Growth Substances of Tulip: The Activity of Gibberellin-like Substances in Field-grown Tulips from Planting until Flowering

Abstract

Summary The activity of gibberellin-like substances (GLS) was determined, using a lettuce hypocotyl bioassay, for the various bulb and plant components of tulip cv. «Apeldoorn» growing in the field in southern England. Plants were sampled at intervals from October (planting time) until the following April (flowering time). Two peaks of GLS activity were found over the course of the samples. The first of these occurred in December or early-January in most components, prior to the satisfaction of the cold requirement. In the acidic fraction there was a peak of GLS activity in the December sample in leaf and daughter bulb (DB) extracts, and in the early-January sample in extracts of the stem and mother bulb scale components; high activity was also found in the young flowers sampled in October and in the basal plate (BP) region containing actively growing root initials sampled on the same date. In the basic fraction, the peak occurred in the December samples of all components (except the outer fleshy bulb scales) preceding the main peak in the acidic fraction. In the bound fraction the peak occurred in December in the flower extracts and in early-January in root, BP, inner scale, leaf and stem extracts, but was absent in extracts of the other components. During this time, the GLS activity of the acidic, basic and bound fractions of the whole bulb increased from 83, 1 and less than 1 to 1308, 431 and 130 ng/bulb, respectively. The second peak occurred around rapid shoot extension and flower maturation (February to April samples), but there was less consistency in its date in the various plant components.