全 文 :红芽芋茎尖的包埋玻璃化法超低温保存∗
王艾平ꎬ 尹明华ꎬ 洪森荣∗∗
(上饶师范学院生命科学学院ꎬ 江西 上饶 334001)
摘要: 对红芽芋 (Colocasia esculenta var. cormosus ‘Hongyayu’)茎尖的包埋玻璃化法超低温保存技术进行了
研究ꎮ 茎尖从培养 8周的试管苗上切下并包埋成海藻酸钙凝胶珠ꎬ 并在 MS+3 5 mgL-1 6 ̄BA+0 5 mgL-1
IBA+ 0 1 mgL-1 GA3+0 3 molL
-1蔗糖的液体培养基中预培养 24 hꎬ 随后用 2 molL-1甘油+0 4 molL-1
蔗糖的混合物在 25 ℃下装载 30 minꎬ 并用 PVS2在 25 ℃脱水 20 min 后将包埋的茎尖直接投入液氮保存ꎮ
保存 1 d后取出材料在 40 ℃水浴快速复温 3 min后ꎬ 吸去冷冻管中 PVS2ꎬ 并用 MS+3 5 mgL-1 6 ̄BA+0 5
mgL-1 IBA+0 1 mgL-1 GA3+1 2 molL
-1蔗糖的液体培养基在 25 ℃洗涤 3次ꎬ 每次 10 minꎮ 最后将茎尖接
种于 MS+3 5 mgL-1 6 ̄BA+0 5 mgL-1 IBA+0 1 mgL-1 GA3的固体培养基上ꎬ 暗培养 3 d后转入正常的光
周期中培养ꎮ 红芽芋茎尖冻后成活率约为 80%ꎬ 其再生植株没有发生形态学的变化ꎮ 这种包埋玻璃化法
程序有望成为红芽芽茎尖超低温保存的常规方法ꎮ
关键词: 超低温保存ꎻ 包埋玻璃化法ꎻ 红芽芋ꎻ 茎尖
中图分类号: Q 943ꎬ S 632 3 文献标志码: A 文章编号: 2095-0845(2015)06-801-12
Cryopreservation of in vitro ̄Grown Shoot Tips of Red
Bud Taro by Encapsulation ̄Vitrification
WANG Ai ̄pingꎬ YIN Ming ̄huaꎬ HONG Sen ̄rong∗∗
(College of Life Sciencesꎬ Shangrao Normal Universityꎬ Shangraoꎬ Jiangxi 334001ꎬ China)
Abstract: A simple procedure for cryopreservation of in vitro ̄grown shoot tips of red bud taro (Colocasia esculenta
L. Schott var. cormosus ‘Hongyayu’) by encapsulation ̄vitrification is investigated. Shoot tips were excised from 8 ̄
week ̄old stock shoots and encapsulated into alginate ̄gel beads. Encapsulated shoot tips were precultured in liquid
MS medium supplemented with 3 5 mgL-1 6 ̄BAꎬ 0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3 and 0 3 molL
-1 sucrose for
24 hꎬ then they were loaded with a mixture of 2 molL-1 glycerol plus 0 4 molL-1 sucrose for 30 min at 25 ℃ . After
dehydration with PVS2 at 25 ℃ for 20 minꎬ the encapsulated and dehydrated shoot tips were plunged directly into
liquid nitrogen. After rapidly rewarming in a 40 ℃ water bath for 3 minꎬ PVS2 was drained from the cryotubes and
replaced third with liquid MS medium supplemented with 3 5 mgL-1 6 ̄BAꎬ 0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3
and 1 2 molL-1 sucrose and each kept for 10 min at 25 ℃and then post ̄cultured on solidified MS medium supple ̄
mented with 3 5 mgL-1 6 ̄BAꎬ 0 5 mgL-1 IBA and 0 1 mgL-1 GA3 in the dark for 3 days and then transferred to
the light conditions. The average survival rate amounted to about 80%. Plantlets regenerated from cryopreserved shoot
tips were morphologically uniform. This encapsulation vitrification procedure promises to become a routine method for
the cryopreservation of shoot tips of Chinese genuine red bud taro.
植 物 分 类 与 资 源 学 报 2015ꎬ 37 (6): 801~812
Plant Diversity and Resources DOI: 10.7677 / ynzwyj201515067
∗
∗∗
Funding: Science and Technology Ground Plan Project of College and University in Jiangxi Province in 2013 (KJLD13088)ꎻ Agricultural
Science and Technology Support Program of Science & Technology Department of Jiangxi Province (20122BBF60126) and Na ̄
tional Natural Science Fund in China (31360072)
Author for correspondenceꎻ E ̄mail: hongsenrong@163 com
Received date: 2015-04-22ꎬ Accepted date: 2015-06-23
作者简介: 王艾平 (1961-) 男ꎬ 教授ꎬ 主要从事植物组织培养方面的研究ꎮ
Key words: Cryopreservationꎻ Encapsulation ̄vitrificationꎻ Red bud taro (Colocasia esculenta var. cormosus ‘Hongy ̄
ayu’)ꎻ Shoot ̄tips
Colocasia esculenta L. Schott var. cormosus
‘Hongyayu’ (Araceae)ꎬ known as red bud taro in
Chinaꎬ is one of the most economically important
herbaceousꎬ vegetatively propagated tuber crop (Liꎬ
2012). All parts of the plant including cormꎬ stalkꎬ
leaves and flowers are edible and contain abundant
starchꎬ proteinꎬ vitaminꎬ polysaccharides and vari ̄
ous trace elements and have been used as an immu ̄
nostimulant (Jiang et al.ꎬ 2012). In recent yearsꎬ it
has also become a popular tonic and health foodꎬ
therefore the demand for red bud trao has increased
dramatically. In Chinaꎬ C esculenta L. Schott var.
cormosus ‘Hongyayu’ is a genuine taro belong to
Yanshan Countyꎬ Shangrao Cityꎬ Jiangxi Province
and mainly cultivated in the southeast of China (Xi ̄
aoꎬ 2006)ꎬ Yanshan County is the only county red
bud taro green food raw material standard production
baseꎬ whose red bud taro was awarded national pol ̄
lution ̄free green food certificate. At presentꎬ the
planting area of red bud taro in Yanshan County is
68 × 104 haꎬ with an annual output of 150 000 tons.
Yanshan County has become the biggest red bud taro
base in East China area.
As with any clonally propagated cropꎬ germ ̄
plasm resources of red bud taro are mainly conserved
vegetatively in field gene banks or greenhouse. Jian ̄
gtian agricultural science and technology limited
company in Yanshan County of Jiangxi Province has
a breeding project of red bud taro (Li et al.ꎬ 2009).
In this caseꎬ howeverꎬ valuable materials are often
exposed to pestsꎬ diseasesꎬ and soil or climatic stres ̄
ses. In additionꎬ the routine maintenance of plants in
field gene banks is highly expensive due to the large
size of these plants. There is a growing need for
cryopreservation of the germplasm collections of red
bud taro.
For many cropsꎬ cryopreservation is currently
being applied to overcome the limitations encoun ̄
tered by traditional germplasm conservation strategies
in field (Engelmann ̄Sylvestre and Engelmannꎬ 2015).
Cryopreservationꎬ i e. storage at the temperature of
liquid nitrogenꎬ is an increasingly important aspect
of plant biotechnologyꎬ sinceꎬ in the future it will be
necessary to establish safe repositories for patented
cultures of commercial interest ( Liu et al.ꎬ 2015ꎻ
Vieira et al.ꎬ 2015). Furtherꎬ this method enables
us to preserve tissue cultures with valuable morpho ̄
genetic or biochemical traits (Panta et al.ꎬ 2015).
In recent yearsꎬ cryopreservation procedures
such as vitrificationꎬ encapsulation ̄dehydrationꎬ drop ̄
let ̄vitrification and encapsulation ̄vitrification have
been developed (Sakai and Engelmannꎬ 2007ꎻ Kac ̄
zmarczyk et al.ꎬ 2011ꎻ Tahtamouni et al.ꎬ 2015ꎻ
Gantait et al.ꎬ 2015). Encapsulation ̄vitrificationꎬ
generally including precultureꎬ loadingꎬ dehydra ̄
tionꎬ coolingꎬ rewarming and post ̄cultureꎬ is a sim ̄
plified cryostorage procedure because it does not re ̄
quire the use of expensive cooling devices (Shin et
al.ꎬ 2014) and the encapsulated materials are much
easier to manipulate and permit greater flexibility in
handling large amounts of material ( Sharaf et al.ꎬ
2012ꎻ Gogoi et al.ꎬ 2012). Recently the cryopreser ̄
vation by encapsulation ̄vitrification has been applied
to a wide range of plant species such as apple
(Paulꎬ 2000)ꎬ mint (Hirai and Sakaiꎬ 1999a)ꎬ
potato (Hirai and Sakaiꎬ 1999b)ꎬ strawberry (Hirai
et al.ꎬ 1998)ꎬ ‘Troyer’ citrange (Wang et al.ꎬ 2002)ꎬ
cassava (Charoensub et al.ꎬ 2004)ꎬ carnation (Hal ̄
magyi and Deliuꎬ 2007).
Cryopreservation has also been applied to taro
genetic resources. Shimonishi et al. ( 1993) report
for the first time the cryopreservation of taro embryo ̄
genic callus by slow cooling. Howeverꎬ shoot tips are
better materials compared with cell and callus cul ̄
tures because they result in true ̄to ̄type progeny in
higher frequency than cultured cells and callus and
have no genetic changes during the growth phase be ̄
fore and after storage (Sharaf et al.ꎬ 2012). In re ̄
208 植 物 分 类 与 资 源 学 报 第 37卷
cent yearsꎬ the use of taro shoot ̄tips for germplasm
cryopreservation has been achieved by vitrification
(Takagi et al.ꎬ 1994ꎬ 1997ꎬ 1998ꎻ Sant et al.ꎬ
2006) and by droplet vitrification ( Sant et al.ꎬ
2008).
After cryopreservation by vitrification and the
average rate of taro shoot recovery amounted to a ̄
round 80% (Takagi et al.ꎬ 1997). While the best
mean recoveries for three cultivars of tropical taro
(Colocasia esculenta var. sculenta (L.) Schott) were
only 21%ꎬ 29% and 30% for E399ꎬ CPUK and
TNSꎬ respectively and cryopreservation by vitrifica ̄
tion was evaluated with five other taro cultivars with
no success (Sant et al.ꎬ 2006). The application of
the droplet vitrification cryopreservation technique to
taro accessions from a range of Asia Pacific countries
significantly improve improved the mean post ̄thaw
survival rates to 73% - 100% from 21% - 30% ob ̄
tained with the cryo ̄vial vitrification protocol (Sant
et al.ꎬ 2008). Thereforeꎬ for different varieties of
taroꎬ different cryopreservation procedures need fur ̄
ther improvement. Howeverꎬ to our knowledgeꎬ there
are no reports on the cryopreservation of red bud taro
shoot tips by encapsulation ̄vitrification. The objec ̄
tive of the present study wasꎬ thereforeꎬ to develop a
simple effective method for the cryopreservation of
shoot tips of C esculenta L. Schott var. cormosus
‘Hongyayu’ by encapsulation ̄vitrification.
1 Materials and methods
1 1 Plant materials and in vitro culture
Field ̄grown cormels of C esculenta L. Schott
var. cormosus ‘Hongyayu’ were obtained from Jian ̄
gtian agricultural science and technology limited
companyꎬ Yanshan Countyꎬ Jiangxi Provinceꎬ China.
Firstlyꎬ the cormels were immersed in 70% ethanol
for 20 s followed by 0 1% HgCl2 for 12 min and
washed three times with sterile distilled water re ̄
spectively. In vitro stock plantlets of C esculenta L.
Schott var. cormosus ‘Hongyayu’ were obtained by
culturing 0 3-0 6 mm ̄long shoot tipsꎬ isolated from
sterilized cormels (Takagi et al.ꎬ 1997) and propa ̄
gated on solidified MS (Murashige and Skoogꎬ 1962)
basal medium supplemented with 3 5 mgL-1 6 ̄BAꎬ
0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3ꎬ 20 gL
-1 su ̄
crose and 6 5 gL-1 agar at pH 5 8 (Liꎬ 2012).
Shoots from the in vitro ̄grown stock plants were pro ̄
liferated on solidified MS basal medium containing 3
mgL-1 6 ̄BAꎬ 0 5 mgL-1 NAAꎬ 20 gL-1 sucrose
and 6 5 gL-1 agar at pH 5 8 (Liꎬ 2012ꎻ Takagi et
al.ꎬ 1997). The shoots constituted the stock materi ̄
als used for subsequent investigations and were sub ̄
cultured every 8 weeks. All of the cultures were
maintained at a constant temperature of 25 ℃ and
exposed to a 16 / 8 ̄h ( light / dark) photoperiod with
a light intensity of 36 μmolm-2 s-1 provided by
cool ̄white fluorescent tubes. Immediately prior to
useꎬ shoot tipsꎬ 0 8-1 0 mm long containing 1 leaf
primordiaꎬ were excised from axillary buds of 8 ̄
week ̄old stock shoots (Takagi et al.ꎬ 1997ꎻ Sant et
al.ꎬ 2006ꎬ 2008).
1 2 Cryopreservation
Excised shoot tips were suspended in calcium ̄
free MS inorganic medium supplemented with 2%
Na ̄alginate and 0 4 molL-1 sucrose. The mixture
including shoot tips was dispensed with a sterile pi ̄
pette into 0 1 molL-1 CaCl2 plus 0 4 molL
-1 su ̄
crose solution for 30 min at 25 ℃ to form Ca ̄alginate
beads ( 4 mm in diameter) . Each bead contained
one shoot tip. These beads were surface ̄dried by
plating them on a sterilized filter paper and then pre ̄
cultured.
Shoot tips were precultured after being excised
from 8 ̄week ̄old stock shoots and encapsulated into
alginate ̄gel beads. The following parameters of the
preculture protocol were studied:
(1) Effect of sucrose concentration in precul ̄
ture medium: Encapsulated shoot tips were precul ̄
tured in a liquid MS medium containing various con ̄
centrations of sucrose (0ꎬ 0 15ꎬ 0 3ꎬ 0 45ꎬ 0 6
molL-1 ) supplemented with 3 5 mgL-1 6 ̄BAꎬ
0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3 for 24 h.
(2) Effect of sucrose preculture duration: En ̄
capsulated shoot tips were precultured in a liquid MS
3086期 WANG Ai ̄ping et al.: Cryopreservation of in vitro ̄Grown Shoot Tips of Red Bud Taro by
medium containing 0 3 molL-1 sucrose supplemen ̄
ted with 3 5 mgL-1 6 ̄BAꎬ 0 5 mgL-1 IBAꎬ 0 1
mgL-1 GA3 for 0ꎬ 12ꎬ 24ꎬ 48ꎬ 60 h respectively.
Precultured shoot tips were loaded with a mix ̄
ture of 2 molL-1 glycerol plus 0 4 molL-1 sucrose
at 25 ℃ for 0ꎬ 10ꎬ 20ꎬ 30ꎬ 40ꎬ 50ꎬ 60 min respec ̄
tively. Cryoprotected shoot tips were transferred to a
2 mL plastic cryotube (Containing 5 beads) and 1
mL ̄PVS2 was then added.
The following parameters of the dehydration pro ̄
tocol were studied:
(3) Effect of dehydration duration at 25 ℃:
Encapsulatedꎬ precultured and loaded shoot tips were
dehydrated with PVS2 at 25 ℃ for different intervals
(0ꎬ 10ꎬ 20ꎬ 30ꎬ 40ꎬ 50ꎬ 60 min).
(4) Effect of dehydration duration at 0 ℃: En ̄
capsulatedꎬ precultured and loaded shoot tips were
dehydrated with PVS2 at 0 ℃ for different lengths of
time (0ꎬ 10ꎬ 20ꎬ 30ꎬ 40ꎬ 50ꎬ 60 min).
After dehydration with PVS2ꎬ the encapsulated
and dehydrated shoot tips were plunged directly into
liquid nitrogen (LN) for 1 d.
After rapidly rewarming in a water bath at 25 ℃ꎬ
40 ℃ and 45 ℃ for 3 min respectivelyꎬ PVS2 was
drained from the cryotubes and washed third with
liquid MS medium containing various concentrations
of sucrose (0ꎬ 0 4ꎬ 0 8ꎬ 1 2ꎬ 1 6 molL-1) sup ̄
plemented with 3 5 mgL-1 6 ̄BAꎬ 0 5 mgL-1 IBAꎬ
0 1 mgL-1 GA3 (pH 5 8) and each kept for 10 min
at 25 ℃ and then post ̄cultured on solidified MS me ̄
dium supplemented with 3 5 mgL-1 6 ̄BAꎬ 0 5 mg
L-1 IBA and 0 1 mgL-1 GA3 . The following param ̄
eters of the post ̄culture protocol were studied:
(5) Effect of 3 ̄day dark culture prior to 16 h
photoperiod: Encapsulatedꎬ preculturedꎬ loadedꎬ de ̄
hydratedꎬ cryopreservedꎬ thawedꎬ loaded shoot tips
were post ̄cultured in the dark for 3 days and then
transferred to the light conditions (under 16 h photo ̄
period at 36 μmolm-2s-1).
(6) Effect of 16 h photoperiod without 3 day
dark culture: Encapsulatedꎬ preculturedꎬ loadedꎬ
dehydratedꎬ cryopreservedꎬ thawedꎬ unloaded shoot
tips were directly post ̄cultured under 16 h photoperi ̄
od at 36 μmolm-2s-1 .
Surviving shoot tips were transferred to solidi ̄
fied MS medium containing 3 mgL-1 6 ̄BA and 0 5
mgL-1 NAA under 16 h photoperiod at 36 μmol
m-2 s-1 for shoot growth and after one month the
shoots transferred to solidified hormone ̄free MS roo ̄
ting medium under 16 h photoperiod at 36 μmol
m-2 s-1 . The survival rate was estimated as the per ̄
centage of the total number of shoot tips that devel ̄
oped a plantlet after 4 months culture.
The recovery and plant regeneration of cryopre ̄
served shoot tips was studied by the following two
groups:
(7) Treatment group: Shoot tips were excised
from 8 ̄week ̄old stock shoots and encapsulated into
alginate ̄gel beads. Encapsulated shoot tips were pre ̄
cultured in a liquid MS medium containing 0 3 mol
L-1 sucrose supplemented with 3 5 mgL-1 6 ̄BAꎬ
0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3 for 24 h and
then loaded with a mixture of 2 molL-1 glycerol
plus 0 4 molL-1 sucrose for 30 min at 25 ℃ . Cryo ̄
protected shoot tips were transferred to a 2 mL plas ̄
tic cryotube and PVS2 was then added. After dehy ̄
dration with PVS2 at 25 ℃ for 20 minꎬ the encapsu ̄
lated and dehydrated shoot tips were plunged directly
into liquid nitrogen (LN) for 1 d. After rapidly re ̄
warming in a 40 ℃ water bath for 3 minꎬ PVS2 was
drained from the cryotubes and replaced third with
liquid MS medium supplemented with 3 5 mgL-1
6 ̄BAꎬ 0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3 and 1 2
molL-1 sucrose ( pH 5 8) and each kept for 10
min at 25 ℃ and then post ̄cultured on solidified MS
medium supplemented with 3 5 mgL-1 6 ̄BAꎬ 0 5
mgL-1 IBA and 0 1 mgL-1 GA3 in the dark for 3
days and then transferred to the light conditions (un ̄
der 16 h photoperiod at 36 μmolm-2s-1). Surviving
shoot tips were transferred to solidified MS medium
containing 3 mgL-1 6 ̄BA and 0 5 mgL-1 NAA
under 16 h photoperiod at 36 μmolm-2s-1 for growth
and after one month the shoots transferred to solidi ̄
fied hormone ̄free MS rooting medium under 16 h
408 植 物 分 类 与 资 源 学 报 第 37卷
photoperiod at 36 μmolm-2s-1 .
(8 ) Control group: Shoot tips were excised
from 8 ̄week ̄old stock shoots and cultured on solidi ̄
fied MS medium supplemented with 3 5 mgL-1 6 ̄
BAꎬ 0 5 mgL-1 IBA and 0 1 mgL-1 GA3 in the
dark for 3 days and then transferred to the light con ̄
ditions ( under 16 h photoperiod at 36 μmolm-2
s-1). Surviving shoot tips were transferred to solidi ̄
fied MS medium containing 3 mgL-1 6 ̄BA and 0 5
mgL-1 NAA under 16 h photoperiod at 36 μmol
m-2 s-1 for growth and after one month the shoots
transferred to solidified hormone ̄free MS rooting me ̄
dium under 16 h photoperiod at 36 μmolm-2s-1 .
After 4 months cultureꎬ various phenotypic char ̄
acteristics (height of plantletꎬ length of rootꎬ num ̄
ber of rootꎬ and number of leaf) of the regenerated
plantlets of the treatment group and the control group
were estimated.
1 3 Statistical analysis
Each cryopreservation experiment included at
least 15 shoot tips. Each cryopreservation experiment
was repeated three times. All data were subjected to
analysis of variance (one way ANOVA) and signifi ̄
cance (P < 0 05) was determined with Duncan’ s
multiple range test. Statistical tests were performed
by the help of SPSS statistical package version 19 0.
2 Results
2 1 Effect of preculture duration and sucrose con ̄
centration in preculture medium on regeneration
The results (Fig 1) demonstrate that high su ̄
crose concentrations (0 3 - 0 45 molL-1) during
preculure improve survival rate of shoot tips after
cryopreservation. Survival rates above 80% were only
noted with sucrose concentrations of 0 3 to 0 45 mol
L-1 . The survival rate of 82 5% obtained with 0 3
molL-1 sucrose differed significantly from that not ̄
ed with other sucrose concentrationsꎬ and 0 3 mol
L-1 sucrose can thus be considered optimal for re ̄
growth. Survival decreased to 37 6% in the presence
of 0 6 molL-1 sucrose and to 21 5% with 0 mol
L-1 sucrose and to 42 1% with 0 15 molL-1 sucrose.
Thusꎬ preculture using liquid MS medium containing
0 3 molL-1 sucrose supplemented with 3 5 mgL-1
6 ̄BAꎬ 0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3 for 24 h
was an important step for the successful cryopreser ̄
vation of red bud taro by encapsulation ̄vitrification.
As shown in Fig 2ꎬ the survival rate increased with
increasing preculture timeꎬ highest survival rate was
achieved (84 2%) when preculturing for 24 hꎬ and
then rapidly declined when preculturing for 48 h or
60 h. At the same timeꎬ The benefit of preculture
shoot tips before their loading was also tested using
liquid MS medium containing various concentrations
of sucrose supplemented with 3 5 mgL-1 6 ̄BAꎬ
0 5 mgL-1 IBAꎬ 0 1 mgL-1 GA3 for 24 h.
Fig 1 Effect of sucrose concentration in preculture medium on reg ̄
eneration of cryopreserved red bud taro shoot tips by encapsulation ̄
vitrification. Bars correspond to SE of means of three replications.
Values with different letters are significantly different using
Duncan’s Multiple Range Test (P<0 05)
Fig 2 Effect of preculture time on regeneration of cryopreserved red
bud taro shoot tips by encapsulation ̄vitrification. Bars correspond
to SE of means of three replications. Values with different
letters are significantly different using Duncan’s
Multiple Range Test (P<0 05)
5086期 WANG Ai ̄ping et al.: Cryopreservation of in vitro ̄Grown Shoot Tips of Red Bud Taro by
2 2 Effect of duration of loading treatment on
regeneration
To determine the appropriate loading time for
red bud taro shoot tipsꎬ different periods of time in a
mixture of 2 molL-1 glycerol and 1 6 molL-1 su ̄
crose at 25 ℃ before dehydration with PVS2 were
examined. As shown in Fig 3ꎬ loading was very ef ̄
fective in improving the survival rate of encapsulated
vitrified shoot tips cooled to -196 ℃ in comparison
with the unloaded shoot tips. Survival rate was 0 for
non ̄loaded shoot tips. Precultured shoot tips which
were loaded for 30 min produced the highest percent ̄
age of shoot regeneration (79 8%). Increasing the
loading period from 40 to 60 minꎬ the shoot tip sur ̄
vival rate decreased instead. Based on this resultꎬ
Fig 3 Effect of loading time on regeneration of cryopreserved red
bud taro shoot tips by encapsulation ̄vitrification. Bars correspond
to SE of means of three replications. Values with different
letters are significantly different using Duncan’s
Multiple Range Test (P<0 05)
a 30 minute loading time of 2 molL-1 glycerol plus
0 4 molL-1 sucrose was adopted as the loading time
for red bud taro shoot tips in subsequent experiments.
2 3 Effect of duration and temperature of ex ̄
posure to PVS2 on regeneration
To optimize the duration and temperature of ex ̄
posure to PVS2 controlling the regeneration of shoot
tips during encapsulation ̄vitrificationꎬ we dehydra ̄
ted encapsulatedꎬ precultured and loaded shoot tips
with PVS2 solution for various lengths of time at 0 ℃
and 25 ℃ before immersion in LN. As shown in
Fig 4 and Fig 5ꎬ exposure to PVS2 for 50 min at 0 ℃
or 20 min at 25 ℃ gave high survival rate for the
shoot tips testedꎬ but the highest rate of shoot regen ̄
eration (83 2%) was obtained by exposure to PVS2
for 20 min at 25 ℃ . Based on statistical analysisꎬ
this value is significantly different from that (71 1%)
of shoot tips treated for 50 min at 0 ℃ (P<0 05).
Howeverꎬ exposure to PVS2 for 30 to 60 min at 25 ℃
or for up to 60 min at 0 ℃ decreased shoot survival
rate. Thusꎬ in all experimentsꎬ shoot tips were pre ̄
viously dehydrated with PVS2 for 20 min at 25 ℃
prior to a plunge into LN.
2 4 Effect of cryopreserved storage duration on
regeneration
In order to examine the regeneration of the shoot
tips for long term storage in LNꎬ the shoot tips of red
bud taro were cryopreserved in LN for 1 to 150 days
Fig 4 Effect of exposure to PVS2 at 25℃ on regeneration of
cryopreserved red bud taro shoot tips by encapsulation ̄vitrifi ̄
cation. Bars correspond to SE of means of three replications.
Values with different letters are significantly different
using Duncan’s Multiple Range Test (P<0 05)
Fig 5 Effect of exposure to PVS2 at 0℃ on regeneration of
cryopreserved red bud taro shoot tips by encapsulation ̄vitrifi ̄
cation. Bars correspond to SE of means of three replications.
Values with different letters are significantly different
using Duncan’s Multiple Range Test (P<0 05)
608 植 物 分 类 与 资 源 学 报 第 37卷
by encapsulation ̄vitrification. Long term storage in
LN did slightly vary the regeneration percentage of
shoot tips surviving LN exposure (Fig 6)ꎬ statisti ̄
callyꎬ howeverꎬ the difference is not significant.
Fig 6 Effect of cryopreservation time on regeneration of cryopreserved
red bud taro shoot tips by encapsulation ̄vitrification. Bars correspond
to SE of means of three replications. Mean comparisons of each
survival rate were not significant (P>0 05)
2 5 Effect of rewarming on regeneration
To test the effect of rewarming on regenerationꎬ
encapsulated vitrified shoot tips in LN were thawed
rapidly in a water bath at 25 ℃ꎬ 40 ℃ and 45 ℃ for
3 min respectively. As shown in Fig 7ꎬ rewarming
rapidly in a water bath at 25 ℃ and 45 ℃ produced
low levels of shoot survival rate (62 7% and 49 8%
respectively). Rewarming at higher temperature (40 ℃)
had a much higher survival rate (80 9%) than that
at lower temperature (25 ℃ and 45 ℃).
Fig 7 Effect of rewarming temperature on regeneration of cryopreserved
red bud taro shoot tips by encapsulation ̄vitrification. Bars correspond
to SE of means of three replications. Values with different
letters are significantly different using Duncan’s
Multiple Range Test (P<0 05)
2 6 Effect of sucrose concentration in unloading
medium on regeneration
To investigate the effect of sucrose concentration
in unloading medium on regenerationꎬ the cryopre ̄
served shoot tips by encapsulation ̄vitrification was
unloaded third with liquid MS medium containing
various concentrations of sucrose supplemented with
3 5 mgL-1 6 ̄BAꎬ 0 5 mgL-1 IBAꎬ 0 1 mgL-1
GA3 (pH 5 8) and each kept for 10 min at 25 ℃ .
As shown in Fig 8ꎬ regrowth after immersion in LN
increased with the increasing of the concentration of
sucrose in unloading medium and shoot tips unloa ̄
ded with 1 2 molL-1 sucrose showed the highest
survival rate (85 4%).
2 7 Effect of post ̄culture on regeneration
The effect of post ̄culture on regeneration is shown
in Fig 9. The survival rate of cryopreserved shoot
tips by encapsulation ̄vitrification varied considera ̄
blyꎬ depending on the light culture conditions after
cooling. When shoot tips were post ̄cultured in the
dark for 3 days and then transferred to the light con ̄
ditions (under 16 h photoperiod at 36 μmolm-2s-1)ꎬ
the survival rate was maximum (82 6%). Howeverꎬ
when shoot tips were directly post ̄cultured under 16 h
photoperiod the survival rate decreased to 69 8%.
2 8 Plant regeneration
Successfully encapsulatedꎬ vitrified and warmed
Fig 8 Effect of sucrose concentration in unloading medium on reg ̄
eneration of cryopreserved red bud taro shoot tips by encapsulation ̄
vitrification. Bars correspond to SE of means of three replications.
Values with different letters are significantly different using
Duncan’s Multiple Range Test (P<0 05)
7086期 WANG Ai ̄ping et al.: Cryopreservation of in vitro ̄Grown Shoot Tips of Red Bud Taro by
Fig 9 Effect of post ̄culture on regeneration of cryopreserved
red bud taro shoot tips by encapsulation ̄vitrification. Ars
correspond to SE of means of three replications. Values
with different letters are significantly different using
Duncan’s Multiple Range Test (P<0 05)
shoot ̄tips remained green continuously after platingꎬ
resumed growth within a week and developed normal
shoots directly within three weeks without intermedi ̄
ary callus formation. Surviving shoot tips were trans ̄
ferred to solidified MS medium containing 3 mgL-1
6 ̄BA and 0 5 mgL-1 NAA under 16 h photoperiod
at 36 μmolm-2 s-1 for proliferation and after one
month the shoots transferred to solidified hormone ̄
free MS rooting medium under 16 h photoperiod at
36 μmolm-2s-1 and developed into plantlets within
2 months of culture. Various phenotypic characteris ̄
tics ( height of plantletꎬ length of rootꎬ number of
rootꎬ and number of leaf) of the regenerated plant ̄
lets of the treatment group and the control group
were estimated. As shown in Fig 10 and Fig 11ꎬ re ̄
generated plants derived from cryopreserved shoot
tips by encapsulation ̄vitrification were morphologi ̄
cally identical to controls and no morphological ab ̄
normalities were observed.
3 Discussion
The present results have demonstrated the feasi ̄
bility for the cryopreservation of red bud taro (C escu ̄
lenta L. Schott var. cormosus ‘Hongyayu’) shoot tips
by encapsulation ̄vitrification.
In the encapsulation ̄vitrification methodꎬ shoot
tips are dehydrated by a highly concentrated vitrifi ̄
cation solution (PVS2). Howeverꎬ the direct exposure
Fig 10 Comparison of morphological indexes of treatment group (with
cryopreservation) and control group (without cryopreservation). Bars
correspond to SE of means of three replications. Mean comparisons
of each of the morphological indexes between the two types
of plantlets were not significant (P>0 05)
Fig 11 Regeneration plantlets of treatment group
(Leftꎬ with cryopreservation) and control group
(Rightꎬ without cryopreservation)
of less tolerant shoot tips to PVS2 results in harmful
effects due to osmotic stress and chemical toxicity
(Sakai and Engelmannꎬ 2007). The harmful effects
due to dehydration can be alleviated or eliminated by
adequate preculture with high concentration of su ̄
crose (Sharaf et al.ꎬ 2012). Precultures of excised
shoot tips with different concentrations of sucrose
prior to loading treatment have been reported to be
effective in improving post ̄LN survival rates of shoot ̄
tips of some taro varieties. When shoot tips of three
C esculenta var. esculenta (L.) Schott cultivars (E399ꎬ
CPUK and TNS) were precultured on MS with 0 3
molL-1 sucrose in the dark for 16 h at 25 ℃ prior
to loadingꎬ the best recoveries were 21%ꎬ 29% and
808 植 物 分 类 与 资 源 学 报 第 37卷
30% respectively (Sant et al.ꎬ 2006). Howeverꎬ after
16 hours of preculture in 0 3 molL-1 sucrose under
a 16 h phtoperiod at 25 ℃ before cooling in LN by
vitrificationꎬ the average recovery rate of C esculenta
var. antiquorum cv. ‘Eguimo’ and C esculenta var.
antiquorum cv. ‘Dodare’ shoot tips could reach 83 1%
and 67% respectively (Takagi et al.ꎬ 1997). There ̄
foreꎬ preculture time and sucrose concentration in
preculture medium are mainly depending on plant
species and varieties. In the present studyꎬ culturing
encapsulated red bud taro shoot tips in liquid MS
medium supplemented with 0 3 molL-1 sucrose for
24 h was effective in inducing dehydration and cool ̄
ing tolerance. Preculturing for 12 h resulted in lower
survivalꎬ which can be attributed to an insufficient
acquisition of desiccation tolerance or cryoprotection
(Florence et al.ꎬ 1993). Longer periods of precul ̄
ture (>24 h) with 0 3 molL-1 sucrose did not fur ̄
ther improve the percentage of shoot formationꎬ most
likely due to tissue growth and changes in the physi ̄
ological condition (Wang et al.ꎬ 2005a). Similar
high sucrose concentration preculture also resulted in
tolerance of PVS2 dehydration and subsequent cool ̄
ing in droplet vitrificated shoot tips of C esculenta
var. esculenta cultivars (E399ꎬ CPUK and TNSꎬ et
al.) ( Sant et al.ꎬ 2008). before cooling in LN by
vitrification.
Following precultureꎬ shoot tips must be loaded
with a mixture of 2 molL-1 glycerol plus 0 4 molL-1
sucrose prior to exposure to PVS2 in order to prevent
injury by excess osmotic stresses or chemical toxicity
during dehydration (Hirai and Sakaiꎬ 1999aꎻ Hong
and Yinꎬ 2012a). In previous studiesꎬ shoot tips of
C esculenta var. esculenta (L.) Schott cultivars (Sant
et al.ꎬ 2006ꎬ 2008) and C esculenta var. antiquo ̄
rum cv. ‘Eguimo’ and C esculenta var. antiquorum
cv. ‘Dodare’(Takagi et al.ꎬ 1997) have been suc ̄
cessfully cryopreserved by loading for 20 min at 25 ℃
before the exposure to PVS2. In the present studyꎬ a
30 min period of loading treatment with a mixture of
2 molL-1 glycerol plus 0 4 molL-1 sucrose at 25 ℃
was also essential to produce a high survival rate in
cryopreservation by encapsulation ̄vitrification of red
bud taro shoot tips. Accordinglyꎬ loading might be
capable of enhancing the permeation of PVS2 and
provide desired degree of desiccation for red bud taro
shoot tips. Our results appeared to agree with those
of Sarab et al. (2012).
In the encapsulation ̄vitrification methodꎬ shoot
tips are usually dehydrated by PVS2 (Manar et al.ꎬ
2012). Thereforeꎬ the keys to success for cryopr ̄
eservation by encapsulation ̄vitrification are to care ̄
fully control the procedure for dehydration with
PVS2ꎬ which requires the optimum exposure time
and temperature to PVS2. To establish this objec ̄
tiveꎬ a treatment procedure at about 25 ℃ or 0 ℃
has been used (Sant et al.ꎬ 2008). In the present
studyꎬ red bud taro shoot tips treated with PVS2 for
50 min at 0 ℃ or 20 min at 25 ℃ prior to a direct
plunge in LN produced maximum survival rate. Incu ̄
bation time and temperature in PVS2 appears to be
taro ̄variety ̄specific and cryopreservation ̄protocol ̄spe ̄
cific. In cryopreservation of taro shoot ̄tips by vitrifi ̄
cationꎬ it was 12 min at 25 ℃ for shoot tips of three
cultivars of tropical taro (C esculenta var. esculenta
(L.) Schott) (Sant et al.ꎬ 2006) and 20 min at 25 ℃
for shoot tips of C esculenta var. antiquorum cv. ‘Eg ̄
uimo’ and C esculenta var. antiquorum cv. ‘Dodare’
(Takagi et al.ꎬ 1997). But in the cryopreservation
of shoot ̄tips of C esculenta var. esculenta (L.) Schott
cultivars by droplet vitrificationꎬ exposure time and
temperature to PVS2 was 20-40 min at 0 ℃ instead
of 25 ℃ (Sant et al.ꎬ 2008)ꎬ which improved the
survival rates to 73% - 100% from 21% - 30% ob ̄
tained with vitrification protocol (Sant et al.ꎬ 2006).
But the reason why the dehydration of PVS2 at 25 ℃
or 0 ℃ resulted in higher shoot survival are unclear.
The duration of storage generally does not affect
the survival of the shoot tips stored in LN (Yin and
Hongꎬ 2010). The maximal storage duration is theo ̄
retically unlimitedꎬ provided that the samples are
permanently kept at or near the temperature of liquid
nitrogen ( Engelmannꎬ 1991). Both Wang et al.
(2005b) and Tsai et al. (2009) have also demon ̄
9086期 WANG Ai ̄ping et al.: Cryopreservation of in vitro ̄Grown Shoot Tips of Red Bud Taro by
strated successful regeneration of shoot ̄tips of papa ̄
ya following storage in LN for 2 months and 2 years
respectively.
In the current studyꎬ the shoot tips of red bud
taro have been successfully recovered following liq ̄
uid nitrogen storage for 150 days with the same high
survival rate as the shoot tips cryopreserved for one
day. Our results were similar to those obtained in the
cryopreservation of Carica papaya (Kaity et al. 2013).
Howeverꎬ in cryopreservationꎬ rewarming has
been considered to be critical ( Engelmannꎬ 1991ꎻ
Guzmán ̄García et al.ꎬ 2013ꎻ Hülya et al.ꎬ 2013).
In the majority of the casesꎬ rewarming is carried out
rapidly by immersing the cryotubes containing the
samples in a water ̄bath thermostated at around 40 ℃
(Hong and Yinꎬ 2012b). Our results showed re ̄
warming at higher temperature (40 ℃) had a much
higher survival rate than that at lower temperature
(25 ℃ and 45 ℃). Results from this study are con ̄
sistent with results obtained with other taro varieties.
Sant et al. ( 2006) found when shoot ̄tips of three
cultivars of tropical taro (C esculenta var. esculenta
(L.) Schott) (E399ꎬ CPUK and TNS) were warmed
by rapid shaking in a water bath at 40 ℃ for 1 min
30 following cryopreservation by vitrificationꎬ the best
mean recoveries were 21%ꎬ 29% and 30% respec ̄
tively. Takagi et al. (1997) reported that after rapid
warming in a water bath at 40 ℃ following cryopr ̄
eservation by vitrificationꎬ the shoot tip average re ̄
covery rate of C esculenta var. antiquorum cv. ‘Eguimo’
and C esculenta var. antiquorum cv. ‘Dodare’ shoot
tips could reach 83 1% and 67% respectively. How ̄
everꎬ following Cryopreservation by droplet vitrifica ̄
tionꎬ the post ̄thaw survival rates of shoot tips of
tropical taro (C esculenta var. esculenta (L.) Schott)
cultivars reached 73%-100% (Sant et al.ꎬ 2008).
According to viewpoints of Sant et al. (2006ꎻ
2008) and Takagi et al. (1997)ꎬ it was essential to
plate the shoot tips with the unloading for the re ̄
growth of taro shoot tips. They also noted that unloa ̄
ding using 1 2 molL-1 sucrose was beneficial to
post ̄thaw cultures of C esculenta var. antiquorum cv.
‘Eguimo’ and C esculenta var. antiquorum cv. ‘Do ̄
dare’ shoot tips (Takagi et al.ꎬ 1997) and unloading
using liquid MS with 1 2 molL-1 sucrose was favora ̄
ble for regeneration of tropical taro (C esculenta var.
esculenta (L.) Schott) shoot tips (Sant et al.ꎬ 2006ꎬ
2008). In the present studyꎬ unloading third with
liquid MS medium supplemented with 1 2 molL-1
sucrose also could increase the survival rate of cryo ̄
preserved red bud taro shoot tips. Our results also
indicated when shoot tips were post ̄cultured in the
dark for 3 days and then transferred to the light con ̄
ditionsꎬ the survival rate was maximum. Howeverꎬ
when shoot tips were directly post ̄cultured under 16
hphotoperiod the survival rate decreased significant ̄
ly. This suggests that culture in the dark immediately
after rewarming may contribute to improve recovery
by limiting the detrimental photooxidation phenome ̄
na (Benson et al.ꎬ 1989)ꎬ as has been reported in
tropical taro (C esculenta var. esculenta (L.) Schott)
cultivars maintained in the dark for three days and
then transferred to dim light (3 5 μmolm-2s-1) for
one week (Sant et al.ꎬ 2006) or cultured overnight
in the dark (Sant et al.ꎬ 2008) and C esculenta var.
antiquorum cv. ‘Eguimo’ and C esculenta var. an ̄
tiquorum cv. ‘Dodare’ kept in dim light for 10 days
prior to exposure under the light conditions (Takagi
et al.ꎬ 1997).
In conclusionꎬ the encapsulation vitrification pr ̄
ocedure appears to be a simple and efficient method
for cryopreservation of red bud taro shoot tips. Fur ̄
ther studies should be directed at examining the ap ̄
plicability of this technique across taro genotypes.
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218 植 物 分 类 与 资 源 学 报 第 37卷