Analele ştiinţifice ale Universităţii “Al. I. Cuza” Iaşi
Tomul LVI, fasc. 1, s. II a. Biologie vegetală, 2010
ASPECTS OF FLORAL STRUCTURE AND MORPHOGENESIS IN MELISSA
OFFICINALIS L.
RAMONA GALEŞ*, ANA PREOTU*, C. TOMA*
Abstract. The authors investigated the structure and ontogenesis of Melissa officinalis L. flower on
serial sections through the flower in different stages of development.
Key words: Melissa officinalis L., flower, structure, morphogenesis
Introduction
Melissa officinalis L. (lemon balm) is a perennial herb of Lamiaceae family,
grown spontaneous in Romania, only on limited areas in south-west of the country, and
cultivated in gardens and monachal places. The numerous phytochemical researches
revealed the importance of the species as aromatic, melliferous and medicinal plant.
Continuing our studies on this medicinal plant ([1], [2]), the present paper refers to
the reproductive apparatus of Melissa officinalis L., being analyzed several aspects of
flower structure and development.
Material and methods
The material (flowers of different developmental stages) subjected to the histoanatomical analysis were fixed in FEEA mixture and preserved in 70% ethylic alcohol. The
serial sections were performed using the standard paraffin-embedded protocol applied in
plant histo-anatomical researches. Fixed samples were dehydrated by a passage through
ethanol/water solutions and then embedded in paraffin at 65ºC for 24 hours. The embedded
material was cut into 13 µm thick sections with a rotator microtome. The dried serial
sections were deparaffinized, rehydrated in serial dilutions of ethanol (100%, 90%, and
70%), coloured with metilen-blue and ruthenium-red, and finally mounted in Canada
balsam.
The all permanent slides were analyzed in the light microscopy, using a Novex
(Holland) microscope; the micro-photos were made at the same microscope with a Sanyo
digital camera.
Results and discussions
The flower is hermaphrodite and presents a long peduncle. The receptacle is
concave. The corolla is gamopetalous and the calyx is gamosepalous. Both are tubular at
the flower base and have two unequal labia in the upper part of the flower. The ovary is
superior. The stamens have long and unequal filaments.
*
Al. I. Cuza” University of Iasi, Faculty of Biology, Carol I Bd., no. 20A, 700506, Iasi, Romania e-mail:
[email protected]
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The cross-section contour of the flower peduncle is circular with ribs. The
structure is primary. The epidermis composes of tangentially elongated small cells and
numerous multicellular one-serial trichomes,
The cortex is thin (3-4 cells layers), cellulosic- parenchymatous of meatic type.
The vascular tissues form two rings (an external one of phloem and an internal one of
xylem, thicker than the first one) interrupted in the front of the peduncle depressions. The
vessels are disposed in radiary layers. The pith is cellulosic- parenchymatous of meatic type
with more big cells than the cortical ones.
On serial cross - sections from the lower to the upper part of the flower, several
aspects of flower morphogenesis process have been analyzed.
The sepals are the first of the floral organs to appear in. Melissa officinalis L. They
detach from the receptacle like a ring, resulting the tube of the calyx. Ulterior, as the same
way as the calyx tube, the corolla tube is formed, following by the morphogenesis of the
first carpel. The stile of the gyneceum appears at the lower part of the ovary. The stamens
insert on the corolla tube.
The contour of the cross section through the calyx tube is circular with 12
prominent ribs, which represent the nervures of the unite sepals.
In each rib, in a thick parenchyma of meatic type, a small vascular bundle (with
some phloem elements and 2-3 vessels) can be found.
The epidermis cells are covered by a thin cuticle. Two type of hairs (multicelluar
one-serial trichomes and glandular hairs with multicellular secretory had) may be observed.
The mesophyll is homogenous, of meatic type, composed of 3 cellulosicparenchymatous cells layers.
In the internal epidermis, the cells are little, without cuticle. The hairs are not
present.
The contour of the cross - section through the corolla tube is polygonal. Each petal
nervure is formed by a big collateral vascular bundle.
The mesophyll is thin (2 cells layers) and presents numerous aeriferous cavities. In
the lower part of the flower, both corolla epidermises are lake of hairs.
On a cross - section through the upper part of the ovary, 4 lobes can be observed.
The ovary has two lodges, each of them containing a single ovule.
The external epidermis of the ovary wall consists of papilla cells and numerous
trichomes in the upper part, in the region of the four ovary lobes. The parenchyma is thin (3
layers of tangentially elongated cells). The internal epidermis has small tangentially
elongated cells.
The ovules are anatropous and present a single integument.
The androecium consists of 4 stamens. The stamen ontogenesis is typical. In the
first stages, the stamen primordium differentiates a stalked basal region, which will give
rise to the pedicel and filament and a trapezoidal upper region, which becomes the anther.
The filament extends concomitantly with the individualization of the two locules of the
anther. In the next stages of the stamen development, the median longitudinal septum and
then the two lateral ones are formed, which will separate each locule into two polinic sacs.
In the same time, in the median part of the anther, the connective begins to form.
The mature anther has typical structure. The wall consists of small tangentially
elongated cells. The mechanic layer presents radiary elongated cells with thickened and
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lignified longitudinal bands on the lateral walls. In the moment of dehiscence, the anther
has only the epidermis and the mechanic layer.
Conclusions
The floral morphogenesis follows the typical stages described in the majority of
plants. The order of the appearance of the flower elements is as follows: sepals, petals,
stamens and carpels.
The results of this study correlated with the data from the previous papers ([1], [2])
represent a complete characterisation of Melissa officinalis L. plant, which may serve for
further investigations regarding its aromatic, melliferous and medicinal importance.
REFERENCES
1. KLEIMAN C., 2001 - La Reproduction des angiosperms, Ed. Belin, Paris.
2. PĂDURARIU C., GALEŞ R., PREOTU A., M.- M. ZAMFIRACHE, TOMA C., BOZ I., 2009 - Distribution
and morphology of hairs in Melissa officinalis L. vegetative organs, An. Şt. Univ. „Al. I. Cuza” Iaşi, s. II a. Biol.
veget., 55, 2: 21-26.
3. PREOTU A., GALES R., TOMA C., 2009 - Morphological and histo-anatomical characteristics of Melissa
officinalis L. plant, Lucr. Şt. Univ. Şt. Agr. şi Med. Vet. „Ion Ionescu de la Brad” Iaşi, ser. Hortic, 52: 71-76.
4. TOMA I., 2003 - Dezvoltarea florii la Hyssopus officinalis L. (Lamiaceae), Lucrări Stiinţifice, Seria
Horticultură (USAMV Iaşi), 46, 1: 319- 322.
Explanation of plates:
PLATE I
Fig. 1-5. Serial cross-sections from the base to top of Melissa officinalis L. flower
PLATE II
Fig. 6. Cross-section through the calyx and corolla of Melissa officinalis L. flower during the first stages of its
development
Fig. 7. Cross-section through the ovary of Melissa officinalis L. during the first stages of its development
Fig. 8. Longitudinal section through the ovary of a mature Melissa officinalis L. flower, after fecundation
Fig. 9. Longitudinal section through a stamen of Melissa officinalis L. flower during the first stages of its
development
Fig. 10. Cross-section through the anther of a stamen of Melissa officinalis L. flower during dehiscence
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RAMONA GALEŞ and colabs.
PLATE I
Fig. 1
Fig. 2
Fig. 4
Fig. 3
Fig. 5
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RAMONA GALEŞ and colabs.
PLATE II
Fig. 7
Fig. 6
Fig. 8
Fig. 9
Fig. 10
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