Hairy Plants

Glandulat trichome Trichomes (from the Greek for “hair”) are fine out­growths on plants such as hairs. They are highly vari­able in shape, cyto­logy and func­tion, and more than 300 types of plant trich­omes have been described. Trichomes occur on dif­fer­ent sur­faces of almost all angio­sperms and may alter the bound­ary layer above the leaf sur­face, con­trib­ute to light pip­ing, pro­tect against tem­per­at­ure stress, reduce water loss in tran­spir­a­tion or serve as the absorb­ing sur­face in roots.

Besides meta­bol­ic­ally inact­ive or so-called non-glandular trich­omes, bio­syn­thet­ic­ally act­ive glandu­lar trich­omes also exist. They sequester or store plant meta­bol­ites that are often char­ac­ter­istic for spe­cific taxo­nomic groups. The stor­age of bio­act­ive com­pounds in in these struc­tures is fre­quently asso­ci­ated with pro­tec­tion against herb­i­vores and patho­gens, but evap­or­a­tion of volat­ile trich­ome meta­bol­ites also occurs and may have numer­ous physiolo­gical and eco­lo­gical functions.

Previous stud­ies have shown that the leaves of the sun­flower (Helianthus annuus) have two dif­fer­ent types of glandu­lar trich­ome. A recent paper in AoB PLANTS describes detailed res­ults on the mor­pho­logy, loc­al­iz­a­tion and meta­bolic activ­ity of glandu­lar trich­ome in sun­flowers and their occur­rence in related taxa.


Linear glandu­lar trich­omes of Helianthus (Asteraceae): mor­pho­logy, loc­al­iz­a­tion, meta­bol­ite activ­ity and occur­rence. (2013) AoB PLANTS 5: plt028 doi: 10.1093/aobpla/plt028
Capitate glandu­lar trich­omes of sun­flower are well invest­ig­ated, but detailed stud­ies are lack­ing for the lin­ear glandu­lar trich­omes (LGT), a second type of physiolo­gic­ally act­ive plant hair present on the sur­face of sun­flowers. Light, fluor­es­cence and scan­ning elec­tron micro­scopy as well as his­to­chem­ical stain­ing were used to invest­ig­ate the struc­ture and meta­bol­ite depos­ition of LGT. Consisting of 6–11 lin­early arranged cells, LGT were found on the sur­face of most plant organs of Helianthus annuus. They were asso­ci­ated with the leaf vas­cu­lar sys­tem, and also occurred along peti­oles, stems and the abaxial sur­face of chaffy bracts, ray and disc florets. The highest dens­ity was found on the abaxial sur­face of phyl­lar­ies. Phenotypically sim­ilar LGT were com­mon in all spe­cies of the genus, but also occurred in most other gen­era of the Helianthinae so far screened. Brownish and fluor­es­cent meta­bol­ites of an as yet unknown chem­ical struc­ture, together with terpen­oids, were pro­duced and stored in apical cells of LGT. The depos­ition of com­pounds gradu­ally pro­gressed from the tip cell to the basal cells of older trich­omes. This pro­cess was accom­pan­ied by nuc­leus degrad­a­tion in metabolite-accumulating cells. The loc­al­iz­a­tion of these trich­omes on prom­in­ent plant parts of the apical bud and the capit­u­lum com­bined with the accu­mu­la­tion of terpen­oids and other as yet unknown com­pounds sug­gests a chemo-ecological func­tion of the LGT in plant–insect or plant–herbivore interaction.


AJ Cann. ORCID 0000-0002-9014-3720

Alan Cann is a Senior Lecturer in the School of Biological Sciences at the University of Leicester and formerly Internet Consulting Editor for AoB.