Download histology of the foliar trichomes in some

Annals of RSCB
Vol. XVI, Issue 1
HISTOLOGY OF THE FOLIAR TRICHOMES IN SOME
PELARGONIUM L'HERIT SPECIES
Rodica Bercu, Livia Broască
DEPARTMENT OF BOTANY, FACULTY OF NATURAL AND AGRICULTURAL
SCIENCES “OVIDIUS” UNIVERSITY, CONSTANTZA
Summary
This paper is a part of a complex study concerning ornamental plants histoanatomy and
proposes a histological analysis of the leaf trichomes (hairs) of three Pelargonium species,
popular ornamental plants known as geraniums: Pelargonium grandiflorum (Andr.) Willd.,
Pelargonium peltatum (L.) Aiton ex L'Herit, Pelargonium zonale (L.) L'Herit. Anatomically,
is clear that the main criterion for the foliar trichomes differentiation both epidermal and
glandular trichomes, are the length, structure (differences in shape and dimensions of the foot
cells) and their density both on the upper and lower epidermis and among the species blades.
The protective trichomes of all three species are simple unicellular with a sharp apex. Rare 4celled protective trichomes occur. The glandular trichomes are all many-celled composed of
five cells for P. zonale and P. grandiflorum and two for P. peltatum, the last cell being the
one-celled gland (more voluminous for P. peltatum) with secretive product inside. The
protective and secretive trichomes of the petiole are almost the same as regard their structure
with those of the blade.
Key words: blade, histology, secretive trichomes, protective trichomes, Pelargonium.
[email protected]; [email protected]
Pelargonium grandiflorum is a
shrubby, glabrous and glaucous, in mature
stage.
Introduction
Genus Pelargonium L'Herit is
originally from South Africa and includes
over 175 species according to some
authors or, even more than 300 species
after another. The plants, known improper
as "geranium" have entered Europe in the
eighteenth century and have spread rapidly
in all its areas. They are herbaceous plants,
perennial, pubescent, rarely high, stems
soft, succulent and rich foliage (Charrier,
2000, Mc Hoy, 1996). The species of this
genus are very diverse, general
appearance, color of flowers, but
especially
after
leaf
morphology.
Geraniums are classified in the family
Geraniaceae ornamental plants, most
species being bred for their decorative
flowers and, some, liked the smell of the
leaves. Fragrant leaves of these species
contain geraniina a rate higher or lower.
This substance is used to obtain oils with
therapeutic properties (Viljoen et al.,
1995).
Pelargonium grandiflorum (Andr.) Willd.
The plant leaves have long petioles,
palmately 5–7-nerved, deeply 5–7-lobed
with the lobes coarsely toothed. The
stipules are ovate and mucronate. The
leaves are not zoned and the flowers are
larger often in different combinations of
colors (from white to red) and shades
(Raimondo et al. 2009; Van der Walt,
1977; Nichols, 2005).
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Pelargonium
peltatum
is
a
climbing,
semi-succulent
perennial,
trailing through other trees and shrubs in
its habitat. The climber has long, straggling
shoots, which can reach a height of 2m.
This plant is characterized by its ivyshaped leaves. Some of the leaves have
distinctive zonal markings, but this is not a
common characteristic. It produces clusters
of flowers varying from mauve or pinkish
mauve to pale pink or white. It flowers
mainly in September to December (Van
der Walt, 1977).
The flower color ranges from rosepink to all shades of red as well as pure
white. The distinctly irregular flowers are
borne
in
a
typically
umbel-like
inflorescence.
P.
zonale
flowers
throughout the year with a peak in spring
(September-November) (Della Beffa,
1999, Turner, 1998).
The literature references are
focused mostly on the leaf cytology,
morphology and petiole anatomy, in
particular for P. zonale species, lack a
histological trichomes study especially
concerning those of P. grandiflorum and P.
peltatum. On the other hand trichomes are
the criteria for identification of species.
Material and methods
The plants were collected from
S.C. IRIS International S.R.L. greenhouse.
Paradermal sections of mature and juvenile
leaves were performed by the usually
metods used in vegetal histology (Bercu &
Jianu, 2003). The samples were stained
with saphranin 1% (Dilcher, 1974).
Histological observations and micrographs
were performed with a BIOROM –T bright
field microscope, equipped with a
TOPICA 6001A video camera.
Pelargonium peltatum (L.) Aiton ex L'Herit
This erect or scrambling softly
woody shrub Pelargonium zonale usually
grows up to 1m but it can reach heights of
3m. The branches are almost succulent and
are usually covered with hairs, while the
older stems harden with age. The large
palmately-nerved leaves are often smooth
and a characteristic dark horseshoe-shaped
mark is often present.
Results and discussions
Pelargonium grandiflorum leaves
present, mostly in juvenile stages, trichomes
while the mature leaves are almost
glabrous. Upper and lower epidermis
possesses
protective
and
glandular
trichomes (Peterson et al., 2008). The
protective trichomes of the upper epidermis
are longer or shorter (probably the latter in
training) with a sharp apex and widened at
the base. They are composed of 3 cells with
peripheral cytoplasm and nucleus inside,
covered by cuticle on the outside. They are
short, straight, very few are inclined (Fig. 1,
A, B). The glandular trichomes consist of
five cells with a widened basal cell, a long
narrow cell, followed by a slightly wider
cell than those of the second and the last
cell which is the one-celled more or less
spherical gland with the product of
secretion inside (Fig. 1, C, D).
Pelargonium zonale (L.) 'Herit
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In the lower epidermis as well are
long and short protective trichomes
(probably in training) (Batanouny, 1992).
They may be straight, tilt the middle or
may be sickle-shaped. They consists of
three, rarely four cells (Fig. 2, A, B).
The lower epidermis possesses glandular
trichomes similar in structure to those on
the upper epidermis, but they are more rare
(Fig. 2, C, D).
Fig. 1. Trichomes of the upper epidermis of Pelargonium grandiflorum: protective trichomes (A,
B, x, 60; x 200); glandular trichomes (C, D, x 185, x 400): G- the gland, TF- trichome foot.
The petiole protective trichomes
equate the appearance and structure of the
lower epidermis trichomes, but rare The
petiole glandular trichomes, even if are 3celled, are shorter than those of the blade.
Like
the
previous
species,
Pelargonium peltatum presents trichomes
on the entire surface of the leaf in juvenile
stage. At maturity the leaves are almost
glabrous. Paradermal sections disclose that
the upper epidermis is provided with
protective and glandular trichomes. The
many-celled protective trichomes are
uniseriate, consisting of three, rare four,
cells, arrising from an epidermal socle
(Bavaru & Bercu 2002). The basal and
second cells are shorter and slightly
widened comparatively to the latter
sharpened cell. The trichomes are covered
by a thick cuticle (Fig. 3, A).
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Fig. 2. Trichomes of the lower epidermis of Pelargonium grandiflorum: protective trichomes (A,
B, x 75, x 80); protective and glandular trichomes - amsamble(C, x 50), glandular tricnome (D, x
200): E- epidermis, S- socle.
The glandular trichomes are dense
comparativelly with the protectives,
simple, many-celled too with a short feet,
composed of two cells, a long widened
basal cell. In the foot cells may be
observed the usually cytological elements
such as in the protective trichomes cells.
The second cell is shorter and more or less
rectangular in shape. The last cell is the
one-celled and voluminous gland,
containing the secretive product (Fig. 3,
B). Resemble the lower epidermis is
provided with protective and glandular
trichomes too. Protective trichomes are
smaller and rarer than those of P. zonale.
They may be tilt from the middle or
entirely curved form the base (Fig. 4, A).
The small glandular trichomes are formed
by two cells, as well, the latter being the
one-celled spherical secretive one (Fig. 4,
B).
The petiole possesses rarest
protective and glandular trichomes than
those of the blade.
Both types of trichomes (secretive
and glandular) are similar to those of the
lower epidermis.
Pelargonium zonale (L.) L'Herit
exhibits in epidermal paradermal sections,
as Marais (2005), reported for other
Pelargonium species (P. moniliformis)
protective trichomes, interspersed with soft
patent hairs, both on the upper and lower
epidermis.
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Fig. 3. Trichomes of the upper epidermis of Pelargonium peltatum: protective trichome (A, x
145); glandular trichome (B, x 400).
Fig. 4. Trichomes of the lower epidermis of Pelargonium peltatum: protective trichomes (A, x
60); glandular trichome (B, x 300).
The protective trichomes of the
upper epidermis are uniseriate manycelled, provided with three or four cells,
externally covered by a thick cuticle.
Inside is one nucleus, cytoplasm and a
large vacuole. The protective trichomes are
pointed at the top arrising on an epidermal
socle. Some are slightly inclined to the
right or left on the epidermis surface.
However most of them are stiff (Fig. 5, A,
B).
The glandular trichomes are in a
small number comparatively to the
protective trichomes. The glandular
trichomes, as Bavaru & Bercu (2002) and
Esau (1963) reported, are longer composed
of four or five cells, covered by a thick
cuticle.
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Fig. 5. Trichomes of the upper epidermis of Pelargomium zonale: protective trichomes- ansamble
(A, x 70), protective trichome - detail (B, x 140); glandular trichome– detail (C, x 120).
Fig. 6. Trichomes of the lower epidermis of Pelargonium zonale: protective trichomes (A, x 160);
protective and glandular trichomes (B, x 145).
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density, both for those on the upper and
lower epidermis and among the three
species blade.
Generally, the protective and
glandular trichomes of the petiole are the
same as regards their structure and lenght
with those of the blade but rare (mostly the
secretive trichomes) for P. peltatum and P.
grandiflorum. P zonale trichomes are
dense on the blade lower epidermis
comparatively those of the upper
epidermis.
Cells are becoming narrower
towards the top, and the last is the onecelled gland, spherical in shape possessing
the product of secretion (Fig. 5, C).
The protective trichomes of the
lower epidermis even more dense, they are
longer than those of the upper epidermis,
although there are small hairs too. Most of
them are likely, very few, straight, formed
by three or four cells (Fig. 6, A, B). The
glandular hairs are also larger and more
numerous than those of the upper
epidermis surface. They consist of four or
five cells, ending with the spherical gland
cell (Andrei, 1978) (Fig. 6, B).
The petiole protective trichomes
are patent soft, many-celled, like those of
the lower epidermis and the glandular can
be equated with those of the upper
epidermis being short and extremelly rare
(1-2 on the petiole surface).
References
Andrei, M.: Anatomia plantelor, 1978. Edited by
Didactică şi Pedagogică, Bucureşti.
Batanouny, K.H.: Anatomy of Plants, 1992. Edited by
Univ. Press, Cairo.
Bavaru A., Bercu R.: Morfologia şi anatomia plantelor
2002. Edited by Ex Ponto, Constanţa.
Bercu R., Jianu, D.L.: Practicum de Morfologia şi
anatomia plantelor. 2003. Edited by “Ovidius”
University Press, Constanţa.
Charrier, M. (réalisation): Jardins Ręvés et Réussis.
Catalogue Végétal Sélection 2001. Jardilland S. A.,
(Paris), 8: 111-112, 2000.
Della Beffa, M.: Plante de apartament, 1999. Edited
by All, Bucureşti.
Dilcher, D.: Aproaches to the identification of the
angiosperm leaf remains. The Botanical Review
(Bot. Garden, New York), 40: 24-103, 1974.
Esau, K.: Plant anatomy. 1963. Edited by Wiley &
Sons, New York.
Marais E. M.: Differences between Pelargonium
moniliforme (Geraniaceae) and the closely. South
African Journal of Botany, 71(2): 221–227, 2005.
Mc Hoy, P.: Les plantes d’appartament, 1996. Edited
by Celiv, Paris.
Nichols, G.: In the ivy league: the indigenous garden.
Farmer's Weekly, 28 Jan.: 78, 79, 2005.
Peterson, R.I., Peterson, C.A., Melville, L. H.:
Teaching plant anatomy through laboratory
exercises, 2008. Edited by NRC Press, Ottawa,
Ontario.
Raimondo, D., Von Staden, L., Foden, W., Victor,
J.E., Helme, N.A., Turner, R.C., Kamundi, D.A.,
Manyama, P.A. (eds): Red List of South African
plants, 2009. Edited by South African National
Biodiversity Institute, Pretoria.
Turner, R.G.: Botanica - the most complete garden
encyclopedia ever published, 1998. Edited by
Barnes and Noble Books, New York.
Van der Walt, J.J.: Pelargoniums of southern Africa,
1977. Edited by Purnell, Cape Town.
Viljoen, A. M., Demarne, F. E., Van der Walt, J.J. A,
Swart J. P. J.,: A study of variation in the essential
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(Geraniaceae), S. Afr. J. Bot., 61(3): 105-113, 1995.
Conclusions
Without exception, two types of trichomes
are present, protective and glandular, on
the blade and petiole of the studied leaves,
even if they are numerous in the juvenile
stage in P. grandiflorum or almost absent
in mature blade of P. peltatum.
The blade protective trichomes are
mostly three-celled and uniseriate,
possessing a basal socle, a more or less
long foot, the latter with a sharp apex (all
species). Rare 4-celled trichomes occur.
Differences arise in particular as regards
the trichomes lenght (long for P. zonale
and P. grandiflorum and smaller for P.
peltatum), density and shape (stright for all
species, rare curved, less for P. zonale
trichomes).
The trichomes density differs on both
upper and lower blade surfaces too, being
rare in the latter for P. grandiflorum and P.
peltatum. Comparativelly, the blade
trichomes of P. zonale density is inversed.
The glandular trichomes are
uniseriate for all species, differences
arrising as regards the number of the feet
cells and the size of the last cell – the gland
cell. Other diferences arise as regards the
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