Germination of Chaenorrhinum minus seeds in response to gibberellin treatments

Seeds of Chaenorrhinum(1) minus (L.) Lange (Scrophulariaceae) exhibit embryo dormancy when released from capsules of the parent plant, but can be induced to germinate when chilled or treated with gibberellins (GAs). GAs found to have activity in breaking dormancy of C. minus seeds were GA(3), GA(4), GA(7), and GA(4+7). The degree of germination success, however, depended on pH, concentration, duration of incubation, and on the kind of GA applied. Newly mature seeds treated with GA(3) at a range of pH values had optimum germination success in the pH range 8.5-10; by contrast, seeds that were stored for 10 months at room temperature had optimum germination success in the pH range 5.5-8. GA(7) was the most active of the GAs tested: in a 96 h incubation, the GA(7) concentration required for 50 % germination was approximately 0.3 mmol . L(-1), compared to 2.5 mmol . L(-1) for GA(4) and 100 mmol . L(-1) for GA(3). In addition, the maximum proportion (approx. 85%) of seeds that germinated in GA(7) was greater than in the other GAs. GA(4) and GA(4+7) produced almost identical responses, showing that the effects of GA(4) and GA(7) in the mixture were not additive. Two other GAs, GA(13) and GA(7)-isolactone, were completely ineffective in breaking dormancy. These results are discussed in terms of the affinity of the various GAs for possible receptor sites in C. minus seeds.