title: Antagonistic action of low-fluence and high-irradiance modes of response of phytochrome on germination and beta-mannanase activity in Datura ferox seeds.
abstract: Seed germination is often induced by a pulse of red light perceived by phytochrome and cancelled by a subsequent pulse of far-red light. When the pulse of red light is followed by several hours of darkness, a pulse of far-red light is no longer effective and prolonged far-red is necessary to block germination. The aim was to investigate whether the red light pulse and prolonged far-red light act on the same or different processes during germination of Datura ferox seeds. Forty-five hours after the inductive red light pulse, germination could not be blocked by one pulse or six hourly pulses of far-red light, but was significantly reduced by 6 h of continuous far-red light. The pulse of red light increased embryo growth potential and the activities of beta-mannanase and beta-mannosidase extracted from the micropylar region of the endosperm. Continuous far-red light had no effect on embryo growth potential or beta-mannosidase activity, but severely reduced the activity of beta-mannanase. The effect of far-red light had the features of a high-irradiance response of phytochrome. Both germination and beta-mannanase activity were restored by a pulse of red light given after the end of the continuous far-red treatment. It is concluded that the low-fluence response and the high-irradiance response modes of phytochrome have antagonistic effects on seed germination and that the control of beta-mannanase activity is one process where this antagonism is established.
authors.affiliation: IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, CONICET, Av. San Martín 4453, 1417, Buenos Aires, Argentina.
authors.forename: L
authors.initials: L
authors.lastname: de Miguel
authors.forename: M J
authors.initials: MJ
authors.lastname: Burgin
authors.forename: J J
authors.initials: JJ
authors.lastname: Casal
authors.forename: R A
authors.initials: RA
authors.lastname: Sánchez
mesh_terms: D013286:Datura stramonium / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D018525:Germination / Q000528:radiation effects*; D008027:Light; D008361:Mannosidases / Q000378:metabolism*; D010834:Phytochrome / Q000502:physiology*; D010946:Plants, Medicinal; D010947:Plants, Toxic; D012639:Seeds / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D044902:beta-Mannosidase
chemical_list: D010834:Phytochrome; D008361:Mannosidases; D044902:beta-Mannosidase