The levels of auxin, gibberellin, and cytokinin were measured using bioassay methods in pruned and unpruned apple trees (Malus domestica Borkh. cv. McIntosh). Vigorous shoot growth following heavy dormant pruning was accompanied by an increase in cytokinin concentration in the tissues in the early spring. As cell division and cell expansion progressed, the levels of auxin and gibberellin increased. The gibberellin activity in samples from pruned trees was 3 times higher than in samples from unpruned trees. Pruning diminished the midsummer level of cytokinins in the annual shoots.
California, Davis, for the gift of 3 H-(3,4) gibberellin A 1 . The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this
Products Corp., Denver, for MicroCel E; Imperial Chemical Industries for gibberellin (GA 4+7 ); and the Known-You Seed Co., Kaohsiung, Taiwan, for papaya seeds. The cost of publishing this paper was defrayed in part by the payment of page charges. Under
temperature and photoperiod during vernalization on flower initiation and revealed that a long-day photoperiod promoted flower development and elongation of the flower stalk after flower initiation. Gibberellins are known to play important roles in a number of
helping with the data analysis and Sonja Maki for her valuable suggestions and comments. We are grateful to W. Rademacher and BASF for supplying the ring D-modified gibberellins and prohexadione-Ca and to Richard Pharis for providing the GA 4 .
network of five flowering pathways that involve response to daylength, vernalization, carbohydrates, gibberellins, and an age-related autonomous pathway. However, the five pathways ultimately converge on the floral integrator genes leafy ( LFY
are also reported to limit scion vigor by increasing the proportion of annual shoots that end extension growth early during the growing season ( Robitaille and Carlson, 1976 ; van Hooijdonk et al., 2010 ). Unlike cytokinins, gibberellin(s) applied to
gibberellin levels in potato plants ( Okazawa, 1959 , 1960 ). Conversely, Gregory (1956) also noted that short days and low night temperatures (“inducing conditions”) promote tuberization, and Dostal (1945) and Madec (1963) provided evidence for a
Gibberellins (GAs) are increasingly proving to be a crucial regulator of plant growth and a controlling factor of plant architecture. They regulate various physiological and biochemical processes of plant growth and development, promote germination
vivo is still lacking. Table 1. Gibberellins (GAs) previously identified in apple. Genes regulating key steps in GA synthesis have also been investigated in apple and are shown to be tissue-specific. In ‘Fuji’ apple, MdGA20ox1 [GA-20oxidase (catalyzes