Changes in ABA turnover and sensitivity that accompany dormancy termination of yellow-cedar (Chamaecyparis nootkatensis) seeds.
Yellow-cedar (Chamaecyparis nootkatensis [D. Don] Spach) seeds exhibit prolonged coat-imposed dormancy following their dispersal from the parent plant. Analyses were undertaken using S-(+)-[(3)H] abscisic acid (ABA) to monitor the capacity of embryos to metabolize ABA following their isolation from seeds subjected to various dormancy-breaking and control treatments. Radiolabelled phaseic acid (PA) and dihydrophaseic acid (DPA) were detected in embryos and, to a greater extent in the surrounding media, by 48 h regardless of whether the embryos had been excised from seed previously subjected to only a 3 d soak or to a full dormancy-breaking treatment. Of the two enantiomers of ABA, only the natural S-(+)-ABA effectively inhibited germination of isolated embryos. A metabolism-resistant synthetic ABA analogue S-[8',8',8',9',9',9']-hexadeuteroabscisic acid, S-(+)-d6-ABA, consistently slowed the germination rate of excised embryos to a greater extent than that caused by natural S-(+)-ABA. The deuterium-labelled ring methyl groups of the analogue made it more resistant to oxidation by yellow-cedar embryos and thus rendered the analogue more persistent and possessing greater activity. With increasing time of exposure to moist chilling, yellow-cedar embryos became increasingly insensitive to both ABA and to the analogue. Subjecting seed to chemical treatments (GA(3) in combination with 1-propanol) prior to moist chilling strongly enhanced the germinability of whole seeds. This treatment also had a relatively greater impact on ABA metabolism than did moist chilling alone, as indicated by a greater capacity of S-(+)-d6-ABA to inhibit the germination of embryos as compared to S-(+)-ABA. Moist chilling was most critical for reduced ABA sensitivity of embryos. A change in the embryo's ability to metabolize ABA and reduced embryo sensitivity to ABA are two factors associated with dormancy termination of whole seeds of yellow cedar; a change in only one of these factors is insufficient to elicit high germinability.
Schmitz
Nancy
N
Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
Abrams
Suzanne R
SR
Kermode
Allison R
AR
D000433:1-Propanol / Q000494:pharmacology; D000040:Abscisic Acid / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D029780:Chamaecyparis / Q000187:drug effects / Q000502:physiology*; D003903:Deuterium; D004305:Dose-Response Relationship, Drug; D018525:Germination / Q000187:drug effects; D005875:Gibberellins / Q000494:pharmacology; D007536:Isomerism; D012639:Seeds / Q000187:drug effects / Q000502:physiology; D013997:Time Factors
D005875:Gibberellins; D000040:Abscisic Acid; D000433:1-Propanol; D003903:Deuterium; C007842:gibberellic acid