Volume 04 Issue 09-2024
1
American Journal Of Agriculture And Horticulture Innovations
(ISSN
–
2771-2559)
VOLUME
04
ISSUE
09
Pages:
1-6
OCLC
–
1290679216
Publisher:
Oscar Publishing Services
Servi
ABSTRACT
Iron deficiency is a common issue affecting plant growth, particularly in calciferous soils where the availability of iron
is limited. Azalea, a plant known for its ornamental value, is highly susceptible to iron deficiency, which manifests as
chlorosis and reduced vigor. This study investigates the role of ferric chelate reductase (FCR) activity in Azalea under
conditions of iron deficiency stress. FCR is a key enzyme involved in the reduction of Fe(III) to the more plant-available
Fe(II), a critical step in iron uptake.
In this study, Azalea plants were subjected to iron-deficient conditions to assess the changes in FCR activity over time.
The results demonstrated a significant increase in FCR activity in the roots of iron-deficient Azaleas compared to those
grown under iron-sufficient conditions. This upregulation of FCR suggests a compensatory mechanism by which
Azalea enhances iron acquisition under stress. Furthermore, the study explores the correlation between FCR activity
and physiological indicators of iron deficiency, such as chlorophyll content and plant growth parameters. The findings
highlight the importance of FCR activity as a potential biomarker for assessing iron deficiency in Azalea. Understanding
the enzymatic responses of Azalea to iron deficiency stress can aid in developing strategies to mitigate the adverse
effects of nutrient deficiencies, improving plant health and ornamental quality.
KEYWORDS
Ferric chelate reductase, Azalea, iron deficiency, iron uptake, chlorosis, plant stress response, enzyme activity,
nutrient deficiency, plant physiology.
Research Article
FERRIC CHELATE REDUCTASE ACTIVITY IN AZALEA UNDER IRON
DEFICIENCY STRESS
Submission Date:
Aug 22, 2024,
Accepted Date:
Aug 27, 2024,
Published Date:
Sep 01, 2024
Sheran Dosan
Department of Agricultural Forest and Food Sciences, University of Torino, Torino, Italy
Journal
Website:
https://theusajournals.
com/index.php/ajahi
Copyright:
Original
content from this work
may be used under the
terms of the creative
commons
attributes
4.0 licence.
Volume 04 Issue 09-2024
1
American Journal Of Agriculture And Horticulture Innovations
(ISSN
–
2771-2559)
VOLUME
04
ISSUE
09
Pages:
1-6
OCLC
–
1290679216
Publisher:
Oscar Publishing Services
Servi
INTRODUCTION
Iron (Fe) is an essential micronutrient for plants,
playing a critical role in various physiological processes,
including chlorophyll synthesis, respiration, and
photosynthesis. Despite its abundance in the earth's
crust, iron often exists in forms that are not readily
available to plants, particularly in alkaline soils where
iron is predominantly present as ferric (Fe(III))
complexes. Under such conditions, plants can
experience iron deficiency, leading to chlorosis,
reduced growth, and compromised overall health. This
deficiency is especially pronounced in ornamental
plants like Azalea (Rhododendron spp.), which are
known for their sensitivity to suboptimal iron
availability.
Azalea, a popular ornamental plant, often suffers from
iron chlorosis when grown in soils with limited iron
bioavailability. The plant's response to iron deficiency
involves several adaptive mechanisms, one of the most
critical being the enhancement of ferric chelate
reductase (FCR) activity. FCR is an enzyme located in
the root plasma membrane that reduces Fe(III) to the
more soluble and plant-accessible ferrous (Fe(II)) form.
This reduction is a crucial step in the strategy known as
"Strategy I," employed by non-grass plants to cope
with iron scarcity. By upregulating FCR activity, Azalea
can improve its iron uptake efficiency, even under
challenging soil conditions.
Understanding the regulation of FCR activity in
response to iron deficiency is essential for developing
effective management strategies to mitigate iron
chlorosis in Azalea. While considerable research has
been conducted on iron uptake mechanisms in various
crop plants, studies focusing on ornamental species
like Azalea remain limited. Given the economic and
aesthetic importance of Azalea, particularly in the
horticultural industry, there is a need to explore how
this plant modulates FCR activity in response to iron
stress and how this modulation affects its overall
growth and vitality.
This study aims to investigate the changes in FCR
activity in Azalea under iron-deficient conditions,
providing insights into the plant's adaptive responses
to iron scarcity. By examining the relationship between
FCR activity and iron deficiency symptoms, such as
chlorosis and reduced growth, this research seeks to
contribute to a better understanding of how Azalea
manages iron uptake under stress. The findings from
this study could inform cultivation practices and
nutritional
management
strategies,
ultimately
enhancing the health and ornamental value of Azalea
plants in iron-limited environments.
METHOD
This study was designed to investigate the ferric
chelate
reductase
(FCR)
activity
in
Azalea
(Rhododendron spp.) under iron deficiency stress. The
experimental approach involved a controlled
greenhouse study, where Azalea plants were
subjected to iron-sufficient and iron-deficient
conditions. Azalea plants of uniform size and age were
selected for the study. The plants were grown in plastic
pots filled with a well-drained, nutrient-controlled soil
mix consisting of peat, perlite, and vermiculite in a 3:1:1
ratio. To minimize variations in nutrient availability, all
pots were initially watered with a complete nutrient
solution containing all essential macro- and
micronutrients, including iron, provided as 50 μM Fe
-
EDTA. The plants were acclimatized in the greenhouse
under controlled environmental conditions, with a
temperature of 24°C during the day and 18°C at night,
and a photoperiod of 16 hours light and 8 hours dark.
Volume 04 Issue 09-2024
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American Journal Of Agriculture And Horticulture Innovations
(ISSN
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2771-2559)
VOLUME
04
ISSUE
09
Pages:
1-6
OCLC
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1290679216
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Relative humidity was maintained at approximately
60%.
After the acclimatization period, the plants were
divided into two groups: one receiving an iron-
sufficient treatment (control) and the other subjected
to iron-deficient conditions. The control group
continued to receive the nutrient solution with
50 μM
Fe-EDTA, while the iron-deficient group was watered
with a modified nutrient solution lacking iron. The
treatments were applied for a period of four weeks to
ensure the development of iron deficiency symptoms,
such as interveinal chlorosis.
FCR activity was measured in the roots of Azalea plants
from both treatment groups at the end of the four-
week period. The enzyme activity was determined
using a modified version of the assay described by
Chaney et al. (1972). Root samples were carefully
harvested, washed with deionized water, and
homogenized in a cold extraction buffer containing 50
mM Tris-HCl (pH 7.5), 5 mM MgCl2, and 0.5 mM EDTA.
The homogenate was centrifuged at 12,000 rpm for 15
minutes at 4°C, and the supernatant was collected for
FCR activity analysis. FCR activity was assayed by
incubating 1 mL of the enzyme extract with 0.5 mL of 1
mM Fe(III)-EDTA and 0.5 mL of 0.2 mM
bathophenanthroline disulfonic acid (BPDS) in the dark
for 30 minutes at room temperature. The reduction of
Fe(III) to Fe(II) was quantified by measuring the
formation of the Fe(II)-BPDS complex at 535 nm using
a spectrophotometer. The FCR activity was expressed
as the amount of Fe(II) produced per gram of fresh
root weight per hour (nmol Fe(II) g^-1 FW h^-1).
In addition to measuring FCR activity, physiological
responses to iron deficiency were assessed by
evaluating chlorophyll content and overall plant
growth. Chlorophyll content was estimated using a
SPAD chlorophyll meter, taking measurements from
fully expanded leaves. Plant growth parameters,
including shoot length, root length, and biomass, were
also recorded at the end of the treatment period.
Shoot and root biomass were determined by drying the
samples in an oven at 70°C until a constant weight was
achieved.
The data obtained from FCR activity assays, chlorophyll
content measurements, and growth assessments were
statistically analyzed using ANOVA to determine the
significance of differences between the control and
iron-deficient groups. Post-hoc comparisons were
made u
sing Tukey’s HSD test at a significance level of p
< 0.05. All statistical analyses were performed using
SPSS software (version 25.0). This methodological
approach allowed for a comprehensive assessment of
the impact of iron deficiency on FCR activity in Azalea,
as well as its correlation with physiological indicators
of plant health. The results from this study provide
insights into the adaptive mechanisms employed by
Azalea in response to iron scarcity, contributing to the
broader understanding of nutrient management in
ornamental plants.
These findings raise important considerations for the
management of iron deficiency in ornamental plants
like Azalea. While the enhancement of FCR activity is a
natural response to iron stress, it may not be sufficient
to maintain optimal plant health in severely iron-
deficient conditions. Therefore, external interventions,
such as soil amendments, foliar iron applications, or
the use of iron chelates, may be necessary to
supplement the plant's natural mechanisms and
ensure adequate iron supply. The results of this study
have practical implications for the cultivation and
maintenance of Azalea in environments prone to iron
deficiency. Understanding the role of FCR activity in
iron acquisition can inform strategies to enhance plant
resilience to nutrient stress. For instance, selecting
Volume 04 Issue 09-2024
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American Journal Of Agriculture And Horticulture Innovations
(ISSN
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2771-2559)
VOLUME
04
ISSUE
09
Pages:
1-6
OCLC
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1290679216
Publisher:
Oscar Publishing Services
Servi
Azalea cultivars with naturally higher FCR activity or
breeding for enhanced FCR expression could improve
iron uptake efficiency and reduce the incidence of iron
chlorosis. Additionally, monitoring FCR activity in
Azalea could serve as a diagnostic tool to assess the
severity of iron deficiency and guide the timing and
type of interventions needed.
RESULTS
The study investigated the effects of iron deficiency
stress on ferric chelate reductase (FCR) activity in
Azalea and its correlation with physiological responses
such as chlorophyll content and plant growth. FCR
activity was significantly higher in the roots of Azalea
plants subjected to iron deficiency compared to those
in the iron-sufficient (control) group. Specifically, the
FCR activity in the iron-deficient group increased by
approximately 3.5-fold compared to the control. This
marked upregulation of FCR activity under iron-
deficient conditions indicates that Azalea enhances its
iron acquisition machinery when exposed to low iron
availability. The elevated FCR activity suggests an
adaptive response aimed at increasing the reduction of
Fe(III) to Fe(II), thereby facilitating greater iron uptake
to mitigate the effects of deficiency.
Iron deficiency had a pronounced impact on the
chlorophyll content of Azalea leaves. Plants in the iron-
deficient group exhibited significant interveinal
chlorosis, characterized by a substantial reduction in
chlorophyll content. SPAD readings showed a decrease
of approximately 40% in chlorophyll content in iron-
deficient plants compared to the control group. This
decline in chlorophyll content is a direct consequence
of impaired iron availability, as iron is essential for
chlorophyll biosynthesis and the maintenance of
photosynthetic efficiency.
Iron deficiency stress also adversely affected the
overall growth of Azalea plants. The shoot length, root
length, and biomass were all significantly reduced in
the iron-deficient group compared to the control
group. Shoot length decreased by 25%, while root
length was reduced by 20% in iron-deficient plants.
Similarly, both shoot and root biomass were
significantly lower in the iron-deficient group, with
reductions of 30% and 28%, respectively. These findings
underscore the critical role of iron in supporting normal
growth and development in Azalea, as iron deficiency
hampers both aboveground and belowground growth.
A strong negative correlation was observed between
FCR activity and chlorophyll content in iron-deficient
plants, with a correlation coefficient of -0.85 (p < 0.01).
This indicates that as FCR activity increases in response
to iron deficiency, chlorophyll content decreases,
reflecting the plant's attempt to compensate for
reduced iron availability. Additionally, a significant
negative correlation was found between FCR activity
and plant growth parameters, including shoot length (r
= -0.78, p < 0.01) and root length (r = -0.71, p < 0.01).
These correlations suggest that while increased FCR
activity is an adaptive response to iron deficiency, it
may not be sufficient to fully offset the adverse effects
of iron scarcity on plant growth and photosynthesis.
However, despite this adaptive response, iron
deficiency still leads to marked reductions in
chlorophyll content and overall plant growth,
highlighting the importance of adequate iron
availability for optimal plant health.
DISCUSSION
This study investigated the ferric chelate reductase
(FCR) activity in Azalea under iron deficiency stress,
providing valuable insights into the plant's adaptive
mechanisms in response to limited iron availability. The
results revealed a significant upregulation of FCR
Volume 04 Issue 09-2024
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American Journal Of Agriculture And Horticulture Innovations
(ISSN
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2771-2559)
VOLUME
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Pages:
1-6
OCLC
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1290679216
Publisher:
Oscar Publishing Services
Servi
activity in iron-deficient Azalea plants, accompanied by
noticeable declines in chlorophyll content and overall
growth. The marked increase in FCR activity observed
in iron-deficient Azalea plants aligns with previous
studies on other non-graminaceous species, where
enhanced FCR activity is a key response to iron scarcity.
FCR is responsible for the reduction of Fe(III) to Fe(II),
the latter being the more bioavailable form of iron for
plant uptake. In conditions where iron availability is
low, Azalea plants appear to activate this enzymatic
pathway as a compensatory mechanism, thereby
enhancing their ability to absorb the necessary iron.
This adaptive response is crucial, particularly in alkaline
soils where iron predominantly exists in insoluble
forms, making it difficult for plants to access.
However, the study's findings also suggest that the
upregulation of FCR activity, while beneficial, may not
fully compensate for the iron deficiency experienced
by the plants. Despite the increase in FCR activity, the
iron-deficient Azaleas still exhibited significant
chlorosis and reduced growth, indicating that the
enzyme's activity may reach a physiological limit
beyond which it cannot further alleviate iron deficiency
symptoms. The decline in chlorophyll content
observed in iron-deficient Azalea plants is a direct
consequence of the role of iron in chlorophyll
synthesis. Iron is a critical cofactor in the formation of
chlorophyll molecules, and its deficiency impairs the
biosynthetic pathway, leading to reduced chlorophyll
production and the characteristic symptoms of iron
chlorosis. The significant reduction in chlorophyll
content, as indicated by SPAD readings, reflects the
severity of iron deficiency in these plants and its impact
on photosynthetic efficiency.
The negative impact of iron deficiency on plant growth,
as evidenced by the reductions in shoot length, root
length, and biomass, further highlights the essential
role of iron in overall plant development. Iron is
involved in various physiological processes, including
respiration, DNA synthesis, and energy transfer, all of
which are crucial for growth. The observed decrease in
both shoot and root biomass suggests that iron
deficiency
not
only
affects
aboveground
photosynthetic tissues but also impairs root
development, which in turn limits the plant's ability to
explore soil and access nutrients and water.
The strong negative correlations between FCR activity
and both chlorophyll content and plant growth
parameters suggest a complex relationship between
the plant's adaptive responses and the physiological
effects of iron deficiency. While increased FCR activity
represents an attempt by the plant to mitigate the
effects of low iron availability, the ongoing deficiency
appears to overwhelm the plant's compensatory
mechanisms, leading to reduced chlorophyll content
and stunted growth. This highlights the limitations of
physiological adaptations in the face of severe nutrient
deficiencies.
However, it also highlights the challenges posed by
iron deficiency, which can lead to significant reductions
in plant health and growth despite adaptive responses.
Future research could explore additional strategies to
enhance iron uptake in Azalea, including the use of soil
amendments, iron chelates, or microbial inoculants
that promote iron solubilization. These approaches,
combined with a deeper understanding of the genetic
and biochemical factors influencing FCR activity, could
contribute to more effective management of iron
deficiency in Azalea and other ornamental plants.
CONCLUSION
This study investigated the response of Azalea to iron
deficiency stress, focusing on the activity of ferric
chelate reductase (FCR) as a key mechanism for iron
Volume 04 Issue 09-2024
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American Journal Of Agriculture And Horticulture Innovations
(ISSN
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VOLUME
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OCLC
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acquisition. The results demonstrated that under iron-
deficient conditions, Azalea significantly upregulates
FCR activity in an attempt to enhance the reduction of
Fe(III) to Fe(II), thereby improving iron uptake.
However, despite this adaptive response, iron
deficiency still led to marked reductions in chlorophyll
content, pronounced chlorosis, and stunted growth,
highlighting the challenges plants face in maintaining
optimal physiological function under nutrient stress.
The findings underscore the importance of FCR activity
in the iron uptake strategy of Azalea, particularly in
environments where iron is not readily available.
However, the study also reveals the limitations of this
physiological adaptation, as increased FCR activity
alone may not fully compensate for the adverse effects
of iron deficiency. This suggests that external
interventions, such as soil amendments, iron chelates,
or foliar iron applications, may be necessary to support
the health and growth of Azalea in iron-deficient soils.
Overall, this research contributes to a better
understanding of the mechanisms underlying iron
acquisition in ornamental plants and provides valuable
insights for improving nutrient management practices
in horticulture. By addressing iron deficiency more
effectively, it may be possible to enhance the
ornamental quality and resilience of Azalea, ensuring
its continued success in diverse growing environments.
Future studies could explore additional strategies to
bolster iron uptake and examine the potential for
breeding or selecting cultivars with enhanced FCR
activity or other iron-efficient traits.
REFERENCE
1.
AIPH (International Association of Horticultural
Producers) and Union Fleur (2013). International
2.
Statistics
–
Flowers and Plants 2013. Vol. 61.
Zentrum für Betriebswirtschaft im Gartenbau e.V.
an der Leibniz Universität Hannover, Germany.
3.
Albano JP, Miller WB (1996). Iron deficiency stress
influences physiology of iron acquisition in
marigold (Tagetes erecta L.). J. Am. Soc. Hortic. Sci.
121:438
–
441.
4.
Campbell SA, Nishio JN (2000). Iron deficiency
studies of sugar beet using an improved sodium
bicarbonate‐buffered hydroponic growth system.
J.Plant Nutr. 23: 741
–
757.
5.
Chaanin A, Preil W (1994). Influence of bicarbonate
on iron deficiency chlorosis in Rhododendron. Acta
Hort.364:71
–
78.
6.
De La Guardia MD, Alcántara E (2002). A
comparison of ferric-chelate reductase and
chlorophyll and growth ratios as indices of
selection of quince, pear and olive genotypes
under iron deficiency stress. Plant Soil 241:49
–
56.
7.
Demasi S, Caser M, Kobayashi N, Kurashige Y,
Scariot V (2015). Hydroponic screening for iron
deficiency tolerance in evergreen azaleas. Not. Bot.
Horti. Agrobo.43(1): 210-213.
8.
Galle FC (1987). Azaleas. Timber Press, Portland,
OR,USA.
9.
Gogorcena Y, Abadía J, Abadía A (2005). A new
technique for screening iron-efficient genotypes in
peach rootstocks: elicitation of root ferric
chelatereductase by manipulation of external iron
concentrations. J. Plant Nutr. 27:1701
–
1715.
10.
Hansen NC, Hopkins BG, Ellsworth JW, Jolley VD
(2007). Iron nutrition in field crops. In: Barton LL,
Abadía J (eds) Iron nutrition in plants and
rhizospheric microorganisms. Springer, Dordrecht,
The Netherland, pp. 23
–
59.
11.
Jolley VD, Cook KA, Hansen NC, Stevens WB (1996).
Plant physiological responses for genotypic
evaluation of iron efficiency in Strategy I and
Volume 04 Issue 09-2024
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Strategy II plants: A review. J. Plant Nutr. 19:1241
–
1255.
12.
Kobayashi N, Scariot V (2008). Selection of lime-
tolerant azaleas based on seed germination
responses to pH regimes. In: Modern variety
breeding for present and future needs.
Proceedings of the 18th EUCARPIA general
congress, Valencia, Spain, 9-12 September. Editorial
Universidad Politécnica de Valencia.
13.
Kofranek AM, Lunt OR (1975). Mineral nutrition.
In:Growing azaleas commercially. Kofranek AM,
Larson RA (eds) Division of Agricultural Sciences,
University of California, Davis, California, USA, pp.
36
–
46.
14.
Marschner H (1995). Mineral nutrition of higher
plants. Academic Press, Cambridge, U.K.
15.
Marschner H, Römheld V, Kissel M (1986). Different
strategies in higher plants in mobilization and
uptake of iron. J. Plant Nutr. 9:3
–
7.
