4. Discussion
Generally cotton plants are rich in phenolic compounds which
hinder the growth of the explant tissues in tissue culture medium
and eventually result in their death. It is undesirable for the growth
of any plant tissues under in vitro condition. Phenolic compounds
are usually secreted in medium from cut part of the plants while
preparing explants for in vitro culture. Phenolic secretion affects
the tissue growth, results in browning of medium and
finally leads
to death of the explants. This is the serious problem in cotton tissue
culture which makes its regeneration a difficult one. In order to avoid this major issue, it is necessary to
find an optimum carbon
source for efficient in vitro culture of cotton. Secretion of phenolic
compounds as a wounding response inhibited in vitro explant
growth in sugarbeet and garden beet [10]. Sucrose as a carbon
source supports growth of plant cells under in vitro condition [7].
Medium supplemented with 3% sucrose showed highest phenolic
concentration while the lowest was observed from 0% sucrose in
callus culture of Sugar beet [32]. The same observation was
reported by [13] about the influence of sucrose on phenolic
concentration in avocado. Enzymes such as polyphenoloxidase
(PPO) and peroxidase (POD) were reported to be responsible for
blackening in vitro cultures and catalyzing oxidation of phenolic
compounds [20,5,30]. Kahn [13] suggested that the degree of
blackening is related to phenolic concentration and activity of the
PPO enzyme. Andersone and Ievinsh [2] suggested that reduced
peroxidase and polyphenoloxidase activity increases the ability of
tissues to initiate growth in vitro. Chemical, enzymatic and physical
treatments can be used to prevent PPO-catalyzed tissue blackening
[16]. However these treatments often cannot be used in in vitro
culture. PVP has been added to the medium to alleviate the effects
of browning in Haworthia cultures [29] and to control phenolic
secretion during multiple shoot induction of Ricinus communis [9].
In contrary to the above said reports, addition of the anti-oxidants
PVP and ascorbic acid to the medium did not visibly reduce the
browning in the cultures of Aloe polyphylla and browning increased
within hours of subculturing on medium supplemented with PVP
4. DiscussionGenerally cotton plants are rich in phenolic compounds whichhinder the growth of the explant tissues in tissue culture mediumand eventually result in their death. It is undesirable for the growthof any plant tissues under in vitro condition. Phenolic compoundsare usually secreted in medium from cut part of the plants whilepreparing explants for in vitro culture. Phenolic secretion affectsthe tissue growth, results in browning of medium andfinally leadsto death of the explants. This is the serious problem in cotton tissueculture which makes its regeneration a difficult one. In order to avoid this major issue, it is necessary tofind an optimum carbonsource for efficient in vitro culture of cotton. Secretion of phenoliccompounds as a wounding response inhibited in vitro explantgrowth in sugarbeet and garden beet [10]. Sucrose as a carbonsource supports growth of plant cells under in vitro condition [7].Medium supplemented with 3% sucrose showed highest phenolicconcentration while the lowest was observed from 0% sucrose incallus culture of Sugar beet [32]. The same observation wasreported by [13] about the influence of sucrose on phenolicconcentration in avocado. Enzymes such as polyphenoloxidase(PPO) and peroxidase (POD) were reported to be responsible forblackening in vitro cultures and catalyzing oxidation of phenoliccompounds [20,5,30]. Kahn [13] suggested that the degree ofblackening is related to phenolic concentration and activity of thePPO enzyme. Andersone and Ievinsh [2] suggested that reducedperoxidase and polyphenoloxidase activity increases the ability oftissues to initiate growth in vitro. Chemical, enzymatic and physicaltreatments can be used to prevent PPO-catalyzed tissue blackening[16]. However these treatments often cannot be used in in vitroculture. PVP has been added to the medium to alleviate the effectsof browning in Haworthia cultures [29] and to control phenolicsecretion during multiple shoot induction of Ricinus communis [9].In contrary to the above said reports, addition of the anti-oxidantsPVP and ascorbic acid to the medium did not visibly reduce thebrowning in the cultures of Aloe polyphylla and browning increasedwithin hours of subculturing on medium supplemented with PVP
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