Occurrence of an inhibitor in wheat endosperm as revealed by embryo transplantation in irradiated seeds

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Seeds (caryopses) of durum wheat var. Cappelli were soaked in water for 24 hr at 20°C to soften them enough for excision of embryos with scutellum. After irradiation of half of the soaked seeds (2–10 kr of X-rays), embryos were excised from both irradiated and unirradiated seeds and the following transplantations were made: (1) unirradiated embryo on irradiated endosperm, EM ( u) /EN ( i) and (2) unirradiated embryo on unirradiated endosperm, EM ( u) /EN ( u) (homotransplant, to serve as control). In 1962 and 1963, using seeds of the crops of 1961 and 1962 respectively, it was demonstrated that endosperms of after-ripened seeds stimulated growth in the EM ( u) /EN ( l) seedlings. Evidence was found that this stimulatory effect results from the destruction—or inactivation—by radiation of an inhibitor present in the endosperm of after-ripened seeds. The inhibitor is not present, in detectable amounts, in the endosperm of seeds during the total period of dormancy (first three months or more after harvest). The results are discussed in relation to the general problem of growth responses, including stimulation, in irradiated seeds.