No abstract

The influence of acid scarification on the responsiveness of curly dock (Rumex crispusL. ♯ RUMCR) seeds to physical and chemical factors was studied. Scarification made the seeds responsive to GA4+7(a mixture of gibberellin A4+ A7) and markedly improved the responsiveness to light, moist-chilling, and a 1-h 40-C temperature shift. Scarification reduced the mechanical restraint of the seedcoat by 0.4 to 0.8 MPa. Removal of the entire pericarp induced 69% germination in the dark. Moist-chilling treatment of seeds reduced the soaking period needed for maximum response to the high-temperature shift from 24 to 6 h. The embryo growth potential generated by moist-chilling was less in magnitude than that by the reduction in seed coat restraint by scarification. Induction of secondary dormancy was prevented to a marked degree in scarified (chilled or unchilled) seeds during polyethylene glycol-6000 (PEG) treatment in light or in the presence of GA4+7while intact seeds rapidly became secondarily dormant in light. The ability of scarified seeds to remain germinable or nondormant for a longer period than the intact seed in low water potential imbibing medium may be due to a net reduction (by 0.4 to 0.8 MPa) in the impact on the embryo of germination-preventing forces (low water potential plus mechanical restraint of the seed coat).

Print) 2380-4084 (Online) Journal homepage: http://www.tandfonline.com/loi/thsb20 Molecular cloning and characterization of the genic male sterility related gene CYP86MF in Chinese cabbage (Brassica campestris L. ssp. chinensis Makino var. communis Tsen et Lee)

'Grand Rapids' lettuce Lactuca sativa L. seeds germinate readily at 15°C but poorly at 25°C in darkness. When held in dark at 25°C for an extended period, the ungerminated seeds become dormant as shown by their inability to germinate or transfer to 15°C in darkness. Induction of dormancy at 25°C was prevented by exposure to CN-, azide inhibition by SHAM2, an inhibitor of alternative oxidase pathway of respiration (19). In a later study (28), using sealed containers, these authors demonstrated that CN-insensitivity to germination reported previously was due to a loss of CN-by volatilization from unsealed dishes. In a more recent report, Zagorski and Lewak (30) showed that HCN applied for 1 or 22 h in a sealed container at 25°C, following a 2 h soak at 5°C, enhanced dark germination of lettuce.Studies with lettuce (10, 28, 29), soybean (20), mungbean (4), cocklebur (9), pear (1), and other seeds indicate that electron transfer to 02 during imbibition is predominantly via the Cyt pathway. An engagement of alternative oxidase pathway seems to occur in the presence ofCyt oxidase inhibitors in plant systems including seeds (1,6,8,29).In the present study, we have examined the effect of Cyt and alternative oxidase inhibitors as well as other factors on germination and dormancy inducing processes ofGrand Rapids lettuce seeds during dark incubation. The results indicate that seeds have two dynamic energy-coupled processes: germination and dormancy induction. Depending upon whether one or both processes are blocked, an engagement of germination or dormancy induction process or prevention of both processes may occur. MATERIALS AND METHODSSeed Source. Lettuce (Lactuca sativa) L. cv Grand Rapids, 1978 and