INTRODUCTION
Aloe vera (L.) Burm. f. is a well-known medicinal succulent appreciated for its pharmaceutical, nutraceutical, and cosmetic uses globally (Manye et al. 2023). Its inherent adaptation to dry and semi-dry habitats is primarily due to its CAM photosynthetic process, which improves water-use efficiency by enabling carbon fixation at night and reducing transpiration during the day (Males 2017). The gel from A. vera leaves is a complex mixture abundant in bioactive substances like acemannan, anthraquinones, and aloins, which have shown anti-inflammatory, antioxidant, and wound-healing effects (Eshun and He, 2004). Even with extensive research on the chemical makeup of A. vera gel, the specific anatomical and physiological processes that contribute to its drought resistance and metabolite production are still not thoroughly investigated. The majority of studies conducted so far have concentrated on the biochemical analysis of leaf extracts but have neglected the structural adaptations that enable survival in water-scarce habitats (Hamman 2008). The fleshy leaf tissues, comprising hydrenchyma for storing water and chlorenchyma for photosynthetic activity, are essential for CAM functionality and the buildup of secondary metabolites, but quantitative anatomical studies of these tissues in A. vera are limited.
Comprehending these anatomical characteristics is crucial for clarifying how A. vera maintains water conservation while producing bioactive substances, particularly during environmental stress. Additionally, the distribution of bioactive metabolites in particular tissue compartments and their connection to anatomical characteristics have not been thoroughly examined. This gap hinders our capacity to optimize A. vera farming for improved therapeutic effectiveness and stress resistance. Comparative anatomical research among various Aloe species has revealed considerable variability associated with ecological adaptation (Pérez-López et al. 2023). Tackling this gap could enhance breeding and biotechnological strategies focused on boosting crop performance and metabolite production under different ecological conditions. This research aims to fill these gaps through a comprehensive examination of leaf anatomical structures in different A. vera species.
Coarse stereopsis and fine stereopsis are two main aspects of depth perception. Coarse stereopsis (also known as qualitative or gross stereopsis) is used to detect stereoscopic motion which is changes in binocular disparities in a real-life three-dimensional scene over time in ones surrounding (Barry 2009). Fine stereopsis (quantitative stereopsis) enables an individual to perceive the depth of an object in central visual area (pannum’s fusional area). Fine stereopsis is essential to perform fine motor tasks (Barry 2012). TNO (Toegepast Natuurwetenschappelijk Onderzoek) test is used for assessment of stereopsis (Fig. 2)
Stereo acuity development in children with normal binocular single vision. The lower limits of stereo acuity compatible with normal binocular single vision were 3 1/2 years, 3,000 seconds; 5 years, 140 seconds: 5 1/2 years, 100 seconds; 6 years, 80 seconds; 7 years, 60 seconds; and 9 years, 40 seconds (Shah et al. 2009).
MATERIALS AND METHODS
An experiment was conducted to study the stomatal changes on the adaxial and abaxial surfaces of the leaf laminae of ten Aloe species: A. vera, A. karabergensis, A. striata, A. spinosissima, A. pachygaster, A. microstigma, A. hemingii,
A. globuligemma, A. eru and A. conifera. Leaf samples were collected in November, December and January at the Old Botanical Garden of the University of Agriculture, Faisalabad. The samples were first fixed in FAA (formalin acetic acid alcohol) for 24 hours and then transferred to 70% ethanol for preservation. The leaf lamellae were cut by hand to produce anatomical preparations. The sections were then subjected to the following staining procedure.
The leaf lamellae were carefully peeled from selected specimens and immersed in 30% ethanol for 10–15 minutes. The tissues were then successively placed in 50% ethanol for 10–15 minutes and then in 70 ethanol. After dehydration with ethanol, the samples were stained with a few drops of safranin for 5 minutes. Excess safranin was removed by washing the tissue three times in 90% ethanol for 5 minutes. The tissues were then washed 2–3 times in 100% ethanol and cleared with a graded series of xylene (25%, 50% and 100%). Each section was permanently embedded in a drop of Canada balsam. Microscopic images of the samples were taken using a compound light microscope. Stomatal density was determined according to the method described by Salisbury. The stomatal index was calculated according to the formula of Paul et al. (2017).
RESULTS
Number of stomata
Graphical analysis revealed that A. pachygaster exhibited the highest number of stomata on both the adaxial and abaxial surfaces. In contrast, the lowest stomatal density was recorded in A. microstigma on both surfaces. Overall, significant interspecific variation was observed in stomatal number across the studied Aloe species (Fig.1A).
Number of epidermal cells
The highest number of epidermal cells was observed in A. hemingii on both leaf surfaces, whereas A. microstigma exhibited the lowest count. The data demonstrated statistically significant differences in epidermal cell number among the different Aloe species (Fig.1B).
Length of guard cells
The longest guard cells were measured in A. pachygaster at both upper and lower epidermal layers. Conversely, the shortest guard cells were found in A. globuligemma. The results indicated substantial variation in guard cell length across the Aloe species (Fig.1C).
Width of guard cells
The maximum guard cell width was recorded in A. striata and A. hemingii on both leaf surfaces, while A. vera exhibited the minimum width. Significant differences in guard cell width were noted among the evaluated Aloe species (Fig.1D).
Length of epidermal cells
The greatest
epidermal cell length was observed in A. conifera on both the adaxial and abaxial surfaces. In contrast,
%2023010105%20Ok_files/image001.png)
A.
pachygaster showed the
shortest epidermal
cells. Overall, significant differences were detected in epidermal cell length
among the species (Fig.1E).
%2023010105%20Ok_files/image002.png)
Width of epidermal cells
The width of the epidermal cells varied significantly between the Aloe species studied, with clear differences observed between the upper and lower epidermal layers. A. karasbergensis and A. hemmigii had the widest upper epidermal cells, while their lower epidermal cells were comparatively narrower. Similarly, A. spinosissima and A. conifera had relatively wide upper epidermal cells, with slight differences compared to the lower epidermis. A. microstigma showed almost equal widths in both layers, indicating a uniform epidermal thickness (Fig. 1F). These results highlight significant interspecific variation in epidermal cell width.
Length of the stomatal pore
Results revealed that A. spinosissima exhibited the greatest stomatal pore length on both epidermal surfaces, whereas the shortest pores were observed in A. conifera. The results revealed statistically significant differences in stomatal pore revealed statistically significant differences in stomatal pore length among the studied species (Fig.1G).
Width of stomatal pore
The highest stomatal pore width was found in A. spinosissima, while A. conifera exhibited the minimum pore width at both the adaxial and abaxial surfaces. The data indicate significant interspecific differences in pore width (Fig. 1H).
Stomatal index
The highest stomatal index was calculated in A. pachygaster, while the lowest was observed in A. microstigma on both leaf surfaces. Overall, the stomatal index showed significant variation among the Aloe species analyzed (Fig. 1–3).
DISCUSSION
Least number of stomata was observed in A. microstigma at both lower and upper epidermis while it is observed that maximum number of epidermal cells was observed in A. hemingii at both lower and upper epidermis. However least number of epidermal cells was present in A. microstigma at both lower and upper epidermis. Observations showed that the maximum length of guard cells was present in A. pachygaster at both lower and upper epidermis. However, the minimum length of guard cells is present in A. globuligemma at both lower and upper epidermis. Oyeleke et al. (2004) also reported that the maximum width of guard cells was present in A. striata and A. hemengii at upper and lower epidermis. However, the minimum width of guard cells was noted in A. vera at both lower and upper epidermis. Camargo and Marenco (2011) confirmed that maximum number of stomata was observed in A. pachygaster at both lower and upper epidermis (Fig. 1-3).
However, the minimum length of epidermal cells is present in A. pachygaster at both lower and upper epidermis. Coopoosamy et al. (2011) also confirmed that the maximum width of epidermal cells was seen in A. karabergensis and A. spinosissima at upper and lower epidermis. However, the minimum width of epidermal cells was present in A. vera at both lower and upper epidermis while the maximum length of pore was found in A. spinosissima at upper and lower epidermis. However, the minimum length of pore was measured in A. conifera at both lower and upper epidermis. Results showed that the maximum width of pore was present in A. spinosissima at upper and lower epidermis. Lake et al. (2000) observed that the maximum stomatal index was present in A. pachygaster at upper and lower epidermis. Moreover, the minimum stomatal index was measured in A. microstigma at both lower and upper epidermis. Overall result showed significant differences in stomatal index in different Aloe species. In short, Aloe species indicated great variations in the leaf stomatal number, distribution, size and frequency. This information can be used to assess the photosynthetic performance and biomass yield of these species, which may carry implications for their commercial and medicinal importance (Tinti et al. 2023).
CONCLUSION
It was observed that stomatal index and
density show significant differences among different
Aloe species. Results revealed that maximum number of stomata
was seen in A.
pachygaster while the minimum number
is observed in A.
microstigma. Further studies shows that number of epidermal cells was higher in A. hemingii
while least number
of epidermal cells are present
in A. microstigma. However,
stomatal size was larger in A. pachygaster and A. striata while it was reduced in
A. vera and A. conifera at both upper and
lower epidermis. The information obtained from this study can be used to assess the photosynthetic performance and dry
matter yield of these species.
ACKNOWLEDGMENTS
The author expresses her sincere gratitude to the Institute of Botany, University of Agriculture, Faisalabad, for their invaluable assistance in plant sampling and analysis
DATA AVAILABILITY
The data will be made available on a fair request.
ETHICS APPROVAL
Not applicable to this paper.
FUNDING SOURCE
This project is not funded by any agency
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