MORPHOLOGICAL AND ANATOMICAL STUDIES OF YAKON (POLYMNIA SONCHIFOLIUS POEPP. & ENDL.)

Abstract

Introduction. Yacon (Polymnia sonchifolia Poepp. & Endl., synonym Smallanthus sonchifolius (Poepp.) H. Rob.,) is a perennial herbaceous plant from the genus Smallanthus (Polymnia), from the Asteraceae family. The east slopes of Andes on the territory fromVenezuela to the southwestern part ofArgentina are the homeland of this species [2, 4].

Yacon's caulis is green with anthocyanin spots on its upper part. The leaves are big with unevenly serrated edges. Their dorsal side is dark green, and their ventral side is more lightly colored. The big veins and petioles of the leaves have dense and coarse trichomes. Yellow or bright orange flowers form pseudanthiums situated on long peduncles. Yacon forms underground organs of two kinds: rhizomes and root tubers. Rhizomes form sprouts that give rise to the new plants. Multiple thin roots extend from the rhizomes; they thicken as they grow, taking the pear- or spindle-shaped form [2].

Yacon's root tubers are used for diabetes mellitus, obesity, atherosclerosis [5, 6], and in case of gastrointestinal diseases [3, 5].

The goal of our research was to study the morphological and anatomical structure of these organs and determine their diagnostic properties.

Research techniques. We used fresh, dried and fixed (glycerol-ethanol-water 1:1:1 mixture) leaves and root tubers of yacon. The plant material was offered by Professor L.T. Mischenko – the leading scientific employee of the Educational andScientificCenter "Institute ofBiology". Leaves and root tubers harvested in 2014 were used for experimental studies. The preparation of micropreparations and macro- and microscopy of plant objects were performed by common methods using microscopes MBR-1 and MBI-6 LOMO [1]. Microphotographs were made using the camera D-580 ZOOM/C-460 ZOOM/X-400.

Results and discussion.

Macroscopic features of leaves. The leaves are wide ovate shaped, petiolated, big, sinulated with unevenly serrated edges. The big veins and petioles of the leaves have dense and coarse trichomes. The width of lamina is up to32 cm, width –22 cm. The dorsal side of the leaves is dark green, and their ventral side is more lightly colored. The smell is faint. The taste is bitter-sweet.

Microscopic features of leaves. The dorsal epidermis of the yacon leaves on the tip is presented with paddle-shaped cells with narrow and sinuous walls.  There are few stomas; they are big and oval-shaped. The stomatal complex is anomocytic. Epidermis is unevenly covered with trichomes: there are more of them along the veins, and the leaf surface is more sparsely covered. There are two main types of trichomes: covering and glandular. There are rosettes in the base of trichomes. Often the leaf epidermis is covered with big roundish 2-cell glands.

The ventral epidermis, unlike the dorsal, on the tip of the leaf and in its center is presented by parenchymal cells with sinuous walls. There are many stomas; they are big. The stomatal complex is anomocytic. The pubescence is dense; the types of trichomes are the same as on the dorsal side. They evenly cover the whole epidermis, but the glandular ones are more frequent.

Macroscopic analysis of yacon root tubers. The root tubers are big, pear- or spindle-shaped, fleshy and succulent. The peel is delicate, from yellow to light brown in color; the color of the pulp is from white to yellow. On the cross-section the rays of secondary xylem are clearly visible; they channel off the central part of the root tubers. The smell is faint. The taste is sweet.

Microscopic features of root tubers. The root tuber on the cross-section has a roundish shape, is light brown in color and covered with a layer (3-5 layers) of dark brown periderm. The periderm is underlaid by cork parenchyma that consists of parenchymal cells. They are densely arranged in even layers one above the other. The cellular walls of cork parenchymal cells are straight and thin. The internal part of cork parenchyma is clearly separated by the layer of endodermis. The cork parenchyma contains isolated schizogenetic repositories with brown secretion. Phloem is poorly defined and presented by sieve tubes with companion cells, and small celled phloem parenchyma. The cells of xylem parenchyma have narrow lumen. Their walls on the tip are brown colored; their size increases below the tip, they have square shape and straight thin cellular walls. The parenchyma of the central cylinder is presented by small-sized cells with straight cellular walls. Histochemical reactions for detection of inulin prove the presence of polysaccharide spherocrystals.

Conclusions. The morphological and anatomical study has determined the macro- and microscopic species characteristics of yacon leaves and root tubers.