THE RESPONSIVENESS OF AVENA-FATUA ALEURONE PROTOPLASTS TO GIBBERELLIC-ACID

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-degrees-C and 4 +/- 2-degrees-C for three years was assessed. Protoplasts isolated from aleurones of seed stored at 25-degrees-C produced substantially more alpha-amylase in response to 10(-7) M GA3 than those isolated from aleurones of seed stored at 4-degrees-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 alpha-amylase. The dose response of aleurone protoplasts to GA3, measured as alpha-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, alpha-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 alpha-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-degrees-C produce considerably more alpha-amylase, > 130-fold higher than the minus GA3 control, than those from seed stored at 4-degrees-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-degrees-C. Seed stored at 4-degrees-C retained the dormancy characteristics present immediately after harvesting.