1. , r':-f '
BIOJOURNAL, VOL. 11 NO. 1 & 2, T55-160 JUNE & DECEMBER, lggg
ESTIMATION OF PHYTOHORMONES IN NORMAL
AND INFECTED ONION LEAVES BY
ALTERNARIA CEPTILAE
B. Annadurai and D. B. Moilag1
Department of Biochemistry and Molecular Biology, University of Madra, Madras- 600 025
ABSTRACT
Auxin content, which has a maior role in disease resistance, was estimated in normal
as wellas in infected onion leaves. Auxin content in normal leaves slowly decreases when
the groMh advances. ln diseased onion leaves, the auxin content in the lesion area increases
till the 16th day after inoculation and decreases thereafter.The effect of f ive phytohormones
on the mycelial growth of A. cepulae in the culture medium and on the activity of endo pG
was examined in 100-ppm concentration of Naphthalene acetic acid. lndole butyric Acid
and lndole acetic acid showed inhibitory effect on pectic enzymes. Effect of phytohormones
in disease resistance and hyperauxiny due to pathogenesisis discussed.
INTRODUCTION
Phytohormones occur in traces and are constantly maintained at low level by the plants
(Albersheim et.al, 1959, Bateman, 1966 and Cooper !t.at, tszs;.This constani levet of a
phytohormone is disturbed by different factors.The chief one is infection. During infection
phytohormones either directly or indirectly prevent the action of the parasites.
The phytohormones may also counter the various physiological manifestations
triggered by parasites. Guiscafre-Arillago,1949a reported that2-4aicnloro phenoxy Acetic
acid (2,4D) inhibited directly the growth ot Penicillium dicitatum and phomopsis citri.
It was reported that in several plant diseases. Phytohormones and phenols inhibit the
activity ol cellwall degrading enzymes (Dekkar, 1g63, Desai et.al., 1974, Dubey et.al. 1976
and Fehrman et.al. 1967)- Bateman (1966) suggested that the phytohormones have a rote in
disease resistance- sanderson (1965) reported that the o*ioition producls of phenolic
compounds also act as enzyme inhibitors. Plant pathologists have been trying to control
the plant diseases with the help of various phytohormones (Guiscatre-Rrilllgo, tg49u,
Hancock et.al, 1964 and Jacobs, 1979). Oku and Nakanishi (1962) reported that lnd-ole Acetic
Acid sprayed on rice plants stimulated phytoalexin synthesis. Fehrman and Dimond (1967)
reported that lndole Acetic Acid trated Potato tubers and their phenol levels increased.The
higher concentration of auxin influenced the phytoalexin production in the tissue cultures
ot Phaseolus vulgaris.
Department of Botany and Biochemistry, c. Abdul Hakeem colleg;, M;lv[haram_
632509, Vellore District, Tamilnadu.
1.
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2. ANNADIJRAI AND MOTLAG
Garg and Mehrotra ('lgr7)reported that gibberellin suppresses the activity of cellulases
and polygalacturonase ol Fusarium sotanif pisr. Mehta and Mehta (1979) observed that GA
inhibited polygalacturonases, pectin trans eliminase and pectin methylesterase' Dekker
(1963) oOservea that kinetin inhibited the development of powdery midew' ln this paper the
auxin levels in normal and diseased levels estimated'The effect of phytohormones on crude
enzyme preparation and on purified EPG was studied'
i nuxtN coNTENT lN NoR..,iAL otllott
LEAVE6
?50
150
100
50
.0
4 Days I days 12 dalrs 16 daYs 20 daYs
AGE OF LEAVES
I
The Fungus
lsolates ol Alternaria cepulaeobtained from the diseased onion leaves were used for
the interaction study.
Estimation of auxin
The auxin content was estimated by adopting the methods of Mahadevan and sridhar
(1e82).
Effect of PhYtohormones on endoPc
1ml of the purified enzyme (7-ml/ml w/v) was incubated with equal volume of 10 ppm,
and 100-ppm concentration of lndole Acetic Acid. !ndole Butyric Acid. Naphthalene Acetic
Acid, GA and Kinetin 0.5 ml of the incubated enzyme was tested for reducing sugar by the
methods of Nelson (1941) and Somogyi(1952)'
Estimation of endoPG activitY
EPG activity was estimated using the Nelson (1944) and Sonnogyi (1952) method'
RESULTS AND DTSCUSSION
Estimation of auxin content in normal onion Ieaves is shown inTable 1.The auxin
content was maximum on 4th day while it slowly decreases'from the 8th day onwards'
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3. BIOJOURNAL, JUNE & DECEMBEB,1999
Table - 1
Estimation of auxin content in normal onion leaves :
Auxin contents Significance
Sl.No. Age of Leaves
1.
2.
3.
4.
5.
4 days 5
8 daYs 5
12 days 5
16 days 5
200.25 x,12-24
80.50 t 4.50
56.75 t 4.11
28.25 t3.43
4.50 t 1.10
++
++
++
++
++
Values expressed are the mean values 6 SD
d.f. = Degrees of freedom = n' 1 observation
Auxin content is expressed as pgof IAA present in one mlof ethanolextract as assessed
Table - 2
from standard IAA graPh.
AUXIN CONTENT tN LEAFBLIGHT AREA
300
250
200
150
100
50
0
I
I
I
l=su.l
TE
z
o
aul
J
z
F
zUJ
F
z
o
o
2
=f
E:l-l
"r.""o$t*".""*.,S"*"oSu*C
DAYS AFTER TNOCULATICN
Estimation of auxin content in leafblight area of onion leaves affected by A' cepulae
Sl.No. Age of Leaves
inoculation
Auxin content in lesion
area Per ml 6 SD
Significance
1.
2.
3.
4.
5.
6.
4 days
8 daYs
12 days
16 daYs
20 daYs
24 daYs
5
5
5
5
5
5
50.2566.53
120.5068.18
170.7566.33
240.25612.25
180.75610.27
6.0061.25
++
++
++
++
++
++
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4. ANNADURAI AND MOTLAG
Values expressed are the mean value 6 SD
f. = degrees of freedom = n-1 observations.
Auxin content is expressed as pg of tAA present in one ml of ethanot extract.
The results reveal that there is a positive correlation between resistance and
concenlration of phytohormones by the host plant against the leaf blight causing fungus A.
cepulae.
The estimation of auxin in normal leaves (Table - 1) indicates that the auxin level
deceases as growth advances. Leopol et.al. (1983) stated that this is due to the transport ol
auxin to the actively growing regions.
Studies on the estimation of auxin content in the blight area affected by A. cepulae
show that from the 4th day after inoculation, the auxin content increases upto 50 pg. On
16th day the auxin content is found to be 240-pg ml. Pilet (1960) suggested that this increase
be due to the translocation of auxin from active site to the site of infection. The results
obtained are similar to the results of Page and Selman (1959). Pilet (1960) and Sepueira and
Kelman (1962).
The effect of phytohormones on mycelial growth ol A. cepulae suggests that almost
all hormones inhibited the growth at 100-ppm concentration. Out of two different
concentrations, 100-ppm concentration of Naphthalene Acetic Acid, Kinetin, and lndole
Butyric Acid and lndole Acetic Acid inhibited the growth very well. The results agree with
the f indings of Guiscaf re Arillago (1949) and Davis and Dimond (1953). Results of the effect
of phytohormones on endo PG activity indicaie that Naphthalene Acetic Acid, lndote Butyric
Acid and lndole Acetic Acid inhibited the endo PG activity at 100-ppm concentration.The
inhibitory effect of Kinetin.and Gibberellic acid is upto 40% the results are in agreement
with the findings of Sinha and Wood (1967, 1968). Thakur and Chenula (1974), Plich (1926)
and Mehta (1979).
When the effect of phytohormones on the EPG activity was tested invitro was found
that at 10-ppm concentration GA and Indole Butyric Acid are less effective. At 100-pm
concentration almost all phytohormones have inhibitory effect on EPG upto 95%.The slight
difference in inhibition may be due to the intermediate compounds formed in the culture
medium.
ACKNOWLEDGEMENT
The author B.A. is gratefulto Dr. S. C. Dhar and Dr. R. Puvana Krishnan, Scientists at
the Department of Biotechnology, CLRI, Chennai for laboratory facilities and useful
suggestion and UGC, New Delhifor research grant.
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5. BIOJOURNAL, JUNE & DECEMBER, 1999
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6. ANNADURAI AND MOTLAG
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