Beachy, R.N.

Fauquet, Claude

Rance, I.

Sivamani, E.

Wenzhong, T.

Horizon / Pleins textes

. 
Chinese Journal of Genetics 
Volume 21, Number 3., 15 99 ' 
I ! 
IMPROVEMENT OF PLANT REGENERATION 
FREQUENCY IN VITRO IN INDICA RICE 
Tian Wenzhong,@ 
Iam Rance, Elunialai Sivamani, 
auquet and Roger N. Beachy Claud 
lnkxnatio P Laboratory forTropical Agricultural Biotechnology, 
The Scripps R d  Institute, La Job, CA 92037, USA 
In order to improve the frequency of plant regeneration from callus in indica rice, the influ- 
ences of different factors on plant regeneration were investigated. Supplement with 
cytokinins (KT, BAP, Zeatin or 2ip, lmg / L) and NAA(1 mg / L), or supplement with 
thidiazuron ( O S  mg / L) in the induction medium or subculture medium; and partial 
desiccation of callus before transfer to regeneration medium have been found significantly 
increase the frequency of plant regeneration in indica riœ. 5 - 14 folds more plants were ob- 
tained than untreated control by the combination of these treatments with indica varieties 
TN1 , IR72 and IR@. 
KcY WORDS: Indica rice, Tissue culture, Regeneration plant - - _  . _  
Received: December 2,1993 
INTRODUCTION 
Rice (Oryza sativa L) is one of the most important œreal crops. About 40% the world's popu- 
lation, especially the people in many developing countries, are living on this important crop. Them 
fore, the improvement of rice varieties is a pressingissue at the moment. 
It is hoped that this task will be completed by directed genetic manipulation at the single cell, 
and tissue, or organ level, thereby shortening the time required for breeding p l a n t h t h  disease and 
insect resistance, improving nutritional quality and stress tolerance. I t  is therefore essential to devel- 
op efilcient methods for the transformation of beneficial genes in rice plants and regeneration of 
rice plants. 
Japonica and Indica rice are two major subspecies growing in dflerent regions of the world. 
Successful plant regeneration of Japonica rice has already been reported using tissue culture proce 
durcs for transformation [I4' . But the use of the same protocol with Indica rice varieties, such as 
IR72, IR64, and TNl , results in a very low regeneration ability. However indica rice varieties are of 
grcater importance and irreplaceable, because they provide the principle food source in most of the 
regeneration in indica rice to increase the frequency of plant regeneration from rice calli. Tbese fac 
3 world's tropical regions. Therefore we have to investigate the influence of Werent factors on plant '. 
0 Institute of Genctics, Academia Siniff Beijing, 100101, China 
I 2 Chinese Journal of Genetics 
*I 
tors are the following: new hormone combination in induction medium or subculture medium or 
addition of TDZ; and partial desiccation treatment of calli and so on. 
MATERIALS A N D  METHODS 
1.1 Plant matcriak 
Seeds of thc indica rice varieties TNl, IR72 and IR64 wrer obtained from the International 
Rice Research Institute (Los Banos, Philippines). Mature and immature seeds were used as explants 
to induce callus. 
Mature or immature dehuched seeds were surface sterilized with 70% ethanol for 1 minute, 
and 25% bleach of commercial for 45 minutes, rinsed 4-5 times with sterilized water, then placed 
on various induction mcdia according to the experiment. 
1.2 Mcdium 
1.2.1 Induction Medium and Subculture medium The basic medium is NB medium (as 
described previously, i.e. N6 medium Is’ macroelements, B5 medium “O) microelements and B5 
medium vitamins), Caseine enzymatic hydrolysate 300 mg / L, proline 500 mg / L, plus 2, 4-D 
2mg/ L, pH 5.8, agarose (Sigma) 4 g /  L. 
We have compared different hormone combination in the induction medium and subculture 
medium, such as 2,4-D 1 or 2 mg/ L with NAA 1 to 3 mg/ L, and kinetin, BAP, zeatin, 2ip or 
thidiazuron (TDZ) 0.5 to 1 mg / L. 
The basic regeneration medium is NB medium or MS m e  1.2.2 Regeneration Medium 
plus NAA 0.5-0.05mg / L BAP 3 mg / L, pH 5.8-6.0, and phytagel (Sigma) 2.5 g / L. 
We have tried using kinetin, zeatin, 2ip and TDZ instead of BAP in the regeneration medium. 
dium Cl91 
1.2.3 Medium for Growth of Plantlets 
I 
I 1 / 2 MS medium ‘”’ salts, B5 medium ‘‘O) vitamins, NAA 0.05 mg/ L, pH 5.8, phytagel 
(Sigma) 2.5 g / L. 
13 Culture condition and trcatmcnt 
1.3.1 After seeds were inoculated on induction medium in dark, at 26C for 2-3 weeks, the calli 
were transferred onto regeneration medium or propagated in the same condition for subculture. 
The calli onto the regeneration medium under light were induced the differentiation of green 
spots and small shoots. Then the green calli were transferred on hormone-fke medium or only 
plus 0.05 mg/ L NAA medium in order to allow rooting and shoot growth in about three addi- 
 ona al weeks. 
1.3.2 Desiccation Before the calli were transferred onto regeneration medium, the calli were 
partially desiccated. To do so, calli were placed on one or two layers of filter paper in a Petri dish. 
The Petri dishes were kept at 26C in dark for 2 to 6 days (depending on the size of the callus), so 
that they lost about 40 to 65% of their water content (difference between the weight before and d- 
Sometimes desiccation were also applied to the calli which did not regenerate, or the small 
shoo& did not germinate on regeneration medium for long tem. 
1.3.3 Light microscopy observation The callis on different induction medium were fured in 
HistoChoice Tissue Fixative (Amresco), then samples were dehydrated, embedded, cut sections and 
o ter the treatment). Then, the calli were transferred to regeneration medium. ‘. 
3 i Volume 2 1, Number 3 
< 
stained with Periodic acid-Schiff (PAS) '*' . Then kt ions  of callus were observed under micro- 
scope. 
2 R a u b  and Discussion 
Experi- medium Resource of NO. of callus 
ment Callus tested 
11 
NBK medium IO 
NB medium Mature seed 30 
NBK medium 21 
Immature NB medium seed I 
II 
21 Effect of diffcrent hormonc combinafions in induction and subculture media 
cration medium, only obtained a very poor regeneration frequency in indica rice (about @lo%). 
can improve later regeneration frequency. 
The calli induced on N B  medium supplemented with 2,4-D alone were transferred to regen- 
We found that supplement with NAA, Kinetin and 2,4-D in induction or subculture medium 
0.0 
rgen& 
rated plant 
O 
1 
O 
8 
Table 1 
I TNl 
E f k t  of Supplement of K T  and N A A  in Induction Medium on Regeneration Frequency in 
NB medium 
NBK medium 
NB medium 
NBK medium 
NB medmm 
Mature seed 54 O 
52 7 
Subculture 89 O 
91 11 
Subculture 59 O 
m 
NBK medium 
NB medium 
V 
65 6 
Subculture 66 1 
NBK medium I ' I 69 I 18 
Re enerated 
' 0.0 
10.0 
p a n t %  5 
0.0 
38.1 
0.0 
13.46 
0.0 
12.09 
0.0 
. 9.23 
1 .O5 
26.09 
Note:NBmedium:+2,4-D2mg/ L;NBKmedium:+&4-D2mg/ L+KT lmg/ L + N M  l m g / L  
The calli, which were induced and grown on NB medium containing 2,4-D 2 mg / L, Kinetin 
1 mg / L and N A A  1 mg / L, provided better regeneration frequencies than 2 , d D  2 mg/ L 
alone. This experiment has been repeated more than 6 times in TNl , one time was immature seeds 
as explants, two times were mature seeds as explants, tree times were subcultures, and the results of 
every time were the same (Table 1). 
We have obtained similar results in TR72, IR64 and other varieties. 
i, '. 
We found that supplied N A A  and cytokinin in induction medium or subculture medium can 
improve the quality of the callus. The morphology of callus grown on the that on N B  medium sup 
plement with 2,4-D, N A A  and kinetin were more embryogenic, granular, and compact than NB 
4 Chinese Journal of Genetics 
I 
, 
medium with 2,4-D alone. (Fig. A and B) 
From the histological section we can see that there were many old, empty cells or the cells with 
thinner cytoplasms, bigger vacuoles, and smaller nuclears in the calli induced on 2,4-D alone m e  
&um. However the cells with thjcker cytoplasms, bigger nucleus and some of them being in a vig- 
orous mitosis in the calli induced on medium cantaining 2, 4-Dy NAA and kinetin. (Fig. C and D) 
Thc quality of callus is very importent for the regeneration, and improvement of the quality of 
callus in the induction and subculture medium is also very importent for increasing the regeneration 
frequency. 
We have tricd using zeatin, 2ip and thidiazuron O Z )  as supplement in induction medium, or 
subculture medium most of them resulted in higher frequencis of plan regeneration from TN1, 
IR72 and IR64. For example, Fig 1. shows the effect of different hormone combination in hduG 
tion medium on IR64 plant regeneration. The highest frequency (44.64%) of plant regeneration 
have been obtained from the calli induced on NB medium containing 2,4-D 2mg/ L, NAAl 
mg/LandTDZlmg/L .  
Fig I Effect of Different Hor"e Combination in Induction medium on Regeneration 
Frequency in IR64 
l 
Note: NB: NB medium + 2,4-D 2mg / L 
NBK: NB medium + 2,4-D 2mg / L +  KT Img/ L+ NAA lmg/ L 
NBB:NBmedium +2,4-D 2mg/L+BAP lmg/L+NAA lmg/L  
NBZ: NB medium + 2,4-D 2mg / L + Zeatin lmg / L + NAA lmg / L 
NB2iP: NB medium + 2,4-D 2mg/ L +  2 p  lmg/ L+ NAA lmg/ L 
. NBTDZ:NBmedium+2,4-D 2mg/L+TDZlmg/L+NAA l m g / L  
The thidiazuron is a substituted phenylurea, it exhibits strong cytokinin -like activity. TDZ 
> Volume 21, Numbex3 
I 
! No.of regene- 
Variety MediLlm No.of callus rated 
plant tested 
5 
Regeneration YO 
! can induce cytokinin autonomy in callus cul’hues, and stimulate ethylene production. It has been I 
I demonstrated that TDZ can induce shoot differentiation, embryogenesis and organogenesis in tis 
sue culture in bean [3,15], peanut [20], rubus [8], geranium. [ll]; and white ash [l]; and cassava [17]. 
In our experament the calli in Indica rice grown on TDZ medium calfi dserentiated small 
shoots and roots after one week (Fig E), then were transferred to cytokinin-free medium, and 
plantlets were 
grown up soon. (Fig F). 
Further experaments of TDZ demonstrated that using TDZ alone in subculture medium was 
better for plant regeneration in Indica rice. Than TDZ combined with 2,4-Dy or TDZ combined 
with 2,4-D, NAA, and 2,4-D alone (control) (Table 2). 
David S. Koetje et al. (1989) reported that plant regeneration on N6 medium exhibited a dra- 
matic 2,4-D dose response with increasing concentrations of 2,4-D above 0.5mg/ L being 
increasingly inhibitory to plant development. Dzerential response to medium may also have re 
sulted in an auxin: cytokinin ratio which inhibits embryo germination in some genotypes. So we 
suggesed that it is beneficial to keep certain auxin: cytokinin ratio in induction or subcultuce me 
d u m  in indica rice. Sometimes, we need a higher concentration of cytokininiFor example we have 
obtained 93.7% plant regeneration frequency from the calli grown on the medium containing 
2,4-D2mg/L+KTI mg/L+BAPImg/L+NAA Img/L. 
However the cytokinin can promote chloroplast development and chlorophyll synthesis [9]. 
Sometimes we can get 100% green callus, but only a few plants can be obtained. As soon as green 
calli with unequal are formed differentiation, they should be transferred onto 1 / 2 MS hormone 
free medium or desiccated,so that they can regenerate or geminate. 
TNl 
Table 2 
Function of T Z  in ‘Induction Medium 
1 41 2 5.13 
2 92 22 25.05 
~ 
1 R64 
3 75 30 39.61 
4 55 25 . 45.37 
1 60 2 3.33 
2 64 10 15.63 
3 50 7 14.00 
4 56 12 21.43 
~ 
Note: mediuml: NB+2,4-D 2 mg/ L 
medium 2: NB+2,4-D 2mg/ L+TDZO.Smg/ L 
medium 3 NEH-Z.4-D 2mg/ L+TDZ 05mg / L+NAAlmg/ L 
mcdium 4: NB+TDZO.Smg / L 
2.2 The Effect of Partial Desiccation on Regeneration Ability: Tf callis undergo the partial 
6 Chinese Journal of Genetics 
NoDesic. 1 
desiccation befer transfered to regeneration medium, plant regeneration frequency. could be obvi- 
ously enhanced. 
We have repeated 8 times with TNl , 4 times with IR72, and 2 times with IRM. Table 3 shows 
the efficient effkct of partial desimtion..The plant regeneration frequency of TNl with desiccation 
increased more than one fold, IR72 increased 3 folds, and IR64 increased neerly 3 folds. 
Partial NoDesic. 1 Desic. Nodesic. 1 ;$:! 
Some of the green calli o r  small shoots on the regeneration medium or 1 / 2 MS medium can 
not diffcrcntiate to plantlets, or small shoots cannot germinate, We have to desiccate. About 70% 
regenerated plants have been obtained from these green calli or small shoots wich had beenkept in 
previous medium about two months. 
Seeds inoculated 
Plants regenerate 
% of regeneration 
mean 
deflation) 
ITabk 3 
Effect of Partial Desiccation on Regeneration 
520 903 279 316 235 213 
165 609 43 193 44 157 
31.7 67.4 15.5 61.1 18.7+ 2.9 73.75 6.7 
(+15.1 (4-11.23) (4-17.9 ( t17 .2 )  
I TN1 : I  1 R72 1 . 1R64 
I l l l l l 
Nok: Induction medium w m  NB, NBK and NBB. 
Regeneration medium: NB+BAP 3mg / LTNAA 0.5 mg/ L. 
Somatic embryo desiccation has been reported to enhance development in grape [12], soybean 
[I 31, wheat [4], spruce [21] and cassava. RecentIy,'Masayoshi Tsukahara and Takayasu Hirosawa 
(1992) reported that simple dehydration treatment promotes plant regeneration of rice callus in 
Japonica rice [16]. 
It has been reported that water stressed plants showed higher abscisic acid (ABA) biosynthetic 
activity [18,23,24], and, consequently a higher level of ABA content in water stressed plants, Brown 
et al. (1989) reported that ABA and mannitol promoted somatic embryogenesis in wheat [2]. How- 
ever Massayoshi Tsukahara and Takayasu Hirosawa reported that the effects of ABA and 
mannitol in the regeneration medium on the regeneration frequency didn't have significant effects 
within the concentration range tested. We suppose. that not only the reduction ofthe water content 
of callus in a certain duration, but also s k a t i o n  of callus in a Certain duration, by desiccation pro- 
voked the cell physiological and biochemical change, which is necessary for scient regeneration. 
2.4 Tbc Effcct of dif€crcnt cytokinin on differentiation 
We have tried using different cytokinin (KT.BAP, zeatin, 2ip) and TDZ in the regeneration 
medium in TNI, IR64 and IR72. 
We have repeated 4 times. The results of each time were varied. The responses of different va- 
rieties to different cy-rokinin were different. We think, due to cytokinin supplemented in induction 
medium or subculture medium, the regeneration function of medium was not very obvious, be 
D 
cause some of calli have been differentiated in induction medium and subculture medium. Some ' b  
limcs-thc calli wcrc only transrerred to hormone-free medium, they can regenerate and germinate. 
Tf the concentration of cytokinin was too high in regeneration medium, the calli maybe turned to 
brown and died. 
For example, 80% regeneration frequency obtained from the calli of T'NI grown on NB m e  
_ _  
Volume 21 , Number3 7 
I 
I 
dim containing TDZ 0.5mg / L when wereitransferred to 1 / 2 MS medium but if transferred to 
RN regeneration medium (containing BAP 3mg/;L) only 17.86% regeneration frequency has been 
But when the concentration of cytokipin in cells is not enough, it needs supplying some I 
1 
i 
i obtained. 
cytokinin. 
Conclusion 
l '  
j 
I 
i i 
Combination of some of these treatments (to supply some cytokinin and NAA in induction 
medium or subculture medinm, or only using TDZ for improving the quenlity of callus, and before 
the callis were treansferred to regeneration medium, they were partiaIly desiccated) lead to even 
higher regeneration efiiciencies, and we have obtained 5-14 folds more plants than control. So far 
the best frequencies we have obtained are 93.7%, 74.4 and 79.1% respectively from TNl,  IR72 and 
R64. 
We have to notice that the best medium and combinations of treatment daer  for different 
cultivar. Thcrefore, there is not a highly eficient standard protocol for all indica varieties. 
Acknowlcdgmcnis 
We appreciate the Rockfeller Foundation and ORSTOM (a French public research organiza- 
tion), because this work was supported in part by a grant from the Rockfeller Foundation, other 
supports were provided by ORSTOM. WZiTian was a mipient of a visiting scientist fellowship 
from the Rockfeller Foundation.,We are grateful to IRR1 for rice seeds. The authors express thank 
to Dr. Rongda Qu and Dr. Helena M and DI!. Christian Schopke, for helpful discussion. 
I ;  
I /  
' R C f C ~ ~  
[l] Bates, S., et al, 1992. Plant e l l  Tissue and Organ Culture, (31):21-29. 
[2] Brown, C., et al, 1989. Plant Physiol, (133):727-733. 
[3] Capelle, S.C., et al, 1983. Plant Physiol., (73):796802. 
[4] Carman, J., 1988. Planta, (175):417-424. / 
[5] Chu, C., et al, 1975. Science Sinica, (18):659-668. 
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[a Clark, G., in Staining Procedures.(Fourth Edition), Williams and Wilkins, 1981.: p. 
[IDavid, S.K.,etal,PlantPhysiol., 1989. (135):184-190. 
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[18] Milborrow, B., Annu Rev Plant Physiol, 1974. (25):259-307. 
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$6 
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j 
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22]Wright, S.and.H.R., 1970. In: Carr DJ (ed) Plant growth substance Springer, Berlin Heidelberg 
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New York, 291-298. I ’  
I F;tpres : ! 
A. The callus grown on’NB medium (+2,4-D 2mg / L), showing more soft callus. 
B. The callus grown on NBK medium (+2,4-D 2mg / L + KT lmg/ L + NAA lmg / L), 
C. Light micrograph of the callus on NB medium, showing many old empty cells (10 X 40). 
D. Light micrograph of thc callus on NBK medium,’Showhg many vgorous cells (10 X 40). 
E. The callus grown on NB medium containing TDZ 0.5mg / L after one week differentiated 
F. The callus growm on NB medium containing TDZ 0.5mg / L afler one week transferred to 
showing more embryogenic, granular, and compact structure. 
small shoot. 
1 / 2 MS cytokinin-free medium was grown up plantlet. 
! 



Improvement of plant regeneration frequency in vitro in indica rice

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