Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

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B. Rathinasabapathi and R. Kaur
3.2.13. Cold Acclimation
Extended stay of cold-tolerant plants under cold temperature (below 5 o C) makes them
more freezing tolerant due to activation of cold acclimation response (COR) genes (also
see Chapter 5). This process is generally termed as cold acclimation or cold hardening
(Strand et. al., 2003). Artus et. al. (1996) demonstrated that constitutive expression of
the cold regulated Arabidopsis COR15a gene affects both chloroplast and protoplast
freezing tolerance. Kaye et. al (1998) made transgenic tobacco plants that constitutively
expressed the spinach cold acclimation proteins (CAP85 and CAP160).
3.2.14. Carbohydrate Metabolism
Cold acclimation and winter survival in plants is strongly associated with the revival of
photosynthesis at low temperature (Stitt and Hurry, 2002), and storage of soluble carbohydrates,
like sucrose and raffinose (Olien and Clark, 1993). Transgenic Arabidopsis
plants with overexpression of sucrose phosphate synthase (sps) showed improved
photosynthesis and increased sucrose flux in comparison to both plants with antisense
repression of either cytosolic fructose-1,6-bisphosphatase (fbp) or SPS at 5 0 C (Strand
et. al., 2003). Down-regulating a-galactosidase (Lea-Gal gene) in petunia using antisense
technology resulted in an increase in freezing tolerance as α-galactosidase is responsible
for the degradation of raffinose (Pennycooke et. al. 2003). Transgenic tobacco
plants accumulating high levels of proline, fructans, or glycine betaine exhibited tolerance
to cold temperature (Konstantinova et. al., 2002; Parvanova et. al., 2004).
Overexpression of glutathione S-transferase/glutathione peroxidase resulted in plants
tolerant to chilling stress (Roxas et. al., 1997). A novel plant NADPH-dependent aldose/
aldehyde reductase, was identified in cultured bromegrass cells associated with the
induction of freezing tolerance (Lee and Chen, 1993).
3.2.15. Shading Stress
Biomass production is highly dependent upon optimum supply of nutrients and efficient
photosynthesis, whereas the harvest index and economic yield are governed by
allocation of assimilates within the developing plant. Under crowding and shading
conditions in a single as well as mixed cropping pattern, struggle for light energy calls
up for shade avoidance syndrome manifested by quick growth, and extension of stem
and petiole at the expense of leaves, storage and reproductive organs thus making
plants vulnerable to lodging, diseases and insect pests, and ultimately, a lower harvest
index (Morgan and Smith, 1976; Deregibus et. al., 1983; Rousseaux et. al., 1999; Smith,
2000). Light reflected from adjacent vegetation is rich in far-red (FR) and depleted in red
(R) wavelengths due to its absorption by chlorophyll. This alteration in light quality is
sensed by photoreceptors called phytochromes (Quail, 1998). Phytochromes present in
two photo-interconvertible forms, an inactive, R-absorbing Pr-form and an active, FR