Taxonomic traits in the microstructure of flowers of parasitic Orobanche picridis with particular emphasis on secretory structures

Abstract

Orobanche picridis is an obligate root parasite devoid of chlorophyll in aboveground organs, which infects various Picris species. Given the high level of phenotypic variability of the species, the considerable limitation of the number of taxonomically relevant traits (mainly in terms of generative elements), and the low morphological variation between species, Orobanche is regarded as one of the taxonomically most problematic genera. This study aimed to analyse the taxonomic traits of O. picridis flowers with the use of stereoscopic and bright-field microscopy as well as fluorescence, scanning, and transmission electron microscopy. The micromorphology of sepals, petals, stamens, and pistils was described. For the first time, the anatomy of parasitic Orobanche nectaries and the ultrastructure of nectaries and glandular trichomes were presented. Special attention was paid to the distribution and types of glandular and non-glandular trichomes as well as the types of metabolites contained in these structures. It was demonstrated that the nectary gland was located at the base of the gynoecium and nectar was secreted through modified nectarostomata. The secretory parenchyma cells contained nuclei, large amyloplasts with starch granules, mitochondria, and high content of endoplasmic reticulum profiles. Nectar was transported via symplastic and apoplastic routes. The results of histochemical assays and fluorescence tests revealed the presence of four groups of metabolites, i.e. polyphenols (tannins, flavonoids), lipids (acidic and neutral lipids, essential oil, sesquiterpenes, steroids), polysaccharides (acidic and neutral polysaccharides), and alkaloids, in the trichomes located on perianth elements and stamens.

Comparative Floral and Pollen Micromorphology of Leonurus japonicus and L. macranthus (Lamiaceae)

“…Thus, the high density of non-glandular and glandular trichomes, especially on the abaxial side of the calyx and lip, may have several roles in the two Leonurus species, including physical protection and deterrence of herbivory. Recent investigations have also suggested that edible floral non-glandular trichomes, which contain starch, may act as a food reward for visitors and pollinators [65,66], and that most lamiacean plants produce and store aromatic com-pounds, essential oils, or floral scents-which may increase the attractiveness of flowers to insects [67][68][69][70][71]-in glandular trichomes, especially the peltate and capitate glands on the calyx and corolla [23,30,[67][68][69]. Thus, field surveys and histochemical studies are necessary to explore whether the floral non-glandular trichomes of Leonurus can be provided as a food material to pollinators and to describe secondary metabolic compounds.…”

Orobanche dominae (Orobanchaceae), a new species described from Tunisia, North Africa

“…Orobanche species are characterized by slight morphological diagnostic characters; hence, they are difficult to distinguish in terms of taxonomy (cf. Domina et al, 2011;Zare & Dönmez, 2013;Zare et al, 2014;Konarska & Chmielewski, 2019). Moreover, dried specimens lose colors and become brownish to blackish, making herbarium specimens difficult to identify (see e.g., Manen et al, 2004;Piwowarczyk et al, 2011Piwowarczyk et al, , 2014Piwowarczyk et al, , 2015.…”

“…Moreover, dried specimens lose colors and become brownish to blackish, making herbarium specimens difficult to identify (see e.g., Manen et al, 2004;Piwowarczyk et al, 2011Piwowarczyk et al, , 2014Piwowarczyk et al, , 2015. Therefore, the presence of the host-plant may facilitate to some extent identification of the Orobanche species growing nearby (see e.g., Hipkin, 1992;Carlón et al, 2015;Konarska & Chmielewski, 2019).…”

Glandular trichomes of Robinia viscosa Vent. var. hartwigii (Koehne) Ashe (Faboideae, Fabaceae)—morphology, histochemistry and ultrastructure

“…Glandular trichomes are characteristic for representatives of many botanical families, e.g. Asteraceae (Muravnik et al 2016;Xiao et al 2016), Cannabaceae (Mahlberg and Kim 2004), Geraniaceae (Boukhris et al 2013), Lamiaceae (Maurya et al 2019), Orobanchaceae (Konarska and Chmielewski 2020), Scrophulariaceae (Attar et al 2007), Solanaceae (Bergau et al 2016), Verbenaceae (Silva et al 2016), and Fabaceae (Barros et al 2017a;Vargas et al 2019). Glandular trichomes produce, store, or secrete mainly lipophilic substances, i.e.…”

“…Glandular trichomes produce, store, or secrete mainly lipophilic substances, i.e. fats, waxes, essential oils, and resins (Stojičić et al 2016;Citti et al 2019; Konarska and Chmielewski 2020). However, the secretion often contains polysaccharides and proteins (Tozin and Rodrigues 2017), alkaloids (Munien et al 2015), or phenolic compounds (Jachuła et al 2018).…”