7.3.3 Plant Tissue Culture Methods
Transgenic crop plants with higher yield, improved quality and desired
characteristics of texture, aroma and flavour have been developed by inserting
genes of known function (Speirs et al. 2000; Lewinsohn et al. 2001). Plant tissue
culture method (PTC) is the culturing of plant cells on solid or in liquid culture.
Although, the methods of PTC have been in use for the past hundred years, but they
have been introduced for the production of aroma compounds only in the 1970s. It is
now used for the commercial production of existing and novel flavours (Fu 1999;
Boskovic-Dörnenburg and Knorr 2010). Tissue culture methods have already been
employed for propagation of commercially important plants, for example, CFTRI
has standardized the technology and methods of processing for the mass propagation
of Vanilla planifolia by tissue culture techniques (https://www.cftri.res.in/
technologies/MFP/vtc.pdf). One of the advantages of PTC is that unlike whole
plants, these methods are not limited to geographic locations or the seasons. The
aroma compounds can be isolated from cells or the medium with relative ease.
However, this production method is quite expensive as the precursors are the
compounds which are produced in relatively low amounts. The additional expenses
are the cost of the medium and the purification of the compounds for food grade.
Moreover, PTC can only be used effectively in systems for which the biochemical
pathway of the aroma compounds is already known (Harlander 1994; Hrazdina
2006).
Plant cell cultures are normally grown under sterile conditions in which a part
taken from the plant, known as an explant, is surface-sterilized. The explant is placed
on a solid medium which contains major and minor salts, a carbon and energy
source, normally sucrose and the growth regulators auxins and cytokinins to form an
undifferentiated mass of cells called callus. When callus is added to a liquid medium,
it forms the suspension cultures (Harlander 1994). Suspension cultures generally
have a faster growth rate, are more homogeneous than callus material and thus can be
cultivated on a large scale in bioreactors. High yielding plant cultures are screened
and selected. The culture conditions are manipulated to stimulate the accumulation
of secondary products. Other methods such as elicitation, permeabilization, product
removal, immobilization and differentiation can also be used to enhance the production of secondary products (Scragg 2007). The transformed shoot cultures of Mentha
exhibited the synthesis of monoterpenes in mint oil (Rhodes et al. 1991).
The flavour compound/ aroma such as 2,3-butanedione, apple aroma, cinnamic
acid, caryophyllene, basmati flavour, cocoa flavour, flavanol, garlic, monoterpenes,
onion, triterpenoid and vanillin have been produced from plant tissue cultures of
Agastache rugosa (Kim et al. 2001), Malus sylvestris, Nicotiana tabacum and
Lindera strychnifolia (Drawert et al. 1984), Oryza sativa (Suvarnalatha et al.
1994), Theobroma cacao (Townsley 1972), Polygonum hydropiper (Nakao et al.
1999), Allium sativum (Ohsumi et al. 1993), Perilla frutescens (Nabeta et al. 1983),
Allium cepa (Prince et al. 1997), Glycyrrhiza glabra glandulifera (Ayabe et al.
1990), Vanilla planifolia (Dornenburg and Knorr 1996), respectively, via tissue
culture methods. Multiple shoots of Vanilla planifolia were induced from nodal
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Transgenic crop plants with higher yield, improved quality and desired
characteristics of texture, aroma and flavour have been developed by inserting
genes of known function (Speirs et al. 2000; Lewinsohn et al. 2001). Plant tissue
culture method (PTC) is the culturing of plant cells on solid or in liquid culture.
Although, the methods of PTC have been in use for the past hundred years, but they
have been introduced for the production of aroma compounds only in the 1970s. It is
now used for the commercial production of existing and novel flavours (Fu 1999;
Boskovic-Dörnenburg and Knorr 2010). Tissue culture methods have already been
employed for propagation of commercially important plants, for example, CFTRI
has standardized the technology and methods of processing for the mass propagation
of Vanilla planifolia by tissue culture techniques (https://www.cftri.res.in/
technologies/MFP/vtc.pdf). One of the advantages of PTC is that unlike whole
plants, these methods are not limited to geographic locations or the seasons. The
aroma compounds can be isolated from cells or the medium with relative ease.
However, this production method is quite expensive as the precursors are the
compounds which are produced in relatively low amounts. The additional expenses
are the cost of the medium and the purification of the compounds for food grade.
Moreover, PTC can only be used effectively in systems for which the biochemical
pathway of the aroma compounds is already known (Harlander 1994; Hrazdina
2006).
Plant cell cultures are normally grown under sterile conditions in which a part
taken from the plant, known as an explant, is surface-sterilized. The explant is placed
on a solid medium which contains major and minor salts, a carbon and energy
source, normally sucrose and the growth regulators auxins and cytokinins to form an
undifferentiated mass of cells called callus. When callus is added to a liquid medium,
it forms the suspension cultures (Harlander 1994). Suspension cultures generally
have a faster growth rate, are more homogeneous than callus material and thus can be
cultivated on a large scale in bioreactors. High yielding plant cultures are screened
and selected. The culture conditions are manipulated to stimulate the accumulation
of secondary products. Other methods such as elicitation, permeabilization, product
removal, immobilization and differentiation can also be used to enhance the production of secondary products (Scragg 2007). The transformed shoot cultures of Mentha
exhibited the synthesis of monoterpenes in mint oil (Rhodes et al. 1991).
The flavour compound/ aroma such as 2,3-butanedione, apple aroma, cinnamic
acid, caryophyllene, basmati flavour, cocoa flavour, flavanol, garlic, monoterpenes,
onion, triterpenoid and vanillin have been produced from plant tissue cultures of
Agastache rugosa (Kim et al. 2001), Malus sylvestris, Nicotiana tabacum and
Lindera strychnifolia (Drawert et al. 1984), Oryza sativa (Suvarnalatha et al.
1994), Theobroma cacao (Townsley 1972), Polygonum hydropiper (Nakao et al.
1999), Allium sativum (Ohsumi et al. 1993), Perilla frutescens (Nabeta et al. 1983),
Allium cepa (Prince et al. 1997), Glycyrrhiza glabra glandulifera (Ayabe et al.
1990), Vanilla planifolia (Dornenburg and Knorr 1996), respectively, via tissue
culture methods. Multiple shoots of Vanilla planifolia were induced from nodal
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T. Malik and S. Rawat