In
general,
the
pollen
of
the
three
tomato
genotypes
under
study
showed
similar
responses
to
the
high
temperature
concerning
the
increase
of
phenolic
content
in
pollen
grains
.
Under
stress
conditions
plants
mount
a
broad
range
of
defense
mechanisms
including
the
rapid
and
transient
generation
of
reactive
oxygen
species
(Bolwell,
Vojtaszek,
1977)
.
This
oxidative
burst
has
been
suggested
to
be
a
trigger
of
stress
responses
in
plants
(Low
and
Merida
1996)
.
To
avoid
oxygen
mediated
toxicity
the
scavenging
of
reactive
oxygen
species
by
some
phenolics,
especially
flavonoids,
is
critical
as
they
may
act
as
endogenous
antioxidants
because
of
their
radical
scavenging
ability
(Castellucio
et
al
.
,
1995,
Yamasaki,
1997)
.
It
is
well
documented
that
heat
stress
results
in
the
production
of
both
superoxide
anions
and
hydrogen
peroxide
indicating
that
the
heat
treated
plants
underwent
an
oxidative
burst
(Vallerian
-
Bindschedler
et
al
.
,
1998)
.
In
addition,
heat
treatment
of
plants
is
associated
with
the
accumulation
of
phenolic
compounds
in
their
leaves
(Ferraris
et
al
.
,
1987)
.
It
can
be
accepted
that
the
observed
increase
of
the
percentage
of
pollen
grains
containing
phenolic
compounds
is
a
response
reaction
of
tomato
pollen
to
the
heat
stress
.
However,
the
enhancement
of
the
different
classes
of
phenolic
compounds
in
tomato
pollen
after
heat
stress
did
not
correlate
with
the
thermotolerance
of
the
sporophyte
uniformly
.
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Figure
1,
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page