Vol.2, No.3, 191-197 (2011)
doi:10.4236/as.2011.23026
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Agricultural Scienc es
Effects of autoclaving on the physiological action of
paclobutrazol
Dimas Mendes Ribeiro, Caroline Müller, Jackson Bedin, Glayton Botelho Rocha, Raimundo
Santos Barros*
Depto de Biologia Vegetal/Universidade Federal de Viçosa, Viçosa, Brazil; *Corresponding Author:
Received 3 March 2011; revised 6 May 2011; accepted 25 July 2011.
ABSTRACT
Besides being employed as an efficient plant
growth retardant for field, garden and potted
plants, paclobutrazol (PBZ) is also used in labo-
ratory experiments, mainly in aseptic cultures,
both in autoclaved and non-autoclaved form.
Therefore it is not known if autoclaving can par-
tial or completely inactivate the product, thus
decreasing its efficacy. Thus a simple experi-
ment was carried out to assess to what extent
the autoclaving proce s s can affect some growth
components and dry mass accumulation and
partition in sunflower seedlings, by employing
the techniques of Plant Growth Analysis. Auto-
claving did not modify either qualitative or
quantitatively any of the plant responses to PBZ
as well their reversions by gibberellic acid.
Keywords: Autoclaving; Dry Mass Accumulation;
Gibberilins; Growth; Paclobutrazol; Sunflower
1. INTRODUCTION
Paclobutrazol [PBZ; common names: Bonzi, Clipper-
S, Clipper-T, Cultar, PP333; chemical name: IUPAC:
(2RS,3RS )-1 -4-(ch loroph enyl)-4,4- dimethyl-2 -(1H,1 ,2,4-
triazol-1-yl)p entan-3-ol] is an efficient plant growth re-
tardant listed for usage by the Plant Growth Regulation
Society of America [1]. Its optical enantiomer 2S,3S dis-
plays a pronounced plant growth regulatory activity,
whereas the 2R,3R enantiomer is more active in the in-
hibition of sterol biosynthesis, exhibiting fungicidal
properties. The growth retarding form of PBZ (S-enan-
tiomer) keeps certain structural similarities with ent-
kaurene and ent -kaurenol, key compounds in the path-
way to gibberellins (GAs) biosynthesis, and hence may
inhibit cytochrome P450 monooxygenases, impairing the
oxidation of ent-kaurene to ent-kaurenoic acid [2,3]. As
a result PBZ can cause a substantial depletion in the lev-
els of active GAs throughout the plant [3], leading to a
kind of dwarfism [1]. Some effects of PBZ on plants are:
development of dark green color in leaves [2]; stimula-
tion of flowering, likely as a result of a decrease in
vegetative growth [4,5]; hastened leaf fall in autumn and
emergence delay in spring in deciduous plants [2]; yield
increase in apples [6], Jathropa curcas [7] and other
cultivated species.
Water solubility of PBZ is very poor, about 0.12 mM
(35 mg·dm–1; [1,2]), the compound being mostly immo-
bile in the phloem sieve tube elements. Due to that when
sprayed in the plants its action is much localized. A more
uniform distribution is seen when it is provided by trunk
injection or soil application, because in this case the
product is transported via xylem vessels [8]. This low
solubility has brought about some troubles especially
when the compound is used under laboratory conditions.
For instance in order to achieve reproducible results on
the inhibition of seed germination of Townsville stylo
(Stylosanthes humilis) PBZ had to be autoclaved [9]. The
autoclaved product is also largely employed in aseptic
culture experiments [10-12], although the non-auto-
claved form is identically used [13-15]. Sometimes the
condition of the PBZ (autoclaved or non- autoclaved)
employed in the experiments is not even mentioned [16].
Since PBZ is “stable at all temperatures up to 50˚C for at
least six months” [1,2] and that during the autoclaving
process temperature as high as 120˚C is achieved, it is
likely that heating leads to degradation of the compound,
rendering PBZ completely or partially inactive. As a
consequence the effective amount of PBZ that elicits a
physiological action is not known when the product is
autoclaved. In order to throw some light to this problem
a simple assay was designed as to compare the effects of
autoclaved and non-autoclaved PBZ on the growth and
dry mass accumulation of seedlings of sunflower (Heli-
anthus an nuus L.).
2. MATERIALS AND METHODS
Seeds of sunflower ‘Agará 4’ plants were sown in 400

D. M. Ribeiro et al. / Agricultural Science 2 (2011) 191-197
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
192
cm3 plastic pots containing a 2:1:1 mixture of red-yellow
latosol soil, sand and cattle manure in a greenhouse in
Viçosa (20˚45′ S, 42˚15′ W), Minas Gerais state, Brazil.
Upon seedling emergence, soil was fertilized with 0.2 g
of NPK (25-5-20). When ca 7 - 10 cm high, seedlings
were thinned to two plants per pot. On the occasion 5
cm3 PBZ (10% a.i.; Wisser Importer, SP, Brazil) suspen-
sion (containing 2.5 or 5 mg) were distributed with a
pipette on the soil surface of each pot (day 0, Figure 1
and Table 1).
Autoclaving of PBZ was accomplished in an auto-
clave (Sercom, Model HA, SP, Brazil), for 20 min, under
121˚C and a pressure 120 kPa. Nine and 16 days after
PBZ application, seedling apices were sprayed until
complete wetness with a 0.1 mM gibberellic acid (GA3;
SIGMA, MI, USA) solution also containing 0.05%
Tween 80. Stem length, as measured from soil surface to
the uppermost visible node, was registered at each other
day. At the end of the experiment the plants were har-
vested, their roots were washed and leaves (unfolded ≥
1.5 cm) and internode number counted. Following sepa-
ration roots stems and leaves were oven-dried at 70˚C
for about 72 h, and afterwards their dry mass determined.
Organ lengths and dry masses constituted thus the pri-
mary data upon which the Growth Analysis techniques
were used according to Richards [17] and Hunt et al.
[18].
Statistical design was based on a completely random-
Figure 1. Growth increase in stem length of sunflower seedlings as affected by autoclaved (AUTOCL)- and non-autoclaved (NON-
AUTOCL)-PBZ applied in the soil surface at the dosage 5.0 mg per pot at the day 0. At days 9 and 16 following PBZ application,
GA3 (0.1 mM) was sprayed at the shoot apex of the plants, as indicated by the arrows. The pattern of growth curves in response to
2.5 mg PBZ per pot was exactly the same as shown in the figure, except for the magnitude of the values. Full circles: -GA3; Hollow
circles: GA3-treated. Each point and bars represent means ± SE of 10 plants.
Tab le 1. Increase in stem (STM) length, mean internode (INT) length and stem growth rate of sunflower plants before (0 - 9th day)
and after (10th - 22nd day) the first plant spraying with GA3. In this table and Ta bl es 2 and 3 numbers following PBZ represents its
doses (mg) applied in each pot. GA3 was sprayed at the concentration 0.1 mM. CTL-control. (Means to be compared within columns;
values followed by the same letter do not differ significantly at 5% by Tukey test. Data analysis by Scott-Knott test also showed that
the effects of autoclaved and non-autoclaved PBZ were similar).
STM length INT length STM growth rate (cm·day–1)
Treatment (cm) (cm) (0 - 9th day] (10 - 22nd day)
CTL 19.6 ± 2.7 c 2.19 ± 0.30 c 0.65 ± 0.08 a 1.00 ± 0.15 b
CTL + GA3 36.2 ± 2.1 a 3.3 ± 0.17 a 0.80 ± 0.04 a 2.21 ± 0.14 a
Non-autoclaved:
PBZ 2.5 5.0 ± 0.3 d 1.14 ± 0.06 d 0.31 ± 0.03 bc 0.15 ± 0.01 c
PBZ 5.0 4.1 ± 0.3 d 0.93 ± 0.04 d 0.26 ± 0.02 bc 0.16 ± 0.01 c
PBZ 2.5 + GA3 28.1 ± 0.7 b 3.05 ± 0.14 b 0.28 ± 0.02 bc 2.06 ± 0.04 a
PBZ 5.0 + GA3 29.5 ± 0.8 b 3.09 ± 0.05 b 0.22 ± 0.02 c 2.20 ± 0.07 a
Autoclaved:
PBZ 2.5 5.4 ± 0.3 d 1.17 ± 0.04 d 0.33 ± 0.01 bc 0.21 ± 0.01 c
PBZ 5.0 4.5 ± 0.2 d 1.00 ± 0.06 d 0.27 ± 0.02 bc 0.18 ± 0.01 c
PBZ 2.5 + GA3 29.5 ± 2.2 b 3.15 ± 0.08 ab 0.39 ± 0.03 b 2.01 ± 0.15 a
PBZ 5.0 + GA3 25.6 ± 0.4 b 2.78 ± 0.11 bc 0.28 ± 0.02 bc 1.83 ± 0.03 a

D. M. Ribeiro et al. / Agricultural Science 2 (2011) 191-197
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
193193
ized distribution with five replicates, each one consti-
tuted of a pot with two plants, per treatment. The Tukey
mean separation test, at 5% level, was employed to de-
tect differences amongst treatments. As Scott-Knott test
clusters means without superimposing their significances,
it was employed further as to subsidize the Tukey’s
analyses. In this way probable differences and similari-
ties among the treatments could be further confirmed.
3. RESULTS AND DIS CUSSION
The first signs of PBZ action were observed by the
development of a dark-green color in growing leaves [2]
3 - 4 days after application of the product to the soil. The
new appearing leaves then became smaller [19], exhib-
iting a thicker and wrinkled aspect [20]. Thereafter the
growth rate of PBZ-treated plants decreased substan-
tially (Figure 1, Tab l e 1) and the apical internodes and
leaves started displaying a rosette form. This dwarfism
syndrome was similarly exhibited by autoclaved and
non-autoclaved PBZ-treated plants, with no quantitative
differences between the plants of the two treatments
(Tukey and Scott-Knott tests, 5% level). Each one of
those symptoms was properly reverted by GA3, the re-
sponses also not being affected by the autoclaving of
PBZ.
Stem growth pattern followed the well-characterized
sigmoidal logistic model [17,18]. As Figure 1 and Table
1 show stem length resulted much longer in the control
and in all GA3-treated plants than in PBZ-inhibited
plants. Again, differences in stem length in response to
autoclaved and non-autoclaved PBZ were too small to
have assumed any statistical significance. A dramatic
change in the growth pattern of PBZ-treated plants was
observed following GA3 application (Figure 1). Growth
rates increased substantially, sometimes higher than 10-
fold (Ta bl e 1); in this way, at the end of the experiment
the stem length of these plants surpassed that of the con-
trol non-treated plants.
Leaf and internode number (about the half of the leaf
number, within a range 10.0 - 11.6 internodes per plant,
not shown) were not affected by any of the treatments,
showing that in sunflower they constitute highly con-
served traits. Hence the much reduced stem length
caused by PBZ (Figure 1, Table 1 ), was a consequence
of the very shorter internodes, an effect also reverted by
GA3 notwithstanding whether PBZ was autoclaved or
not (Table 1).
Total dry mass accumulated per plant did not respond
to any of the treatment, autoclaved PBZ included (Fig-
ure 2, Table 2). In this context, in some plant species
GAs affect positively the net CO2 assimilation (A) whilst
in others it is not affected [21]. Sunflower thus, seems to
belong to the latter group. This fact must be a conse-
quence of a similar A displayed by PBZ-treated and non-
treated sunflower seedlings [22]. Similarly dry mass
allocation to leaves and to the stem-root system was not
affected either by PBZ or GA3 (Figure 2, Table 2). The
regulators, however, affected the dry mass partition
within the stem-root system (see below).
Since leaf dry mass per plant was not affected by the
regulators which also did not affect leaf number, the
mean individual leaf dry mass was also kept similar
amongst all the treatments (range 79.0 - 99.0 mg, not
shown). As a consequence of the similar total dry mass
per plant and also of a similar leaf dry mass per plant,
leaf mass ratio (LMR), the ratio between leaf to total
plant dry mass [23], did not show any significant differ-
ence among the treatments (Ta b l e 3 ). Though the mean
individual leaf dry mass did not vary among the treat-
ments, they profoundly affected leaf size as mentioned
above. As described earlier leaf size was drastically re-
duced by PBZ, as also found in Zinnia and Geranium
[24]. In order to hold the same dry mass in a much re-
duced area PBZ-treated leaves have to be thicker, a point
examined in a side experiment with the third uppermost
leaves in the stem (showing symptoms of PBZ action).
Ta bl e 2 . Dry mass (DRM) of roots (ROT), stem (STM), leaves (LFY) of sunflower plants. Also shown are stem plus root (STM +
ROT), total (TOT) dry mass per plant, and mean internode (INT) dry mass. (Means to be compared within columns; values followed
by the same letter do not differ significantly at 5% level by Tukey test. Data analysis by Scott-Knott test also showed that the effects
of autoclaved and non-autoclaved PBZ were similar).
Treatment ROT (g) STM (g) LFY (g) STM+ROT (g) TOT (g) INT (mg)
CTL 0.56 ± 0.07 abcd 0.85 ± 0.14 ab 0.75 ± 0.04 a 1.40 ± 0.16 a 2.15 ± 0.16 a 81 ± 15 abc
CTL + GA3 0.38 ± 0.03 d 1.05 ± 0.11 a 0.77 ± 0.03 a 1.43 ± 0.13 a 2.20 ± 0.17 a 100 ± 10 a
Non-autoclaved:
PBZ 2.5 0.70 ± 0.03 ab 0.64 ± 0.04 bc 0.98 ± 0.06 a 1.34 ± 0.06 a 2.31 ± 0.23 a 56 ± 4 bcd
PBZ 5.0 0.70 ± 0.08 ab 0.50 ± 0.06 c 0.81 ± 0.05 a 1.20 ± 0.13 a 2.01 ± 0.17 a 46 ± 5 d
PBZ 2.5 + GA3 0.49 ± 0.06 bcd 1.06 ± 0.06 a 0.80 ± 0.03 a 1.55 ± 0.10 a 2.36 ± 0.13 a 92 ± 7 a
PBZ 5.0 + GA3 0.51 ± 0.04 bcd 1.05 ± 0.02 a 0.91 ± 0.03 a 1.56 ± 0.03 a 2.47 ± 0.02 a 94 ± 2 a
Autoclaved:
PBZ 2.5 0.80 ± 0.06 a 0.56 ± 0.04 bc 0.74 ± 0.09 a 1.36 ± 0.09 a 2.10 ± 0.17 a 57 ± 3 bcd
PBZ 5.0 0.64 ± 0.05 abc 0.53 ± 0.05 bc 0.87 ± 0.04 a 1.17 ± 0.07 a 2.04 ± 0.11 a 51 ± 5 cd
PBZ 2.5 + GA3 0.47 ± 0.04 bcd 1.02 ± 0.08 a 0.91 ± 0.07 a 1.49 ± 0.11 a 2.40 ± 0.17 a 90 ± 4 a
PBZ 5.0 + GA3 0.40 ± 0.03 cd 0.99 ± 0.03 a 0.88 ± 0.07 a 1.39 ± 0.06 a 2.27 ± 0.12 a 87 ± 4 ab

D. M. Ribeiro et al. / Agricultural Science 2 (2011) 191-197
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
194
Figure 2. Dry mass accumulation by sunflower seedlings and partitioning among leaves (hollow rectangles),
stem (hatched rectangles) and roots (full rectangles). Total plant dry mass, total leaf dry mass and stem plus
root dry mass did not show any statistical significance among the treatments; differences were exhibited be-
tween shoot and root dry mass of plants of the several treatments (Tukey’s and Scott-Knott’s tests, 5% level).
Figures represent the amounts of PBZ in mg applied to each pot. For each pair of data of control (0), auto-
claved (AUTO)- and non-autoclaved (NON)-PBZ treatments, the 1st element of the pair refers to –GA3 treat-
ment and the second one to +GA3 treatment. Bars represent ± SE around means of 10 plants.
Specific leaf area (SLA, obtained by dividing the area by
leaf dry mass [23]), was about 31.7 in control leaves,
26.5 - 28.8 in PBZ-treated leaves and 36.9 - 43.0 m–2·kg–1
in GA3-treated leaves. PBZ (autoclaved and non-auto-
claved) thus induced the formation of small and thicker
leaves, an effect promptly reverted by GA3.
Shoot-root system dry mass as a whole did not re-
spond to any of the regulators employed (Figure 2, Ta-
ble 2). Since total dry mass per plant was not affected as
well, the ratio stem-root to total plant dry mass (range
0.57 - 0.66) was equally not affected by them (Tab le 3).
Within that system itself each one stem and root dry
mass was, nevertheless, greatly affected (Figure 2, Ta-
ble 3). As shown in Figure 1, stem expansion was
highly responsive to the regulators. Hence the system
stem-root seemed to be the main target for the action of
PBZ and GA3. When dry mass of stems and roots were
considered separately they showed a large variation in
response to treatments (Figure 2, Ta b le s 2 and 3), PBZ
(autoclaved and non-autoclaved) favoring dry mass al-
location to roots and GA3 to stems. Hence the ratio root
to total plant dry mass (root mass ratio, RMR; [22]) was
larger in PBZ-treated plant whereas stem to total plant
dry mass (stem mass ratio, SMR) was larger in all (in-
cluding the reversion of PBZ effects) GA3-treated plants
(Table 3). In agreement with these observations, the root
biomass accumulation was also increased in uniconazol-
and PBZ-treated plants of Arabidopsis [25]. Moreover
these data are in close accordance with recent genetic
tudies which revealed good correlation between a low s

D. M. Ribeiro et al. / Agricultural Science 2 (2011) 191-197
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
195195
Table 3. Some allometric relationships in sunflower plants as affected by PBZ and GA3. Root mass ratio (RMR, fraction of root mass
to total plant dry mass); stem mass ratio (SMR, fraction of stem mass to total plant dry mass), leaf mass ratio (LMR, fraction of leaf
mass to total plant dry mass); STM + ROT:TOT (stem plus root to total plant dry mass); root to shoot dry mass (ROT:SHT); root to
stem plus root dry mass (ROT:STM + ROT); and dry mass distribution over the stem length unit (DRM/LNT). (Means to be com-
pared within the columns. Values followed by the same letter do not differ significantly at 5% level by Tukey test. Data analysis by
Scott-Knott test also showed that the effects of autoclaved and non-autoclaved PBZ were similar).
Treatment RMR SMR LMR
STM + ROT:
TOT ROT:SHT ROT: STM + ROT
STM DRM/
LNT (g·m–1)
CTL 0.26 ± 0.03 cd 0.39 ± 0.05 a 0.35 ± 0.03 a 0.64 ± 0.07 a0.35 ± 0.05 cd 0.41 ± 0.05 b 3.6 ± 0.8 b
CTL + GA3 0.17 ± 0.01 e 0.47 ± 0.02 a 0.35 ± 0.02 a 0.64 ± 0.04 a0.21 ± 0.01 e 0.27 ± 0.01 c 2.6 ± 0.2 b
Non-autoclaved:
PBZ 2.5 0.30 ± 0.01 bc 0.27 ± 0.01 b 0.42 ± 0.02 a 0.58 ± 0.04 a0.44 ± 0.03 bc 0.53 ± 0.02 a 4.9 ± 0.4 a
PBZ 5.0 0.35 ± 0.02 ab 0.24 ± 0.01 b 0.41 ± 0.02 a 0.59 ± 0.05 a0.54 ± 0.03 ab 0.59 ± 0.08 a 4.9 ± 0.3 a
PBZ 2.5 + GA3 0.20 ± 0.01 de 0.45 ± 0.01 a 0.34 ± 0.01 a 0.66 ± 0.02 a0.26 ± 0.02 de 0.31 ± 0.02 bc 3.0 ± 0.1 b
PBZ 5.0 + GA3 0.21 ± 0.02 de 0.42 ± 0.01 a 0.37 ± 0.01 a 0.63 ± 0.02 a0.26 ± 0.03 de 0.33 ± 0.02 bc 3.0 ± 0.1 b
Autoclaved:
PBZ 2.5 0.38 ± 0.02 a 0.27 ± 0.01 b 0.35 ± 0.02 a 0.65 ± 0.05 a0.62 ± 0.05 a 0.59 ± 0.02 a 4.8 ± 0.2 a
PBZ 5.0 0.31 ± 0.03 abc 0.26 ± 0.02 b 0.43 ± 0.01 a 0.57 ± 0.02 a0.46 ± 0.03 bc 0.55 ± 0.03 a 5.0 ± 0.4 a
PBZ 2.5 + GA3 0.20 ± 0.01 de 0.42 ± 0.01 a 0.38 ± 0.01 a 0.62 ± 0.02 a0.25 ± 0.01 de 0.32 ± 0.01 bc 2.9 ± 0.1 b
PBZ 5.0 + GA3 0.18 ± 0.01 e 0.43 ± 0.01 a 0.39 ± 0.01 a 0.61 ± 0.03 a0.22 ± 0.01 de 0.29 ± 0.01 c 3.1 ± 0.1 b
GA regime and biomass accumulated in the roots [26].
A pattern emerges as to explain the results on dry
mass distribution in sunflower plants when the relation-
ships between length and dry mass of the stem as af-
fected by PBZ and GA3 are taken into account. It is well
known that GA3 stimulates stem growth towards the
shoot main axis direction which is translated into inter-
node expansion (Figure 1, Ta b l e 1 ). PBZ, on the other
hand, inhibits stem elongation leading to much smaller
cells. GA3-treated stems accumulate much more dry
mass just because they are much longer than PBZ-
treated stems (Figure 2, Tables 1 and 2). By taking into
account the dry mass distribution over the stem length
unit, it is seen that both autoclaved and non-autoclaved
PBZ-treated stems similarly “concentrate” more dry
mass than GA3-treated stems (Table 3), being thus
“denser”. It is deduced that dry mass accumulation by
individual cells of PBZ-treated plants may approach or
even reach its potential, what did not absolutely occur in
GA3-treated stems.
Given that dry mass accumulation by the stem-root
system does not vary with treatments (Figure 2, Table 2)
a model can then be proposed that fits to the above facts.
In GA3-treated plants stem elongates excessively but dry
mass accumulation (about 60% of dry mass accumulated
by PBZ-treated stems, on a length unit basis, i.e., far
from its maximum potential, see Table 3) does not keep
pace with that process, leading to the production of nar-
rower and elongated stems. Nevertheless, due to this
high elongation (Figure 1, Table 1), stem constitutes the
main sink of the stem-root system and thus in GA3-
treated plants little dry mass remains to be allocated to
the roots (Tab le 3). A low root to shoot ratio (or root to
stem plus root) thus results (Table 3). In PBZ-treated
plants, stems are very short and although they accumu-
late more dry mass per volume unit (“denser” cells, Ta-
ble 3), they are too small to constitute a strong assimilate
sink. The surplus of assimilates produced by the plant is
then directed towards the roots, what explains the high
root to shoot (or root to stem plus root) ratio displayed
by PBZ-treated plants (Ta ble 3). Curiously, these calcu-
lations led to similar results as the ones obtained in [21]
with tomato using much more sophisticated techniques.
By working with the A70 (moderately deficient) and
W335 (extremely deficient) GA slow-growing mutants,
those authors showed that the shoot constituted the main
target for GA action. Accordingly, as growth in shoot
elongation was much smaller in GA-deficient tomato
plants much more assimilate was left to be partitioned
into the roots as compared with the wild type plants.
Summarizing, this dry mass accumulation pattern was
due to stem growth as affected by GAs and not to be
regulator by itself. Since total dry mass in sunflower
plants did not respond to the regulators herein employed
being kept more or less constant (Table 2), a good theo-
retical exercise would be to forecast where the assimi-
lates would come from in case the cells affected by GA3
would accumulated dry mass to their full potential.
In summary when investigating the effects of auto-
claving in PBZ physiological action on the growth and
dry mass partition in sunflower seedlings, no significant
difference in the inhibitory effects of autoclaved and
non-autoclaved form was found and in the reversion of
those effects by GA3, as well. Hence, the amounts (lev-
els) of autoclaved PBZ employed in aseptic cultures or
used for other purposes in laboratory or field conditions
could be considered as the real one and equivalent to the
amounts of the non-autoclaved form. This has already
been put forward in [10], without showing any evidence,
however. As expected the main effects of PBZ and GA3
were observed in shortening and elongation of seedlings
stems, respectively. The body of evidences leads to the

D. M. Ribeiro et al. / Agricultural Science 2 (2011) 191-197
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
196
conclusion that GA deficiency caused by PBZ (or in
GA-deficient mutants) resulted in a pronounced stem
growth decrease and hence as stem-root system dry mass
did not vary to a large extent, assimilates are directed
towards the roots. Unequivocally, in the present investi-
gation, not at all affected by both GA3 and PBZ (auto-
claved and non-autoclaved) were mean leaf and inter-
node number, total plant dry mass, leaf dry mass per
plant, and the stem-root system dry mass per plant as a
whole.
4. ACKNOWLEDGMENTS
Thanks are due to FAPEMIG (Foundation for Research Sponsoring
of Minas Gerais State) for the scholarships granted to DMR (Post-
Doctoral training), JB and GBR (Scientific Initiation training), and for
the financial support in several occasions. CAPES (Coordination for
Improvement of Higher Education Training) awarded a scholarship to
CM. CNPq (Brazilian Council for Science and Technological Devel-
opment) has maintained RBS as an associated Fellow Researcher
member since long ago.
REFERENCES
[1] PGRSA (2007) Plant growth regulation handbook of the
Plant Growth Regulation Society of America. 4th Edition.
The Plant Growth Regulation Society of America, Ath-
ens.
[2] ICI (Imperial Chemical Industries) and PLC (1986) Plant
protection division. Clipper, Surrey.
[3] Rademarcher, W. (2000) Growth retardants: Effects on
gibberellins biosynthesis and other metabolic pathways.
Annual Review of Plant Physiology and Plant Molecular
Biology, 51, 501-531.
doi:10.1146/annurev.arplant.51.1.501
[4] Kulkarni, V.J. (1988) Chemical control of tree vigour and
promotion of flowering and fruiting in mango (Mangif-
era indica L.) using paclobutrazol. The Journal of Hor-
ticultural Science, 63, 557-566.
[5] Wilkinson, R.I. and Richards, D. (1991) Influence of
paclobutrazol on growth and flowering of Rhododrendon
‘Sir Robert Peal’. HortScience, 26, 282-284.
[6] Tukey, L.D. (1983) Vegetative control and fruiting on
mature apple trees treated with PP333. Acta Horticulture,
137, 103-109.
[7] Gosh, A., Chikara, J., Chandhari, D.R., Prakashi, A.R.,
Boricha, G. and Zala, A. (2010) Paclobutrazol arrests
vegetative growth and unveils unexpressed yield poten-
tial of Jathropa curcas. Journal of Plant Growth Regula-
tion, 29, 307-315. doi:10.1007/s00344-010-9137-0
[8] Early, J.D. and Martin, G.C. (1988) Translocation and
breakdown of 14C-labeled paclobutrazol in ‘Nemaguaro’
peach seedlings. HortScience, 23, 196-200.
[9] Müller, C. (2007) Efeito do paclobutrazol na germinação
e no metabolismo do etileno em sementes de Stylosantes
humilis HBK. M.Sc. Dissertation, Universidade Federal
de Viçosa, Viçosa.
[10] Snir, I. (1988) Influence of paclobutrazol on in vitro
growth of sweet cherry shoots. HortScience, 23, 304-305.
[11] Panaia, M., Senaratna, T., Bunn, E., Dixon, K.W. and
Sivasithamparam, K. (2000) Micropropagation of the
critically endangered Western Australian species, Sy-
monanthus bancroftii (F. Muell.), L. Haegi (Solanaceae).
Plant Cell Tissue and Organ Culture, 63, 23-29.
doi:10.1023/A:1006457624282
[12] Albany, N.R., Vilchez, J.A., Garcia, L. and Jiménez, E.
(2005) Comparative study of morphological parameters
of Grand Nain banana (Musa AAA) after in vitro multi-
plication with growth retardants. Plant Cell Tissue and
Organ Culture, 83, 357-361.
doi:10.1007/s11240-005-6307-z
[13] Haughan, P.A., Burden, R.S., Lenton, J. and Goad, J.
(1989) Inhibition of celery cell growth and sterol bio-
synthesis by the enantiomers of paclobutrazol. Phyto-
chemistry, 3, 781-787.
doi:10.1016/0031-9422(89)80115-3
[14] Chen, J.-T. and Chang, W.-C. (2003) Effects of GA3,
ancymidol, cycocel and paclobutrazol on direct somatic
embryogenesis of Oncidium in vitro. Plant Cell Tissue
and Organ Culture , 72, 105-108.
doi:10.1023/A:1021235700751
[15] Kucharska, D. and Olikowska, T. (2008) The influence of
paclobutrazol in the rooting medium on the quality of
chrysanthemum vitroplants. The Journal of Fruit and
Ornamental Plant Research, 16, 417-424.
[16] Kyte, L. and Kleyn, J. (1996) Plant from test tubes: An
introduction to micropropagation. 3rd Edition. Timber
Press, Portland.
[17] Richards, F.J. (1969) The quantitative analysis of growth.
In: Steward, F.C., Ed., Plant Physiology—a Treatise,
Academic Press, New York, 3-76.
[18] Hunt, R., Causton, D.R., Shipley, B. and Askey, A.P.
(2002) A modern tool for classical plant growth analysis.
Annals of Botany, 90, 485-488. doi:10.1093/aob/mcf214
[19] LeCain, D.R., Schekel, K.A. and Wample, R.L. (1986)
Growth retarding effects of paclobutrazol on weeping fig.
HortScience, 21, 1150-1152.
[20] Bultynck, L. and Lambers, H. (2004) Effects of applied
gibberellic acid and paclobutrazol on leaf expansion and
biomass allocation in two Aegilops species with con-
strasting leaf elongation rates. Physiologia Plantarum,
122, 143-151. doi:10.1111/j.1399-3054.2004.00383.x
[21] Nagel, O.W. and Lambers, H. (2002) Changes in the
acquisition and partitioning of carbon and nitrogen in the
gibberellin-deficient mutants A70 and W335 of tomato
(Solanum lycopersicum L.). Plant, Cell and Environment,
25, 883-891. doi:10.1046/j.1365-3040.2002.00871.x
[22] Auras, N.E. (1997) Efeitos do paclobutrazol sobre a mor-
fologia e anatomia foliar, crescimento e parte aérea, dis-
tribuição de biomassa e trocas gasosas em girassol. D.Sc
Dissertation, Universidade Federal de Viçosa, Viçosa.
[23] Hunt, R. (1990) Basic growth analysis. Unwin Hyman,
London.
[24] Cox, A.C. and Keever, G.J. (1988) Paclobutrazol inhibits
growth of Zinnia and Geranium. HortScience, 23,
1029-1030.
[25] Bidadi, H., Yamaguchi, S., Asahina, M. and Satoh, S.
(2010) Effects of shoot-applied gibberellin/gibberellin-
biosynthesis inhibitors on root growth and expression of
gibberellins biosynthesis genes in Arabidopsis thaliana.
Plant Root, 4, 4-11. doi:10.3117/plantroot.4.4

D. M. Ribeiro et al. / Agricultural Science 2 (2011) 191-197
Copyright © 2011 SciRes. http://www.scirp.org/journal/AS/Openly accessible at
197197
[26] Gou, J., Strauss, S.H., Tsai, C.J., Fang, K., Chen, Y., Ji-
ang, X. and Busov, V.B. (2010) Gibberellins regulate lat-
eral root formation in Populus through interactions with
auxin and other hormones. The Plant Cell, 22, 623-635.
doi:10.1105/tpc.109.073239
List of abbreviations:
CLT: control; DRM: dry mass; GA, GA3: gibberellins,
gibberellic acid; LFY, leaf; LNT: length; PBZ: pa-
clobutrazol; ROT: root; SHT: shoot; STM: stem; TOT:
total.