Agriculture Reference
In-Depth Information
Table
Effect of site of application of paclobutrazol on shoot extension and leaf
production of 'M.
.
' rootstock shoots during
days following treatment
Number of new
Shoot
Site of application
unrolled leaves
extension (cm)
One-year-old wood
.
.
Laminae
.
.
Petioles
.
.
Shoot tip
.
.
New stem
.
.
Shoot tip
+
new stem
.
.
Complete shoot
.
.
Untreated
.
.
LSD . between any two values
.
.
From Richardson and Quinlan ( ). Reproduced with permission.
Cytokininsaregenerallyconsideredtoregulatecelldivision,andalsoplayan
important role in budbreak and therefore help determine the number of shoots
(seepp.
)foundamarkedresponseofappleshootgrowth
in
vitro
tobenzyladenine.Applicationsofthisinthefieldhavesometimesincreased
and sometimes reduced mean shoot length.
-
). Jones(
Effects of other plant parts on shoot extension
Leaves, as the source of carbohydrates produced by photosynthesis, play a
major role in all plant growth. Rapidly growing shoot tips are a strong sink for
assimilates, and after the first five or sixshoot leaves have been produced cur-
rent photosynthesis becomes a more important carbon source than reserves
(Hansen,
). Photosynthates from the upper leaves of the shoot are in gen-
eral exported upwards, those from the lower part being exported to other
parts of the tree. This pattern can, however, be influenced by factors which
affect the balance of assimilate supply and demand, e.g. by fruiting and by
partial defoliation of the shoot (Hansen,
,
; Quinlan,
,
): it
is therefore not simply a function of pre-existing vascular connections.
Leaves also have effects on shoot extension growth in ways other than
through their supply of assimilates. Kato and Ito (
) found that apple
shoot growth was promoted by the removal of expanded leaves. This effect
was a consequence of increased internode length and was associated with an
increase in shoot auxin content. Abbott (
) found that removal of young
expanding leaves was followed by a virtual cessation of stem elongation and
then by an increase in this to result in longer shoots and a later termination of
growth. Barlow and Hancock (
) and Kato and Ito (
) also found that
