Page 454 - Biosystems Engineering

428 Cha pte r F i f tee n

Therefore, part of the calcium that would be normally destined for
the long shoots is now being directed toward the fruits.
The long period between application of IAA and time of radioac-
tive calcium application makes it possible that the auxin effect con-
sists of auxin stimulation of the vascular connection between the fruit
54
and the branch that sustains it. There are examples in literature that
auxin treatment increases the amount of calcium in the fruit. 42,47 The
failure of the auxin application to substantially increase the Ca con-
2
tent of normal, pollinated fruits sometimes also happens. This is
probably due to the presence of seeds, which may produce sufficient
auxin for this purpose. Then the exogenous auxin supply would not
be effective.
The effect of auxin in daminozide-treated branches in 1987
was similar to that in branches not treated with this retardant. IAA
applied in the earlier term decreased Ca uptake by whole segments
45
45
(Table 15.2). Also, Ca uptake by long shoots was relatively lower but
that was taken up by the fruits increased. The effect of auxin in the
second term in these branches (daminozide treated) was insignifi-
cant, as in the branches not treated with retardant.
In 1988, auxin applied in the second term on daminozide-treated
branches diminished calcium uptake by fruits, regardless of the
method of treatment (Table 15.3). IAA treatment in the first term was
45
without effect. There was no IAA influence on Ca content in short or
long shoots.
The results suggest that exogenous auxin applied 2 weeks after
blooming may increase the accumulation of calcium in fruits but only
when the retardant is not very effective. When the retardant aug-
ments calcium accumulation in fruits, the effect of auxin given on the
same branch 2 weeks after blooming is not significant.
It is well known that it is difficult to predict the calcium content
in apples after retardant treatment. This group of chemicals may
influence Ca uptake by direct or indirect ways that may act indepen-
2
dently, and their effects are combined. Therefore, it does not seem
that exogenous auxin can be a useful tool for improving calcium
nutrition of fruits on retardant-treated trees.
Gibberellin A applied on long shoots only significantly decreased
3
the amount of Ca taken up by whole investigated fragments of a
45
plant. However, the percentage of calcium supplied to the fruits
increased, whereas that in long shoots and in short shoots remained
similar as in the controls (Table 15.3).
It seems surprising that gibberellin, which stimulated the growth
of long shoots (Basak, results unpublished), augmenting its needs for
Ca, concomitantly caused an increase of calcium accumulation in
fruits. A possible explanation for this may lie in the known stimula-
tory effect of gibberellin on the formation of vascular systems. 22,54
Because GA is also transported basipetally, it can stimulate the devel-
opment of vascular tissues in the short shoot to which the fruit is