1-D) growth were determined directly from the photographs. Gametophytes were scored as 1-D if a filament could be seen emerging from a 2-D grouping of cells. Sample size consisted of 50 or more gametophytes for each treatment. RESULTs-Growth in red light-Spores of P. aquilinum were inoculated into petri plates and were allowed to develop in white light at about 900 ergs/cm2/sec for a period of 13 days. Following germination, which occurred at day 4, cultures were removed from white light at one day intervals, photographed, and then placed in red light at about 150 ergs/cm2/sec. The growth of the gametophytes in white light, in terms of increase in cell number, is illustrated in Fig. 1. At this intensity of white light there is no distinct 1-D stage preceding the development of a 2-D gametophyte. The gametophytes at day 4 consisted of from 1 to 2 spherical cells. About day 8 a characteristic heart-shaped gametophyte was observed. |
Plný text