Anatomical Studies of Lagenaria siceraria (Mol.) Standl and Cucumis sativa L. (Cucurbits.)
The study was carried out on the histology of two cucurbits Lagenaria scieraria (Mol.) Standl. and Cucumis sativa L. The transverse hypocotyl and epicotyl section shows ridges alternately with furrows and root is circular. The complete cylinder of extra xylary fibres in cortex is typical of the cucumber family. Nine bicollateral vascular bundles each are situated in an inner and an outer circle. Articulated ramified sap filled idioblasts are a special feature not described until now in Cucurbits.
Received: March 03, 2011;
Accepted: May 05, 2011;
Published: June 10, 2011
Lagenaria scieraria (Mol.) Standl. (Bottle gourd) is native of Africa,
it is named because of bottle like shaped of its fruit (Singh
et al., 1999). It is a tendril climber with hollow angular stem and
large, long petiolated and palmetely lobed leaves. The flowers are yellow unisexual
and produced in the leaf axiles. The fruit is a pepo which develops from the
receptacular tissue and epicarp. Cucumis sativa L. has been cultivated
for at least 3000 years in western Asia. The cucumber is a creeping vine that
roots in the ground and grows up or other supporting frames, wrapping around
ribbing with thin spiraling tendrils. The plant has large leaves that form a
canopy over the fruit. The melon-like fruits of the Nara plants are the main
staple of the local people (Henschel et al., 2004)
and the roots are of importance for the pharmaceutical industry. In diagnostic
key to taxa, anatomical characters are frequently useful at all levels. Some
anatomical works on the histology of different families was done by Myrtaceae
(Tantawy, 2004) Leguminoceae (Begum
et al., 2007; Islam et al., 2005,
2007; Edeoga et al., 2007).
MATERIALS AND METHODS
Two 15 cm long twigs from aboveground and one 5 cm long piece of a stem from
under soil were collected, dissected in approximately 3 cm long pieces and then
fixed immediately in an ethanol and water mixture (1:1). A sledge microtome
(Reichert, Vienna) was used to prepare transverse and longitudinal sections
approximately 35-45 μm thick. The sections were stained in picric acid
(saturated solution) and acid fuchsin (1%), both dissolved in distilled water
or in safranin (1 g/100 mL a.d.) and astra blue (0.5 g astra blue and 2 g tartaric
acid 100 mL-1 a.d.). Specimens were viewed using a CH3-microscope
(Olympus) and images captured using camera (Nikon).
RESULTS AND DISCUSSION
Root: The primary root was tetrarch in these plants, in which the pith
was absent and central region was made up of few metaxylem cells. The development
of vascular cambium was normal and almost similar to that described earlier.
It was initiated by the divisions in parenchymatous cells present below the
phloem strands to form the cambium stripes which united with the cambium stripes
developed by the divisions of pericyclic cells. The cambium originated from
two different types of cells had different activity. The vascular cambium originated
in the pericycle produced only ray parenchyma cells. The cambium formed on the
inner region of the primary phloem produced secondary conducting elements and
associated cells of xylem and phloem (Fig. 1a, b). This was
resulted into formation of four wedge shaped sectors of secondary conducting
tissues separated by wider ray parenchyma (Fig. 1c, d,
Fig. 2b). The ray cells were not observed in the region of
secondary conducting elements (Fig. 1c, d,
Hypocotyl: Since leaves are absent, the photosynthetically active tissue
is located in the stems. The epidermis in investigated plant species was one
layered. Epidermal cells were of different size, thin walled, tubular, squarish
or rectangular. The epidermal cells were moderately cuticularised. Many eglandular,
uniseriate, trichomes of various shapes were observed.
||(a) transverse section of a root of C. sativa (c, d)
C. sativa (b) L. siceraria
||(a) transverse section of a hypocotyl of L. siceraria (c,
d) C. sativa (b, d) Vascular bundle of C. sativa B. L.
Hypodermis was present situated immediately below the epidermis. It was composed
of 2-5 or more layers of spherical or rounded collenchyma cells having thickenings
at corners. Cortex was consisted of several layers of parenchyma cells.
||Transverse section of epicotyl (a) C. siceraria and
(b) C. sativa IFC: Inter fascicular cambium, VI: Vascular bundle
of inner ring, VO: Vascular bundle of outer ring
The starch grains were observed in the cortical cells of bottle gourd. The
vascular bundles were bicollateral and arranged in two circles. The outer circle
was made up of five larger bundles and the inner was of four vascular bundles
in bottle gourd (Fig. 2a). There were four vascular bundles
in each circle in cucumber. In each bundle the xylem was flanked by outer and
inner phloem (Fig. 2c, d). These bundles
were characterized by the presence of outer and inner intrafasicular cambia.
The outer cambium was present between xylem and outer phloem whereas inner cambium
was between xylem and inner phloem (Fig. 2c). The vascular
bundles were separated by small, compact, oval or spherical interfasicular parenchyma
cells (Fig. 2a).
Epicotyl: Epicotyls of both selected plants were angular with ridges
and shallow furrows. Epidermis was single layered with rectangular, tubular
or squarish cells which were compactly arranged, thin walled. Hypodermis was
made up of 2 to 6 layers of collenchyma cells. Cortex was parenchymatous. The
cortical cells were oval or roundish, thin walled and had minute intercellular
spaces. Endodermis was consisted of cells similar to the cortex but the cells
of this layer were comparatively smaller in the size. The vascular system was
made up of discrete bundles arranged in two circles or rings around the central
pith (Fig. 3a, b). In bottle gourd and cucumber,
the vascular bundles were large and bicollateral where the xylem was flanked
by outer and inner phloem (Fig. 3a, b).
||Transverse section of Lagenaria stem showing secondary growth.
ifc: Interfascicular cambium, FC: Fascicular, iphl: internal phloem, ephl:
external phloem, xy: xyle
In these bundles outer and inner cambia were present as in hypocotyl of these
two plants. The secondary growth was similar to that observed in the hypocotyl
(Fig. 4). The bicollateral strands were in two rings. Interfasicular
cambium was produced by the divisions in parenchyma cells which were united
with intrafasicular cambium. The formation of secondary vascular tissues was
restricted by interfasicular cambium. Therefore, the vascular tissues were present
in the form of strands (Fig. 3a, b).
The roots of investigated plants were devoid of hypodermis. In most of the
dicotyledones cortex of root consists of parenchyma cells (Fahn,
1982; Patel, 1999; Shah, 2001;
Garasia, 2002). The cortex was parenchymatous in the
investigated plants. Many intercellular spaces were observed in the cortical
cells similar results was obtained by Prodhan et al.
(2001). This is the characteristic of the root cortex (Fahn,
In these hypocotyls, the origin of cambium zone was normal by the union of
interfasicular and intrafasicular cambia. The secondary vascular tissues were
produced by intrafasicular cambium while the interfasicular cambia formed only
ray parenchyma. Therefore, the secondary vascular tissues appeared as larger
strands. Similar cambial activity was observed by Kartusch
and Kartusch (2008) in the Acantosicyos horridus of Cucurbitaceae.
Such cambial activity is common in vines (Esau, 1965,
Palisade like cells are situated on both borders of the furrows. The gas exchange
is therefore reduced (Hebeler et al., 2004) and
a supplementary protection against high irradiation must be present. For a stem
in an upright position the amount of the absorbed light will be minimal during
the hours with the strongest irradiance (Von Willert et
al., 1992). A certain part of the incoming light is to be reflected,
as indicated by the silvery pale-green appearance of the plant.
Another mechanism of adaptation to the harsh environmental conditions is the
formation of hummocks. The greater part of the plant is buried in the moist
sand of the hummocks, where no assimilation occurs. The chloroplasts of the
palisade-like cells retrogress into leucoplasts. Thus only a small part of the
plant is able to assimilate and transpiration is presumably absent from the
buried parts (Kutschera et al., 1997).
The presence of a ramified system of idioblasts might be of importance. The
idioblasts of A. horridus are a series of fused cells filled with an aqueous
solution containing among others a high concentration of cucurbitacines typical
for Cucurbitaceae (Braemer, 1893; Kartusch
and Kartusch, 2008). Solereder (1899) as well as Metcalfe
and Chalk (1950) have pointed to the lack of internal secretory structures
in the cucumber family but Cortesi, 1960 cited in Kartusch
and Kartusch (2008) observed simply or compound idioblasts in Bryonia, Citrullus
and Ecballium. In L. siceraria, the idioblasts are stained selectively
and intensively with acid fuchsin-picric acid, thereby showing a primary nature
of their cell walls (Bruni and Tosi, 1980). These solution-filled
idioblasts may act as a water-storage compartment, thus balancing the water
management. Therefore we conclude that the main stress factor in the case of
A. horridus is high irradiation and that its anatomical and physiological
adaptations have developed in relation to this stress.
The authors are thankful to the Head, Dept. of Bioscience, V N South Gujarat University, Surat, Gujarat for providing laboratory facilities.
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