Genomics and Applied Biology 2015, Vol. 6, No. 4, 1-6
5
was maintained by M
1
than M
2
during the growth
period. All the sub-plot treatments exhibited their
significant differences. Among the subplot treatments,
higher polyphenol oxidase activity was registered by
S
1
followed by S
2
, S
10
and S
4
in the given stage. The
lowest enzyme activity was, however, showed by S
11
and S
12
in main and ratoon crop.
The significant variations among the interaction
treatments revealed the influence of main plots on sub
plot for regulating the enzyme activity. The treatment
M
1
S
1
showed a higher value of 1.36, followed by
M
1
S
2
, M
1
S
3
and M
1
S
4
. However a considerable
reduction in PPO activity could also be observed due
to interaction with M
2
and subplot treatments. M
2
S
1
,
M
2
S
2
, M
2
S
3
, and M
2
S
4
recorded about 6.3 to 9.8 per
cent reduction. M
2
S
5
, M
2
S
6
, M
2
S
7
, and M
2
S
8
showed
about 12.4 to 15.0 per cent reduction, whereas, M
2
S
9
,
M
2
S
10,
M
2
S
11
and M
2
S
12
registered about 20.8 to 22.6
per cent reduction over the M
1
and subplot treatments
in main and ratoon crop.
3 Discussion
In the present study, proline content increased relative
to the degree of water deficit stress. Proline acts as an
osmolyte and helps the plants to maintain tissue water
potential under all kinds of stresses. Proline, as an
osmoprotectant, is largely confined to the cytoplasm and
is mostly absent from the vacuole (Mc Neil et al.,
1999). It plays a key role in the cytoplasm as a
scavenger of free radicals as well as a mediator in
osmotic adjustment and also increases the solubility of
sparingly soluble proteins (Saradhi et al., 1995). Shen
et al. (1990) advocated that water stress enhanced the
accumulation of proline in many plant species and it
might function as a source of solute for intercellular
osmotic adjustment under water stress. Stewart (1978)
suggested that proline might severe as a storage
compounds for reduced carbon and nitrogen during
stress. Proline might regulate the osmotic balance of
the cell thus relieving the negative effect of stress
(Reddy et al., 2004). In the present study also,
cultivars like Karpuravalli, Karpuravalli x Pisang jajee,
Saba and Sannachenkathali had higher amount of
proline accumulation particularly at 7
th
MAP followed
by Poovan, Ney Poovan, Anaikomban and
Anaikomban x Pisang jajee than cultivars of Matti,
Matti x Anaikomban, Matti x cultivar rose and Pisang
jajee x Matti. These findings are further supported by
the results of Mohd Razi Ismail (2004) in banana,
which explained that the enhancement in free proline
content could occur either due to
‘de novo’
synthesis
of proline or breakdown of proline-rich protein or shift
in metabolism.
3.1 Polyphenol Oxidase
(PPO) is a copper-containing enzyme, responsible for
the enzymatic browning reaction occurring in many
fruits and vegetables damaged by improper handling
etc. (Meyer and Boyer, 1976). Accumulation of
polyphenols in the plants is controlled by PPO, also
known as phenolase, catalyzing the oxidation of
o-diphenols to o-diquinons, as well as hydroxylation
of monophenols. Activities of these enzymes increase
in response to different types of stresses, both biotic
and abiotic (Farooq, 2009). Chararra et al., (2001)
reported that PPO activity in banana converted certain
phenol compounds to highly reactive quinones in the
presence of molecular oxygen. Quinones readily
bound to proteins to form complexes, which were
more resistant to breakdown by plant and microbial
enzymes. Fukumoto et al. (2002) reported that
decreased activity under oxidative stress period led to
forming symptoms such as brown pitting, necrosis,
deterioration of mitochondrial activity and cell
damage associated with increased deposition of
phenolic compounds. In the present study, a
significantly higher rate of PPO activity was observed
under water deficit conditions. The enzyme activity
was however increased when the twelve cultivars
were influenced with water stress. The cultivars of
Matti, Matti x Anaikomban, Matti x cultivar rose and
Pisang jajee x Matti had increased PPO activity of
about 56 per cent over control, whereas cultivars of
Karpuravalli, Karpuravalli x Pisang jajee, Saba and
Sannachenkathali resulted in 9 to 10 per cent increase
in enzyme activity, indicating higher increase in
enzyme activity of susceptible cultivars to the water
deficit treatment. Similar results were made by
Keshavkant (2000); Ose et al., (1999) who found that
the considerable reduction in PPO activity during
oxidative stress period, particularly in leaves can be
explained by the location of this enzyme in the leaf
