The responsiveness of Avena fatua aleurone protoplasts to gibberellic acid

Abstract

The sensitivity to gibberellic acid (GA₃) of aleurone protoplasts isolated from a single harvest of an inbred line of Avena fatua seed that had been after-ripened over anhydrous CaCl₂ at 25±2°C and 4±2°C for three years was assessed. Protoplasts isolated from aleurones of seed stored at 25°C produced substantially more α-amylase in response to 10⁻⁷ M GA₃ than those isolated from aleurones of seed stored at 4°C. The apparent difference in responsiveness does not appear to be due to a change in the duration of the lag phase between addition of GA₃ and the production of α-amylase. The dose response of aleurone protoplasts to GA₃, measured as α-amylase production, is complex and appears to have three phases. Protoplasts from seed stored at both temperatures respond appreciably to 10⁻¹⁴ M GA₃. With increasing concentrations of GA₃, up to 10⁻⁹ M, α-amylase production increases similarly in protoplasts from both lots of seed, reaching a level approximately 2.7–3.8 times greater than when no GA₃ is applied. GA₃-induced α-amylase production increases markedly as the concentration is raised from 10⁻⁹ M to 10⁻⁶ M, and the response then appears to be saturated. Over this part of the response curve protoplasts from the two seed lots differ markedly in their responsiveness to GA₃. Those from seed stored at 25°C produce considerably more α-amylase, >130-fold higher than the minus GA₃ control, than those from seed stored at 4°C, <35-fold higher than the minus GA₃ control. This apparent difference in the responsiveness of aleurone protoplasts to GA₃ could be correlated with the loss of embryo dormancy in seed stored at 25°C. Seed stored at 4°C retained the dormancy characteristics present immediately after harvesting.