Agriculture Reference
In-Depth Information
processes such as membrane lipid peroxidation, protein oxidation, enzyme
inhibition and damage of nucleic acids (Grene, 2002) The biotech tools
available aim at expression of ROS scavenging enzymes like superox-
ide peroxidase, ascorbate peroxidase, catalase, glutathione peroxidase and
peroxiredoxin. In cooperation with the antioxidants like ascorbic acid and
glutathione, these scavenging enzymes detoxify the ROS and prevent seri-
ous damage to the cells (Scheller and Haldrup, 2005).
Another important messenger during drought stress adaptation is the
phytohormone abscisic acid (ABA). ABA biosynthesis is initiated by de-
creasing water potential, and seems to be essential for the activation of
many protective measures towards abiotic stresses. In drying soil, an ABA
signal can be produced early during stress in the roots and be transported
via the phloem to the shoot. There, ABA accumulation represents an im-
portant signal for the closure of stomata in response to drought stress. ABA
induces changes in the turgor of guard cells and the changed guard cell
expansion leads to stomatal closure. Biosynthesis of proline for instance in-
creases the concentration of compatible osmoprotectants in the cells, while
aquaporins can facilitate water permeability of cellular membranes and
maximize water uptake potential of the plant, and ROS scavenging pro-
teins can limit damage by secondary oxidative stress (Chaves et al., 2003).
The specific function of the majority of drought-induced genes is, however,
still unknown and revelation of their function should give new insights into
the plant protective mechanisms against drought. Strategies to mitigate the
drought stress aim at expression of ABA and proline in the cells.
13.5.6 SALT STRESS
High concentrations of salt (i.e., ions, mostly Na+) in the soil solution
can impair water and nutrient uptake, reduce growth and photosynthetic
activity. Furthermore high salinity can lead to an unfavorable Ca2+ or K+
to Na+ ratio, toxic intracellular Na+ concentrations and peroxidation of
membrane lipids (Levitt, 1980).
13.5.6.1
CONVENTIONAL APPROACHES
Using the available sources of resistance one can incorporate tolerant/re-
sistant species in the breeding program to transfer the genes of interest. In
