Characteristics of composition and content of auxins in tissues of Siberian apple tree Malus baccata L. Borkh.

It is known that the highest content of auxins is found primarily in the areas of active mitosis, including young leaves, apical meristems, cambium, embryos and endosperm, as well as developing fruits, which determines, among other things, plant habitus and fruit size. In agriculture and biotechnology, auxins (indole-3-butyric acid (IBA) and indole-3-acetic acid (IAA) are used to stimulate lateral development, including in apple tree rootstocks. Despite the crucial role of endogenous IBA in rooting, its presence in apple tree tissues remains unconfirmed, although its content in planta was shown for many other plants. Therefore, in this work, the composition and content of auxins in 2 tissue types of Siberian apple tree of lowand high-growing forms, along with the presence of IBA in them, was compared. Tissues of ovary and bark of Siberian apple tree (Malus baccata L. Borkh.) of 2 forms (low and tall) growing on an experimental plot of Siberian Institute of Plant Physiology and Biochemistry SB RAS were used in the study. Bark samples were collected from the 1st year shoots at the stage of intensive sap flow. The ovary samples were collected in July at the stage of active growth. Auxins purified by solid-phase extraction were analysed by GC-MS. In addition to IAA-3, the following auxins were found in fast-growing tissues of the Siberian apple tree both in the cambium layer of annual gain during intensive sap flow and set fruit during the active growth stage: IBA, indole-1-acetic acid, indole-3-carboxylic acid and indole-3-propionic acid. Similar to other plants, the content of these auxins was significantly lower than that of endogenous IAA.