全 文 ：浙江大学学报(农业与生命科学版)　36(3):237～ 245 , 2010
Journal of Zhejiang University(Agric.& Life Sci.)
Article ID:1008-9209(2010)03-0237-09 DOI:10.3785/j.issn.1008-9209.2010.03.001
　　Received date:2009-05-11
Foundation i tem:Project sup ported by H en gshui College Foundation(2009026).
Biography:MA Guang , male , born in 1977 in Jining , Shandong Province , Ph.D , engaged in Plant Developm ental Biology.
E-mail:m aaohan@163.com.
Effects of thidiazuron and N6-benzylaminopurine on endogenous hormone
levels during regeneration of Brassica campes tris ssp.Rapi f era
MA Guang 1 , 2 , GUO Ji-ping 1 , 3(1 .Department of L i f e Sciences , Hengshui College , Hengshui , Hebei 053000 ,
China;2 .College o f Li f e Sciences , Northeast Forestry University , Harbin 150040 , China ;3 .College o f Food
Science and Engineering , H arbin Institute o f Technology , Harbin 150090 , China)
Abstract:To investiga te the r eason tha t thidiazuron(TDZ)is mo re effectiv e than N6-benzylaminopurine
(6-BA) in regeneration o f Brassica cam pestris L.ssp.rapi f era (Matzg.)Sinsk (syn.B.rapa ssp.
rap i f era), shoot reg ener ation was achieved fr om co ty ledona ry petiole of in v itro cultures using
Murashige and Skoog(MS)medium supplemented with 1-naphthalene-acetic acid(NAA)and TDZ or 6-
BA.The regene ration results suggested tha t the optimal combination w as TDZ 4.0 mg L-1+NAA 1.0
mg L-1 or 6-BA 5.0 mg L -1+NAA 1.0 mg L-1 , r espectively , and the shoo t fr equency w as 80.4%
and 30.2%, r espectively.The different effects o f the tw o combinations on the endogenous indole-3-acetic
acid(IAA), zeatin(Z), gibberellic acids(GAs)and abscisic acid(ABA)contents in coty ledonary petiole
e xplants we re studied.Highe r endogenous IAA and Z levels induced by TDZ 4.0 mg L-1 +NAA 1.0
mg L-1 than 6-BA 5.0 mg L-1 +NAA 1.0 mg L-1 w ere observed.The endogenous GAs and ABA
contents induced by the tw o combina tions w ere similar , respectively.The ratio of IAA/ABA and IAA/Z
bo th shifted tow ards IAA.The ratio o f IAA/ABA induced by TDZ w as highe r than 6-BA , and no visible
diffe rent effect on IAA/Z betw een TDZ and 6-BA.The results revealed tha t higher lev els o f IAA , and
ratio of IAA/ABA were two critical fac to rs , but ABA and GAs had no effect on mo re effective
regenera tion induced by TDZ than 6-BA.The roles of Z and IAA/Z w ere uncer tain and should be
investig ated in fur ther w o rks.
Key words:B rassica campestris ssp.rapi f era;Brassica rapa ssp.rapi f era;TDZ;6-BA;endogenous
ho rmone;regenera tion
CLC number:Q 946.885　　　Document code:A
马 光1 , 2 , 郭继平1 ,3(1.衡水学院 生命科学系 ,河北 衡水 053000;2.东北林业大学 生命科学学院 ,黑龙
江 哈尔滨 150040;3.哈尔滨工业大学 食品科学与工程学院 , 黑龙江 哈尔滨 150090)
TDZ和 6-BA对芜菁离体再生过程中内源激素水平的不同影响(英文).浙江大学学报(农业与生命科学
版), 2010 , 36(3):237-245
摘　要:为研究外源 TDZ和 6-BA对芜菁离体再生过程中内源激素的影响来阐明 TDZ 在促进芜菁离
体再生方面比 6-BA 更为有效的原因 ,采用不同浓度的 TDZ 和 6-BA 分别配合不同浓度 NAA 诱导芜菁
带柄子叶离体再生.结果表明:适合芜菁带柄子叶离体再生的外源激素浓度组合分别是 TDZ 4.0 mg
L-1+ NAA 1.0 mg L-1和 6-BA 5.0 mg L-1+ NAA 1.0 mg L-1;在这 2种组合诱导下的不定芽再生
浙江大学学报(农业与生命科学版)
率分别是 80.4%和 30.2%.分别测定在这 2 种外源激素组合诱导下带柄子叶外植体内源生长素
(IAA)、玉米素(Z)、赤霉素(GAs)和脱落酸(ABA)的绝对含量 , 并计算 IAA/ABA 和 IAA/Z 之间的
相对含量.结果表明:TDZ 4.0 mg L-1+ NAA 1.0 mg L-1的激素组合诱导带柄子叶外植体产生内源
IAA和 Z 的水平峰值显著高于 6-BA 5.0 mg L-1+ NAA 1.0 mg L-1的激素组合;而在 2 种外源激素
组合诱导条件下 ,内源 GAs 和 ABA 的含量差异不显著;IAA 的绝对含量左右了 IAA/ABA 和 IAA/Z
的变化趋势.综合内源激素的绝对含量和相对含量 , TDZ 比 6-BA 更好地诱导芜菁分化效果的关键因素
是由于 TDZ 诱导外植体产生了更高水平的 IAA 含量和 IAA/ABA 比值.TDZ 和 6-BA 诱导产生不同水
平的内源 Z和 IAA/Z 的作用还不明确.
关　键　词:Brassica campestris ssp.rapi f era;Brassica rapa ssp.rapi f era;TDZ;6-BA;内源激素;
再生
　　The importance of plant g row th regulators
and plant hormones in bo th stages of plant
regeneration has been widely documented during
the last decades.Plant g row th regulators added
exogenously exert part of their effect by
modifying the concentrations of endogenous
hormones[ 1] .It is generally accepted that the
plant hormones (cy tokinin and auxin) act to
control in plant regeneration , although the
biochemical , physiological and genetic factors
involved in this regulation remain poorly
defined[ 2] .
　　Turnip [ Brassica campestris L. ssp.
rapi fera(Matzg.)Sinsk , syn.B.rapa L.ssp.
rapi fera] is a cultivated widely vegetable , oil and
fodder crop of the mustard family , having a
large , fleshy , and edible root.It is a cool-weather
crop and well adapted for the northern parts of
China , Japan , Korea , Europe , United States and
Canada.Because of their importance in crop
production , there is an increasing interest to
develop technology of rapid and high-f requency
regeneration fo r breeding new cultivars.
　　Because turnip is not only a Brassica species
with AA genome but a crop w ith sw ollen root , it
is a most recalci trant Brassica species.Its
regeneration frequency induced by 6-BA is low.
The rate of regeneration induced by TDZ is far
more than 6-BA repo rted in other Brassica
species[ 3-4] .But the reason that TDZ is mo re
effective in regeneration than 6-BA remains not to
be resolved.To explain the reason , this study
focused on variation of endogenous hormone
levels such as indole-3-acetic acid(IAA), zeatin
(Z), gibberellic acids(GAs , GA 1 and GA3)and
abscisic acid (ABA)in regeneration of turnip
induced by the combination of TDZ +NAA and
6-BA +NAA , respectively.
1　Materials and methods
1.1　Plant material and shoot regeneration
　　Seeds ofTsudaturnip(B.campestris ssp.
rapi fera)were preserved in the culture collection
of the School of Life Sciences , Northeast Forestry
University , Harbin , China.The seeds were
carefully selected for unifo rmity and surface
sterilized by immersing in 70%ethanol for 3 min ,
followed by immersion in 30% solution of
commercial bleach (sodium hypochlorite),
containing 1 drop of Tw een 20 in every 100 mL of
the solution , for 20 min.Then they were
cultured in Murashige and Skoog (MS)medium ,
which contained 50 mL of medium composed of
MS salt mixture , 20 g L-1 sucrose , and
Gamborg s B5 vitamins at pH 5.8 before
autoclaving for 15 min at 121 ℃, and was
solidified with 0.7% agar.They w ere placed in
darkness at 26 ℃ for 48 h , and then under cool
w hite fluorescent light at 50μmol m-2 s-1 at 26
℃ for 48 h in a grow th chamber.
　　Cotyledonary petiole explants were
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马 光,郭继平:TDZ 和 6-BA 对芜菁离体再生过程中内源激素水平的不同影响(英文)
aseptically excised f rom 4-day-old seedlings
germinated from the seeds mentioned previously.
Cotyledons attached w ith petioles were excised
from the cotyledonary node so as not to include
the apical meristem.The explants were placed on
the shoot regeneration medium with cut ends of
the explants touching the medium.
　　For ini tiation of shoots , tw o types of
regeneration mediums w ere used to induce shoot
regeneration in this study.The first was MS
supplied w ith different concentrations(1.0 , 2.0 ,
3.0 , 4.0 , 5.0 , 6.0 and 7.0 mg L-1)of TDZ in
combinations with dif ferent concentrations(0.5 ,
1.0 , 1.5 , 2.0 mg L-1) of NAA.And the
second w as MS supplied with different
concentrations (1.0 , 2.0 , 3.0 , 4.0 , 5.0 , 6.0
and 7.0 mg L-1)of 6-BA in combinations with
different concentrations(0.5 , 1.0 , 1.5 , 2.0 mg
L-1) of NAA.All plant g row th factors w ere
added before autoclaving.5.0 mg L-1 AgNO3
was added to each medium af ter autoclaving.
Explants were cultured under the same light and
temperature condition for raising seedlings
described above w ith 8 h darkness and 16 h light.
1.2 　 Sampling , extraction , purification and
quantitation of endogenous plant hormones
　　The cotyledonary petiole explants cultured in
shoot regeneration medium supplied with TDZ
4.0 mg L-1 +NAA 1.0 mg L-1 (named
explant T)and medium supplied with 6-BA
5.0 mg L-1 +NAA 1.0 mg L-1 (named
explant B)for 0 , 2 , 4 , 6 , 8 , 10 , 12 , 14 , 16 d
were used for plant hormone ext ration.
　　Hormone levels were determined by ELISA
according to the method of Yang et al.[ 5] and
Tang et al[ 6] .Explants were ground with 80%
methanol containing 1.0 mmol L-1 butylated
hydroxytoluene and ext racted with 100 mg of
polyvinylpyrrolidone (PVP) per gram fresh
material for 4 h at 4 ℃in darkness.The resulting
ext ract was loaded onto Chromosep C18 columns
(C18 Sep-Park Cartridge , Waters Corp.,
Millford , MA).The columns w ere prew ashed
with 10 mL 100%(W/V)and 5 mL 80%(V/V)
methanol , respectively.The hormone fractions
were eluted w ith 10 mL 100%(V/V)methanol
and 10 mL ether f rom the columns and dried
under N2 , and dissolved in 2 mL phosphate buf fer
saline(PBS)containing 0.1%(V/V)Tween 20
and 0.1% (W/V) gelatin (pH 7.5) for the
analysis by ELISA.
　　The mouse monoclonal antigens and
antibodies against IAA , GAs , ABA and Z , and
IgG horseradish peroxidase used in ELISA were
produced at the Phytohormones Research
Institute , China Ag ricultural University.Each
well on the microtit ration plate was coated with
100μL coating buf fer (1.5 g L-1 Na2 CO3 , 2.93
g L-1 NaHCO3 , and 0.02 g L-1 NaN3 , pH
9.6)containing 0.25 μg mL-1 antigens against
the hormones.The coated plates w ere incubated
fo r 4 h at 37 ℃ for GAs , and ABA and Z , and
overnight at 4 ℃ for IAA , and then kept at room
temperature for 30 to 40 min.After washing four
times with PBS +0.1% Tween 20 buffer (pH
7.4), each w ell w as filled with 50 μL of either
pollen grain extracts or IAA , GAs , ABA and Z
standards(0 to 2 000 ng mL-1 dilution range),
and 50 μL of 20 μg mL-1 antibodies against
IAA , GAs , ABA and Z , respectively.The plate
w as incubated fo r 3 h at 28 ℃for GAs , ABA , Z ,
and overnight at 4 ℃ for IAA , and then w ashed
as above.One hundred microlitres of 1.25 μg
mL-1 IgG-horseradish peroxidase substrate were
added to each w ell and incubated for 1 h at 30 ℃.
The plate w as rinsed five times wi th the above
PBS and Tween 20 buffer , and 100 μL color-
appearing solution containing 1.5 mg mL-1 0-
phenylenediamine and 0.008%(V/V)H2O2 was
added to each well.The reaction w as stopped by
the addition of 50μL 6 mol L-1 H2 SO4 per w ell
w hen the 2 000 ng mL-1 standard had a pale
color , and the 0 ng mL-1 standard had a deep
color in the wells.Color development in each w ell
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浙江大学学报(农业与生命科学版)
was recorded using an ELISA Reader (model
EL310 , Bio-TEK , Winooski , VT) at optical
density A490 nm .IAA , GAs , ABA and Z contents
were calculated following Weiler et al[ 7] .
1.3　Data analysis
　　The level of each hormone per sample w as
measured 5 times and the values were corrected
for recovery.Microsof t Excel 2003 w as used for
statistical analysis.
　　Data for hormonal levels were based on two
independent experiments , which gave similar
results , but the values given in this paper w ere
from one experimental series.
2　Results and discussion
2.1　Regeneration from cotyledonary petiole
explants
　　Seven days af ter inoculation , the cut surfaces
of the explants sw elled , but no callus w as
observed almost , and the green shoot bud
regenerated direct ly from the cut surfaces of the
explants by day 14.
　　Combinated with whether TDZ or 6-BA ,
NAA had a significant ef fect on regeneration with
highest regeneration frequency at the
concentration of 1.0 mg L-1.At the less and
higher concentrations , the regeneration f requency
were less(Fig.1 and Fig.2).
　　When concentration of TDZ w as 1.0 mg
L
-1 , no shoot regenerated. The optimal
concentration of TDZ was 4.0 mg L-1(Fig.1).
For 6-BA , the concentrations of 1.0 mg L-1 and
2.0 mg L-1 could no t induce shoo t regeneration ,
and i ts optimal concentration w as 5.0 mg L-1
(Fig.2).
　　Combinated with NAA to induce turnip
shoot regeneration , the effect of TDZ w as much
higher than 6-BA(Fig.1 and Fig.2).
　　A TDZ 4.0 mg L-1 + NAA 1.0 mg L-1
combination produced the highest percent
regeneration of 80.4%(Fig.1), but a 6-BA 5.0
mg L-1 + NAA 1.0 mg L-1 combination only
produced the highest percent regeneration of
30.2%(Fig.2).The tw o combinations were
selected for investigating their effect on the level
of endogenous hormone in explants.
Fig.1　Shoot regeneration from cotyledonary petiole
explants treated with TDZ + NAA
Fig.2　Shoot regeneration from cotyledonary petiole
explants treated with 6-BA + NAA
2.2　Change of endogenous hormone
2.2.1 　Change of endogenous IAA 　　The
following results could be concluded from Fig.3.
In explants T and explants B , the initial levels(at
day 0) of endogenous IAA increased af ter
initiation and reached a maximum value (at day
4).The maximum value of endogenous IAA in
explants T was far higher than that in explants B ,
then the tw o maximum values decreased and
reached a minimum value.For explant T , a
minimum value reached at day 10 , and for explant
B , a minimum value reached at day 12.The two
240 第 36卷　
马 光,郭继平:TDZ 和 6-BA 对芜菁离体再生过程中内源激素水平的不同影响(英文)
minimum values did not show significant
difference.After reaching the minimum value ,
the levels of endogenous IAA in explants in two
types of explants increased and almost resumed to
thei r initial levels.
Fig.3　Effects of TDZ 4.0 mg L-1+ NAA 1.0 mg
L-1 and 6-BA 5.0 mg L-1+ NAA 1.0 mg
L-1 on the endogenous levels of IAA in
cotyledonary petioles
　　The peak in IAA concentration was observed
in two types of explants after 4 d cultures
(Fig.3), indicating that the tissue increased and
then accelerated synthesis of this ho rmone in its
active form.The level of endogenous IAA in
explant T was alway s higher than explant B ,
which suggested that TDZ could stimulate the
synthesis of IAA more effectively than 6-BA ,
especially in initial stage. During somatic
embryogenesis , high endogenous IAA levels have
also a positive correlation with a high
embryogenic capacity
[ 8] , but once embryogenic
development is established and has prog ressed to
some degree , levels of IAA decrease again[ 9] .In
this study , the higher level of endogenous IAA in
explant T can make more cells acquire
embryogenic characteristics. Once the cells
acquire embryogenic characteristics , the levels of
endogenous IAA in bo th two types of explants
decreased until the minimum values reached.For
explant T and explant B , the adventitious shoots
started ini tially at day 10 and day 12 ,
respectively , which w ere consistent w ith the time
when minimum values of endogenous IAA were
observed.Level of endogenous IAA increased
again after the minimum values of IAA were
observed.The higher level of endogenous IAA
made explant T shoot more quickly.Our result
about the variation of endogenous IAA was
consistent with tw o main stages of
regeneration[ 10] . Day 4 with maximum of
endogenous IAA was a symbol of t ransformation
f rom induction stage to expression stage.The
transformation w as also observed in variation of
IAA/Z and IAA/ABA ratio.The precursors of
IAA , β-indolylethylamine and tryptophan ,
increased in the seedling of earthnut cultured in
the medium with TDZ[ 11] .2-(4-Chlorophenoxy)-
2-methy lpropionic acid , the inhibitor of
endogenous IAA biosynthesis , can reduce the rate
of somatic embryos in earthnut[ 11] and
geranium[ 12] .These results were consistent with
ours.However , some studies suggested that TDZ
could not increase the content of endogenous
IAA , and TDZ could enhance the effect of IAA
by its interaction with IAA instead of enhance of
the IAA content
[ 13] .
2.2.2 　 Change of endogenous Z 　 　 The
endogenous Z level in explant T and explant B
increased and reached a maximum value (at day
10 in explant T , at day 12 in explant B), then
decreased dramatically.At maximum point ,
endogenous Z level in explant T w as higher than
explant B significantly(Fig.4).
　　In this study , the content of Z induced by
combination of TDZ and NAA was higher than
combination of 6-BA and NAA.Guiderdoni et
al.[ 14] reported higher levels of zeatin in non-
embryogenic calluses than in the embryogenic
calluses of sugarcane.Some researches indicated
that TDZ could induce the biosynthesis of
cy tokinin and inhibit deg radation of endogenous
auxin[ 15] .TDZ can enhance the activity of the
enzymes which make cytokinin-nucleotide acid
transform to cy tokinin-nucleotide , and i t also can
241　第 3期
浙江大学学报(农业与生命科学版)
Fig.4　Effects of TDZ 4.0 mg L-1+ NAA 1.0 mg
L-1 and 6-BA 5.0 mg L-1+ NAA 1.0 mg
L-1 on the levels of endogenous Z in
cotyledonary petioles
inhibit the decomposition ability of cytokinin
oxidase on endogenous zeatin
[ 16] .When somatic
embryos were induced by TDZ in earthnut ,
adenine , zeatin , dihydro-zeatin were accumulated
and isopenteny ladenine decreased which also
resulted f rom the inhibi tion on cy tokinin oxidase
of TDZ
[ 17] .Diaminopurine , inhibitor of adenine
phosphoribosyltransferase , can decrease the
content of adenine , zeatin , dihydro-zeatin and
increase the content of isopentenyladenine , which
reduced the rate of somatic embryos induced by
TDZ
[ 11-12] .So , it can be concluded that TDZ
could increase the accumulation of endogenous Z
to induce somatic embryos.
　　Nagata et al.[ 18] found that TDZ and BA
both could be identified and combined with
cytokinin-specific binding protein (CSBP), and
TDZ combined with CSBP w as more stable than
BA.Their results suggested that cytokinin
activity of TDZ was higher than purine cytokine ,
which was the reason about more content of Z
induced by TDZ than BA in our study.Different
results were obtained in the w orks about the
effect of exogenous BA on endogenous content of
Z.In tissue culture of Actinidia deliciosa petioles
induced by exogenous BA , the content of
endogenous Z declined significantly.However , in
tissue culture of tobacco , the result w as
contrary[ 19] .
2.2.3　Change of endogenous ABA and GAs
The levels of endogenous ABA in explant T and
explant B did not show any dif ference.They
show ed an enhancement until 4 day s of culture
and then decreased(Fig.5).
Fig.5　Effects of TDZ 4.0 mg L-1+ NAA 1.0 mg
L-1 and 6-BA 5.0 mg L-1 + NAA 1.0 mg
L-1 on the levels of endogenous ABA in
cotyledonary petioles
　　Explant T showed a level of endogenous
GAs very similar to explant B.Contrary to the
levels of ABA , the levels of endogenous GAs
decreased at the early stages and then increased
(Fig.6).
Fig.6　Effects of TDZ 4.0 mg L-1+ NAA 1.0 mg
L-1 and 6-BA 5.0 mg L-1 + NAA 1.0 mg
L-1 on the levels of endogenous GAs in
cotyledonary petioles
　　For the ef fects on endogenous GAs and
ABA , there were no significant dif ferences
between combination of TDZ and NAA and
242 第 36卷　
马 光,郭继平:TDZ 和 6-BA 对芜菁离体再生过程中内源激素水平的不同影响(英文)
combination of 6-BA andNAA in this study.Few
works were reported about the regulation of TDZ
or 6-BA on GAs and ABA.GAs can inhibit the
somatic embryo s of geranium in induction and
expression stages , and inhibitors of GAs can
increase the rate of somatic embryos induced by
TDZ in geranium[ 12] .When TDZ was sprayed on
leaves of geranium or panax , shoots w ere
inhibited
[ 20] .The internodes of shoots induced by
TDZ were often shorter than normal ones.So ,
TDZ can change the metabolic process of GAs in a
mode of negative regulation.In this study , GAs
contents w ere in a low level w hen shoot w as
induced by TDZ or 6-BA in turnip , which w as
consistent wi th the reported results.
　　 In some studies , TDZ can decrease the
content of endogenous ABA [ 21] .Reduction of
endogenous ABA levels in cultured leaves of
Pennisetum purpureum in the medium with 6-BA
and 3 ,4-dichlorophenoxyacetic acid inhibited their
capaci ty to produce somatic embryos[ 22] , while it
promoted the acquisition and conservation of an
embryogenic state in calli of Hevea brasi liensis in
the medium with 6-BA , NAA and 2 ,4-D [ 23] .In
the medium with 6-BA and IBA , the content of
ABA in explants increased firstly and then
decreased
[ 21] .In this study , the similar modes of
endogenous ABA in explants of turnip induced by
combination of TDZ and NAA , and combination
of 6-BA and NAA were observed.Therefore , it
seems that the ef fects of 6-BA on endogenous
ABA depend on the plant material and culture
conditions.
2.2.4 　Change of endogenous IAA/ABA and
IAA/Z　　In both types of explants w here IAA/
ABA balance shif ted towards IAA , explants T
had a higher ratio than explants B especially from
day 2 to day 8 (Fig.7).At day 4 when the
maximum value of IAA/ABA was observed , the
ratio of IAA/ABA of explant T w as 1.5 times
than explant B.At day 10 , when the minimum
value of IAA/ABA was observed , the ratio of
IAA/ABA of explant T was almost equal to
explant B.After day 10 , the ratio of IAA/ABA
of explant T was higher than explant B again , but
the dif ference was less significant than that f rom
day 2 to day 8.
Fig.7　Effects of TDZ 4.0 mg L-1+ NAA 1.0 mg
L-1 and 6-BA 5.0 mg L-1 + NAA 1.0 mg
L-1 on the ratios of IAA/ABA in cotyledonary
petioles
Fig.8　Effects of TDZ 4.0 mg L-1+ NAA 1.0 mg
L-1 and 6-BA 5.0 mg L-1 + NAA 1.0 mg
L-1 on the ratios of IAA/Z in cotyledonary
petioles
　　In Fig.8 , IAA/Z ratio in both types of
explants w as also always shifted tow ards IAA.
Differing from IAA/ABA , IAA/Z ratio in
explant T changed in a similar model to explant
B , and there were no significant difference
between them.The maximum values of IAA/Z in
bo th two types of explants were observed at day
2.The minimum values of IAA/Z in explant T
and explants B were observed at day 10 and day
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浙江大学学报(农业与生命科学版)
12 , respectively.
　　In 1957 , Skoog and Miller [ 24] hypothesized
that the route of development of regenerants in
cell culture was determined by the relative ratio of
auxin to cy tokinin.The importance of this ratio in
explants , more than their IAA and/or ABA
content , for the induction and expression of
somatic embryogenesis was identified in leaves of
Medicago falcata by Ivanova et al.[ 25] , who
established a posi tive correlation between auxin-
favorable values and the embryogenic capacity of
the explants.We showed the IAA/ABA and
IAA/Z ratio s of explant T and explant B in turnip
in Fig.7 and Fig.8 , respectively.In spite of
significant difference observed in the levels of IAA
and Z betw een explant T and explant B , there
were small differences being observed in the levels
of IAA/Z ratio in either types of explants.Thus ,
with respect to the effects on endogenous IAA or
Z , the difference between combination of TDZ
and NAA and combination of 6-BA and NAA
mainly lied in their absolute values , rather than
the ratios between them.With respect to IAA/
ABA ratio , the ratios of explant T w ere higher
than explant B , especially f rom day 2 to day 6.In
Cory lus avellana L. cotyledons cultured in
medium added with 6-BA and IBA , the IAA/
ABA ratio in the embryogenic genotype of
hazelnut(cv.Casina)was nearly twice as high as
that in the non-embryogenic one (cv.Negret ta),
in spi te of the small differences observed in the
levels of each individual phy tohormone [ 21] .
3　Conclusion
　　From the results above , it can be concluded
that the higher level of endogenous IAA was a
critical role accounting for reason that TDZ w as
more efficient than 6-BA when turnip
regeneration with cotyledonary petiole as explant.
Besides , higher IAA/ABA ratio induced by TDZ
which also resulted f rom the higher level of
endogenous hormone was another reason.
Though endogenous Z levels induced by TDZ
were higher than that by 6-BA , the role of
endogenous Z was not clear for small dif ference of
IAA/Z ratio between the explants cultured with
TDZ and NAA and those cultured with 6-BA and
NAA.
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