Anatomical structure of leaves in Magnolia kobus, M. obovata, M. denudata in the first stages of ontogenesis

Abstract

In the ontogenesis of woody plants in general, and magnolia species in particular, the virginal age is quite long, and therefore is critically important from the point of view of selecting optimal conditions for growing plants. The study was conducted on biennial plants of deciduous magnolias: Magnolia kobus Sarg., M. obovata Thunb., M. denudata Desr. The studied plants were at the beginning of the virginile stage of development. The material for the investigation is selected from plants, which were planted by us in the research area of A. V. Fomin Botanical Garden of the Taras Shevchenko National University of Kyiv. In this study, we used scanning electron and light microscopes to examine the ultrastructure of the surface of leaves of the studied species. The histological characteristics of the leaves of the studied species are similar. They are hypostomatic. Their stomata are of the paracytic type, they are evenly distributed on the abaxial surface of the leaves. The epidermal cells of the studied species of the genus Magnolia have tortuous (cells located on the periphery of the leaf) or straight (cells located on the veins) outlines and rectangular (cells located on the veins) or flattened (cells placed on the periphery of the leaf) projection. The cuticle is relatively thin, located on both the abaxial and adaxial surfaces of the leaves. Epicuticular wax is observed of three types in the studied species: films (M. denudata), crust (M. kobus, M. obovata) and wax granules (M. denudata, M. obovata). The amount of wax and pubescence is greater on the abaxial surface in M. obovata; very weak pubescence and waxy layer is observed only on the abaxial surface of the leaf in M. kobus, weak pubescence is present on both sides in M. denudata. In all species of the genus Magnolia pubescence is simple, formed by hairs that "accompany" the veins. There are two main types of lamina relief in the studied species: reticular (M. obovata, M. denudata (subtype reticular-collicular)) and pitted (M. kobus). The species clearly differ in this feature, so we believe that the type of relief of the lamina can be used as an additional diagnostic feature to distinguish species of the genus Magnolia. Magnolia denudata is characterized by a small number of stomata, while M. obovata and M. kobus are characterized by their average number. The Stomata Index varies from 2.8 in M. denudata to 1.02 in M. kobus. The lamina is the thickest in M. obovata, the thinnest is in M. kobus, but the total thickness of the epidermal tissue as a percentage of the thickness of the leaf is, in descending order: M. denudata (29%), M. kobus (24%), M. obovata (18%). The mesophyll varies from homogeneous-spongy (in M. kobus) to layered (in M. obovata, M. denudata) type. The number of layers of cells that form the mesophyll in all studied species is from 4 to 6. Thus, M. kobus is characterized by the least specialized type of mesophyll. The vascular system in the studied plants is represented by small central and lateral vascular bundles. The ground tissue is present only in the central and large side bundles. In the early stages of ontogenesis the studied plants are typical mesophytes with hypostomatic leaves adapted to exist in sufficiently moist conditions in soil and air. In practical terms, the results of investigation can be used to select optimal conditions for growing plants at the initial stages of ontogenesis.