Nuclear ratios and complementation in common-A heterokaryons of Schizophyllum commune.

Seed germination of Melampyrum lineare Desr. requires activation (20 C storage or treatment with gibberellic acid) followed by an extended period of exposure to cold. Without these conditions seeds remain dormant. Seed structure and pattern of development following activation are described. Aseptic culture of embryos excised from dormant seeds showed growth to be possible on agar containing glucose but not on agar containing potato starch. Embryos excised from gibberellin-activated seeds or embryos growing on agar containing gibberellin grew at the same rate on glucose but could not grow on starch. Thus the gibberellin-sensitive dormancy mechanism does not involve synthesis or activation in the embryo of starch-digesting enzymes. This could mean that such a mechanism is located in the endosperm or that the mechanism in Melamnpyrum is different from that described for barley and for oats OUR PREVIOUS investigations (Curtis and CantIon, 1963; Cantlon et al., 1963) showed Melampyrum lineare Desr., a chlorophyllous, hemiparasitic angiosperm, to have an unusual germination pattern. Germination proceeds only after activation followed by an extended period of exposure to cold (4 C). In the laboratory seeds are activated either by exposure to higher temperatures (20 C) which activates up to 40%Jo of a seed batch, or by treatment with gibberellin (GA) at 20 C which activates up to 100% of seeds. After activation followed by an extended period of cold exposure (6-10 weeks), seeds germinate in the cold. Remloval to higher temperature before this prevents germlination. Under field conditions activation is apparently achieved by exposure to normal higher temperatures (> 15-40 C). Up to 40% are activated immediately following seed set and the remainder in subsequent summers. In the Michigan populations some viable seed normally carries over in the litter at least into the third year. A germination pattern such as that of Melampyrum lineare involving two separate temperaturedependent steps with exogenous GA acting specifically on one of them is apparently unique. We therefore thought that this plant might prove a 1 Received for publication August 10, 1964. This work was supported by grant GB-1220 from the National Science Foundation. useful experimental subject for a study of the germination process and the role in this of exogenous GA. The present paper presents data on thesequence of events leading to germination in theintact seed and some preliminary studies ow growth of excised embryos. A\IATERIALS AND METHODS Seeds of Melampyrum lineare were collected in late summer of 1963 from natural populations of the parasite growing in a jack pine forest in Crawford County, 1\lichigan. Seeds were cold stored immediately followingcollection, and after 6-8 weeks of cold ca. 15% germinated as a result of activation prior to col-lection. The remaining nonactivated seeds re-mained dormant and were used after ca. 6 months of cold storage. Seeds were activated by soaking in 2000 ppm GA for 24 hr at 20 C followed by washing in running tap water for 5 muin. This procedure re-sults in activation of 100% of seeds. Gibberellin was purchased from the Nutritional Biochemical Co. as a preparation described as 75% potassium salt of gibberellic acid. Solutions were prepared byadding a minimal quantity of potassium hydroxidesolution to dissolve the GA and subsequently neutralizing with hydrochloric acid. For aseptic culture of embryos, seeds were soaked in 1% sodium hypochlorite solution for 1 hr and then washed with sterile distilled water.. This content downloaded from 157.55.39.92 on Wed, 22 Jun 2016 07:07:08 UTC All use subject to http://about.jstor.org/terms