PLANT-REGENERATION FROM BARLEY CALLUS - EFFECTS OF 2,4-DICHLOROPHENOXYACETIC ACID AND PHENYLACETIC ACID

The use of the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) has played an important role in the production and maintenance of toti potent cereal callus. However, 2,4-D has been implicated in the loss o f totipotency from barley callus. To examine the effect of 2,4-D on ba rley callus, regenerability and karyotype were examined over time as i nfluenced by cultivar differences and 2,4-D levels, during a period in which initially vigorous plant regeneration typically declines dramat ically. Higher (20.4-27.1 mu M) versus lower (6.8-13.5 mu M) concentra tions of 2,4-D were positively associated with the number of green pla ntlets recovered from calli maintained for 10 and 16 weeks before tran sfer to regeneration media, and with the longevity of regenerability. There was a positive relationship between 2,4-D concentration and norm al karyotype. We also investigated the use of phenylacetic acid for th e initiation of regenerable barley callus. Very poor callus growth and plant regeneration was supported by phenylacetic acid.