Coping Abiotic Stress with Plant Volatile Organic Chemicals (PVOCs): A Promising Approach - Crop Improvement: New Approaches and Modern Techniques - page 295

Table 9.1 List of cloned genes involved in the biosynthesis of monoterpenes
Gene Organism References

Linalool synthase Clarkia breweri ; Arte-

misia annua L.

Dudareva et al. ( 1996 ); Cseke
et al. ( 1998 ); Jia et al.
( 1999 )

(-)- Limonene synthase Abies grandis ; Mentha

spicata

Colby et al. ( 1993 ); Bohlmann
et al. ( 1997 )

( + )- Limonene synthase Agastache rugoa Maruyama et al. ( 2002 )

Abies grandis Bohlmann et al. ( 1997 )

(-)- Pinene synthase

Myrcene synthase Abies grandis , Quercus

ilex L .; Arabidopsis
thaliana

Bohlmann et al. ( 1997 );
Bohlmann et al. ( 2000 );
Fischbach et al. ( 2001 )

β- Ocimene synthase Arabidopsis thaliana Bohlmann et al. ( 2000 )

Salvia offcinalis Wise et al. ( 1998 )

( +)- Bornyl diphosphate synthase ,
1,8 cineole synthase and
( + )- Sabinene synthase

(-)-β- Phellandrene synthase ,
(-)- camphene synthase, Terpi-
nolene synthase and (-)- limo-
nene /(-)-α- pinene synthase

Abies grandis Bohlmann et al. ( 1999 )

( E )- Beta farnesene synthase Citrus junos Maruyama et al. ( 2001 )

monoterpenes exhibit more effectiveness in scavenging antioxidants. On the other
hand, the less volatile isoprenes pool up in membrane and intercellular spaces and
thus become more effective antioxidants in the aqueous phase. Volatile sesqui-
terpenes are produced in high levels in ozone-resistant tobacco upon exposure to
ozone. It is thus possible that volatile isoprenoids constitute one of the non-enzy-
matic oxidative defense systems thereby, reducing the oxidative damage caused by
abiotic stresses.
Monoterpenes have different effects on plant growth and development, depend-
ing on their structure and the quantity. Thus α-pinene exerts protective effect on
the photosynthetic apparatus, while α-terpinol shows toxicity. Monoterpenes exog-
enously applied at levels of 0.5 g/l exhibited toxicity in plant cell cultures (Brown
et al. 1987 ). Monoterpenes such as cineole, thymol, geraniol, menthol and camphor
induced oxidative stress and lipid oxidation in maize roots (Zunino and Zygadlo
2004 ) while, β-myrcene, limonene, β-ocimene and γ-terpinene generated ROS and
oxidative damage (Singh et al. 2009 ). Menthol has shown an increase in cytosolic
free calcium ions which can generate signal transduction pathways in cucumber
roots (Maffei et al. 2001 ). The aliphatic monoterpenes (ocimene and myrcene) in-
duced considerable changes in the transcription of several hundred genes in Ara-
bidopsis, many of them are designated as transcription factors, stress and defence
genes (Godard et al. 2008 ). Several genes involved in the biosynthesis of terpenes
have now been cloned in different plants (Phillips et al. 2006 ; Christianson 2006 ;
Degenhardt et al. 2009 ). Table 9.1 lists some of the genes involved in the synthesis
of monoterpenes.