Basic HTML Version
Molecular Microbiology Research (Online) 2013, Vol.3 No.3 20-29
ISSN 1027-5595
http://mmr.sophiapublisher.com
24
Figure 2 Native page profile of defence enzymes in response to
plant oil, bio control agents and micronutrient in physic nut
Note: A: Peroxidae; B: Polyphenol oxidase; Lane 1: Copper
sulphate; Lane 2: Lemon grass oil; Lane 3: Pseudomonas
fluorescens; Lane 4: Bacillus EPCO16; Lane 5: Control
General phenylpropanoid metabolism is defined as the
sequence of reactions involved in the conversion of
L-phenylalanine to activated cinnamic acids. The first
enzyme of this path way is PAL that catalyzes the
trans elimination of ammonia from L-phenylalanine to
form trans cinnamic acid which in turn enters different
biosynthetic path ways leading to lignin. Similarly
studies in cucumber revealed that PAL is a key
enzyme in the production of phenolic and phytoalexin.
Systemic increase in the PAL activity upon treatment
with PGPR has been reported in several crops
including pigeon pea and rice (Meena et al., 2000).
Induction of PAL by fluorescent pseudomonads was
reported in cucumber against
P. aphanidermatum
(Chen et al., 2000), Tomato against
F. oxysporum
f.sp.
lycopersici
(Ramamoorthy et al., 2002) and in mango
against
C. gloeosporioides
(Vivekanadhan et al.,
2004). Present study showed that PAL activity was
gradually increased in physic nut leaves and following
treatments with
P. fluorescens
,
Bacillus
EPCO16,
Copper sulphate and Lemon grass oil reached
maximum level at 5
th
day after treatment when
compared to control. The enzyme activity
subsequently declined. Among them, Pf1 recorded
maximum PAL activity (22.303 n mol of
transcinnamic acid min
-1
g
-1
of fresh tissue) followed
by
Bacillus
EPCO16 (21.030 n mol of transcinnamic
acid min
-1
g
-1
of fresh tissue).
2.1.2. Peroxidase (PO)
The present study results are supported by several
authors including peroxidase is involved in
lignification
leading
to
disease
resistance.
Polymerization of cinnamyl alcohols to lignin is
catabolised by PO. For lignifications specific cell wall
peroxidases are thought to be required to generate
H
2
O
2
and monolignol radicals. Constabel et al. (1998)
proved that PO could be induced upon induction by
Jasmonic acid. The bacteria and the pathogens
induced one acidic peroxidase isozyme in the roots.
Two other isozymes induced by the pathogen were not
found to be induced by PGPR (Chen et al., 2000).
Karthikeyan et al. (2009) reported that soil and foliar
application of
P. fluorescens
(Pf1) induced the
accumulation of phenolics and enhanced the activities
of peroxidase, phenylalanine ammonia lyase and
polyphenol oxidase in black gram against
Urdbean
leaf crinkle virus
(ULCV) in blackgram. New
isoforms of peroxidase and polyphenol oxidase were
also induced by the treatment.
2.1.3. Poly phenol oxidase (PPO)
The present study revealed that the poly
phenoloxidase (PPO) activity gradually increased in
physic nut leaves and following treatments with
P.
fluorescens
,
Bacillus
EPCO16, Copper sulphate and
Lemon grass oil reached maximum level at 5
th
day
after treatment when compared to control. Poly phenol
oxidases (PPO) are enzymes which use molecular
oxygen to catalyse the oxidation of monophenolic and
orthophenolic compounds. PPO usually accumulated
upon wounding in plants. Similarly increased
activation of PPO could be detected in the cucumber
leaf in the vicinity of lesions caused by some foliar
pathogens. Moreover PPO can be induced through
octadecanoid defense signal pathway and specific
isoforms of PPO were induced in plants treated with
the PGPR formulation after challenge inoculation with