Effects of Light Reduction, Water Deficiency, and Nitrogen Fertilization on Morphological and Phytochemical Parameters of Glandular Trichomes of Origanum vulgare L.
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Beschreibung
Origanum vulgare L. (Lamiaceae) is a perennial aromatic herb mostly known as a popular spice. The secondary metabolites of Origanum plants are responsible for antimicrobial, antiviral, and antioxidative effects of this spice. The aroma and taste of Origanum are related to its essential oil, which is biosynthesized and secreted by the glandular trichomes. Two types of glandular trichomes, peltate and capitate glandular trichomes, have been observed on Origanum plants.
Several studies have shown that morphological and chemical characteristics of glandular trichomes of plants can be influenced by environmental factors. However, these factors have not been fully studied in O. vulgare. In the current thesis, two aims were followed: 1. Characterization of trichomes structure as well as the content and composition of essential oil in different O. vulgare L. subspecies. 2. To clarify the effect of light reduction, water supply, and nitrogen fertilization on the size and density of trichomes as well as the content and composition of its essential oil.
In order to answer these questions, three pot experiments with four O. vulgare subspecies were carried out in 2011 and 2012. The following subspecies were included: (1) ssp. vulgare, (2) ssp. hirtum (Link) Ietswaart, (3) ssp. viride (Boissier) and (4) a hybrid of ssp. viride (Boissier) Hayek and O. majorana L. Scanning electron microscopy was used for micro morphological analysis of trichomes. Hydrodistillation and solvent extraction with dichloromethane were used to extract the essential oil. The content and composition of essential oil were determined by using GC-MS method. Furthermore, yield parameters were measured.
The obtained results showed that the indumenta of the investigated Origanum plants consisted of non-glandular trichomes, peltate glandular trichomes, and capitate glandular trichomes. Variations determined by subspecies were found concerning the size and density of trichomes as well as content and composition of the essential oil. O. vulgare L. ssp. hirtum was characterized by high density of large peltate trichomes and higher essential oil content compared to other subspecies. In ssp. hirtum and ssp. viride, the important bioactive compounds thymoquinone and thymohydroquinone have been detected.
Reduced light intensity led to smaller size of glandular trichomes and modified composition of essential oil in Origanum plants. There were no differences between the treatments concerning the essential oil content. Accordingly, it is suggested that both the biosynthesis and the emission of essential oil was higher under normal light conditions compared to reduced light intensity.
Induced drought stress and lower nitrogen application led to reduced essential oil content in the samples. The profile of essential oil was modified by water supply and nitrogen fertilization as well. Only the size of capitate glandular trichomes was decreased by drought stress. Furthermore, it was found that the genotype had a significant influence on size and density of glandular trichomes as well as on the essential oil content and composition.
It can be concluded that reduced light intensity, drought stress, and lower nitrogen fertilization were limiting factors for the growth of the investigated O. vulgare L. subspecies. Under the current conditions these factors cannot be considered as a trigger for essential oil biosynthesis in Origanum plants. It is suggested that the formation of glandular trichomes is more genetically determined. The present findings are also of practical relevance due to their easy application for the discrimination of O. vulgare L. subspecies according to the micro-morphological parameters.
Autor*in
Marzieh Shafiee Hajiabad