Loranthaceae which is the most distributed family of the group of parasitic plants called mistletoe has been plagued with alarming rates of misidentification at the generic and specific levels [
Anatomical and micromorphological characteristics of leaves, stems, and roots have played important roles in plant taxonomy, especially at the generic and specific levels. Studies in this field have attracted the attention of plant morphologists and systematists to resolve taxonomic conflicts in different groups of plants [
Secondary metabolites produced by plants are believed to be stored in various organs including the leaves, stems, and roots. The epidermis of most plants also contains hairs which are functionally classified as glandular or nonglandular trichomes. Glandular trichomes are specialised secretory structures that vary in size, form, location, and function in different plant species [
The leaves of the mistletoe were collected from mature rubber trees in the Rubber Research Institute of Nigeria. The site is located on latitude 6°00′–6°15′N and longitude 5°30′–5°45′E and at about 27 m above sea level. The sample was authenticated by Dr. Emmanuel I. Aigbokhan at the Plant Biology and Biotechnology Department, University of Benin (UNIBEN), and a voucher specimen (UBH10284) was deposited at the UNIBEN herbarium.
Light microscopic examinations of the leaves were done by obtaining peels from the adaxial and abaxial surfaces of matured fresh leaves. The peels were placed on glass slides with 1-2 drops of nile blue sulfate stain, covered, and observed under a Zeiss light microscope. The photomicrographs were taken with a digital camera (DCM 510, 5 M pixels, CMOS chip) that was fitted to the light microscope.
Fresh leaves and stems (transverse) were cut into segments of 4–6 mm in length and fixed in 6% glutaraldehyde with pH 7.3 for 12 h. The sections were rinsed with 0.05 M sodium cacodylate buffer (pH 7.5). Each sample was later rinsed in distilled water and dehydrated in a graded series of ethanol 10–100% for 20 min per rinse. The sections were dried in a Hitachi HCP-2 critical point dryer and mounted on aluminium stubs with double-sided carbon coated sputter coating with gold palladium (Elko IB-3 Ion Coater). The samples were examined at varying magnifications using JEOL (JSM-6390LV) scanning electron microscope (SEM) that was operated at 10–15 kV accelerated voltage. The energy dispersive X-ray spectroscopy (EDX) involved both fixing and dehydration procedure as in SEM, while the elemental analysis was done using energy dispersive X-ray analyser which was coupled to SEM, manufactured by Thermo Electron Corporation, 6733B-IUUSN, USA. The Noran system six software was used for imaging.
The photomicrographs of the light and scanning electron microscope of
Photomicrographs of the light microscopy of
SEM photomicrographs of
SEM photomicrographs; (a)–(c) showing lenticel on the midrib of the abaxial surface at different magnifications.
This study revealed densely packed stellate trichomes with globular center tapering towards the tips, often overlapping themselves on the abaxial surface (Figures
The stem was characterised by unusual xylem conducting cells known as graniferous tracheary elements. The tracheary elements were tightly packed with grains of size
SEM photomicrograph of a transverse section of graniferous tracheary elements (gte) showing the grains (gr) at varying magnifications (a–c).
Results of the X-ray microanalyses of some points on the leaf epidermis, a crystal deposit, and the grains in the xylem of
Percentage atomic compositions of the elements in
Elements | Atom (%) | |||
---|---|---|---|---|
Abaxial | Adaxial | Crystal | Granules | |
Carbon | 62.52 ± 1.03 | 55.81 ± 1.24 | 6.73 ± 0.86 | 34.94 ± 4.03 |
Oxygen | 23.67 ± 1.03 | 29.18 ± 0.92 | 54.77 ± 0.78 | 40.14 ± 3.60 |
Sodium | 0 | 0 | 0.30 ± 0.07 | 0 |
Nitrogen | 6.61 ± 2.57 | 0 | 0 | 6.18 ± 6.83 |
Calcium | 1.23 ± 0.11 | 0 | 0.11 ± 0.04 | 0 |
Potassium | 0.02 ± 0.04 | 0 | 1.51 ± 0.05 | 0 |
Aluminum | 0.24 ± 0.05 | 0.99 ± 0.07 | 13.86 ± 0.18 | 0 |
Silicon | 0.34 ± 0.05 | 7.62 ± 0.18 | 16.11 ± 0.20 | 0 |
Sulfur | 0.20 ± 0.08 | 0 | 0.02 ± 0.07 | 0.47 ± 0.61 |
Iron | 0.22 ± 0.08 | 0 | 2.07 ± 0.21 | 0 |
Zinc | 0 | 0 | 0.21 ± 0.17 | 0 |
Magnesium | 0 | 0 | 0.43 ± 0.07 | 0 |
Gold | 4.87 ± 0.58 | 6.40 ± 0.92 | 3.67 ± 0.53 | 18.28 ± 3.82 |
EDX photomicrographs and spectra of the abaxial (a) and adaxial epidermis (b).
EDX photomicrographs and spectra of the crystal deposit (a) and granules in the tracheary elements (b).
Variations in frequency, types, distribution, and arrangement of stomata are features which serve taxonomic importance at the generic level of classification [
Scientific interest in leaf trichomes is based on their functions which include lowering of leaf temperature, increase in tolerance to freeze, storage of phytochemicals, protection of the inner tissues from UV radiations from sun, water retention, protection against insect herbivores and airborne fungi [
The SEM result of the xylem revealed numerous tracheary elements that were filled with grains which in accordance with Fineran [
This study showed that the xylem of
Some crystal deposits were observed on the leaf surfaces (Table
The major elements on the crystals were Si (
Calcium is assumed to initiate closer of the stomata and hence plays a role in transduction [
Being a plant widely utilised in alternative medicine, the tiniest information which could be useful in identifying it is of most prerogative. This study has highlighted detailed descriptive information of the micromorphological structures of
The authors declare that there are no competing interests on this work.
Authors appreciate the financial support of the Govan Mbeki Research Development Center, University of Fort Hare, South Africa, and the Rubber Research Institute of Nigeria, Iyanomo.