Dormancy and seasonal changes of plant growth regulators in hazel buds

Levels of indole-3-acetic acid (IAA), abscisic acid (ABA) and total phenolic compounds have been determined in hazel ( Corylus avellana L. cv. Negreta) buds. IAA and ABA were quantified by flame ionization detector gas-chromatography, and the phenolic content determined by a colorimetric technique. The highest level of free ABA occurs in autumn, approximately at the onset of winter dormancy, and it is lowest just before bud burst; suggesting that ABA plays an important role in the induction and maintenance of winter dormancy. The opposite result was obtained for IAA; the level of this regulator was low in autumn and showed a sharp increase just before budbreak. With respect to phenols, an apparent correlation can be observed between them and ABA in at least some of the fractions studied (acid and residual), so that they may enhance the inhibitory effect of ABA. The IAA/inhibitor balance showed a clear correlation with dormancy. In autumn (dormant buds), this balance is in favour of the inhibitors while the balance shifts towards IAA at the end of winter.