The Cytology and Derivation of a Temperature‐sensitive Meiotic Mutant in the Fern Ceratopteris

Abstract

Meiotic mutants were obtained from an inbreeding program following a hybridization between two diploid species of the homosporous fern Ceratopteris. The mutants are characterized by high levels of asynapsis at high temperatures (27 C, 33 C) and by aberrant spindle function at low temperatures (18 C). Spore viabilities vary with temperature and are highest at 23 C. Occasional restitution during the first division results in the production of dyads of diploid spores, some of which are viable. The inbreeding program was characterized by the expression of high levels of apparent heterozygosity in spite of intragametophytic selfing. It appears that segregation within the inbreeding program was responsible for the production of the mutants. The apparent heterozgosity and segregation can be explained by a previously documented genetic system within the polyploid homosporous ferns.

A drought‐driven model for the evolution of obligate apomixis in ferns: evidence from pellaeids (Pteridaceae)

“…Harlan and deWet, 1975; Morzenti, 1967), these problems are avoided in mitotic division, and it is, thus, unsurprising that PE in ferns is observed in both autopolyploid and allopolyploid lineages (Gastony and Gottlieb, 1985; Gastony and Windham, 1989). Second, environmental cues may be an important catalyst for the formation of restitution nuclei (Hickok, 1977b; Haufler et al, 1985). For example, an association has been detected between low temperature (18°C) and an increased incidence of meiotic restitution resulting from aberrant spindle formation in Ceratopteris (Hickok, 1977b).…”

“…Second, environmental cues may be an important catalyst for the formation of restitution nuclei (Hickok, 1977b; Haufler et al, 1985). For example, an association has been detected between low temperature (18°C) and an increased incidence of meiotic restitution resulting from aberrant spindle formation in Ceratopteris (Hickok, 1977b). The association between low temperature and increased incidence of whole‐genome duplication via mitotic/meiotic restitution is consistent with observations of triploid populations at the northern edge of the otherwise diploid species’ ranges (e.g., in Cystopteris protrusa ; Haufler et al, 1985).…”

“…These modifications—whose coordination might span ca.100–200 years, from one generation to the next—appear to be driven by environmental conditions. Available evidence suggests that there are tangible associations between obligate apomixis and a plurality of abiotic factors, including temperature, substrate composition, and water availability (e.g., Bell, 1959; Whittier, 1964a, b; Hickok, 1977b; Padhya and Mehra, 1981).…”

Characterization of Four Members of the Alpha-Tubulin Gene Family in Ceratopteris richardii

“…This report describes the application of DNA sequencing and genetic linkage mapping to the alpha-tubulin genes of Ceratopteris richardii and shows how such studies can further enhance the utility of this model system. Initial successes with Ceratopteris were in the areas of cytogenetics (e.g., Hickok, 1976Hickok, , 1977aHickok, , 1977bHickok, , 1978Hickok, , 1979aHickok, , 1979bKlekowski, 1973, 1974), physiology and development, and Mendelian genetics (reviewed in Hickok, 1987;Hickok et a/., 1987Hickok et a/., , 1995. More recent studies have focused on the molecular genetics of Ceratopteris (Minister et a/., 1997;Hasebe et al, 1998;Aso et al, 1999;Stout et a/., 2003;Rutherford et al, 2004;Salmi et al, 2005).…”