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

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B. Rathinasabapathi and R. Kaur
Figure 1 .
A model for metabolic engineering for stress tolerance
3. PATHWAY ENGINEERING
3.1. Osmotic Stress
Organisms adapted to high salinity and drought, accumulate cytoplasmic solutes that
act as protectants of membranes and proteins against damage by stress (also see
Chapter 2 and 3). Small and very soluble molecules including proline and beta-alanine,
quaternary ammonium compounds such as glycine betaine, proline betaine and betaalanine
betaine, sugar alcohols like mannitol, sorbitol and pinitol and, nonreducing
sugars such as trehalose, function as osmoprotectants in various organisms
(Rathinasabapathi, 2000 and 2002; Figure 2). These, jointly named as compatible sol-
utes, help stressed plants by increasing the osmotic pressure within the plant and
driving the gradient for water uptake under stress, therefore preventing water loss
temporarily but facilitating to maintain permanent normal physiological ion balance
(Yancey et. al. 1982). They also stabilize membranes and other macromolecular structures
(Rhodes and Samaras, 1994).