Anatomical structure of leaves , stems and roots of hemiparasitic plants Thesium ebracteatum Hayne ( Santalacea R . Br . ) from the Urals

The paper presents the results of structure researches of Thesium ebracteatum Hayne. plants from the Ural populations. The anatomic description includes the characteristic of leaves and roots, the stems structure in its top, middle and lower part. Some stomatografic parameters of leaves are calculated. This is the fist anatomical report on the important diagnostics signs of Thesium ebracteatum Hayne plants.


Introduction
Detailed anatomical studies of Thesium ebracteatum Hayne plants from the Urals were not carried out.This species is known from sites in central Europe, European part of Russia, Western Siberia and in the Urals.It is a native herb of forest lawns and thickets of bushes.It is perennial hemiparasitic herb with a subterranean rhizome and numerous storage lateral root with haustorial connections.The aerial shoots annual, erect or ascending at the top, 10-30 cm tall, usually unbranched, glabrous, rarely leafy.At the top of the shoots presents bracts devoid of flowers; leaves linear, glabrous.Inflorescence is a simple, unbranched brush; flower on short stalk with one bract, bracts like the leaves but decreasing in size, perianth tubular, upward strongly wrapped.Capsule on the stalk is elliptical, with longitudinal branching veins, three times larger than the remaining part of the perianth.The paper presents the studies of anatomical structure of the leaf, stem and roots of Thesium ebracteatum plants from the Urals populations.

Materials and Methods
The plants were collected from the mountainous areas of Middle Ural (Sverdlovsk region) in two populations nearby Nizhnyaya Irga, Ust'-Bayak.Specimens for morphological study were dried according to standard herbarium techniques and stored in the Herbarium of Institute of Plant and Animal Ecology, Ural Branch of the Russian Academy of Sciences (SVER).The materials for anatomical study were preserved in 70% alcohol in the field.Anatomical observations were performed on transverse sections of root and stem (in its top, BIO Web of Conferences 11, 00022 (2018) https://doi.org/10.1051/bioconf/20181100022Prospects of Development and Challenges of Modern Botany average and lower part) cut by rotary microtome Microm HM (Carl Zeiss, Germany), and surface sections of leaves cut by hand.All slides were observed by light microscopes Micros (Austria) and Zeiss Axioscopus (Carl Zeiss, Germany).Well-staining sections were photographed.Stomatal index (SI) has been calculated according to Salisbury (1927) [1].All measurements and observations were made ten times on different slides.All microscopic measurements were made with the aid of an occular micrometer.

Results and Discussion
Leaf features of the species are shown in Figure 1.In surface preparations, the epidermal cells are covered by a thick cuticular layer.The leaf is amphystomatic with oval paracytic stomata.Epidermal cell walls are not undulate.The cells of the epidermis are isodiametric and polygonal with straight walls except in the coastal regions where they are narrow, elongated parallel to the veins.Upper epidermal cells have the same size as the lower ones; trichomes are absent, leaf margin with sharp papillae.Stomata orientation was random.Guard cells are elliptical, pores are elongated.Average size of guard cells in microns is 31 in lengths (varies from 16 to 38), 23 in widths (varies from 14, to 35).SI adaxial epidermis 12,8 and abaxial epidermis 11,3.The presens of stomata in adaxial and abaxial epidermis in equal parts may be the adaptive advantages to hemiparasitic nutrition.Lamina is dorsiventral.Mesophyll consists of 1 layer of elongated palisade cells and 2 or 3 layers of isodiametric, spongy parenchymatic cells have small intercellular cavities.A transverse section taken from the top, middle and lower part of the stem was observed (Fig. 2, 3А).The epidermal cells are covered by cuticular layer, trichomes are absent.Stem cortex consists of 2-5 layers of usually oval cells.Some cortex cells contain secretes at the top and middle part of the stem.The sclerenchimatic sheath is upper the vascular bundles.Cambium is distinguishable.Secondary thickening develops from a conventional cambial ring.In the lower part of the stem secondary thickening tissues predominate.Vascular bundls consists of secondary phloem and xylem.Xylem has vessels.Vessel end-walls are simple.Vessels have not vestured pits.Pith cells are large and spherical.Cavity arises in the middle and lower part of the stem.
The subterranean rhizome structure is similar to those of the stem.A transverse section taken from the lateral roots was observed (Fig. 3Б).The features of the primary structure are retained.The typical primary root is bounded by an exodermis.The centre of the root made up entirely of many-layered cortex, what have cavities and cells with starch.The https://doi.org/10.1051/bioconf/20181100022Prospects of Development and Challenges of Modern Botany inner side is an endodermis.Next follows the pericycle, and then the vascular system is in the middle.Vessel wall pittings and thickenings are similar to those of the stem.

Discussion
Thesium L. with ca.330 species counts the highest number of species of any genus in Santalales [2].The Santalaceae family (Santalaceae R.Br.) is represented in Russia by 12 species, 3 species are found in the Urals.All of them are hemiparasitic herbs from the genus Thesium L. Several studies demonstrate geographical distribution of Thesium species [3][4], biochemical features [5], physiology of host plant-parasitic plant interaction in comparison with others parasitic plants [6], host range and selectivity [7], active ingredients of medicinal material of Thesium [8].This reflects the general trends in the study of the biology of hemiparasitic plants.The analysis of functional features of adaptation to parasitism in plants is considered as importance [9,11,14].The anatomical studies of Thesium species in the Urals have never been done before.We performed analysis of available data on the structure of root-hemiparasitic Scrophs such as Rhinanthus, Melampyrum, Odontites species and others [10][11][12][13][14] in comparison with Thesium ebracteatum.Root-hemiparasitic Scrophs have leaves with hydathodes and trichomes [11][12][13], stems and roots with ring cambium [11,14] [10].All roots hemiparasitic plants had haustorial connections, but we noticed that hemiparasitic Scrophs had significant differences from Thesium in leaves, roots and stems structure.It is confirmed that not only the parasitic way of life affects the nature of the vegetative organs adaptations.An anatomical structure of leaves, roots and stems reflects primarily belonging to the taxonomic group of hemiparasitic plants.
This study was supported by the Russian Foundation for Basic Research (project no.АААА-А17-117072810011-1).