Annals of Botany 84 : 657–664, 1999
Article No. anbo.1999.0961, available online at http:\\www.idealibrary.com on
Glandular Hairs of Salvia officinalis : New Data on Morphology, Localization and
Histochemistry in Relation to Function
G. C O R S I* and S. B O T T E G A
Department of Botanical Sciences, UniŠersity of Pisa, Via Luca Ghini 5, 56126 Pisa, Italy
Received : 1 June 1999
Returned for Revision : 6 July 1999
Accepted : 30 July 1999
The structure, site and histochemistry of glandular hairs on the vegetative and reproductive parts of SalŠia officinalis
were investigated by UV and conventional light microscopy and by scanning electron microscopy. Five distinct types
of glandular hair (one peltate and four capitate) with different sites, secretory modes and secretions, were identified,
and a functional role postulated for each type. All the hair types show mixed secretions, i.e., hydrophilic and
lipophilic, except type I capitate hairs, which have hydrophilic secretions only. In peltate hairs and in type II capitate
hairs hydrophilic secretion prevails ; in the remaining types, lipophilic secretion dominates. The manner, time and role
of erection of peltate hairs on the reproductive organs and the role of non-glandular hairs are also considered.
# 1999 Annals of Botany Company
Key words : SalŠia officinalis, Labiatae, rising of peltate hairs, capitate hairs, secretion, plant\insect interaction.
INTRODUCTION
Much attention has been dedicated to the morphology of
glandular hairs (almost invariably those on the leaves) of
SalŠia officinalis, although there has been little agreement as
to the types present and their morphology (Singh, Sharma
and Jain, 1974 ; Verza! r-Petri and Then, 1975 ; Gupta and
Bhambie, 1980 ; Bini Maleci, Corsi and Pagni, 1983 ;
Venkatachalam, Kjonaas and Croteau, 1984 ; Werker,
Ravid and Putievsky, 1985). The histochemical studies that
have been performed have usually been limited to the main
types of test for defining whether secretions are lipophilic or
hydrophilic (Verza! r-Petri and Then, 1975 ; Bini Maleci et
al., 1983 ; Werker et al., 1985). Little, if anything, is known
about the functional role of glandular hairs. Only Werker et
al. (1985) postulated that the two types of hairs (capitate
and peltate) described in sage leaves were involved, in
different ways and at different times, in the defence of the
plant against herbivores and pathogens.
The purpose of the present paper was to provide new
elements on the morphology, localization and, above all,
histochemistry of SalŠia officinalis glandular hairs, and
especially to understand their role in interactions of the
plant with its abiotic and biotic environment. Non-glandular
hairs were also examined. The study was carried out using
light and scanning electron microscopy.
MATERIALS AND METHODS
Materials
Material for the present study came from the population of
SalŠia officinalis cultivated in the Botanical Gardens of Pisa.
* For correspondence. Fax : 050 551345, e-mail gcorsi!dsb.unipi.it
0305-7364\99\110657j08 $30.00\0
As a control, we also analysed a population in a private
garden near Pisa. Exsiccata in PI.
Light microscopy
We used : (a) hand sections of leaf and calyx ; sections of
fresh material were cut with a Leitz 1720 cryostat at k14
and k16 mC and semi-thin sections were cut with a Leica
2055 microtome after fixing in FAA (Sass, 1958) and
embedding in epoxy resin (L. R. White resin, London Resin
Co.) ; (b) whole calyces and leaves ; (c) whole calyces and
leaves on damp blotting paper observed by stereomicroscopy
with illumination from below and by light microscopy at
low magnification, as described by Lersten and Curtis
(1991).
All material was subjected to the following histochemical
tests : toluidine blue (O’Brien and McCully, 1981) and
methylene blue (Faure, 1914) as generic stains ; Alkanna
tincture (Faure, 1914) ; Sudan III (Johansen, 1940), Sudan
red 7B (Brundrett, Kendrick and Peterson, 1991) and Nile
blue (Cain, 1947) for total lipids ; Sudan III and glacial
acetic acid (Johansen, 1940) and Nile blue (Cain, 1947) for
essential oils ; Nadi reagent (David and Carde, 1964) for
terpenoids ; ruthenium red (Jensen, 1962) and Delafield
hematoxylin (Faure, 1914) for carbohydrates other than
cellulose ; Sudan red 7B\hematoxylin (Liebman, 1942) for
lipophilic and hydrophilic secretions, simultaneously ;
Coomassie brilliant blue R250 (Fisher, 1968) and Millon
reagent (Faure, 1914) for proteins ; Wagner and Dittmar
reagents (Furr and Mahlberg, 1981) and iodine iodide
solution (Jensen, 1962) for alkaloids ; potassium bichromate
(Faure, 1914) for tannins ; nitroso reaction (Reeve, 1951)
and concentrated hydrochloric acid (Trease and Evans,
1983) for catecholic tannins ; concentrated sulphuric acid
(Geissmann and Griffin, 1971) for sesquiterpene lactones ;
antimony trichloride (Hardman and Sofowora, 1972) for
# 1999 Annals of Botany Company
658
Corsi and Bottega—Salvia officinalis Hairs
F. 1. Peltate hair showing subcuticular chamber (toluidine blue, i800). F. 2. Peltate hair apparently without secretory pores but showing
rupture of cuticle (SEM, i500). F. 3. Peltate hair erect by gross distension of basal cell (SEM, i500). F. 4. Different stages of elongation
of basal cell of peltate hairs (A and B : Sudan red 7B\hematoxylin ; C : Wagner reagent ; D : Sudan III, i300). F. 5. Erect peltate hairs (arrows)
in groove of calyx. The hair is erected by distension of basal cell and raising of surrounding epidermis. Note also type II capitate hairs (arrow
head, SEM, i100). F. 6. Type I capitate hairs (Alkanna tincture, i150). F. 7. Type II capitate hair (toluidine blue, i600). F. 8. Type III
capitate hair showing pore on secretory head (SEM, i1700).
Corsi and Bottega—Salvia officinalis Hairs
steroids ; sodium cobalt nitrite (Dayanandan and Kaufman,
1975) for potassium.
For fluorescence microscopy whole calyces and leaves
were used. Flavonoids were detected by induction of fluorescence with the fluorochromes aluminium chloride and water
or ethanol (Guerin, Delaveau and Paris, 1971). A Leica
DM LB fluorescence microscope with Group A filters (BP
340-380, dichroic mirror 450, LP 430 arrest filter) was
used.
Scanning electron microscopy (SEM)
Leaves and calyces were fixed in glutaraldehyde (2 % with
buffer solution at pH 7n4), dehydrated in an alcohol and
acetone series, critical point dried, sputter-coated with gold
and examined at 15 KV with a Cambridge Stereoscan 90
scanning electron microscope.
RESULTS
Glandular hairs
Peltate and capitate hairs were observed.
Morphology and secretions. The peltate hairs consisted of
a basal cell, a short unicellular stalk and a secretory head,
usually composed of 12 cells (occasionally 16) arranged in a
shield (four central cells surrounded by eight peripheral
ones) (Figs 1 and 3). The anticlinal wall of the stalk cell was
completely cutinized. The cells of the secretory head also
had a thick cuticle which lifted to form a large subcuticular
chamber for the secretory material (Fig. 1).
SEM observation did not reveal any pores or cracks
through which the secretory material could exude. The
material was not released until the cuticle broke, either due
to mechanical events or at the end of the life of the gland
(Fig. 2). On the calyx, the peltate hairs were lifted by a huge
distension of the basal cell (Figs 3 and 4). It is not yet
clear whether distension of the basal cell is due to hormonal
factors or osmosis or both. Specific histochemical tests,
however, revealed high potassium concentrations in the
distending basal cell.
The peltate hairs only appeared raised as the calyx
grew and acquired its final form with grooves and ribs,
not when the calyx was still small and roundish in section.
The first peltate hairs to become raised were situated on the
sides of the ribs adjacent to the grooves. Later, when the
flowers were in anthesis, the extremely numerous hairs in
the grooves also became raised. They were lifted even more
than the hairs on the ribs because, as well as distension of
the basal cell, the epidermis around the gland also protruded
(Fig. 5).
The capitate hairs were quite variable in morphology
and four types could be distinguished. Type I had a
short uni- or bicellular stalk and a large uni- or bicellular
secretory head (Fig. 6). The cuticle was thin and there was
no subcuticular chamber. The secretory material exuded
slowly through the intact cuticle and was released suddenly
if the cuticle ruptured. Type II was very small and had a
unicellular stalk and an oblong cutinized secretory head.
During secretory activity (Fig. 7) it had a small subcuticular
chamber. The secretory material probably exuded through
659
a pore, which was discernable in SEM images. Type III was
large with a long stalk consisting of one–three cells, a neck
cell and a cutinized unicellular head. SEM images of the
head showed a pore (Fig. 8) which exuded secretory
material that often collected as a drop on the deflated, cupshaped head (Fig. 9). Type IV was large and had a long
slender stalk, which, at the end of ontogenesis, consisted of
four cells. It had a neck cell and a very large, wide, cutinized,
unicellular head which was sometimes trapezoid in shape
(Fig. 10). SEM images revealed a small pore that presumably
exuded secretory material (Fig. 11). In the calix, the tiny
type II hair was raised by elongation of the basal cell, as in
peltate hairs (Fig. 7).
Localization. Peltate hairs were situated on the vegetative
and reproductive organs, mainly on leaves and calyces,
respectively. On leaves, they were observed on the upper
surface, essentially on the protuberances delimited by
secondary veins (Fig. 12) and in large numbers on the
abaxial surface, particularly on the secondary veins (Fig.
13). They were observed in large numbers on the sides of the
ribs and even more abundantly in the grooves of the calyx
(Fig. 14).
Type I capitate hairs had the same localization on leaves
as peltate hairs. Those on the calyx were few in number and
located on ribs and in grooves, they being more numerous
at the mouth of the calyx, on the teeth and at their base.
Type II hairs were few in number and scattered on both
sides of leaves, especially on veins, and also on the calyx,
especially on the sides of ribs and in grooves (Fig. 5).
Type III hairs were observed only on leaves ; on the adaxial
surface, they were few in number and situated on the sides
of protuberances and in the deep grooves containing veins ;
on the abaxial surface, they were situated on secondary
veins and in grooves.
Type IV hairs were only observed on the calyx, especially
on the ribs (Fig. 14). They were abundant on the teeth
and particularly on the throat margins (Fig. 33).
Histochemistry. The results of the histochemical tests for
the various types of glandular hairs are shown in Table 1.
The figures give a few examples. The secretions of type I
capitate hairs were essentially hydrophilic. Peltate hairs
and the other types of capitate hairs had mixed secretions
consisting of lipophilic and hydrophilic components, which
were sometimes present simultaneously on the same hair
(Fig. 15), but usually one prevailed over the other. The
peltate hairs on leaves and calyces of blooming and withered
flowers had almost exclusively hydrophilic secretions (Fig.
16). The hydrophilic component prevailed in type II capitate
hairs, the lipophilic, in types III and IV.
Non-glandular hairs
The non-glandular hairs were multicellular, unbranched
and consisted of three–four elongated cells. They were
observed on leaves (Figs 12 and 13) and calyces (Fig. 14).
On the adaxial surface of leaves they were arranged in tufts
on all protuberances. Hence, because protuberances on
young leaves were close together, they formed a dense
downy layer that protected the grooves containing the
secondary veins. In adult leaves, which have a greater
660
Corsi and Bottega—Salvia officinalis Hairs
F. 9. Type III capitate hair with drop of secretion compressing head into typical cup shape (Alkanna tincture, i1100). F. 10. Type IV capitate
hair (Sudan red 7B\hematoxylin, i450). F. 11. Type IV capitate hair showing small pore on secretory head (SEM, i700). F. 12. Peltate hairs
on upper surface of leaf. Note also non-glandular hairs. Type I and II capitate hairs are not visible because of their small size (SEM, i6). F.
13. Peltate hairs and non-glandular hairs on inferior surface of leaf. Type I and II capitate hairs are not visible because of their small size (SEM,
i6). F. 14. Peltate hairs in groove and type IV capitate hairs on rib of calyx (SEM, i100).
surface area, protuberances were separated by wide grooves,
and thus the non-glandular hairs were fewer, and large areas
remained exposed. On the abaxial surface, especially of
young leaves, the hairs were extremely numerous and so
long that they were hardly ever straight, but bent and
contorted. Juvenile calyces (0n3–0n5 cm in length) had very
many long, fine, non-glandular hairs, especially at their
base. As the calyx grew, these hairs decreased in number
and were situated mainly on the sides of the ribs (Fig. 14).
When the flower withered and the calyx dried, there were
very few non-glandular hairs left on the calyx.
Functional role of hairs
To obtain information about the functional role of hairs,
preliminary entomological observations were also carried
Corsi and Bottega—Salvia officinalis Hairs
T     1. Histochemistry of glandular hairs of Salvia
officinalis
Chemical
compounds
Lipids
Carbohydrates
other than cellulose
Essential oils
Terpenoids
Resins
Alkaloids
Proteins
Sesquiterpene
lactones
Steroids
Tannins
Cathecolic tannins
Flavonoids
Type I Type II Type III Type IV
Peltate capitate capitate capitate capitate
hairs
hairs
hairs
hairs
hairs
j
jj
k
jj
j
jj
jj
jk
jj
jk
j
j
j
j
j
j
k
k
k
j
j
j
j
j
j
j
j
k
jj
jk
k
j
k
k
j
j
jj
j
j
j
j
j
j
j
j
j
j
k
j
j
j
j
k
k
k
j
j
j
j
j
knegative ; jkslightly positive ; jpositive ; jjstrongly positive.
out. These involved observing the behaviour on the plant,
capturing and determining [using the analytical key of
Kristjansson and Pinzauti (1995)] all the insects and other
visitors to SalŠia officinalis ranging from pollinators to
phytophages and seed dispersers. The results of the
entomological observation were as follows :
Pollinating insects. The insects captured belonged to the
Hymenoptera : Apis mellifera L. ; Bombus pasquorum Scop.,
B. terrestris L. ; Xylocopa Šiolacea L., X. iris (Christ) ;
Halictus sp. and Lasioglossum sp. ; Anthophora salŠiae
(Panz.), A. acerŠorum L. ; Amegilla albigena Lep. ;
Ammobates sp. ; Megachile pilicrus (Mor.) ; Anthidium
manicatum L. The pollinators approached the flowers and
collected nectar and\or pollen, avoiding contact with the
calyx and landing precisely at the mouth of the zygomorphic
corolla.
Phytophagous insects. These insects feed on sap. Many
insects of the family Aphididae [Aphis passeriniana (Del
Guercio)] were observed and captured. They were most
abundant in spring and during blooming, but were also
present in autumn, on the inferior surface of leaves, where
they, however, were nearly always impeded by the downy
layer of non-glandular hairs and the secretions released by
the glandular hairs. They were observed on the ribs and
grooves of calyces of flower buds and open flowers, towards
the base rather than the teeth. Here again movement of the
aphids was prevented by the many long non-glandular hairs
on the calyces of buds and by the viscous secretions of the
glandular hairs on calyces of flowers in full bloom. Other
phytophagous insects such as Cicadellids e.g. Eupteryx
zelleri (Kirschbaam) were observed in less abundance on the
leaves. They did not appear to be affected by the secretions ;
they jumped from one part to another without touching the
peltate hairs and hence did not become stuck in the viscous
secretions.
Insect seed dispersers. SalŠia officinalis exploits barochory
which is the first agent of diplochory. Despite long
observation, no animal was seen to approach the tetrachenes
661
in the calyces. After barochory one might suppose that
agents such as wind and rain carry the seeds away from the
plant.
DISCUSSION
SalŠia officinalis has only one type of peltate hair consisting
of a short unicellular stalk and a secretory head composed
of 12 cells. This type of hair is found on the vegetative
organs, principally leaves, and reproductive organs, principally calyces. This finding does not entirely agree with that
of Bini Maleci et al. (1983) who reported three types of
peltate hairs, but expressed doubts as to whether what they
observed was actually three different functional stages. On
the other hand, our findings agree with those of Werker et
al. (1985) who, however, only examined leaves.
At anthesis, peltate hairs on the calyx are lifted from the
calyx surface. Our results confirm that this phenomenon is
due to gross distension of the basal cell, as proposed by Bini
Maleci et al. (1983), and often also by raising of the
surrounding epidermis. Since the peltate hairs are mainly
situated in grooves and on the sides of ribs, and the ribs
protrude considerably during flowering, raising of the peltate
hairs presumably enables them to play their role. Histochemical analysis showed that the peltate hairs produced
mixed secretions, with lipophilic and hydrophilic components sometimes simultaneous in the same hair but more
often with one predominating over the other. On leaves and
calyces of flowering and withered flowers, the secretions of
the peltate hairs were almost exclusively hydrophilic.
According to Bini Maleci et al. (1983) and Werker et al.
(1985), the peltate hairs are prevalently lipophilic, producing
a large quantity of essential oils. The many specific
histochemical tests used in the present study enabled us to
detect carbohydrates other than cellulose in large quantities,
essential oils, resins, alkaloids, proteins, sesquiterpene
lactones, steroids, tannins, cathecolic tannins and
flavonoids. Less detailed studies of previous authors (Bini
Maleci et al., 1983 ; Werker et al., 1985) could only provide
a general idea of the type of secretions. Our results did not
reveal any significant differences between peltate hairs on
leaves and calyces. The substances detected by histochemical
methods suggest that these hairs are involved in chemical
defence : alkaloids are poisonous to herbivores, sesquiterpene lactones are bitter and toxic, essential oils [rich in
camphor and thuyone (Corsi et al., 1982 ; Werker et al.,
1985)] are poisonous to most insects, terpenoids are olfactory
deterrents for insects, and steroids, flavonoids and especially
tannins are the strongest insect deterrents known (Harborne,
1993).
Further, the massive presence of viscous, adhesive
polysaccharides, especially in the calyces of blooming
flowers and dry calyces, suggests that there are good
mechanical defences during flowering and seed development.
This is demonstrated by the fact that aphids, which invade
the plant in large numbers to feed on sap, become stuck in
the viscous substances released when they trigger rupture of
the cuticle (Fig. 21). Similar defence mechanisms have been
reported against ticks in certain tropical leguminous plants
(Sutherst and Wilson, 1986) and against aphids in certain
Corsi and Bottega—Salvia officinalis Hairs
662
F 15–33. For legend see facing page.
Corsi and Bottega—Salvia officinalis Hairs
Solanaceae (Gregory et al., 1986). The function of these
polysaccarides in the glandular hairs of the Lamiaceae is not
known (Werker, 1993) and further investigation is still
required.
When pollinators collect nectar they never touch the
peltate hairs ; their secretions cannot therefore be a reward,
as in some plants (Vogel and Cocucci, 1995). It is
nevertheless possible that substances in the essential oils
such as pleasant smelling monoterpenes (Corsi et al., 1982 ;
Werker et al., 1985) guide the insects to the plant. It seems
unlikely that the sticky secretion serves to attach calyces
containing seeds to animals involved in epizoochory, as in
other sages (Bouman and Meeuse, 1992), because no animals
were observed to disperse seeds. The peltate hairs may
defend S. officinalis from competition by other plants, since
terpenes such as camphene, camphor, thuyone and 1,8cineol—typical components of the essential oil of sage—are
powerful allelopathic agents (Harborne, 1993). On the other
hand, a given glandular structure may have different
functions at different times of the ontogenetic cycle of the
plant (Uphof and Hummel, 1962). In the opinion of Werker
(1993) the peltate hairs of aromatic labiates only secrete an
essential oil containing repellent substances which are
effective against herbivores and pathogens.
S. officinalis has four types of capitate hairs that differ in
structure, localization, secretory material and secretory
mode. This disagrees with the findings of Bini Maleci et al.
(1983) and confirms those of Werker et al. (1985) from the
morphological point of view only. The many histochemical
tests used in the present study showed that type I capitate
hairs have hydrophilic secretions containing proteins,
alkaloids, tannins and sesquiterpene lactones. They probably aid the peltate hairs in chemical and, especially,
mechanical defence, at least of the leaves. The other types of
capitate hairs have mixed secretions, like peltate hairs. In
type II hairs the hydrophilic component predominates ; in
types III and IV, the lipophilic component. Specific
histochemical tests showed that type II capitate hairs have
very similar secretions to peltate hairs, but without
sesquiterpene lactones. Their function is probably similar to
that of peltate hairs, though the absence of the lactones
makes them less effective in chemical defence and their small
size makes them less effective in mechanical defence against
predators. The secretions of type III capitate hairs contain
essential oil and minor quantities of carbohydrates other
than cellulose, flavonoids and alkaloids. Since they are only
found on leaves, they could be involved in defence against
663
predators but are particularly effective in preventing
excessive transpiration ; this is a common role of essential
oils.
The secretions of type IV capitate hairs are fairly similar
to those of peltate hairs, except that there is no viscous
hydrophilic component, and instead there is a resin—
containing essential oils—which exudes from the secretory
head and spreads over the stalk and the surrounding
epidermis. As they are only found on the calyx, they
probably also collaborate with peltate hairs in providing
olfactory attractants for pollinators, but their main role is
defence of the fruits and seeds against predators. Considering the evolution of the secretions of peltate hairs
during the life of the calyx, it seems that towards anthesis
and desiccation the peltate hairs are increasingly dedicated
to mechanical defence, whereas chemical defence is probably
the task of type IV capitate hairs. Moreover, the fact that
only type IV hairs are situated on the teeth which bend and
close the tetrachene completely at the end of flowering, and
that these hairs produce resin that exudes and covers the
surrounding epithelium, suggests that they protect the
reproductive structures against excessive transpiration and
entry of water which would cause withering.
The non-glandular hairs on the vegetative and reproductive organs are abundant and longer when the organs
are young. Particularly in the early phases of the ontogenetic
cycle, they presumably collaborate with glandular hairs in
mechanical defence, creating a thick downy layer. They are
certainly also involved in protecting the plant from excessive
transpiration and insolation.
A C K N O W L E D G E M E N TS
Thanks are due to Dr M. Pinzauti for the entomological
confirmations and to Mr A. Masini for technical assistance.
Financial support from M.U.R.S.T. is also acknowledged.
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F. 15. Peltate hair showing hydrophilic (blue staining) and lipophilic (red staining) production (Sudan red 7B\hematoxylin, i180). F. 16.
Calyx of blooming flower with predominantly hydrophilic peltate hairs (Sudan red 7B\hematoxylin, i50). F. 17. Peltate hair positive for
alkaloids (Lugol reagent, i300). F. 18. Peltate hair positive for catecholic tannins (Nitroso reaction, i300). F. 19. Peltate hair positive for
sesquiterpene lactones (concentrated H SO , i400). F. 20. Peltate hair positive for flavonoids (Aluminium chloride, i300). F. 21. Aphid
# %
stuck in secretions of peltate hairs on calyx (fresh material, i150). F. 22. Type I capitate hair positive for proteins (Millon reagent, i400).
F. 23. Type I capitate hair positive for catecholic tannins (Nitroso reaction, i400). F. 24. Type II capitate hair positive for flavonoids
(Aluminium chloride, i400). F. 25. Type II capitate hair positive for steroids (Antimony trichloride, i400). F. 26. Type II capitate hair
positive for tannins (Potassium bichromate, i400). F. 27. Type III capitate hair positive for essential oils (pink staining with Nile blue, i450).
F. 28. Type III capitate hair positive for carbohydrates other than cellulose (Ruthenium red, i450). F. 29. Type III capitate hair positive
for alkaloids (Dittmar reagent, i450). F. 30. Type IV capitate hairs with resin exuding from the secretory head (Nadi reagent, i500). F.
31. Type IV capitate hair with resin containing essential oils (pink staining) exuding from the secretory head (Nile blue, i450). F. 32. Type
IV capitate hair positive for alkaloids (Dittmar reagent, i450). F. 33. Calyx showing type IV capitate hairs (arrows) on teeth (Alkanna tincture,
i15).
664
Corsi and Bottega—Salvia officinalis Hairs
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