Initiation of Flowering and Changes in Endogenous Inhibitors and Promoters in Olive Buds as a Result of Chilling

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Abstract
Olive trees require a period of chilling temperatures, either diurnally fluctuating, or at a constant—but definite—level before inflorescences develop. In this study, bud and leaf samples were taken at weekly intervals during this critical period from trees receiving temperatures favorable for flowering and from trees under temperature conditions known to prevent flowering. Extracts were obtained from these samples, separated by paper chromatography and the different growth‐active materials were bioassayed by the mung bean rooting test for the presence of promoters and inhibitors.Extracts from buds on trees under conditions unfavorable for flowering generally consisted only of promoters. Extracts from buds on trees placed under conditions favorable for flowering showed a definite and consistent pattern for the presence of rooting inhibitors and promoters. Within one or two weeks after being placed under such conditions a strong inhibitor band appeared from Rf 0.50 to 0.70. This persisted for 6 to 7 weeks, gradually decreasing in intensity, followed by promoters at these bands. During this period all other bands, at different Rf values, showed strong promoters.Extracts from leaves on shoots under temperature regimes favorable for flowering showed a pattern like the buds in the appearance and disappearance of inhibitors and at the same Rf values but with about one week lag in time. Bud extracts from defoliated shoots on trees under temperature conditions known to result in inflorescence production failed to show the characteristic inhibitor pattern associated with flowering. Such defoliated shoots do not form inflorescences.