EFFECTS OF SERIAL SUBCULTURE INVITRO ON THE ENDOGENOUS LEVELS OF INDOLE-3-ACETIC-ACID AND ABSCISIC-ACID AND ROOTABILITY IN MICROCUTTINGS OF JONATHAN APPLE

Proliferating axillary shoots of the difficult-to-root apple cultivar 'Jonathan' acquired- an enhanced ability to form adventitious roots with increasing number of subcultures in vitro. The transition between the difficult-to-root and the easy-to-root condition occurred at the fourth subculture. Endogenous levels of free IAA and ABA in shoot tissues were analysed by gas chromatography/mass spectrometry/single ion monitoring (GC/MS/SIM) using negative ion chemical ionisation. Tissues from the mother plants grown in the glasshouse contained more IAA and ABA than those from tissue-culture material. After establishment in vitro there was no variation in the IAA content throughout the subcultures but a decrease in ABA content was observed after the fourth transfer. The IAA/ABA ratio increased from 0.2 in difficult-to-root shoots from the initial culture up to 0.7 in easy-to-root shoots from the long-term subculture.