Cannabis glandular trichomes alter morphology and metabolite content during flower maturation

Abstract

SummaryThe cannabis leaf is iconic, but it is the flowers of cannabis that are consumed for the psychoactive and medicinal effects of their specialized metabolites. Cannabinoid metabolites, together with terpenes, are produced in glandular trichomes. Superficially, stalked and sessile trichomes in cannabis only differ in size and whether they have a stalk. The objectives of this study were: to define each trichome type using patterns of autofluorescence and secretory cell numbers, to test the hypothesis that stalked trichomes develop from sessile‐like precursors, and to test whether metabolic specialization occurs in cannabis glandular trichomes. A two‐photon microscopy technique using glandular trichome intrinsic autofluorescence was developed which demonstrated that stalked glandular trichomes possessed blue autofluorescence correlated with high cannabinoid levels. These stalked trichomes had 12–16 secretory disc cells and strongly monoterpene‐dominant terpene profiles. In contrast, sessile trichomes on mature flowers and vegetative leaves possessed red‐shifted autofluorescence, eight secretory disc cells and less monoterpene‐dominant terpene profiles. Moreover, intrinsic autofluorescence patterns and disc cell numbers supported a developmental model where stalked trichomes develop from apparently sessile trichomes. Transcriptomes of isolated floral trichomes revealed strong expression of cannabinoid and terpene biosynthetic genes, as well as uncharacterized genes highly co‐expressed with CBDA synthase. Identification and characterization of two previously unknown and highly expressed monoterpene synthases highlighted the metabolic specialization of stalked trichomes for monoterpene production. These unique properties and highly expressed genes of cannabis trichomes determine the medicinal, psychoactive and sensory properties of cannabis products.

Grinding and Fractionation during Distillation Alter Hemp Essential Oil Profile and Its Antimicrobial Activity

“…Grinding of the material has been shown to facilitate and to significantly speed up the extraction of EO in other crops such as anise [ 23 ] and junipers [ 24 ]. However, because hemp EO is synthesized and stored in trichomes, which are epidermal structures [ 25 ], volatile fractions can be extracted relatively fast, while the EO in junipers is synthesized and accumulated in endogenous EO structures. The observed delay in EO extraction from ground biomass may be due to different physical and chemical processes developing during the grinding of the material in water, then introducing the slurry in the Clevenger apparatus before extraction.…”

Terpene Synthases and Terpene Variation in Cannabis sativa

“…S3) from individual clonal plants prior to signs of floral senescence. Mature flowers are characterized by apparent lack of unstalked glandular trichomes, as glandular trichomes have matured to the stalked stage (Livingston et al, 2020), and with .80% of pistils turning from white/green to brown. Total RNA was extracted from isolated trichome heads and used for RNA-seq.…”

“…Contigs with .98% predicted amino acid sequence identity were collapsed under the longest representative sequence. These five single-cultivar transcriptomes and the previously published cv PK trichome transcriptome (van Bakel et al, 2011) were searched with BLASTX to identify known (Gunnewich et al, 2007;Booth et al, 2017;Zager et al, 2019;Livingston et al, 2020) as well as new CsTPS sequences. Sequences representing all but three of the previously functionally characterized and unique CsTPSs (a total of 18; Supplemental Table S1) were present in the transcriptomes of at least one of the five cultivars (Booth et al, 2017;Allen et al, 2019;Zager et al, 2019;Livingston et al, 2020).…”

“…The pistillate flowers of cannabis (Cannabis sativa) are densely covered with glandular trichomes that produce and accumulate a resin that is rich in cannabinoids as well as monoterpenes and sesquiterpenes (Turner et al, 1978;Brenneisen and elSohly, 1988;Livingston et al, 2020). Cannabinoids are responsible for the various medicinal and psychoactive properties of cannabis.…”

“…At least 55 different CsTPS gene models have previously been reported (Supplemental Table S1), but only 14 have been functionally characterized, including eight mono-TPSs and six sesqui-TPSs (Gunnewich et al, 2007;Booth et al, 2017;Allen et al, 2019;Zager et al, 2019;Livingston et al, 2020). The 14 functionally characterized CsTPSs account for some of the major terpenes in cannabis (e.g.…”