Trichome

Three-armed, forked trichome (furcate) in the arable cress ( Arabidopsis thaliana )

Glandular hairs as a sticky trap on the round-leaved sundew ( Drosera rotundifolia )

Dense, attractive "silicate hairs" (hispid-urent) as protection against eating. Typical of the predatory plants , here with an ox tongue .

As trichomes (plant hair) is known hair-like structures on the surfaces of plants in size, shape and density vary and perform different functions.

physiology

Trichomes can consist of one or more epidermal cells (as opposed to emergence , which also consists of hypodermic layers). Depending on the plant, they can be found in different forms all over the plant surface. They occur as protective, support and glandular hair and in the root area as absorbent hair. They are sometimes arranged in a regular pattern on the epidermis , the base of which extends over several plant cells (8 to 10 epidermal cells).

Usually the trichome is formed from a single epidermal cell, the DNA content and growth of which is increased many times over. The trichome is hollow and may branch several times at its end in the course of its development. The surface of a trichome is covered with innumerable sharp or warty outgrowths. The cytoplasm and nucleus can only be found in the basal part, where calcium carbonate crystals are also present.

In areas with less precipitation, the density of the trichomes is increased. The more trichomes or the more branched trichomes there are, the higher the refraction of light on the plant surface, which leads to a reduced incidence of light and thus a reduced temperature in the photosynthetically active organs concerned . The increased refraction of light, which ultimately leads to a reduction in water loss, can be recognized well by the silvery white shimmer of some leaves or shoot axes . In contrast to this, there are also so-called hydathodes , which ensure an active release of water. Trichomes also protect the plant from pest infestation as they act as a barrier to insects. Glandular hairs actively deter insects by producing essential oils.

Types

Swell:

Classification according to function

Petiole with glandular hairs in a pleasant columbine . For some species of Eurasian columbines, glandular pilose hairs are important diagnostic features for species separation.

Star hair in 50 million year old Baltic amber, probably from an oak. Image width approx. 1 mm

Detail from the top of a leaf of poison berry , the trichomes of which can secrete hallucinogenic substances.

Glandular hairs; with glands (trichomes with excretory function)
- ( lipophilic trichomes): production of essential oils and z. B. cannabinoids , insect repellants (protection against eating), fungicides, fang hair z. B. in hemp , African violets , sundew , or Rosmarinus officinalis and carnivorous plants .
- ( hydrophilic trichomes):
  - Salt hair , Absalzhaare , bubble hair : A multicellular, kurzgestieltes hair that ends with a large water-storing cell. They excrete excess salt. Especially in salt-tolerant plants (halophytes) that z. B. grow on the seashore. To do this, the salt is transported into the upper, vesicular cell of the two-celled hair. This has a predetermined breaking point. When the hair dies, the bubble will fall off or burst and the salt can be washed out by precipitation.
  - Mucus-forming trichomes: Trichomes secreting mucus, the mucus serves as e.g. B. as an adhesive for the seeds → animal litter or water storage.
  - Colleteren (glue glands, glue, glandular villi, teeth)
  - Digestive hair: In carnivorous plants
  - Stinging hair z. B. nettle
- ( hygroscopic trichomes) absorption hair, suction hair: water absorption e.g. B. Underside of the leaf of the white silver root Dryas octopetala
- ( hydrophobic trichomes): water-repellent trichomes e.g. B. "whisk hair" or "crown of hair" (eggbeater trichomes) z. B. of the swimming fern Salvinia natans ; Trichomes coated with nanoscale wax crystals, which are responsible for the water-repellent character → Salvinia effect .
- Nectaries : hairs secreting nectar, Lonicera japonica (crown), Abutilon (calyx), Tropaeolum majus (crown), Vicia faba (stipules).
Sensory hairs: irritable hairs, for example on the folding traps of certain carnivorous plants
Hydathodes : ensure active water release, especially in tropical plants. A special form of the trichome hydathode is the pearl gland .
Climbing hairs: for example in burdock bedstraw , hops , Phaseolus spec., Common dog's tongue Cynoglossum officinale
Dead hair as protection against dehydration (such as in the Levkojen )

Trichomes have various other functions as well. In general, a dense covering of wool trichomes controls the speed of perspiration. They also reduce the heating effect of sunlight. They help protect the plant body from external damage.

When describing the surface appearance of plant organs, such as stems and leaves, many terms are used in relation to the presence, shape and appearance of the trichomes. The international, English name is often used.

Classification according to the shape of the hair

Simple hair; the simple hair can be single, multicellular ( uni-, multicellular ) and single-row or multi-cell-row.

Individual hairs can come in many different forms.

- dendritic , dendroid ; split forked , ramified dendritic , candelabra like candelabra , shaggy shaggy , treelike tree-like , coral-like coralloid , hedgehog-like echinoid
- malpighian , t-shaped spindle hair ; two-armed hair z. B. Climbing hairs / Klimmhaare ( Malpighiaceae )

Hair with two to five arms; single or multicellular hair with two to five arms.

Star hair; Sitting or stalked hair with numerous long rays that protrude in a star shape - either in one plane or spatially arranged. Star hair is also well known fossil. Presumably derived from oak, it is by far the most common organic inclusion in Baltic amber from the Eocene .

Scale hair (shield hair) (pupil); scaly, scale-like (scaly scales , plate-shaped peltate , elongated , branched, branched dendroid ): almost disc-shaped, multicellular hair that can be sessile or stalked. At the edge they are smooth or serrated by free tips of the cells. ( Bromeliads )

Articulated hair, limb hair: are hair with joints ( jointed ); Trichomes reminiscent of arthropods , e.g. B. when African violet or plantain , with greatly thickened base cell "trumpet hair" (sage leaves).

Tree hair; branched, ramified hair: single or multi-cell hair with a main axis and branches on several levels.

Classification according to appearance, appearance and strength

arachnoid ; dense, like a spider web

bearded ; individual bundles of hair

bristly ; with thick, long, stiff hair

canescent , incanous ; with thick, fine, gray-white hair (gray-felted)

ciliate ; eyelashes, marginally conspicuous

ciliolate ; eyelashes, marginally fine, thinly ciliated

comose ; with a tuft of hair at the tip (apical)

downy ; wool-like, long hair

farinaceous , scurfy ; Scaby, floury, covered with fine granules

felted ; felty, fine, short hair

fimbriate ; frayed hair

floccose , flaky hairy ; with dense, long hair in woolly tufts, bundles (tufts, patches) (pressed hair) (slightly sloping)

glabrescent , subglabrous; almost bald

glabrous , glabrate ; missing hair; Surface smooth

hirsute ; long, coarsely hairy, often stiff, bristly, often not penetrating the skin

hispid ; very long, bristly hair, often penetrating the skin

(hispid-) urent ; with erect, mostly long hair that creates a stimulus when touched

muricate with short, hard, coarse, rounded growths

paleaceous ; covered with chaff, flake leaves ( palea ), chaff- like

pannosis ; matt, felt-like layer of hair

papillate , tuberculate , verrucate ; small, round growths

pilose ; scattered hairs, straight, soft, erect

puberulent ; sparsely hairy, fine, short, also frizzy hair

pubescent ; all types of trichomes

prickly , aculeate ; prickly, not a sting, thorn

scabrous ; with small raised points, scales, dry and often rough, uneven, sandpaper-like

scaberulous ; light, fine sandpaper-like

sericeous , silky ; long, pressed, soft, silky hair

setose ; with bristles ( Setae ) or bristle-like trichomes

setulose ; with fine bristles ( setae ) or bristle-like trichomes

spines , echinates , echinoid ; prickly, sea urchin-shaped, densely covered with stiff bristles or spines

squamose ; with coarse scales

strigulose ; finely covered with straight, (sharp), curved, pressed, stiff hair, all in more or less the same direction, (with a bulbous base)

strigosis ; with straight, (sharp), curved, pressed, stiff hair, all in more or less the same direction (with a bulbous base)

tomentulose ; finely covered (short hair), matt with woolly, soft, short hair, matted

tomentose ; densely covered, matt with woolly, soft, short hair, matted

velutinous with dense, straight, long, soft hair, pile-shaped

velvety ; velvety, fine, short, thick hair

villosulous ; sparse, long, soft hair, often curved but not matted

villous , lanate ; dense, long, soft hair, often curved, but not matted

Importance in plant sciences

The different trichome forms are used to identify plants taxonomically. Since trichomes are formed on the leaf surface according to defined patterns, they are also used as a model for pattern formation in biological systems. The trichome formation in the model plant Arabidopsis thaliana is initiated by the GLABROUS1 protein. Switching off this gene leads to a loss of hair growth. This phenotype has already been used in genome editing experiments. Trichomes can be used as visual markers to optimize genome editing methods such as CRISPR / Cas9 .

literature

Peter Sitte , Elmar Weiler , Joachim W. Kadereit , Andreas Bresinsky , Christian Körner : Textbook of botany for universities . Founded by Eduard Strasburger . 35th edition. Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1010-X .

Individual evidence

^ ^A ^b Michael G. Simpson: Plant Systematics. Academic Press, 2006, ISBN 978-0-12-644460-5 , pp. 399 ff, limited preview in Google Book Search.

↑ WL Theobald, JL Krahulik, RC Rollins: Trichome description and classification from CR Metcalfe, L. Chalk: Anatomy of the Dicotyledons. 2nd edition, Clarendon, Oxford 1979, p. 45; Quoted from: Gerhard Wagenitz : Dictionary of Botany. Morphology, anatomy, taxonomy, evolution. 2nd, expanded edition. Nikol, Hamburg 2008, ISBN 978-3-937872-94-0 , pp. 334, 335.

↑ Apple-of-Peru - Nicandra physalodes , wildflowerfinder.org.uk, accessed June 29, 2020

^ Ramesh C. Gupta: Nutraceuticals. Academic Press, 2016, ISBN 978-0-12-802147-7 , p. 742.

^ ^A ^b ^c J.A. Callow, DL Hallahan, JC Gray: Advances in Botanicel Research: Plant Trichomes. Vol. 31, Academic Press, 2000, ISBN 0-12-005931-2 , pp. 11, 19.

^ ^A ^b Joachim W. Kadereit, Christian Körner, Benedikt Kost, Uwe Sonnewald: Strasburger - Textbook of Plant Sciences. 37th edition, Springer, 2014, ISBN 978-3-642-54434-7 , pp. 85 f.

↑ Jan Medenbach: Oak hairs and flowers in Baltic amber. Archived from the original on October 20, 2012. Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Oberhessische Naturwissenschaftliche Zeitschrift . 60. Retrieved November 21, 2013. @1@ 2 }

^ PH Davis , VH Heywood : Principles of angiosperm taxonomy . Van Nostrandpage, Princeton, New Jersey 1963, p. 154.

↑ M. Hülskamp, A. Schnittger, U. Folkers: Pattern formation and cell differentiation: trichomes in Arabidopsis as a genetic model system . In: International Review of Cytology . 186, 1999, ISSN 0074-7696 , pp. 147-178. doi : 10.1016 / S0074-7696 (08) 61053-0 . PMID 9770299 .

↑ Florian Hahn, Otho Mantegazza, André Greiner, Peter Hegemann, Marion Eisenhut, Andreas PM Weber: An Efficient Visual Screen for CRISPR / Cas9 Activity in Arabidopsis thaliana . In: Frontiers in Plant Science . 8, 2017, ISSN 1664-462X . doi : 10.3389 / fpls.2017.00039 . PMID 28174584 . PMC 5258748 (free full text).

↑ Florian Hahn, Marion Eisenhut, Otho Mantegazza, Andreas PM Weber: Homology-Directed Repair of a Defective Glabrous Gene in Arabidopsis With Cas9-Based Gene Targeting . In: Frontiers in Plant Science . 9, April 5, 2018. doi : 10.3389 / fpls.2018.00424 . PMID 29675030 . PMC 5895730 (free full text).

Web links

Commons : Trichome - collection of images, videos and audio files

VB Gerritsen: more to it than meets the finger. In: protein spotlight. SIB, accessed August 31, 2010 .

[:0-1] A ^b Michael G. Simpson: Plant Systematics. Academic Press, 2006, ISBN 978-0-12-644460-5 , pp. 399 ff, limited preview in Google Book Search.

[2] WL Theobald, JL Krahulik, RC Rollins: Trichome description and classification from CR Metcalfe, L. Chalk: Anatomy of the Dicotyledons. 2nd edition, Clarendon, Oxford 1979, p. 45; Quoted from: Gerhard Wagenitz : Dictionary of Botany. Morphology, anatomy, taxonomy, evolution. 2nd, expanded edition. Nikol, Hamburg 2008, ISBN 978-3-937872-94-0 , pp. 334, 335.

[3] Apple-of-Peru - Nicandra physalodes , wildflowerfinder.org.uk, accessed June 29, 2020

[4] Ramesh C. Gupta: Nutraceuticals. Academic Press, 2016, ISBN 978-0-12-802147-7 , p. 742.

[Callo-5] A ^b ^c J.A. Callow, DL Hallahan, JC Gray: Advances in Botanicel Research: Plant Trichomes. Vol. 31, Academic Press, 2000, ISBN 0-12-005931-2 , pp. 11, 19.

[Joa-6] A ^b Joachim W. Kadereit, Christian Körner, Benedikt Kost, Uwe Sonnewald: Strasburger - Textbook of Plant Sciences. 37th edition, Springer, 2014, ISBN 978-3-642-54434-7 , pp. 85 f.