Asia Pacific
AsPac
J. Mol.Journal
Biol. Biotechnol.,
of MolecularVol.
Biology
12 (1&2),
and Biotechnology,
2004
2004
Vol. 12 (1&2) : 21-25
In Vitro Micropropagation of Ludwigia repens
21
In Vitro Micropropagation of the aquarium plant Ludwigia repens
Meryem Öztürk1, Khalid Mahmood Khawar2, Hasan Hüseyin Atar1,
Cengiz Sancak2 and Sebahattin Özcan2*
1
2
Department of Fisheries, Faculty of Agriculture, University of Ankara, 06110 Diskapi, Ankara, Turkey
Department of Field Crops, Faculty of Agriculture, University of Ankara, 06110 Diskapi, Ankara, Turkey
Received 25 November 2003 / Accepted 20 May 2004
Abstract. Apical meristems, first, second and third-fourth axillary buds of Ludwigia repens were cultured on Murashige and
Skoog (MS) medium containing various concentrations of 6-benzylaminopurine (BAP), thidiazuron (TDZ) and αnaphthaleneacetic acid (NAA) for micropropagation. Micropropagation was best achieved from apical meristem on MS medium containing 0.05 mg dm-3 TDZ and 0.1 mg dm-3 NAA. It was noted that TDZ or BAP had inhibitory effect on shoot
elongation, which was overcome by subculturing shoots on half-strength MS media without growth regulators after 4 weeks
of culture. This also served as rooting media. Rooted plantlets were finally transferred to aquariums containing fresh water
with 100% adaptation.
Keywords. Ludwigia repens, micropropagation, thidiazuron (TDZ), 6-benzylaminopurine, and carry over effect
Abbreviations: MS : Murashige and Skoog; TDZ : thidiazuron [1 Phenyl 3-(1,2,3-thiadiazol -5YL) urea]; BAP : 6-benzylaminopurine; NAA : α-naphthaleneacetic acid
INTRODUCTION
Ludwigia repens, belonging to the family Onargaceae, is an
evergreen amphibian herbaceous plant which is largely found
in Southern parts of North America. Ludwigia sp. is widely
distributed in America, Africa, Asia and Australia (Rataj and
Horeman, 1977) and is mainly used for filtration and cleaning
of water in canals and lakes. Some of the species belonging
to Ludwigia genus are used as vegetables, ornamental
aquarium plants, pollen source for honey bees, fish feed and
medicinal purposes (Brunson, 1988; Chen et al., 1989;
Greenway and Wooley, 1999; Mooi et al., 1999; Kuo et al.,
1999; Brundu et al., 2001). L. repens with small yellow flowers
(Cirik et al., 2001) and pinkish red to bright green leaves is
widely used as an aquarium plant. It grows rapidly in slightly
acidic waters at 19-28 oC (Rataj and Horeman, 1977).
L. repens is propagated from cuttings without ensuring
genetic uniformity by amateur workers, which results in
production of undesired phenotypes and subsequently
influence the quality and regeneration potential of the plants;
as they select the plants randomly without taking necessary
care. This results in negative economic implications for mass
production of this important aquarium plant. In spite of a
considerable progress in developing in vitro micropropagation
protocols in a variety of land plants (Khawar and Özcan,
2002; Özcan et al., 1996; Özcan et al., 1993), aquatic plants
in general have lagged behind to a considerable extent. In
vitro micropropagation of Ludwigia repens has not been
reported previously. The present study describes a rapid,
simple and efficient micropropagation system from several
explants of L. repens. Culture conditions described here may
also be applicable for in vitro micropropagation of other
plants belonging to Ludwigia species.
MATERIALS AND METHODS
Plants of Ludwigia repens were obtained from local dealers
of commercial aquarium plants by ensuring that they were
visibly healthy and free from any signs of stress or surface
blemishes. The selection was further carried out by growing
the plants under environmentally controlled fresh water
aquariums at 28 + 2°C with 12-h photoperiod.
For surface-sterilization, plants were first scrubbed gently
under running tap water for 0.5 h to remove coating layer
of microorganisms ubiquitously found on them. Upper
portions of the shoot twigs containing apical meristem
through fourth axillary bud were isolated and submerged
for 20 min in 30% commercial bleach (Axion) with 1-2 drops
*Author for Correspondence.
Mailing address: Department of Field Crops, Faculty of Agriculture,
University of Ankara, 06110 Dýþkapý, Ankara, Turkey. Tel: +90-3123179815; Fax: +90-312-3179815; E-mail: ozcan@agri.ankara.edu.tr
22
In Vitro Micropropagation of Ludwigia repens
AsPac J. Mol. Biol. Biotechnol., Vol. 12 (1&2), 2004
Table 1. Shoot regeneration from different explants of Ludwigia repens after 8 weeks in culture on MS media supplemented with various
concentrations of 6-benzylaminopurine (BAP), α-naphthaleneacetic acid (NAA) and thidiazuron (TDZ).
Growth reg. (mg dm-3)
BAP
0
0.1
0.2
0.3
0
0
0
NAA
0
0.1
0.1
0.1
0.1
0.1
0.1
TDZ
0
0
0
0
0.05
0.1
0.15
Number of shoots per explant2
Frequency (%) of shoot regeneration
Apic. mer. 1st bud
2nd bud
3rd-4th bud
Apic. mer. 1st bud
2nd bud
3rd-4th bud
87.50a1
52.50bc
37.50c
68.75b
100.00a
100.00a
100.00a
16.75bc
21.50bc
17.50bc
14.00c
30.25ab
38.50a
27.00abc
4.75b
8.75ab
19.00a
18.25ab
20.50a
1.75b
14.50b
2.25c
2.94c
1.81c
3.69c
12.31a
10.69a
7.31b
4.19d
5.36cd
4.38d
3.50d
7.56a
5.94bc
6.75bc
1.19c
2.19bc
4.75a
4.56a
5.12a
0.44c
3.63ab
100.00a
100.00a
56.25d
81.25bc
87.50abc
68.75cd
93.75ab
1.94e
4.31cd
3.06de
4.75cd
10.00a
9.63a
6.81b
Each value is the mean of 4 replicates each with 4 explants.
1
Values with in a column followed by different letters are significantly different at 0.01 level using Duncan’s Multiple Range Test.
2
From explants which regenerated shoots
Table 2. In vitro rooting of regenerated shoots in Ludwigia repens after 4 weeks in half-strength MS medium
Reg. medium
Growth reg. (mg dm-3)
BAP TDZ NAA
0
0
0
0.3
0
0.1
0
0.05 0.1
Root no./ shoot
st
Root length (cm) /shoot
Apic. mer. 1 bud
2 bud
3 -4 bud
Apic. mer. 1st bud
2nd bud
3rd-4th bud
8.89aA1
7.67aA
6.00aA
4.22aB
4.67aAB
4.44aA
8.56aAB
4.11bAB
2.67bB
5.11aA
4.39aAB
3.78aA
3.83aA
4.89aA
4.28aA
4.89aA
3.44abAB
2.67bB
6.56aAB
2.11bB
7.00aA
nd
rd
th
4.28aA
2.56aB
3.83aA
Each value is the mean of 4 replicates each with 4 explants.
1
Values with in a column followed by different lowercase letters and values within a row followed by different uppercase letters are significantly
different at 0.05 level
using Duncan’s Multiple Range Test.
of Tween 20 and continuous stirring. Stirring dispersed the
air bubbles adhering to explants and facilitated even
distribution of the disinfectant. After discarding bleach, the
explants were washed 3 times with sterile water. Apical
meristems, first, second and third-fourth axillary buds from
shoot tips were excised and cultured on to shoot regeneration
media in Magenta GA7 vessels for 4 weeks. Explants were
then cultured to subculture medium for 4 weeks. The number
of explants producing shoots and the number of shoots
per explant were scored after 8 weeks of culture. Well
developed shoots were isolated and rooted in rooting
medium. Rooted plantlets were transferred to fine sand in
aquariums (100 x 30 x 40 cm) with 4 cm spacing at 28 + 2°C
water (pH 6.0) temperature with 12 h photoperiod for 3
months.
The shoot regeneration media consisted of MS mineral
salts and vitamins (Murashige and Skoog, 1962), 3% sucrose,
0.7% agar (Sigma agar type A), 0.1-0.3 mg dm -3 6benzylaminopurine (BAP), 0.1 mg dm-3 α-naphthaleneacetic
acid (NAA) or 0.05-0.15 mg dm-3 thidiazuron (TDZ) and
0.1 mg dm-3 NAA (Table 1). Subculture and rooting medium
consisted of half-strength MS medium, 3% sucrose and 0.7%
agar. The pH of the medium was adjusted to 5.6 with 1N
NaOH or 1N HCl before autoclaving at 1.4 kg/cm2 and 121
°C for 20 min. All cultures were incubated at 24 + 1°C under
cool white fluorescent light (35 µmol photons m-2 s-1) with
16 h photoperiod.
Each treatment had 4 replicates containing 4 explants
for both micropropagation and rooting experiments and was
repeated twice. Significance was determined by analysis of
variance (ANOVA) and the differences between the means
were compared by Duncan’s multiple range test using
MSTAT-C computer program (Michigan State University).
Data given in percentages were subjected to arcsine (√X)
transformation (Snedecor and Cochran, 1967) before
statistical analysis.
RESULTS AND DISCUSSION
Shoot regeneration. Any micropropagation system must
produce large number of genotypically uniform plants
similar to the original plant from which they were propagated.
This aim could be easily achieved using meristematic regions.
After surface sterilization, apical meristem, first, second and
third-fourth axillary buds from shoot tips of the L. repens
were subjected to different concentrations of BAP, NAA
or TDZ, NAA. Shoot initials were clearly visible on all
explants within 6-8 d, which subsequently developed into
AsPac J. Mol. Biol. Biotechnol., Vol. 12 (1&2), 2004
In Vitro Micropropagation of Ludwigia repens
23
Figure 1. In vitro micropropagation of Ludwigia repens (a) Four weeks old regenerated shoots on MS medium containing 0.05 mg dm-3
Thidiazuron and 0.1 mg dm-3 α-naphthaleneacetic acid (b) rooting on ½ strength MS medium (c) successful establishment of rooted
plants in aquariums. Bar= 1 cm.
normal shoots after 7-8 weeks of culture initiation. This
shoot regeneration was accompanied with a minute callus
formation at the cut ends of explants touching the media
containing TDZ and NAA.
Analysis of variance test revealed that explants and
growth regulators interacted significantly with respect to the
percentage of explants producing shoots and mean number
of shoots per explant (p<0.01). All apical meristems
produced shoots on media containing any concentration of
TDZ with 0.1 mg dm-3 NAA; whereas, shoot regeneration
was not consistent on media supplemented with BAP and
NAA (Table 1). Moreover, shoot regeneration frequency was
higher in apical meristems and first node on all media
compared to second and third-fourth bud. This is reduced
in descending order from apical meristem to the third-fourth
axillary buds (Table 1).
The pattern of shoot development was dissimilar
between the media containing BAP and NAA or TDZ and
NAA. TDZ resulted in production of meristematic areas
adjacent to the cut end of meristematic regions and produced
numerous shoots. Extremely low TDZ concentrations were
more effective for shoot proliferation and even a slight
increase resulted in reduction of shoot proliferation. In
general, TDZ and NAA combinations were more effective
in all explants compared to BAP and NAA for shoot
initiation. The results also revealed that apical meristems
were the best and the third-fourth axillary buds are the
poorest explants in terms of shoot regeneration. In case of
all explants, the highest number of shoots per explant was
achieved from apical meristems on MS medium containing
0.05 mg dm-3 TDZ and 0.1 mg dm-3 NAA.
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In Vitro Micropropagation of Ludwigia repens
AsPac J. Mol. Biol. Biotechnol., Vol. 12 (1&2), 2004
It was found that shoots were longer and fewer with green
and wider leaves on growth regulator-free MS media than
media containing any concentration of BAP or TDZ.
Especially, presence of TDZ in the media resulted in
formation of clustered short shoots with very small leaves.
Very similar observation was also described in Cercis canadensis
var alba (Yusnita et al., 1990) and Hibiscus rosa- sinensis (Preece
et al., 1987). Similarly Pijut et al. (1991) found that number
of shoots in Pinus strobus L increased but their elongation
ceased with higher levels of TDZ. The reason for high
activity of low concentration of TDZ has not been
investigated in amphibian plants. We assume that TDZ is
persistent in the plant tissue and presumably metabolize in
a manner similar to that reported for Phaseolus (Mok and
Mok, 1985). They found that even when bean callus was
cultured on medium with [14C]-thidiazuron for 33 d, most
of the label remained in TDZ molecule. A portion of TDZ
was glycolsylated by the bean tissue, possibly to inactivate
the compound for storage.
Since TDZ and BAP stimulate shoot proliferation
tremendously, they have been used for micropropagation
of many plant species. We observed pronounced inhibition
or suppression in elongation and growth of regenerated
shoots after 2-3 weeks on all explants on media containing
any concentration of TDZ or BAP. This suppressive activity
was more severe on media containing TDZ and NAA with
numerous shoots bearing small green red-shaded leaves than
BAP and NAA containing media or growth regulators-free
media which had fewer shoots with large leaves. This
negative effect on shoot elongation was reduced and
minimized by transferring regenerated shoots on secondary
medium containing half-strength MS medium lacking growth
regulators after 4 weeks of culture, where growth accelerated.
This suggests that presence of TDZ or BAP may facilitate
shoot proliferation but is not essential during the growth
and elongation of shoots. Similar results were also obtained
in apple (Fasolo et al., 1989), pear (Singha and Bhatia, 1988),
populus (Russel and McCown, 1986) and rhododendron
(Preece and Imel, 1991).
Rooting development in regenerated shoots.
Regenerated shoots (10-20 mm in length) were excised from
the explants previously cultured on growth regulator-free
MS, MS medium containing 0.05 mg dm-3 TDZ and 0.1 mg
dm-3 NAA or 0.3 mg dm-3 BAP and 0.1 mg dm-3 NAA and
transferred to half-strength MS medium without growth
regulators. All regenerated shoots rooted on this medium
within four weeks (Figure 1b) and it is believed that rooting
of regenerated shoots is difficult because of a “carry over
effect” from cytokinins in the shoot proliferation medium
(Huetteman and Preece, 1993). We found that TDZ or BAP
in regeneration medium did not inhibit the frequency of
rooting as reported by Fasolo et al. (1989), Yunsita et al.
(1990) and Preece et al. (1991). However, shoots regenerated
on media containing BAP or TDZ had significantly reduced
number of roots, compared to the control. The phenomenon
was not consistent for root length. In general, root length
was shorter on shoots regenerated on media containing TDZ
compared to those regenerated on media containing BAP
in all explants except first bud where the reverse was true
(Table 2). This result may be attributed to “carry over effect”
from cytokinins in the regeneration medium. Rooted
plantlets were transferred to aquariums and later established
with 100% success (Figure. 1c). After 4-5 weeks, shade of
redness reduced or diminished completely with uniform
green leaves and roots.
In conclusion, to our knowledge the present study is the
first report for in vitro shoot regeneration of Ludwigia repens.
The procedure described here provides a rapid and prolific
micropropagation system that may also be applicable to other
species belonging to Ludwigia genus with small modifications.
ACKNOWLEDGEMENT
The authors are thankful to the University of Ankara and State
Planning Commission of Turkey (DPT) for financial support
(Project No. 2001 K 120240).
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In Vitro Micropropagation of Ludwigia repens
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