Does boron affect hormone levels of barley cultivars? - EurAsian ...

INTRODUCTION
EurAsian Journal of BioSciences
Eurasia J Biosci 6, 113-120 (2012)
DOI:10.5053/ejobios.2012.6.0.14
Does boron affect hormone levels of barley
cultivars?
Muavviz Ayvaz 1*, Mesut Koyuncu 2, Avni Guven 3, Kurt V. Fagerstedt 4
1 Department of Agricultural Biotechnology, Faculty of Agriculture, Adnan Menderes University, Aydin, Turkey
2 Department of Biology, Faculty of Science and Letters, Gaziosmanpasa University, Tokat, Turkey
3 Department of Biology, Faculty of Science, Ege University, Izmir, Turkey
4 Department of Biosciences, Viikki Biocenter, University of Helsinki, Helsinki, Finland
*Corresponding author: mayvaz@yahoo.com
Abstract
Background: When mineral nutrients are present in excess or in inadequate amounts, their effects
can be severe in plants and can be considered as abiotic stress. In this study, we report how
hormonal levels in barley cultivars respond to the toxic effect of boron, an essential plant
micronutrient.
Materials and Methods: Two different barley (Hordeum vulgare) cultivars (Vamik Hoca and Efes 98)
were used as a study material. Boron was applied in three different concentrations (0, 10, 20 ppm)
to plants that had grown from seeds for four weeks. Plants were harvested, stem-root length and
stem-root dry-fresh weight content were determined. For further analysis, chlorophyll, total protein,
endogenic IAA and ABA content analyses were carried out.
Results: According to the data obtained, plant growth and development decreased with increasing
boron concentrations. With increasing boron concentrations, soluble total protein increased in both
cultivars. Boron application led to increased endogenic IAA content in both cultivars. 10 and 20 ppm
boron application led to increased endogenic ABA content in Vamik Hoca cultivar whereas
endogenic ABA content decreased in Efes 98. Absence of boron application led to increased
endogenic IAA and ABA content in both cultivars.
Conclusions: As a result, the response to boron is different in the two cultivars and Efes 98 may be
more resistant to the toxicity than Vamik Hoca cultivar.
Keywords: Abscisic acid, boron toxicity, Hordeum vulgare, indole acetic acid.
Abbreviations: IAA: Indole acetic acid; ABA: Abscisic acid; TLC: Thin Layer Chromatography; D: Absorbance
values; cv: cultivated variety; B: Boron.
Ayvaz M, Koyuncu M, Guven A, Fagerstedt KV (2012) Does boron affect hormone levels of barley
cultivars? Eurasia J Biosci 6: 113-120.
DOI:10.5053/ejobios.2012.6.0.14
Boron is an essential microelement for plant
growth and development (Warington 1923). On the
other hand toxicity and shortage range are very
narrow in plants (Çelik et al. 1998). Boron shortage
is widely known in soils around the world. On the
other hand toxicity is mostly seen on dry and semidry
regions thus limiting plant growth and causing
yield losses (Nable et al. 1997).
In Central Anatolia boron toxicity is a problem in
agricultural soils (Torun et al. 2002). Boron toxicity
has also been reported in South Australia, in
Mediterranean countries, in California and in Chile
(Aquea et al. 2012), causing yield losses in barley
(Cartwright et al. 1984). Boron functions as a crosslinker
for rhamnogalacturonan-II in the cell
membrane, and also as a component important for
© EurAsian Journal of BioSciences
structural cytoskeleton integrity in plants (O'Neill et
al. 2004). Plant species requiring higher boron are
also rich in the capacity to deposit it in their cell wall
(Marschner 1997). Since the detoxification
mechanism of excess boron is inadequate in plants,
metabolic disruptions evolve as boron binds to
ribose sugar of DNA and NAD + (Loomis and Durst
1992). The boron tolerance capacity of some species
such as barley, wheat, Medicago sp. and peas (Pisum
sativum L.) differ from one another because of their
genetic traits (Nable and Paull 1991, Paull et al.
1992, Karabal et al. 2003). In a study with different
plant species, it has been showed that differences in
boron uptake mechanism are regulated by genetic
traits of the species (Paull et al. 1988, Nable and
Received: October 2012
Accepted: November 2012
Printed: November 2012
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EurAsian Journal of BioSciences 6: 113-120 (2012)
Paull 1991, Bagheri et al. 1996, Jefferies et al. 1999).
Arabidopsis thaliana BOR1 was the first gene shown
to play a role in boron tolerance (Takano et al. 2002).
Parr and Loughman (1983) postulated many
functions for boron in plants in cell wall synthesis
and in cell wall structure, in membranes, in
lignification, in sugar transport, and in carbohydrate
and RNA metabolism. The effect may be through
boron involving in metabolic pathways directly or
through a cascade that is triggered similarly as is
known for the phytohormones. Although a possible
role of boron in auxin or indole-3-acetic acid (IAA)
metabolism was suggested as early as in 1940, the
interaction between boron and auxin has not been
clarified (Coke and Whittington 1968, Hirsch et al.
1982). Lambert et al. (1980) have suggested that in
plant roots boron fertilization leads to decreased
IAA oxidase activity and therefore increased IAA
content. According to Dugger (1983) IAA and IAA
oxidase levels changed in boron deficient
conditions: IAA oxidase activity decreased and IAA
increased (Bryant and Lane 1979, Paull et al. 1992).
On the other hand, abscisic acid (ABA) depresses
plant growth under many stress conditions such as
water deficiency, salt stress, and mineral nutrition
stress (Sharp and LeNoble 2002).
Mineral toxicity is a problem for some parts of
the Turkish soils, and therefore to find out the
physiological responses of plants to toxic mineral
stress is an important issue. In this paper we have
examined whether excess boron leads to a
significant change in IAA and ABA contents of two
different barley cultivars. Our aim is to shed light on
the physiological responses of barley cultivars under
excess boron stress.
In this study two different barley cultivars
(Hordeum vulgare L. cv. Efes 98 and Hordeum vulgare
L. cv. Vamik Hoca) were used as a material. Barley
seeds were soaked with distilled water and placed
on a rolled filter paper in vertical position and then
transferred to plastic pots.
The plants were divided into four groups, each
containing 5 replicate pots. Each group was irrigated
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MATERIALS AND METHODS
Ayvaz et al.
with a Hoagland solution containing 0, 10 and 20
ppm Boron (B) (boron treatments) for 4 w. The
experiment was performed in a controlled climate
room under the conditions of 24°C and photoperiod
of 18/8 h (day/night). Position of the pots was
rotated at random every 4 days during the
experiment to standardize the environmental
conditions. Plants were harvested and leaves were
used for determinations.
Fresh and dry weight, root length and shoot
height of the barley seedling were recorded. For dry
weight seedlings were oven dried at 80°C for 96 h.
Hormone (IAA and ABA) determination
Hormone (IAA and ABA) extraction method was
conducted as described by Scott and Jacobs (1964)
with modifications.
Barley leaves (5 g) was ground in 50 mL of cooled
methanol. After grinding, 5 mL distilled water and
BHT added and left at 0°C for 2 h. Extract was
filtered and evaporated under low pressure at 35°C.
25 mL distilled water added and pH was adjusted to
2.5-3 with 0.1N HCl. the acidic water phase hormone
extract was filtered again and anhydride sodium
sulfate was added and left in a cool, dark place for
overnight. Water-free ethyl acetate phase was
evaporated at 35°C. The residue was dissolved with
1 mL of methanol and was used for TLC.
Thin layer chromatography (TLC)
Extraction and purification of plant hormones
(IAA and ABA) in 1 mL of methanol acid phase was
conducted by Thin Layer Chromatography (TLC).
1 mL of methanol acid phase was applied on
20×20 cm, 0.5 mm Silica Gel 60254 covered TLC
plates with Hamilton micro syringe. Methanol
dissolved IAA and ABA were applied as reference.
TLC plates were run in isopropyl alcohol: ammonia:
distilled water (80:10:10 v/v/v) solution in the dark at
25°C and dried in cool air after the run.
Quantitative determination of IAA and ABA
extracts
IAA and ABA reference Rf value were detected
under 254 nm UV light. Silica gel on the TLC plate
were scraped and transferred into tubes according
to Rf values for the quantitative determination of
IAA and ABA. 5mL of methanol was added to the
tubes and left at for 1 h. After 1 h, extracts were

EurAsian Journal of BioSciences 6: 113-120 (2012)
filtered and filled with methanol to 5 mL volume.
Absorbance at 224 nm for IAA and 263 nm for
ABA was recorded with spectrophotometer.
Quantitative IAA and ABA in μg for 1 g of leaf weight
was calculated according to Yürekli et al. (1974).
Chlorophyll determination
Chlorophyll was extracted by homogenizing of
0.1 g fresh leaves in 10 mL of 80% acetone. After
filtering, extract fill up to 10 mL in volume, the
chlorophyll content was determined via a
spectrophotometer from the acetone extract at 654
nm and 663 nm, as described by Witham et al. (1971).
Absorbance values (D) at 654 nm and 663 nm
were placed in the equation below. Chlorophyll a, b
and total Chlorophyll content as mg in 1 gram of
plant tissue were calculated.
mg Chlorophyll a/g tissue= [12.7 (D663)–2.69 (D645)].(V/1000.Weight) mg Chlorophyll b/g tissue= [22.9 (D645)–4.68 (D 663)].(V/1000. Weight)
mg total Chlorophyll/g tissue= [20.2 (D645)+8.02 (D663)].(V/1000. Weight)
Carotenoid determination
Carotenoid content was determined from the
acetone extract at 450 nm as described by Witham
et al. (1971) via a spectrophotometer. Absorbance
value (D) at 450 nm was placed in the below
equation. Carotenoid contents as mg in 1 g of plant
tissue were calculated.
mg Total carotenoid/g tissue= 4.07 × (D645) –[(0.0435 × Kla amount)+(0.367 × Klb amount)]
Protein determination
Protein concentration was evaluated by the
method of Bradford (1976) using bovine serum
albumin as a standard.
RESULTS
Hordeum vulgare cv. Vamik Hoca and cv. Efes 98
cultivated in 0, 10 and 20 ppm boron concentration
were harvested after 4 w. According to our results;
root length and shoot height of excess boron
applied to Efes 98 and Vamik Hoca cultivars
decreased with increasing boron (Table 1).
Increasing boron conditions led to decreased fresh
Ayvaz et al.
weight in both cultivars compared to control plants.
In both cultivars under boron deficient conditions,
fresh weight did not change compared to control. In
both cultivars dry weight did not change
significantly among different groups except at 20
ppm group (Table 2).
Endogenous ABA content of the cv. Vamik Hoca
leaves increased with increasing boron
concentrations. However, Vamik Hoca cultivar plants
grown in boron deficient conditions had 69% more
IAA and 93% more ABA compared to control. On the
other hand, boron-deficient plants had 54% more
IAA and 72% more ABA when compared with 10 ppm
boron application, whereas Efes 98 cultivar grown in
the absence of boron had a 64% increase in the
content of IAA and 72% in ABA compared to the
control group. When both boron deficient plants
were compared, Efes 98 had 17% more IAA and 17%
less ABA. Control group of Efes 98 had 17% more
IAA and 71% more ABA than Vamik Hoca cultivar. 10
ppm boron applied to Efes 98 resulted in 33% more
IAA and %59 less ABA than in Vamik Hoca cultivar. In
20 ppm boron application groups, there seems no
difference in the amount of IAA, while Efes 98
cultivar contained 66% less ABA than Vamik Hoca
cultivar.
In the boron deficient application group of both
cultivars, endogenic IAA levels were higher than in
the boron applied groups. Also in ABA, boron
deficient application groups had more hormone
than in the excess boron applied groups (Table 3).
Plants grown in boron deficient conditions had
higher chlorophyll a, chlorophyll b and total
chlorophyll content than plants grown in control and
excess boron conditions. On the other hand, in both
cultivars increasing boron concentration gave rise to
significant reduction in chlorophyll pigment levels.
In boron deficient conditions, Efes 98 cultivar
contained 14% more chlorophyll a, 20% more
chlorophyll b and 16% more total chlorophyll
pigment than Vamik Hoca cultivar.
In control group plants, Efes 98 contained nearly
15% more chlorophyll pigment than Vamik Hoca
cultivar. With 10 ppm boron application, 10% more
chlorophyll a, chlorophyll b and total chlorophyll was
detected in Efes 98 than in Vamik Hoca cultivar. On
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EurAsian Journal of BioSciences 6: 113-120 (2012)
Table 1. Root length and shoot height of barley cultivars grown under different boron concentrations.
± standart error, values are in centimeter (cm), cv: cultivated variety, B: boron
Table 2. Fresh and dry weight of barley cultivars grown under different boron concentrations.
± standart error, values are in grams (g), cv: cultivated variety, B: boron
the other hand, with 20 ppm boron application,
there was no difference in the amount of chlorophyll
b among cultivars, whereas 24% more chlorophyll a
and 17% more total chlorophyll was observed in
Vamik Hoca than in Efes 98 cultivar (Table 4 and 5).
When carotenoid pigment values were examined,
in both barley cultivars boron deficient plants had
higher carotenoid compared to excess boron applied
groups. In general, increasing boron led to a
reduction in the amount of carotenoid pigment
(Table 5).
Total protein levels were elevated in excess and
in deficient groups of both cultivars when compared
to control group. Accordingly, 10 and 20 ppm boron
application led to increase in total protein levels in
both Efes 98 and Vamik Hoca cultivar. In addition,
Efes 98 cultivar was found to have higher total
protein content than Vamik Hoca cultivar (Table 6).
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Ayvaz et al.
Table 3. Indole acetic acid and abscisic acid content of different barley cultivars grown under different boron
concentrations.
values are in (μg/g) tissue, cv: cultivated variety, B: boron
DISCUSSION
One of the symptoms of boron toxicity is
inhibition of root growth (Nable 1988, Reid et al.
2004, Choi et al. 2007). Toxicity also causes yield
losses in barley (Cartwright et al. 1984). In a study of
optimizing growth conditions for Brassica oleracea, 1
ppm boron applied plants had the maximum fresh
weight (Shelp and Shattuck 1987). On the other
hand, plants grown in boron deficient conditions did
not show any negative effect on vegetative growth,
whereas plants faced problems in reproductive parts
(Mozafar 1993). According to our results, root length
and shoot height of excess boron applied Efes 98
and Vamik Hoca cultivars decreased with increasing
boron. In both cultivars under boron deficient
conditions, fresh weight did not change compared to
control. Therefore, our results are in line with the
above literature showing increasing boron
concentration led to decreased fresh weight in both

EurAsian Journal of BioSciences 6: 113-120 (2012)
Table 4. Chlorophyll a, chlorophyll b content of barley cultivar leaves grown under different boron concentrations.
Values are in (mg/g) Fresh Weight, cv: cultivated variety, B: boron
cultivars.
Triticum durum Desf. grown under boron
deficiency led to increased IAA content and it
tended to decrease with increasing boron
concentrations (Gemici et al. 2002). In sunflower
(Helianthus annuus L.) IAA content decreased under
boron stress in comparison to the control plants
(Akçam-Oluk and Demiray 2004). According to
Dugger (1983) IAA and IAA oxidase levels changed in
boron deficient conditions: IAA oxidase activity
decreased and IAA contrarily increased (Paull et al.
1992, Bryant and Lane 1979). Under boron deficient
conditions, chlorogenic and caffeic acids accumulate
and this inhibits IAA oxidase activity, leading to auxin
accumulation in the plant tissue (Gupta 2006). In our
study, both cultivars of boron deficient group had
higher endogenic IAA levels than boron applied
groups. Our results are consistent with previous
studies indicating that in excess boron conditions,
Ayvaz et al.
Table 5. Carotenoid and total chlorophyll content of barley cultivar leaves grown under different boron concentrations.
Values are in (mg/g) Fresh Weight, cv: cultivated variety, B: boron
Table 6. Total protein content of barley cultivars grown
under different boron concentrations.
Values are in (mg/mL), cv: cultivated variety, B: boron
IAA oxidase activity may be decreased and IAA
contrarily increased.
ABA is a hormone that regulates stomatal closure
in plants, and hence, reduces water loss via
transpiration (Harris and Outlaw 1991). ABA also
limits shoot growth (Creelman et al. 1990) and leaf
area expansion (Van Volkenburgh and Davies 1983).
In contrast, ABA stimulates root growth (Sharp et al.
1994). In a study with carrot (Daucus carota L.) root
callus under boron stress, ABA content increased
(Demiray and Dereboylu 2006). Our results showed
that boron deficient application groups had higher
hormone content than excess boron applied groups.
When the cultivars were compared for their
endogenic hormone levels, Efes 98 was slightly
higher in quantity which may be a hereditary trait. In
accordance with earlier investigations, boron stress
led to increased endogenous ABA content in our
study.
In a study with barley cultivars under excess
boron, protein content increased, and some toxicity
related proteins were identified (Mahboobi et al.
2000). In our study total protein levels increased in
excess and deficient groups of both cultivars when
compared to control. Our results were in line with
the previous studies.
As a result, barley plants cultivated for 4 w under
boron toxic and deficient conditions showed that
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EurAsian Journal of BioSciences 6: 113-120 (2012)
boron concentrations led to severe damage, yield
losses and changes in hormone and chlorophyll
contents in both cultivars. We concluded that the
118
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Bor, Arpa Çeşitlerinde Hormon Miktarlarını Etkiler mi?
120
Ayvaz et al.
Özet:
Giriş: Mineral besleme elementlerinin fazla yada yetersiz olması bitkilerde ciddi sonuçlara neden olabilen abiyotik
stres olarak tanımlanır. Bu çalışmada bitkiler için gerekli bir element olan borun fazlalığı ve yokluğunda, arpa
çeşitlerindeki hormonal değişim yanıtları çalışılmıştır.
Materyal ve Metot: İki farklı arpa (Hordeum vulgare) çeşidi (Vamık Hoca ve Efes 98) çalışma materyali olarak
kullanılmıştır. Bor üç farklı konsantrasyonda (0, 10, 20 ppm) tohumdan 4 hafta boyunca yetiştilen bitkilere
uygulanmıştır. Bitkiler hasat edilerek, gövde-kök boyu, gövde-kök yaş-kuru ağırlıkları tespit edilmiştir. Daha sonra
klorofil, toplam protein, endogen İAA ve ABA miktar analizleri gerçekleştirilmiştir.
Bulgular: Elde edilen sonuçlara gore, bitki büyüme ve gelişmesi artan bor konsantrasyonlarında azalmıştır. Artan bor
konsantrasyonunda çözülebilen toplam protein miktarı her iki çeşitte artmıştır. Bor uygulaması endogen İAA
miktarının artışına neden olmuştur. 10 ve 20 ppm bor uygulaması Vamık Hoca çeşitinde ABA miktarı artışına, diğer
yandan Efes 98 çeşitinde ise endogen ABA miktarı azalışına neden olmuştur Bor yokluğundaki uygulamada ise her iki
çeşittede endogen İAA ve ABA miktarları artış göstermiştir.
Sonuç: Bor’a olan tepki her iki çeşitte farklıdır. Toksisite yönünden Efes 98 çeşiti, Vamık Hoca çeşitinden daha dayanıklı
olabilir.
Anahtar Kelimeler: Absisik asit, bor toksistesi, Hordeum vulgare, indol asetik asit.