Characterization of essential oil distribution in the root cross-section of Valeriana officinalis L. s.l. by using histological imaging techniques

Abstract

BackgroundThe essential oil is an important compound of the root and rhizome of medicinally used valerian (Valeriana officinalis L. s.l.), with a stated minimum content in the European pharmacopoeia. The essential oil is located in droplets, of which the position and distribution in the total root cross-section of different valerian varieties, root thicknesses and root horizons are determined in this study using an adapted fluorescence-microscopy and automatic imaging analysis method. The study was initiated by the following facts:A probable negative correlation between essential oil content and root thickness in selected single plants (elites), observed during the breeding of coarsely rooted valerian with high oil content.Higher essential oil content after careful hand-harvest and processing of the roots. ResultsIn preliminary tests, the existence of oil containing droplets in the outer and inner regions of the valerian roots was confirmed by histological techniques and light-microscopy, as well as Fourier-transform infrared spectroscopy. Based on this, fluorescence-microscopy followed by image analysis of entire root cross-sections, showed that a large number of oil droplets (on average 43% of total oil droplets) are located close to the root surface. The remaining oil droplets are located in the inner regions (parenchyma) and showed varying density gradients from the inner to the outer regions depending on genotype, root thickness and harvesting depth.ConclusionsFluorescence-microscopy is suitable to evaluate prevalence and distribution of essential oil droplets of valerian in entire root cross-sections. The oil droplet density gradient varies among genotypes. Genotypes with a linear rather than an exponential increase of oil droplet density from the inner to the outer parenchyma can be chosen for better stability during post-harvest processing. The negative correlation of essential oil content and root thickness as observed in our breeding material can be counteracted through a selection towards generally high oil droplet density levels, and large oil droplet sizes independent of root thickness.Electronic supplementary materialThe online version of this article (10.1186/s13007-018-0309-4) contains supplementary material, which is available to authorized users.

Back to the Roots—An Overview of the Chemical Composition and Bioactivity of Selected Root-Essential Oils

“…The remaining oil droplets are located in the inner regions (parenchyma), with varying density gradients from the inner to the outer regions depending on genotype, root thickness, and harvesting depth. Further studies are needed to evaluate the relationship between the EO droplet density and EO content [ 326 ]. However, contrary to previous assumption [ 325 ], no linear relationship between oil drop density and root thickness could be derived [ 326 ].…”

“…Further studies are needed to evaluate the relationship between the EO droplet density and EO content [ 326 ]. However, contrary to previous assumption [ 325 ], no linear relationship between oil drop density and root thickness could be derived [ 326 ]. Despite the harvest process, sowing time and planting density were also found to significantly affect EO yield and percentage.…”

Echinacea and Valeriana Extraction in Different Solutions by Acoustic Influence

“…s.l.) is one of the most popular herbal remedies [8,9]. The entire root system is used for medicinal purposes [10].…”

Dynamic changes of the main active constituents in valerian rhizome and root /Valeriana amurensis Smir. ex Kom.) during different harvest periods

“…Owing to containing a great quantity volatile constituents, the essential oils were usually analysed by capillary GC, GC-MS and other instruments (Gränicher et al, 1995;Bos et al, 1997b;Kovacevic et al, 2002;Sati & Mathela, 2005;Safaralie et al, 2008). Fluorescence-microscopy followed by image analysis of entire root cross-sections V. officinalis, showed that the oil droplets displayed varying density gradients from the inner to the outer regions depending on genotype, root thickness and harvesting depth (Penzkofer et al, 2018). As unique constituent for sedative in the essential oils from underground parts of V. officinalis L. s.l.…”