JP2011155968A - Tissue culture method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for enabling redifferentiation and regeneration from callus to a plant body by using a few kinds of plant growth regulators. <P>SOLUTION: The tissue culture of a Jatropha plant is performed by steps comprising a step for forming a shoot in an MS medium solely containing 0.05-0.6 mg/L, preferably 0.5 mg/L IBA and 1.5-3.5 mg/L, preferably 2 mg/L or 3 mg/L BA as plant growth regulators, a step for elongating the shoot by transplanting the formed shoot to an MS medium solely containing 1.5-3.5 mg/L, preferably 2 mg/L BA as a plant growth regulator, and a step for rooting by transplanting the elongated shoot to a 1/2 MS medium containing 0.1-0.5 mg/L, preferably 0.1 mg/L IBA as a plant growth regulator. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a tissue culture method, more specifically to a tissue culture method of Jatropha plant.

  In recent years, many attempts have been made to produce biodiesel fuel from plants such as corn and sugarcane in preparation for the depletion of fossil fuel resources such as oil. As this plant body, a plant of the genus Jatropha has attracted attention. Plants of the genus Jatropha are non-edible plants that are highly resistant to pests and pathogens and can be cultivated on thin land, so there is no competition with food and farmland, and about 30-40% of Jatropha seeds This is because there are various advantages that oil and fat can be recovered with a high yield.

  However, plants of the genus Jatropha can only be cultivated in subtropical to tropical regions, the number of fruiting is once a year, and the size of the fruit is small, so a large amount of oil collection cannot be expected in natural cultivation.

Therefore, attempts have been made to stably produce plant cultured cells (callus) and to produce biodiesel fuel from callus. For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2009-148192) discloses a method for extracting Jatropha oil from callus cells derived from a plant of the genus Jatropha. This method uses MS (Murashige and Skoog) medium for plant cell culture and various plant growth such as IA (Indole acetic acid), IBA (Indole butyric acid) and 2,4-D (2,4-dichlorophenoxyacetic acid). This is a method in which callus derived using a regulator (PGR: Plant Growth Regulator) is grown in a liquid medium, and then fats and oils are extracted from the grown callus. However, this method has a small amount of fats and oils contained in callus and is not suitable for producing a large amount of fats and oils.

  In order to increase the production amount from the cultivated Jatropha plant, for example, improvement of stress resistance such as drought resistance and cold resistance and improvement of increasing fats and oils in seeds are desired. For these improvements, artificial mating and mutation can be used, but its feasibility is low. Therefore, a method using cell engineering is introduced that introduces a target gene into a plant cell and imparts a desired property.

  By the way, when utilizing cell engineering, it is necessary to redifferentiate plant cells into which a target gene has been introduced into plant bodies. In the past, many attempts have been made to regenerate plant bodies by redifferentiating them from plant cells in plants of the genus Jatropha.

  For example, Patent Document 2 (US Publication No. 2008-0196121) discloses a step of forming a shoot from an explant in an initial medium, a step of transplanting a shoot into a medium for growth and extension, and rooting the extended shoot. And a method of regenerating a plant body of a genus Jatropha plant by a step of transplanting to a culture medium for use. In this method, an MS medium or the like to which a plant growth regulator is added at a concentration of 0.01 mg / L to 10 mg / L is used as each medium, and the medium for growth and extension and the medium for rooting are respectively used. Different plant growth regulators, for example, BAP (6-Benzyl amino purine) is used for the former and a medium supplemented with IBA (Indole acetic acid) is used for the latter.

  Patent Document 3 (WO2008 / 012832) discloses a step of mass-culturing leaf pieces of a Jatropha plant using an initial medium containing TDZ (thidiazuron), BAP and IBA, TDZ, BAP and gibberellic acid. A method of regenerating a plant of a Jatropha plant without passing through a callus by a step of growing and extending in a medium containing IBA and a step of rooting in a medium containing IBA is disclosed.

  Non-Patent Document 1 (Li et al., Establishment of an Agrobacterium-mediated cotyledon disc transformation method for Jatropha curcas, Plant Cell Tiss. Organ. Cult., 2008, Vol.92, No2, pp.173-181) A method for forming cotyledons from a transformant of Jatropha introduced with the Agrobacterium method is disclosed. In this method, callus formation is performed from a transformant of cotyledon explants in an MS medium containing BA (Benzyl adenine) and IBA as plant growth regulators, and BA, IBA and GA3 (gibberellic acid are formed from the formed callus. ) Is formed in a medium containing). And rooting is performed in the MS medium (1 / 2MS medium) of 1/2 concentration containing IBA.

  Non-Patent Document 2 (Ajay C. Deore et al., High-frequency plant regeneration from leaf-disc cultures of Jatropha curcas L .: an important biodiesel plant, Plant Biotechnol. Rep., 2008, 2, 7-11) MS medium containing BA, KN (Kinetin), IAA, and GA3, wherein adventitious shoots are formed from leaf pieces of Jatropha plants by combining two or three of TDZ, IBA, and BA as plant growth regulators Has been reported to cause sprouting and elongation. According to this report, the combination of BA and IBA is good for callus formation, but the combination of TDZ, BA and IBA is preferable for the induction of adventitious buds.

  On the other hand, in the tissue culture of Jatropha plants, the transformation method is also an important factor. For example, Non-Patent Document 3 (Harold N. Trick et al., SAAT: Sonication-assited Agrobacterium-mediated transformation, Transgenic Research 6, 329-336, 1997) and Non-Patent Document 4 (Malabika Roy Pathak et al., An effective method of sonication-assisted Agrobacterium-mediated transformation of chickpeas, Plant Cell Tiss. Organ. Cult., 2008, 93, 65-71) by introducing the gene by sonication in the presence of Agrobacterium A method (SAAT method) is disclosed. And in nonpatent literature 3, redifferentiation from a transformant which carried out ultrasonic treatment and introduced a gene into a plant body is tried. According to this, callus is formed from the transformant in a medium containing 2,4-D, BAP, IAA and acetosyringon as plant hormones, and then shoots are formed in an MS medium containing BAP, KN and IAA. After that, rooting was performed in an MS medium containing NAA (1-naphthaleneacetic acid), IAA, and KN, and the rooted shoot was transplanted to a ½ MS medium. According to the SAAT method, not only genes are stably introduced, but also the introduction rate of genes and the probability of redifferentiation are increased.

  Various tissue cultures are also performed in plants other than Jatropha plants. For example, in Patent Document 4 (JP-A-5-316895), when redifferentiating a shoot from a Menta plant into a plant body, the shoot is elongated in a medium containing a purine base cytokinin, and then plant growth is performed. A method of rooting by transplanting to a medium not containing a regulator is disclosed.

JP 2009-148192 A US Publication No. 2008-0196121 WO2008 / 012832 Publication JP-A-5-316895

Li et al., Establishment of an Agrobacterium-mediated cotyledon disc transformation method for Jatropha curcas, Plant Cell Tiss. Organ. Cult., 2008, Vol.92, No2, pp.173-181) Ajay C. Deore et al., High-frequency plant regeneration from leaf-disc cultures of Jatropha curcas L .: an important biodiesel plant, Plant Biotechnol. Rep., 2008, 2, 7-11 Harold N. Trick et al., SAAT: Sonication-assited Agrobacterium-mediated transformation, Transgenic Research 6, 329-336, 1997 Malabika Roy Pathak et al., An effective method of sonication-assisted Agrobacterium-mediated transformation of chickpeas, Plant Cell Tiss. Organ. Cult., 2008, 93, 65-71

  As described above, in the tissue culture of Jatropha plants, the type and concentration of the plant growth regulator to be used is changed at each stage of shoot formation, elongation, and rooting. It was necessary to combine many plant growth regulators used in the culture medium, and it was necessary to devise the culture environment. There is also a problem that the success rate to germination and rooting is low.

  The present invention has been made in view of the background art described above, and an object of the present invention is to provide a method that enables redifferentiation and regeneration from callus to a plant by using a few kinds of plant growth regulators. .

  The tissue culture method of the present invention is a tissue culture method using cells of the genus Jatropha, wherein a shoot is formed from cells of the genus Jatropha in an MS medium containing only IBA and BA as plant growth regulators; Transplanting the formed shoots into a MS medium containing only BA as a plant growth regulator, and extending the elongated shoots into a 1/2 MS medium containing only IBA as a plant growth regulator. It is a method having a step of rooting.

  According to the present invention, a plant can be regenerated by a tissue culture method with a high formation frequency while using a few types of plant growth regulators.

It is a figure which shows the difference by the infection method of Agrobacterium which used the introduce | transduced GUS activity as a parameter | index. It is a figure which shows the difference by the infection method of Agrobacterium which used shoot formation frequency as a parameter | index. It is a figure which shows the difference by the plant growth regulator which used shoot formation frequency as a parameter | index. It is an image which shows the progress progress of the shoot in the growth medium, and (a) is a state 2 weeks after transplantation, and (b) is a state 4 weeks after transplantation. It is an image showing a shoot in a rooting medium, where (a) is based on a 1 / 2MS medium containing 0.2 mg / L IBA, and (b) is based on a 1 / 2MS medium not containing a plant growth regulator. Show the case.

  The tissue culture method of the present invention is a tissue culture method using cells of the genus Jatropha, wherein a shoot is formed from cells of the genus Jatropha in an MS medium containing only IBA and BA as plant growth regulators; Transplanting the formed shoots into a MS medium containing only IBA as a plant growth regulator and extending the cells, and transplanting the elongated cells into a 1/2 MS medium containing only IBA as a plant growth regulator. A step of rooting. Here, the ½ MS medium is a medium in which normal MS medium components are adjusted to a concentration of ½.

  In the present invention, a plant growth regulator refers to a substance that affects plant elongation and differentiation, and includes both cytokinin, which is said to be involved in cell division, and auxin, which is said to be involved in cell elongation. It is meant to include plant hormones.

  In the present invention, a shoot is used in the meaning normally used in cell culture, and means a state in which the shoots and leaves can be differentiated.

  The plant to which the present invention is applied is a Jatropha genus plant (Jatropha genus plant). Jatropha genus plants are shrubs of Euphorbiaceae native to the tropics. : Japanese name Nishikisango), Jatropha integerrima (Japanese name Nanyo Sakura), Jatropha curcas (Japanese name Nanyo Abragiri) and the like. The plant of the genus Jatropha used in the present invention is not particularly limited, but Jatropha curcas is preferably used in that it has a high content of oil and fat.

  The present invention is a method for tissue culture of Jatropha plant cells to redifferentiate and regenerate plant bodies, and cotyledons are preferably used as the cells. In order to increase the frequency of redifferentiation and the frequency of regeneration, cells constituting the veins are desirably used. The callus induction method is not particularly limited. For example, a medium in which a plant growth regulator such as 2,4-D, NAA, TDZ, BA, or IBA is added to a basic medium such as MS medium or SH123 medium. A guidance method using is used.

  The tissue culture method of the present invention can be applied to either transformed cells or non-transformed cells. Examples of the transformation method include a method using Agrobacterium and a method using a gun shooting method, and any method may be used. Further, the method for infecting Agrobacterium is not limited, and it is not only a simple contact with Agrobacterium in the medium, but also, for example, as described in Non-Patent Document 3, A method of increasing the infectivity of Agrobacterium is preferable, such as SAAT method in which ultrasonic treatment is performed when contacting with the suspension, and Sandvortex method in which vibration is applied in a state where sand is added to a suspension of Agrobacterium. Transformation is performed before callus induction.

  The Sandvortex method is a method devised by the present inventors. This method is a method in which sand is added to a suspension containing plant cells and Agrobacterium holding a target gene to give vibration. The type and particle size of the sand are not particularly limited, but sand that passes through a sieve having an opening of about 3 mm (6 mesh) and remains on the sieve having an opening of about 0.1 mm (100 mesh) is preferable. . If the particle size of the sand is larger than this, it will not be possible to damage the plant cells sufficiently, and if it is smaller, the damage to the plant cells will be large and there is a high risk that callus formation will not be possible. However, there are concerns that it will decline. Specifically, white quartz sand having a size of 50 to 70 mesh can be suitably used.

  Any device can be used for applying vibration as long as sand and plant cells can come into contact with each other and damage the plant cells. However, considering the work efficiency, a rotary type vibration device such as the trade name Vortex is used. A vibration device known as a mixer is preferably used. This vibration device has a disk-shaped rotating member that rotates at high speed. When the bottom of a container such as a test tube is brought into contact with this rotating member, the contact portion with the rotating member rotates, and the container rotates with a cone as a fulcrum and the container vibrates. And the contents are agitated.

  The time for applying vibration is appropriately adjusted. Although it varies depending on the particle size of the sand, the shape of the container, the capacity of the container, etc., the standard is about 10 seconds to 3 minutes, preferably 10 to 30 seconds. If it is shorter than 10 seconds, sufficient damage is not given and gene introduction tends to be insufficient. Further, if the period is longer than 3 minutes, the wound becomes large, the damage to the plant is increased, and the frequency of callus formation is lowered, which may reduce the efficiency of gene introduction.

  In the present invention, shoot formation is performed with an MS medium containing only IBA and BA as plant growth regulators. The IBA concentration is 0.05 to 1.0 mg / L (MS medium), preferably 0.1 to 0.5 mg / L, and most preferably 0.5 mg / L. The BA concentration is 1.5 to 3.5 mg / L (MS medium), preferably 2 to 3 mg / L, and most preferably 3 mg / L. Outside these concentrations, the number of shoots formed decreases and stable shoot growth is not observed. For the shoot formation, a solid medium obtained by adding about 0.7% agar to the medium is preferably used. Similarly, shoots are formed at a high frequency in a medium in which IBA, BA, and TDZ are added to the MS medium. However, when TDZ is added, the number of shoots formed and the number of germinations are larger than when TDZ is not added. However, when TDZ is added, the shoot elongation tends to be slower than when TDZ is not added.

  Shoot formation is performed in an artificial environment in which temperature, humidity, and lighting time are controlled for 4 to 8 weeks. The culture conditions such as temperature and humidity can be changed as appropriate. For example, the culture conditions of 25 to 30 ° C., 65 to 85% RH, about 2,000 Lux, and 16 hours light time are exemplified.

  Next, the shoot obtained from the callus is transplanted to an MS medium containing only BA as a plant growth regulator, and further expanded. Transplantation is performed when germination from the shoot is visually confirmed and thereafter it has been confirmed that it has grown stably. The BA concentration is 1.5 to 3.5 mg / L (MS medium), preferably 2 to 3 mg / L, and optimally 2 mg / L. Outside this concentration, the elongation rate tends to be slow and the number of germination tends to decrease. A solid medium supplemented with about 0.7% agar is also preferably used for this medium. In the medium, not only shoots are elongated, but also new shoots are formed.

  When the shoot has a size of about 2 to 3 cm, the extended shoot is transplanted to a rooting medium. The rooting medium is a medium obtained by adding only IBA as a plant growth regulator to a ½ MS medium in which the MS medium concentration is halved. The IBA concentration is 0.1 to 0.5 mg / L (1/2 MS medium), preferably 0.1 to 0.2 mg / L, and optimally 0.2 mg / L. The medium is also a solid medium supplemented with about 0.7% agar. Note that shoot elongation and rooting are performed under substantially the same culture conditions as during shoot formation.

  As described above, in the present invention, plant growth regulators used in each stage of shoot formation, shoot elongation, and rooting are only two substances, IBA and BA, and plant cells (callus) are few plant growth regulators. ) To plant bodies.

  EXAMPLES Next, the present invention will be further described based on examples. However, the present invention is not limited to the following examples, and all modifications that are included in the scope of the claims and equivalents thereof are included in the present invention. Is intended.

[Adjustment of plant cells]
As a plant cell of the genus Jatropha, a cotyledon of Jatropha curcas was used. The seed nuclei from which the seed coat had been removed were sterilized by immersing them in 70% ethanol for 10 minutes and then in antiformin diluted to 15-30% for 5 minutes, and then germinated in MS medium containing 3% sucrose. .

[Examination of transformation method]
Preparation of Agrobacterium: Agrobacterium used LBA4404 strain (MW Bevan et al. Nucleic Acids Res. 12: 8711-8721 (1984)) in which its Ti plasmid was rendered harmless. In order to confirm the transformation, a commercially available β-glucuronidase (GUS) gene was incorporated into a binary vector and a plasmid pBI121 was purchased and used to transform Agrobacterium (RA Jefferson et al. EMBO J. 6: 3901-3907 (1987)). Agrobacterium LBA4404 / pBI121 carrying the β-glucuronidase (GUS) gene was cultured overnight at 30 ° C. in an L-liquid medium containing kanamycin as a marker at a concentration of 50 μg / ml.

    Next, 3% sucrose was added to the MS medium, and 2 mg / L BA and 0.2 mg / L IBA were added as plant growth regulators. And then transplanted by cutting to a size of about 5 mm and pre-cultured for 1 week under light conditions of 30 ° C., 16 hours light period, 8 hours dark period.

    A suspension of Agrobacterium LBA4404 / pBI121 prepared by the above method was prepared so that the cell turbidity was 0.5 at an optical wavelength of 600 nm and an optical path length of 1 cm. 10 to 12.5 mL of this solution was dispensed into a 50 mL plastic tube, and the pre-cultured cotyledon piece was added. Add an appropriate amount of 50-70 mesh white quartz sand (Sigma-Aldrich) and apply vibration (Sandvortex method) with a rotary vibration device (VORTEX-GENIE 2 MS Equipment Co., Ltd.) or cotyledon piece The suspension was added to the tissue piece by sonication (application of ultrasonic waves), and the tissue pieces were damaged (each treatment time is as shown in Table 1). Then, the cells were statically cultured for 3 days under light-shielding conditions at 25 ° C. to infect Agrobacterium.

    Then, in order to remove Agrobacterium from the plant piece (cotyledon piece) infected with Agrobacterium, it was immersed in sterilized water to which 200 μg / mL Cefotaxime was added for several minutes, and then 3% SHO was added to MS medium. Transplanted into a medium supplemented with sugar, 200 μg / mL Cefotaxime, and 2 mg / L BA and 0.2 mg / L IBA as plant growth regulators.

[Formation of callus and chute]
Subsequently, the cotyledon piece infected with Agrobacterium was added to MS medium with 3 mg / L BA, 0.1 mg / L IBA, 3% sucrose and 200 μg / mL Cefotaxime, and the marker kanamycin at 20 μg / ml. And transplanted to a solid medium (containing 0.7% agar). Thereafter, the formed callus was transplanted to an MS solid medium containing 3 mg / L IBA, 0.5 mg / L BA, 0.7% agar, and 20 μg / ml kanamycin. Culture was performed for 8 weeks in a light-hour environment of 000 lux for 16 hours to form shoots. The GUS activity expressed in the obtained shoots was analyzed by the method of Kosugi et al. (Kosugi et al., An improved Assay for beta-Glucuronidase in Transformed Cell: Methanol Almost Completely Suppresses a Putative Endogenous beta- Glucuronidase Activity. Plant Science. 70, 133-140 (1990)). In addition, as a comparison object, cells were damaged by conventional shaking and ultrasonic treatment instead of Sandvortex, and compared with the Sandvoretx method. The comparison result in GUS activity is shown in Table 1 and FIG. 1, and the comparison result in callus formation number and shoot formation number is shown in Table 2 and FIG. These results are the average of the results of three repeated experiments. In any treatment, it was confirmed that the target gene was stably introduced and the introduced gene was expressed. Moreover, it was confirmed that the transformation was more efficient than the conventional method by the Sandvortex treatment for about 20 seconds. Thus, it has been proved that the Sandvortex method is more advantageous than the conventional shaking method and SAAT method. However, the STTA method can be transformed more advantageously than the shaking method.

  Next, the expression stability of genes based on the difference in the treatment method for transformation was examined. Using the plasmid pREXH1-GUS in which the β-glucuronidase (GUS) gene and the hygromycin resistance gene were incorporated, gene introduction was attempted in the same manner as described above. The gene was introduced by infecting the leaves of the plant with Agrobacterium by ultrasonication. The results are shown in Table 3. In addition, the culture medium which added 20 microgram / ml of hygromycin to the said composition was used for culture | cultivation. In Table 3, the GUS that was expressed was evaluated on a five-stage scale (high expression level: 5-5 low expression level: 1), and the results were averaged ((1st score + 2nd score +... + Nth score) × 100 / 5n: where n is the number of samples) GUS expression (GUS transient expression) and callus formation rate. The expression level of GUS is an index indicating the degree of transient expression, and the callus formation rate is an index indicating the degree of stable expression. Minute sonication has proved effective.

[Investigation of medium for shoot formation]
The medium conditions for shoot formation were examined. Shoot formation was attempted using callus obtained from cells transformed by the Sandvortex method (vibration for 15 seconds). BA, IBA, and TDZ were used as plant growth regulators. Two or three kinds of plant growth regulators were added to the MS medium in the combinations and concentrations shown in Table 3 to prepare a solid medium containing 0.7% agar. The cells were cultured at 25 ° C. for 6 weeks under light conditions of 2,000 Lux under 16 hours light-time culture conditions. The number of explants that formed shoots was counted, and the ratio (frequency (%)) of the number of explants that formed shoots to the number of explants used was determined. The results are shown in Table 3 and FIG. These results are the average of the results of three repeated experiments. The combination of BA (1 mg / L), TDZ (0.5 or 1 mg / L) and IBA (0.1 mg / L) formed shoots with the highest frequency, but BA (2 or 3 mg / L) and IBA (0.1 mg / L) were combined to form shoots with almost the same frequency, and it was found that shoots were formed with high frequency even when a small number of plant growth regulators were used.

[Shoot extension]
Next, for shoot elongation, the formed shoots were transplanted into MS medium containing only BA (2 mg / L) as a plant growth regulator. Using a solid medium containing 0.7% agar, the cells were cultured for 6 weeks under 25 ° C. temperature and 2,000 lux lighting conditions for 16 hours light time. FIG. 4 shows an image showing the progress of the expansion. As understood from FIG. 4, even when only BA was used, shoot elongation was observed well.

[Rooting]
The shoots that subsequently grew to a height of about 2 to 3 cm were transplanted into a rooting medium for rooting. As the rooting medium, a ½ MS medium containing only IBA (0.2 mg / L) as a plant growth regulator and halving the concentration of the MS medium as a basic medium was used. For comparison, a ½ MS medium without IBA (0.2 mg / L) was used. FIG. 5 shows a shoot image after 2 weeks from the transplantation. The culture conditions are the same as those during the shoot elongation. Although rooting and shoot elongation were confirmed in both culture media, better rooting and shoot elongation were confirmed in the medium containing IBA than in the medium not containing IBA. Through the above process, it was possible to regenerate and regenerate the plant body from cotyledons of Jatropha curcasus. Thus, by the method of the present invention, a regenerated product of Jatropha, which is a transformant into which the GUS gene was introduced, was obtained about 24 weeks after infection with Agrobacterium.

  The tissue culture method of the present invention contributes to mass culture and molecular breeding of Jatropha plants that are attracting attention as raw materials for biodiesel fuel.

Claims (8)

A tissue culture method using cells of the genus Jatropha,
Forming shoots from cells of the genus Jatropha in MS medium containing only IBA and BA as plant growth regulators;
Transplanting the formed shoots into an MS medium containing only BA as a plant growth regulator and elongating;
A tissue culture method comprising the step of transplanting the elongated shoot into a 1 / 2MS medium containing only IBA as a plant growth regulator and rooting.   The tissue culture method according to claim 1, wherein an MS medium containing 0.05 to 0.6 mg / L IBA and 1.5 to 3.5 mg / L BA is used in the shoot formation step.   The tissue culture method according to claim 1 or 2, wherein an MS medium containing 1.5 to 3.5 mg / L BA is used in the extension step.   The tissue culture method according to any one of claims 1 to 3, wherein a 1/2 MS medium containing 0.1 to 0.5 mg / L IBA is used in the rooting step. Forming shoots in MS medium containing 0.5 mg / L IBA and 2 mg / L or 3 mg / L BA;
Extending a shoot formed in MS medium containing 2 mg / L BA;
The tissue culture method according to any one of claims 1 to 4, further comprising a step of rooting in a 1/2 MS medium containing 0.2 mg / L IBA.   The tissue culture method according to any one of claims 1 to 5, wherein a shoot is formed from callus.   The cell of the genus Jatropha plant is a cell in which a suspension containing a plant cell, sand and Agrobacterium is imparted with a vibration by a rotary vibration device to infect Agrobacterium. Item 7. The tissue culture method according to any one of Items 1 to 6.   The cell of the genus Jatropha plant is a cell obtained by sonicating a suspension containing a plant cell and Agrobacterium and infecting the Agrobacterium, according to any one of claims 1 to 6. 2. The tissue culture method according to item 1.