The American Journal of Applied Sciences
1
https://www.theamericanjournals.com/index.php/tajas
TYPE
Original Research
PAGE NO.
01-05
10.37547/tajas/Volume07Issue06-01
OPEN ACCESS
SUBMITED
24 April 2025
ACCEPTED
19 May 2025
PUBLISHED
01 June 2025
VOLUME
Vol.07 Issue 06 2025
CITATION
Dr. Leyla M. Sharifi, & Dr. Farhad R. Noorbakhsh. (2025). Nuclear
Ultrastructure in Mesophyll Cells of Salt-Tolerant Artemisia
Marschalliana Leaves. The American Journal of Applied Sciences, 7(06),
01
–
05. Retrieved from
https://theamericanjournals.com/index.php/tajas/article/view/6213
COPYRIGHT
© 2025 Original content from this work may be used under the terms
of the creative commons attributes 4.0 License.
Nuclear Ultrastructure in
Mesophyll Cells of Salt-
Tolerant Artemisia
Marschalliana Leaves
Dr. Leyla M. Sharifi
Department of Plant Biology and Biotechnology University of Tehran
Tehran, Iran.
Dr. Farhad R. Noorbakhsh
Department of Plant Sciences Shahid Beheshti University Tehran, Iran
Abstract:
The nucleus, as the control center of the
eukaryotic cell, plays a pivotal role in orchestrating
cellular responses to environmental stresses, including
salinity. Salt-tolerant plants, such as Artemisia
marschalliana, possess unique adaptive mechanisms to
thrive in high-salinity environments. This study
investigates the distinct structural features of nuclei
within the leaf mesophyll cells of Artemisia
marschalliana,
aiming
to
elucidate
potential
ultrastructural adaptations associated with its salt
tolerance. Using transmission electron microscopy, we
analyzed the chromatin organization, nucleolar
morphology, and nuclear envelope integrity. Our
findings reveal specific nuclear characteristics, including
a well-defined nucleolus with distinct fibrillar and
granular components and a relatively dispersed
chromatin pattern, suggesting active transcriptional and
metabolic processes. These ultrastructural observations
provide insights into the cellular strategies employed by
Artemisia
marschalliana
to
maintain
nuclear
homeostasis and cellular function under saline
conditions, contributing to a deeper understanding of
plant salt tolerance mechanisms.
Keywords:
Artemisia marschalliana, Salt Tolerance,
Nucleus, Ultrastructure, Mesophyll Cells, Transmission
Electron Microscopy, Chromatin, Nucleolus
Introduction:
Salinity is a major abiotic stress factor that
severely limits plant growth and agricultural productivity
worldwide. High concentrations of soluble salts in the
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The American Journal of Applied Sciences
soil adversely affect plants by imposing osmotic stress,
ion toxicity, and oxidative stress, leading to a cascade of
physiological and biochemical disturbances [1]. Plants
have evolved diverse strategies to cope with saline
environments, ranging from salt exclusion and
compartmentalization to osmotic adjustment and
antioxidant defense [1, 3]. Halophytes, such as
Artemisia
marschalliana
, are naturally adapted plants capable of
completing their life cycle in high-salt conditions, making
them valuable models for studying salt tolerance
mechanisms.
The nucleus, housing the plant's genetic material, is
central to orchestrating cellular responses to
environmental cues, including stress [4]. Gene
expression regulation, DNA repair, and ribosomal
biogenesis
—
all critical processes for cellular survival and
adaptation
—
are tightly controlled within the nuclear
compartment. Previous research has shown that salt
stress can induce significant changes in cellular
ultrastructure, including alterations in root cells [1] and
mesophyll cells [3], and can even lead to nuclear and
DNA degradation in sensitive plant species [2]. These
changes often reflect the cell's struggle to maintain
homeostasis under adverse conditions. Furthermore,
metabolism of proteins and nucleic acids undergoes
formative changes under salinization conditions [6],
underscoring the dynamic nature of nuclear activity
during stress.
Despite the general understanding of salt stress impacts
on plant cells, specific ultrastructural adaptations of the
nucleus in highly salt-tolerant species like
Artemisia
marschalliana
remain underexplored. Understanding
the fine structural organization of the nucleus in such
resilient plants can provide crucial insights into how they
maintain genetic integrity, regulate gene expression,
and sustain metabolic activity under conditions that
would be detrimental to glycophytes (salt-sensitive
plants). This study aims to characterize the structural
features of nuclei within the leaf mesophyll cells of
Artemisia marschalliana
, thereby contributing to a more
comprehensive understanding of the cellular basis of
salt tolerance.
2. METHODOLOGY
To investigate the ultrastructural features of nuclei in
leaf mesophyll cells of salt-tolerant
Artemisia
marschalliana
, standard protocols for transmission
electron microscopy (TEM) sample preparation and
observation were followed.
2.1. Plant Material:
Leaves were collected from mature, healthy specimens
of Artemisia marschalliana grown under natural, salt-
tolerant conditions. The plant material was immediately
processed to preserve cellular integrity.
2.2. Tissue Preparation for Electron Microscopy:
Small leaf segments (approximately 1-2 mm²) were
excised from the mesophyll tissue and subjected to a
meticulous fixation process.
•
Primary Fixation: Samples were immersed in a
solution of 2.5% glutaraldehyde in 0.1 M phosphate
buffer (pH 7.2) for 24 hours at 4°C. This step cross-
links proteins, preserving cellular architecture.
•
Washing: Fixed samples were rinsed thoroughly
three times, for 15 minutes each, with 0.1 M
phosphate buffer to remove excess glutaraldehyde.
•
Secondary Fixation: Samples were then post-fixed in
1% osmium tetroxide (OsO₄) in 0.1 M phosphate
buffer (pH 7.2) for 2 hours at 4°C. Osmium tetroxide
stains lipids and further stabilizes cellular
components, enhancing contrast for electron
microscopy.
•
Dehydration: A graded series of ethanol solutions
(50%, 70%, 90%, 100% absolute ethanol) was used
to dehydrate the samples. Each step involved 15-
minute immersions, with three changes in absolute
ethanol to ensure complete water removal.
•
Infiltration and Embedding: Dehydrated samples
were infiltrated with propylene oxide for 30
minutes, followed by a gradual infiltration with
Spurr's resin. Samples were placed in a mixture of
propylene oxide and resin (1:1) for 1 hour, then in
pure resin for 2 hours. Finally, samples were
embedded in fresh Spurr's resin in flat molds and
polymerized at 70°C for 48 hours.
2.3. Sectioning and Staining:
Ultrathin sections (approximately 70-90 nm thickness)
were cut from the embedded blocks using an LKB
Ultramicrotome with a diamond knife. These sections
were then mounted on copper grids (200 mesh). For
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enhanced contrast, the sections were stained
sequentially:
•
Uranyl Acetate Staining: Sections were stained with
2% uranyl acetate solution for 15 minutes at room
temperature.
•
Lead Citrate Staining: Following rinsing, sections
were stained with lead citrate solution for 5 minutes
at room temperature.
2.4. Microscopy and Analysis:
Stained ultrathin sections were examined using a JEM-
100CX Transmission Electron Microscope operating at
80 kV. Images were captured at various magnifications
to observe the overall morphology of mesophyll cells
and, specifically, the detailed ultrastructure of their
nuclei. Qualitative analysis focused on describing the
organization
of
chromatin
(euchromatin
and
heterochromatin distribution), the morphology and
internal components of the nucleolus (fibrillar and
granular regions), and the integrity and pore distribution
of the nuclear envelope. Observations were compared
against general knowledge of plant cell nuclear
ultrastructure to identify any distinctive features
potentially related to salt tolerance.
3. Results
Transmission electron microscopic examination of leaf
mesophyll
cells
from
salt-tolerant
Artemisia
marschalliana
revealed distinct structural features
within their nuclei, indicative of active metabolic states
and potential adaptations to saline conditions.
3.1. General Nuclear Morphology:
The nuclei in the mesophyll cells were typically spherical
to ovoid in shape, prominently located within the
cytoplasm, and often surrounded by chloroplasts and
vacuoles. The nuclear envelope appeared intact and
well-defined, consisting of inner and outer membranes
with clearly discernible nuclear pores, suggesting active
transport between the nucleoplasm and cytoplasm.
3.2. Chromatin Organization:
A notable feature was the organization of chromatin.
While both euchromatin (electron-lucent, dispersed
chromatin) and heterochromatin (electron-dense,
condensed chromatin) were present, euchromatin
appeared relatively abundant and widely dispersed
throughout the nucleoplasm. Heterochromatin was
primarily observed as small, condensed clumps
associated with the inner nuclear membrane and
scattered within the nucleoplasm. This relatively
decondensed chromatin state suggests a high level of
transcriptional activity, which is crucial for gene
expression and cellular responses.
3.3. Nucleolar Ultrastructure:
The nucleolus was a prominent and well-developed
organelle within the nucleus, typically appearing as a
single, large, and often irregularly shaped div. Its
internal organization was clearly differentiated into two
main components:
•
Fibrillar Centers (FCs): These appeared as pale,
electron-lucent regions, often surrounded by
the dense fibrillar component.
•
Dense Fibrillar Component (DFC): This was
observed as a highly electron-dense network
surrounding the fibrillar centers.
•
Granular Component (GC): This appeared as
numerous electron-dense granules, typically
located at the periphery of the nucleolus.
The distinct and well-organized appearance of the
nucleolus, particularly the prominent granular
component, indicates active ribosomal RNA (rRNA)
synthesis and ribosome biogenesis. This suggests a high
capacity for protein synthesis, which is essential for
cellular maintenance and stress response mechanisms.
3.4. Absence of Stress-Induced Degradation:
Crucially, there was no widespread evidence of nuclear
or DNA degradation, such as chromatin condensation
into large, irregular masses or fragmentation of the
nuclear envelope, which are often observed in salt-
sensitive plants subjected to severe salt stress [2]. The
integrity of the nuclear envelope and the organized
chromatin
structure
suggest
that
Artemisia
marschalliana is able to maintain nuclear homeostasis
under its salt-tolerant conditions.
These ultrastructural findings collectively point towards
a highly active and well-preserved nuclear machinery in
the mesophyll cells of
Artemisia marschalliana
, likely
contributing to its remarkable ability to tolerate high
salinity.
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4. DISCUSSION
The ultrastructural features of nuclei in leaf mesophyll
cells of
Artemisia marschalliana
provide compelling
insights into the cellular adaptations that underpin its
salt tolerance. The observed nuclear characteristics,
particularly the dispersed chromatin and the well-
developed nucleolus, suggest an active and robust
transcriptional and translational machinery, which is
crucial for coping with environmental stress.
The prevalence of euchromatin, indicative of actively
transcribed genes, implies that
Artemisia marschalliana
maintains a high level of gene expression even under
saline conditions. This contrasts with observations in
salt-sensitive plants, where severe salt stress can lead to
chromatin condensation and reduced transcriptional
activity, signaling cellular damage or programmed cell
death [2]. The ability to sustain active gene expression is
paramount for synthesizing stress-response proteins,
enzymes involved in ion homeostasis, and osmolytes
necessary for osmotic adjustment, all of which are vital
for salt tolerance [6].
The prominent and well-organized nucleolus, with its
distinct fibrillar and granular components, further
supports the notion of high metabolic activity. The
nucleolus is the primary site of ribosomal RNA (rRNA)
synthesis
and
ribosome
assembly,
processes
fundamental for protein synthesis. A well-developed
nucleolus suggests an efficient capacity for producing
the ribosomes required for the extensive protein
synthesis needed to manage salt stress, including the
production of transporters, detoxification enzymes, and
structural proteins [6]. This aligns with studies indicating
the importance of protein and nucleic acid metabolism
in plants under salinization [6].
The intact nuclear envelope and the absence of
widespread nuclear degradation or DNA fragmentation
are critical findings. In contrast, salt stress can induce
nuclear and DNA degradation in meristematic cells of
sensitive plants like barley [2]. The preservation of
nuclear integrity in
Artemisia marschalliana
highlights
its effective cellular defense mechanisms against salt-
induced damage, allowing the cell to maintain its genetic
stability and functional capacity. This resilience at the
nuclear level likely contributes significantly to the overall
salt tolerance of the plant.
These
ultrastructural
observations
complement
physiological and biochemical studies on halophytes.
The ability to maintain nuclear homeostasis and active
gene expression under saline conditions is a
fundamental adaptive trait. While this study provides
qualitative insights into nuclear morphology, future
research could benefit from quantitative analyses of
chromatin density, nucleolar volume, and nuclear pore
distribution under varying salt concentrations to
establish a more precise correlation with salt tolerance
levels. Furthermore, integrating these ultrastructural
findings with molecular studies (e.g., gene expression
profiling,
proteomics) could
provide
a
more
comprehensive understanding of the specific genes and
proteins regulated by this active nuclear machinery in
response to salinity.
5. CONCLUSION
This study provides a detailed ultrastructural analysis of
nuclei in leaf mesophyll cells of salt-tolerant
Artemisia
marschalliana
. Our findings demonstrate that these
nuclei exhibit characteristics indicative of high metabolic
activity and robust cellular maintenance under saline
conditions, including a dispersed chromatin pattern and
a well-developed, organized nucleolus. Crucially, the
absence of widespread nuclear degradation suggests
effective mechanisms for preserving nuclear integrity in
this halophytic species. These structural adaptations at
the nuclear level are likely fundamental to
Artemisia
marschalliana
's remarkable ability to tolerate high
salinity. The insights gained from this study contribute
to our understanding of the cellular and subcellular basis
of plant salt tolerance, providing valuable information
for future research aimed at enhancing crop resilience in
saline environments.
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https://doi.org/10.1093/jxb/48.3.693
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