During
all
of
the
experiment
high
-
heterosis
F
1
hybrids
had
an
advantage
both
in
growth
rate
and
in
generative
development,
in
comparison
to
low
heterosis
hybrids
or
with
hybrids
where
complete
absence
of
heterosis
was
reported
.
As
for
recombination,
the
first
thing
observed
in
the
experiment
was
a
significant
increase
in
crossing
over
frequency
in
all
hybrids
and
within
both
segments
in
question
in
the
treatment,
the
difference
being
statistically
significant
for
the
hl
-
a
segment
(Table
1)
.
A
similar
reaction
of
tomatoes,
only
with
short
-
term
stresses,
was
mentioned
in
another
article
(Gavrilenko,
1984)
.
It
is
well
-
known
that
temperature
lowering
reduces
the
speed
of
biochemical
reactions,
thus
increasing
the
duration
of
cycles
and
phases
of
various
physiological
processes
(Alexandrov,
1975;
1985),
and
consequently
the
duration
of
conjugation,
synapsis,
crossing
-
over
etc
.
Therefore
it
is
supposed
that
recombination
reactions
to
low
temperature
consists
in
an
increase
in
the
number
of
DNA
breakages
kept
in
pachytene,
accessible
to
an
exchange,
at
the
expense
of
an
avoidance
of
their
reparation
(Lu,
Chiu,
1976)
.
This
assumption
also
explains
well
the
high
stage
-
specific
influence
of
low
temperature
treatment
(Lu,
1975)
.
By
considering
the
effect
separately
in
high
and
low
-
heterosis
hybrids,
the
tendency
for
a
stronger
reaction
to
such
influences
in
the
former
rather
than
in
the
latter
(Table
1),
especially
in
a
segment
hl
-
a,
is
obviously
visible
.
In
both
investigated
pairs
the
frequency
of
crossing
-
over
was
higher
in
case
of
high
-
heterosis
hybrids
.
It
is
essential
that
low
temperature,
acting
on
reparation
of
one
-
strand
breakages
in
pachytene,
can
simultaneously
result
in
a
delay
or
avoidance
of
DNA
reparation
synthesis,
together
with
regeneration
complementation
of
molecular
heterozygosity
sites
.
The
correction
in
sites
of
molecular
heterozygosity
is
an
absolutely
necessary
condition
for
a
normal
end
to
a
recombination
event,
without
it
the
products
of
an
exchange
will
be
nonviable
(Lu,
Chiu,
1976)
.
Therefore
the
result
of
low
temperature
suppression
of
two
types
of
reparations
in
pachytene,
can
be
negative:
under
long
processing,
the
increase
of
potential
sites
of
crossing
over
will
be
compensated
for
by
the
reduction
of
vitality
of
incorrect
products
of
an
exchange
.
This
suggests
that
under
equal
conditions
of
induction
of
recombination
frequency
by
means
of
low
temperature,
it
is
possible
that
a
higher
reparation
ability
of
high
heterosis
hybrids
results
in
less
elimination
of
recombinant
classes
of
gametes
and/or
zygotes,
and
thus
to
the
better
functioning
of
their
metabolic
systems;
thus,
long
-
term
influences
of
low
temperature
can
play
an
important
role
.
This
was
strongly
supported
by
persistence
of
heterosis
in