Abstract:
IAA oxidase is the enzyme to oxidize IAA to Methylene Oxindole which is an
inactive form of auxin. During abiotic stress, auxin content decreases in plant
system because of high IAA oxidase activity. The present study was conducted
with the objectives of estimating IAA enzyme activity in selected chilli cvs.
viz., MI 2, KA 2 and ‘Arunalu’ in response to moisture stress and to determine
the extent of stress tolerance in these cvs. based on this enzyme activity. All the
chilli cvs. were grown in polyethylene bags filled with sandy regosols. Two
levels of moisture (stress and control) were used. Moisture stress was imposed
by withholding water at once from the initiation of flowering up to 15 days
during the flowering stage. Control plants were watered to Field Capacity at 5
days interval. Gypsum blocks were used to assess the moisture levels of plants.
Moisture stress significantly increased the IAA oxidase activity of the three
chilli cvs. The highest IAA oxidase activity (lowest un-oxidized auxin) was
found in ‘MI 2’ where as the lowest IAA oxidase activity (highest un-oxidized
auxin) was found in ‘Arunalu’. ‘KA 2’ showed significantly higher IAA
oxidase activity than ‘Arunalu’. The IAA oxidase system is proved to influence
plant growth by regulating the concentration of endogenous IAA. Plant tissues
capable of rapid growth have been found to exhibit low IAA oxidase activity.
From the above results, it could be stated that ‘Arunalu’ was able to maintain
growth and development better than ‘KA 2’ and MI 2’ chilli cvs. despite a
severe stress situation. As such, ‘Arunalu’ exhibited better stress tolerance than
‘KA 2’ and MI 2’. Moisture stress significantly reduced the fruit yield of all the
chilli cvs. The highest yield was obtained in ‘Arunalu’ and the lowest one was
found in ‘MI 2’ under moisture stress condition. The stress tolerance feature of
‘Arunalu’ characterized by high accumulation of auxin; other words, low IAA
oxidase activity would have influenced plant growth by regulating the
concentration of endogenous IAA. Thus, ‘Arunalu’ was able to thrive and
produce well under water deficit situation.
