Regulative Systems in the Developing Citrus Fruit I. The Hormonal Balance in Orange Fruit Tissues

The regulative systems of auxins, gibberellin-like substances and their inhibitors in citrus fruit were studied. Masking caused by a high content of inhibitors was eliminated by using a refined method of solvent partition. Considerable amounts of auxins and gibberellin-like substances were detected in all stages of fruit development. The auxin system of the citrus fruit is highly complex and consists of various elements which undergo dynamic changes throughout the growth period. The identity of the auxins was studied using IAA-2-¹⁴C, and 88% of the radioactivity specifically migrated into the etheric pH 6.0 fraction. Although the prominent zones of promotion do not coincide with IAA, it can be concluded that the auxin promoters are probably not the “citrus auxin”. Abscisic acid-like inhibitors were found to accumulate in the external layers of the fruit, increasing in content as time advances.