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

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B. Rathinasabapathi and R. Kaur
et. al., 2000). Current engineering approaches depend upon the transfer of one or
several genes encoding either biochemical pathways or endpoints of signaling pathways.
These gene products guard plants against abiotic stresses both in direct and
indirect ways. Major components or targets for engineering stress tolerance in plants
are listed in Table 1.
Even if an investigator knows that a particular pathway can be useful for
manipulation, identifying the enzyme with the “most control” over the pathway flux is
difficult. Early views on metabolic regulation considered that a small number of key
“regulatory” enzymes were rate-limiting in controlling the flux through a multistep pathway.
But this view has been proven wrong by more recent research (Fell, 1992) and the
flux control through a pathway is often shared among the steps. One way to find the
contribution of each step to metabolite flux is to use the metabolic control (MCA)
analysis. MCA analyses require the determination of the metabolite flux through a
pathway after perturbing a single enzyme-catalyzed step. Perturbations can be achieved
using specific inhibitors, mutants or transgenic modifications (Fell, 1997). Computer
modeling of metabolic pathways can greatly facilitate MCA analysis (Lee et. al., 2003).
Table 1. Major metabolic and transport components for engineering abiotic stress
tolerance in plants
Components
Growth regulators
Heat shock proteins
Ion/proton transporters
Mode of action
Modification in hormone homeostasis
Prevention or reversal of protein unfolding
Elimination and sequestration of toxic ions
from the cytoplasm and organelles; ion
uptake and transport
Membrane fatty acid composition Increase in membrane fluidity and chilling
tolerance
Osmoprotectants
Osmotic adjustm ent, protection of proteins and
membranes, scavenging of reactive oxygen
Reactive oxygen scavenger Detoxification of reactive oxygen species
Signaling pathway
Ca 2+ -sensors/phosphorylation intervened
signal transduction
Transcription factors
Transcriptional activation or upregulation of
specific structural genes
Water status
Stomatal behavior; regulation of aquaporin
in tonoplast and plasma membrane