METADATA

Paper history

Received: 26 January 2023

Revised: 30 March 2023

Accepted: 12 April 2023

Published: 25 May 2023

Corresponding author

Email: mariyumshakoor@gmail.com (Mariyum Abdul Shakoor)

Keywords Stomata density Epidermis

Aloe species

Citation

Shakoor MA (2023) Biological significance of changes in stomatal density and stomatal index of Aloe species.

Innovations in STEAM: Research & Education 1: 23010105. https://doi.org/10.63793/ISRE/0005

ABSTRACT

Background: Aloe is a genus containing over 500 species of flowering succulent plants with enormous medicinal potential. Stomatal density and index vary greatly in the different species of this genus.

Objective: Aloe species were collected from the new botanical garden, University of Agriculture, Faisalabad. The size of stomata, the size of epidermal cells, the number of epidermal cells, and the number of stomata per ocular were measured to evaluate the anatomical changes in Aloe species.

Methodology: The experiment was conducted to explore stomata modifications in upper and lower leaf lamina of different Aloe species that are A. vera, A. karabergensis, A. striata, A. spinosissima, A. pachygaster, A. microstigma, A. hemingii, A. globuligemma, A. eru and A. conifera in Nov, Dec and Jan.

Results: Significant interspecific variation was observed in both stomatal index and stomatal density among the studied Aloe species, including A. vera, A. pachygaster, A. eru, A. striata, A. karabergensis, A. hemingii, A. conifera, A. microstigma, and A. globuligemma. Among these, A. pachygaster exhibited the highest stomatal density, whereas A. microstigma demonstrated the lowest.

Analysis of epidermal characteristics revealed that A. hemingii had the greatest number of epidermal cells, while A. microstigma had the fewest. Furthermore, stomatal size was markedly larger in A. pachygaster and A. striata, whereas reduced stomatal size was observed in A. vera and A. conifera across both adaxial and abaxial surfaces. These findings suggest species-specific adaptive responses likely linked to ecological or physiological traits, offering insights into taxonomic differentiation and potential drought resilience mechanisms in Aloe species.

Conclusion: Overall results showed great variations in all parameters in different Aloe species. The information obtained from this study can be used to assess the photosynthetic performance and dry matter yield of these species.

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.

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

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,

A. pachygaster showed the shortest epidermal cells. Overall, significant differences were detected in epidermal cell length among the species (Fig.1E).

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

A B

C D

E F

G H

Fig. 1: Number of stomata (A), number of epidermal cells (B), length of guard cells (C), width of guard cells (D), length of epidermal cells (E), width of epidermal cells (F), length of stomatal pore (G), width of stomatal pore (H) and stomatal index (I) of different Aloe species

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 shows 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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