Cytokinin Reversal of Abscisic Acid Inhibition of Growth and α‐Amylase Synthesis in Barley Seed

The effect of cytokinin, kinetin, on abscisic acid (dormin) inhibition of α‐amylase synthesis and growth in intact barley seed was investigated. Abscisic acid at 5 × 10−5M nearly completely inhibited growth response and α‐amylase synthesis in barley seed. Kinetin reversed to a large extent abscisic acid inhibition of α‐aniylase synthesis and coleoptile growth. The response curves of α‐amylase synthesis and coleoptile growth in presence of a fixed amount of abscisic acid (6 × l0−6M) and increasing concentrations of kinetin (from 5 × l0−7M to 5 × 10−5 M) showed remarkable similarity. Kinetin and abscisic acid caused synergistic inhibition of root growth. Gibberellic acid was far less effective than kinetin in reversing abscisic acid inhibition of α‐amylase synthesis and coleoptile growth. A combination of kinetin and gibberellic acid caused nearly complete reversal of abscisic acid inhibition of α‐amylase synthesis but not the abscisic acid inhibition of growth. The results suggest that factors controlling α‐amylase synthesis may not have a dominant role in all growth responses of the seed. Kinetin possibly acts by removing the abscisic acid inhibition of enzyme specific sites thereby allowing gibberellic acid to function to produce α‐amylase.