Abstract:
Among three AO isoforms detected in pea plants, the
activity of PAO-1 was dominant in leaves of seedlings
and young leaves of mature plants, while PAO-3
revealed the highest band intensity in old leaves and
roots. PAO-1 and PAO-3 are homodimers consisting
of 145 kDa and 140 kDa subunits, respectively, while
PAO-2 is a heterodimer of one 145 kDa and one
140 kDa subunit. In leaves, the activity of PAO-1 disappeared
gradually with leaf ageing, while in roots it
was present only in seedlings but not in mature pea
plants. PAO-3 could oxidize abscisic aldehyde, a precursor
of abscisic acid, indicating the possible
involvement of this isoform in ABA synthesis in pea.
The ability of PAO-3 to oxidize abscisic aldehyde was
higher in old leaves than in young ones and
increased signi®cantly both in roots and leaves of
plants exposed to salinity and ammonium treatments.
A marked increase of the AO protein level was
observed after ammonium application but not under
salinity. Interestingly, the activity of PAO isoforms
may be transcriptionally and post-transcriptionally
regulated during vegetative growth and in response
to stress conditions, and such a regulation might be
particularly important to adjust ABA levels to the
recent requirements of the plant. The observations
suggest that the AO isoforms have different metabolic
roles and that the activity and protein level of
each isoform is regulated not only by environmental
conditions but also through plant developmental
stages.
