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

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Z . Dajic
completed their normal development, including flowering and seed production even at
salinity of 300 mM (Zhifang and Loescher, 2003). Enhanced salinity tolerance of eggplant
was achieved through installing of the bacterial mt1D gene encoding the mannitol
phosphodehydrogenase, an enzyme involved in the mannitol synthesis (Prabhavathi
et al., 2002).
Trehalose is a non-reducing disaccharide that functions as a compatible solute
under abiotic stress in bacteria, fungi and invertebrates (Yeo, 1998). Until recently,
trehalose had only been found in a few resurrection (desiccation- tolerant) plants,
indicating the role of this molecule in adaptations to water stress due its ability to act as
a water substitute on the surface of macromolecules (Öko- Institut, http://
www.plantstress.com/Articles/up_general_files/GE_Tol.pdf). Trehalose accumulates in
plants in a very low concentrations, and might be involved in the ROS scavenging and
signaling cascade (Flowers, 2004). The overexpression of Escherichia coli trehalose
biosynthetic genes (otsA and otsB) in transgenic rice resulted in sustained plant growth,
lower photo-oxidative damage and a more favorable mineral balance under exposure to
salinity (Garg et al., 2002).
Proline is a significant compatible solute in many halophytic species (Stewart
and Lee, 1974), as well as in glycophytes, like Medicago sativa (Fougere et al., 1991)
and Sorghum bicolor (McCree, 1986). Accumulation of proline in rice is a symptom of
salt stress injury, and is due increase of the ornithine delta-aminotransferase (OAT) and
its precursor glutamate (Lutts et al., 1999). Intermediates of proline biosynthesis and
catabolism induced expression of several osmotically regulated genes in rice (Iyer and
Caplan, 1998). The content of transcripts of two cDNA clones from alfalfa, encoding the
first enzyme of proline biosynthesis pathway, MsP5Cs-1 and MsP5Cs-2, increased in
seedlings exposed to 90 mM NaCl (Ginzberg et al., 1999). Transgenic wheat plants
producing proline due to the expression of genes for proline biosynthesis, transferred
from Vigna aconitifolia, exhibited improved tolerance to salinity (Sawahel and Hassan,
2002).
Different classes of proteins of uncertain biochemical function (possibly macromolecule
protection factors) are synthesized under conditions of salt stress, such as:
osmotins, dehydrins, late embryogenesis abundant proteins (LEA) and polyamines,
primarily putrescine and spermine (Tester and Davenport, 2003). Under salinity treatments,
a balance between content of the free and bound polyamines in roots of barley
seedlings might be relevant for salt tolerance (Zhao et al., 2003). There is no much data
on the function of osmotins and dehydrins in conditions of salinity, but they may be
involved in the maintenance of the protein structure (Campbell and Close, 1997). The
late embryogenesis abundant-like proteins (LEA) accumulate in the vegetative tissues
of all plant species in response to osmotic stress, caused by drought, salinity or cold
(Xiong and Zhu, 2002). They probably contribute to the preservation of the structural
integrity of the cell (Winicov, 1998), acting as chaperones to prevent denaturation of
proteins (Xiong and Zhu, 2002). Most of the LEA-like proteins of all organisms are
involved in adaptations to osmotic stress, and interestingly, express features of ribosomal
proteins that interact with RNA (Garay-Arroyo et al., 2000).