This work was conducted to assess the anatomical features of Pistacia atlantica Desf. under Mediterranean semi-arid climate conditions. In this study, phytoecological approach was used at different observation scales including the large ecological scale. 11 samples of P. atlantica species were randomly selected in order to study the anatomy of leaves and branches. The results show that leaves have palisad e parenchyma occup ying almost the entire mesophyll, measuring 100 to 170 μm. While in branches, the only pith occupies 38% followed by the xylem (24%), relative to the rest of the tissue (epidermis, periderm, collenchyma, pericyclic fiber, secretory duct and phloem). The current results suggest that P. atlantica species ha s xeromorphic anatomical characters, giving it great ecological plasticity in an arid environment. Moreover, this study shows that the human activities are causing local extinction of this rare species in Algeria.
Pistacia atlantica Desf. is a tree species of the genus Pistacia L. which is in danger of extinction in Algeria. The species is located in the Algerian north westernmost. The species occupies presently a meager proportion of the territory that it once covered [
The species is economically important in Algeria. It is important to combat soil erosion; it strengthens the soil and is used for reforestation of arid and steep slopes and against landslides. The seeds are edible oil seeds and contain up to 60% fat [
Many taxonomic studies have described the species [
Additionally, the study of the internal anatomy of the plant leaves and branches along their modifications and adaptations remains essential for a better autecological diagnostic of the plant species. Unfortunately in Algeria and specifically in the north westernmost of the country, no work has been published on the anatomical and histometrical characters of this rare species. Therefore, this study objective was to assess the anatomical features of P. atlantica under Mediterranean semi-arid climate.
This study is the first to study the internal structures of leaves and branches of P. atlantica in this region.
The study area is located at the north westernmost Algeria (
The area is characterized by a semi-continental Mediterranean climate. The arid enclave surrounding Maghnia is thus characterized by a thermal continental micro-climate, cold in winter and very hot in summer [
The Emberger’s pluviothermic climagramm (
The Bagnouls and Gaussen (1957) [
The annual rainfall varies between 249 and 327 mm. The monthly rainfall patterns are characterized by two maxima rainfall, one in November and one in March. The spring and winter maxima allow several plant species, such as Stipa tenacissima [
As for the average annual temperatures, they oscillate between 17.67˚C and 20.42˚C. The extreme values are strong limiting factors whose effectiveness depends on certain levels and their frequency of occurrence [
The sample collection was carried out in the Maghnia Tell plain (North westernmost Algeria) characterized by a semi-arid climate. Anatomical sections were performed for the leaves and branches of 11 random samples of Pistacia atlantica. Sample collection was performed at the base of the tree crown. The authors taxonomically identified the plant samples.
Cross sections were done “freehand” and to differentiate between the xylem and phloem we used the double staining with methyl green-red Congo [
All leaves and branches tissues were measured as shown in
The results show the following tissues of the branches:
Tissues | Epidermis | Periderm | Co | pf | sch | Phloem | Xylem | Pith | Total |
---|---|---|---|---|---|---|---|---|---|
Samples | |||||||||
Mean | 10 | 68 | 200 | 38 | 53 | 236 | 392 | 614 | 1611 |
% | 1 | 4 | 12 | 2 | 3 | 15 | 24 | 38 | 100 |
Abbreviation: sch = secretory channel; co = collenchyma, pf = pericyclic fiber.
Tissues | Mesophyll | Main Nervure | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Samples | uep | pp | lep | Total | uep | uco | cvb | lco | uep | Total |
Mean | 17 | 140 | 16 | 173 | 12 | 112 | 177 | 81 | 12 | 394 |
% | 10 | 81 | 9 | 100 | 3 | 28 | 45 | 21 | 3 | 100 |
Abbreviation: lco = lower collenchyma; uco = upper collenchyma, lep =lower epidermis, uep = upper epidermis; cvb = cribro-vascular bundle, pp = palisadic parenchyma.
The Epidermis
This superficial layer is constituted by a single layer of cells with a thickness up to 10 microns. (
The Periderm
The periderm consists of phellem, phellogen and phelloderm whose suber remains the most significant tissue; measuring up to 30 µm to 100 µm with an average of 68 microns (
1) The phellem (suber or cork): The cork cells have regular shapes and are ocher yellow or yellow brown to brown. When young, the suber can keep its natural transparent color (
2) Phellogen: is the subero-phellodermal generator sitting, it is a layer of short lines of initial tabular cells.
3) Phelloderm: is a thin layer of differentiated tabular cells under the phellogen. The phelloderm lignification was observed.
The collenchyma
There is a set of pink or red cells, more or less elongated, spindle-shaped with a cellulosic thickening located at the corners (
The cortical parenchyma
It is absent when the subject is young (
The pericyclic fibers
Highly elongated cells with kidney-shaped wall with a large lignified second-
ary thickening; reach up to 38 microns on average (
Secretory or excretory channels
These circular cavities are limited by one or two layers of small secretory cells regularly arranged (
Phloem
This part consists of a set of parenchyma cells with rather thick walls of a cellulosic nature; phloem fibers and rays. This tissue complex thickness is of 236 microns on average; with an interval between 170 and 400 µm (
Cambium
This is a phloem-woody base generator located between the xylem and phloem, its color is lighter than the phloem (
Xylem
This tissue is made up of various cellular elements: the vessels, the wood fibers and wood parenchyma cells (or medullary rays) (
Pith
This parenchymal tissue fills the center of branches (stems) (
Cross sections of the different leaves revealed that the leaf blade is made of the following tissues: The epidermis; the assimilation tissue (mesophyll); and the conducting bundles (veins and vascular system).
The epidermis
This is the thinner layer of the unicellular cells with a thickness which does not exceed 20 microns. From this epidermis, unicellular hairs called trichomes develop (
The assimilation tissue (mesophyll)
It is, at the leaf blade, the middle part of the leaf, between the epidermises. It is composed of elongated cells, arranged perpendicularly (
The conducting bundles (nervures)
The main nervure is highly prominent on both sides of the leaf. It is formed by 4 opposed cribro-vascular bundles three of which are arranged in a phloem- woody arc facing the ventral side of the leaf blade. In each bundle, the xylem is oriented towards the center and the phloem outwards. Secretory ducts, with a diameter of 30 µm, on the average, are observed in the phloem (of bundles). On the bilateral plane of symmetry, the thickness of all the conducting bundles and secretory channels varies between 90 and 280 µm (
Around the conducting bundles, there is a continuous ring of parenchyma or perivascular sheath (
This study was conducted on the anatomy of Pistacia atlantica leaves and branches and it is the first study to report the anatomical features of P. atlantica under Mediterranean semi-arid climate in Algerian north westernmost.
This study reveals that the internal structure of this species does not escape from all the major anatomical features of most dicotyledonous; but there are some differences that reflect well on this species adaptation to such arid environment.
The study of cross sections of P. atlantica branches reveals a diverse set of tissues of primary and secondary structure by meristematic origin. These coatings cells are usually monolayered and nested within the other like the stones of a puzzle, without intercellular spaces (
Periderm includes: an outer layer of dead cells, the phellem or cork; a generator cell layer, the phellogen producing outward cork cells; and finally an inner layer, the phelloderm, thin, containing living cells produced in the phellogen inner face [
In some vascular plants, including the Chamaephytes and most Phanerophytes like that of Pistacia atlantica Desf., the diameter increment is provided, in addition to periderm by another lateral meristem, deeper, secondary in nature, called the cambium or the phloem-woody generator sitting. Lateral meristems add volume to plants by producing secondary conductors tissues and periderm [
The phloem-woody cambium produces secondary conducting tissues that add directly to the primary elements: the phloem or secondary phloem to the outside and wood or secondary xylem inward. The production of cells on each side of the cambium is not regular [
The thickening of the conducting secondary tissue inevitably leads to the narrowing of xylem and primary phloem. The xylem, which is formed from pro- cambial or cambial cells, is a heterogeneous tissue consisting of both non-con- ducting cells (parenchyma or woody rays and fibers) and conducting cells (vessels); because they are essential to the transportation and storage of water and minerals (crude sap). This is one of the fundamental characters of the degree of drought resistance of P. atlantica. As the xylem, the phloem is not homogeneous; it consists of parenchyma, fibers and conducting elements (sieve tubes), providing the transport of the organic or developed sap to the different parts of the plant.
The medullary rays (parenchymal cells) ensure and provide storage and radial transport of water and assimilate between the xylem and phloem [
As for fiber, their main function is to provide structural support for the plant [
The collenchyma cells can be considered as parenchymal cells, specialized in supporting young tissues [
Raven et al. (2003) [
The two supporting tissues (collenchyma and sclerotic fibers) form with the parenchyma, composed of banal appearance of roughly isodiametric cells, all fundamental tissues. Parenchymal cells provide the major part of plant metabolism; they synthesize and store various organic substances [
At the center of the branches, is the pith, which consists of a storage parenchyma often rich in starch grain. We note that the pith is made up of cells with more or less lignified walls, perforated punctuations or plasmodesmata that allow intercellular communication and a circulation of substances within the cells (
Pith is also characterized by its more or less great development; it reaches a diameter of 610 microns, or 38% on average (
The chemical composition of the walls and vacuolar content is variable and is related to the role of protection from environmental strains (radiation, drought and grazing) [
Observation under a scanning electron microscope revealed more precision on the leaves of P. atlantica, they indicate the presence of two types of trichomes: 1) non-glandular covers (ciliated short hairs at the margin and long hair at the main nervure) and 2) Glandular secretory hairs at the abaxial surface.
Metcalfe and Chalk (1950) [
The leaves conducting system is connected to the xylem and phloem of the stem [
The fundamental leaf tissues take place between the upper epidermis and lower epidermis, in an area called mesophyll (from Greek mesos, “middle” and phullon, “leaf”). The mesophyll is composed mainly of parenchyma cells containing chloroplasts that carry out photosynthesis [
Our observations show that the mesophyll Pistacia atlantica is characterized by a homogeneous structure fully palissadic (
Al-Saghir et al. (2006) [
According to Vidal and Pognonec work (1984) [
In addition to water deficit intensity of the illumination and the position of the leaves relative to solar radiation also reflect the degree of development of the palisadic parenchyma. In the parenchyma, under the effect of intense illumination, there is the reduction of meatuses, the accumulation of starch, differentiation of palisadic tissue whose cells become elongated and the layers more numerous [
The importance of palisadic tissue, that is to say the number of cell layers that constitute it, can vary from one leaf to another in the same subject, depending on the illumination received by the leaves. Deysson (1965) [
Cornic (2007) [
There are cells or group of cells scattered in other tissues and which have the property to produce or secrete substances such as resin in P. atlantica. The resin can contribute to prevent water vapor to escape from leaves [
The results of this study reveal that epidermis of leaves is thick and cutinized; trichomes were present in leaves, development of the palisadic parenchyma (as a result of continued solar radiation and water deficit), reduction and densification of the lacunar parenchyma; the resin was secreted and the vascular system is well developed.
In conclusion, Pistacia atlantica has xeromorphic anatomical characters, giving it a great ecological plasticity in an environmentally stressful medium. The climatic conditions of the Algerian northwester most from the ancient period to date are still favorable for better rehabilitation and maintaining of P. atlantica.
Possible climate changes in the global change phenomenon should not result in rarefactions or significant disappearances of Mediterranean phanerophytes. The most threatened species are much more in the near future as a result of human impacts than under climate variations [
The authors are grateful for Dr. Meriem Kaid-Harche, Director of Laboratory Productions, Plant and Microbial Valuations LP2VM (University of Sciences and Technology, Oran, Algeria) for providing his lab space and equipments to do this work. The authors would like to thank all the lab staff for their help and support in particular Dr. Kheira Errouane who has helped with the histological sections of this species.
Amara, M., Bouazza, M. and Al-Saghir, M.G. (2017) Anatomical and Adaptation Features of Pistacia atlantica Desf. to Adverse Climate Conditions in Algeria. American Journal of Plant Sciences, 8, 137-153. http://dx.doi.org/10.4236/ajps.2017.82011