Cytological Development and Sesquiterpene Lactone Secretion in Capitate Glandular Trichomes of Sunflower

Abstract

The secretion of sesquiterpene lactones (STL) in capitate glandular trichomes from the anther appendages of Helianthus annuus L. (Asteraceae) was observed by light and fluorescence microscopy and HPLC analysis. Disk flowers within the sunflower capitulum showed the known ontogenetic progression from the centre to the margin. During development of the florets, the trichomes in the anther appendages secreted their metabolites into the subcuticular secretion storage space in front of the two apical cells. All stages of forming the cuticular globe, from the pre-secretory to the post-secretory phase, could be observed microscopically and secretory activity was simultaneously monitored. Six germacrolides and heliangolides of known structure were selected for quantitative analysis. The increase in STL content during extension of the subcuticular space was monitored by HPLC analysis. Thereby, the start and termination of STL biosynthesis was defined in relation to other developmental stages of floret ontogenesis, particularly, the pollen formation. Part of the secreted material showed autofluorescence which could be attributed to a hydroxy-trimethoxy-flavone, as determined by NMR and mass spectroscopy. The anther trichomes were cytologically and chemically similar to foliar glandular trichomes of sunflower and represent the multicellular capitate glandular trichome type common to many Asteraceae. The ease with which anther trichomes of H. annuus can be harvested and analyzed suggests that they can provide a valuable model system for investigation of STL and flavonoid metabolism in Asteraceae.

Lettuce Costunolide Synthase (CYP71BL2) and Its Homolog (CYP71BL1) from Sunflower Catalyze Distinct Regio- and Stereoselective Hydroxylations in Sesquiterpene Lactone Metabolism

“…Trichomes in the secretory stage were manually isolated as described (16). The trichomes were collected in 200 l ice-cold RNA extraction buffer (Aurum Total RNA Isolation kit, Bio-Rad).…”

“…This particular sunflower cultivar has abundant trichomes on its florets (ϳ200 per floret), where a diverse array of STLs including a costunolide derivative (haageanolide, Fig. 2B) were isolated and structurally characterized (16). Importantly, the floret trichomes can be visualized by a dissecting microscope, allowing physical separation of pure trichomes by mechanical methods.…”

“…Phytochemical analyses showed that they synthesize structurally related yet distinct STLs (see Fig. 2B) (16,17). For sunflower and lettuce STL biosynthesis, it has been shown that farnesyl diphosphate is cyclized to form C15 hydrocarbon germacrene A by germacrene A synthase (GAS) ( Fig.…”

Bidirectional Secretions from Glandular Trichomes of Pyrethrum Enable Immunization of Seedlings

“…In the Asteraceae family, glandular trichomes are particularly rich in sesquiterpenoids (Seaman et al, 1980;Heinrich et al, 2002;Göpfert et al, 2005;Bertea et al, 2006). Indeed, apart from pyrethrins, pyrethrum extracts also contain a variety of sesquiterpene lactones (STLs), such as pyrethrosin (chrysanthin) (Barton and Demayo, 1957;Barton et al, 1960), chrysanin, dihydro-b-cyclopyrethrosin, chrysanolide, and b-cyclopyrethrosin (Doskotch and Elferaly, 1969;Doskotch et al, 1971).…”

Finishing lambs on a chicory-plantain mixture or a temperate grassbased pasture: live weight gain and gastrointestinal parasitism

“…With respect to plant structures, Marley et al (2006) found a significantly lower recovery of GIN L3 from chicory compared to ryegrass swards; although many factors could be involved, their results could be partially explained by the physical barrier represented by the presence of trichomes in chicory leaves that interfere with larval migration. Glandular trichomes act as metabolic factories in different plant organs where in the case of chicory and other members of the Asteraceae family, sesquiterpene lactones are produced and secreted to a subcuticular storage space at the apex of trichomes or excreted to the plant surface (Göpfert et al, 2005). These terpenoids play an important role as deterrents to herbivory and are toxic to pathogens; therefore, they could also represent a chemical repellent to L3, restraining vertical movement.…”