Oil Secretory System in Vegetative Organs of Three Arnica Taxa: Essential Oil Synthesis, Distribution and Accumulation

Plant Cell Physiol. 2016 May;57(5):1020-37. doi: 10.1093/pcp/pcw040. Epub 2016 Mar 2. . Kromer K1, Kreitschitz A2, Kleinteich T3, Gorb SN3, Szumny A4. Author information 1 Botanical Garden, Plant Tissue Culture Laboratory, University of Wroc ław, ul. Sienkiewicza 23, 50-325 Wroc ław, Poland kromer@biol.uni.wroc.pl krystyna.kromer@uwr.edu.pl. 2 Department of Plant Developmental Biology, Institute of Experimental Biology, University of Wrocław, ul. Kanonia 6/8, 50-328 Wrocław, Poland. 3 Department of Functional Morphology and Biomechanics, University of Kiel, Am Botanischen Garten 1-9, D-24098 Kiel, Germany. 4 Department of Chemistry, The Faculty of Food Science, Wroclaw University of Environmental and Life Sciences, ul. Norwida 25; 50-375 Wrocław, Poland. Abstract Arnica, a genus including the medicinal species A. montana, in its Arbo variety, and A. chamissonis, is among the plants richest in essential oils used as pharmaceutical materials. Despite its extensive use, the role of anatomy and histochemistry in the internal secretory system producing the essential oil is poorly understood. Anatomical sections allowed differentiation between two forms of secretory structures which differ according to their distribution in plants. The first axial type is connected to the vascular system of all vegetative organs and forms canals lined with epithelial cells. The second cortical type is represented by elongated intercellular spaces filled with oil formed only between the cortex cells of roots and rhizomes at maturity, with canals lacking an epithelial layer.Only in A. montana rhizomes do secretory structures form huge characteristic reservoirs. Computed tomography illustrates their spatial distribution and fusiform shape. The axial type of root secretory canals is formed at the interface between the endodermis and cortex parenchyma, while, in the stem, they are located in direct contact with veinal parenchyma. The peripheral phloem parenchyma cells are arranged in strands around sieve tube elements which possess a unique ability to accumulate large amounts of oil bodies. The cells of phloem parenchyma give rise to the aforementioned secretory structures while the lipid components (triacylglycerols) stored there support the biosynthesis of essential oils by later becoming a medium in which these oils are dissolved. The results indicate the integrity of axial secretory structures forming a continuous system in vegetative plant organs. © The Author 2016. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com. KEYWORDS: Arnica; Essential oils; Lipids; Oil bodies; Secretory system; triacylglycerol PMID: 26936790 DOI: 10.1093/pcp/pcw040