Agriculture Reference
In-Depth Information
ABA mediated rice grains fi lling is largely due to increase in
SUS activity and SUS protein expression (Tang et al. 2009).
Cold acclimation of plants is a highly active process
resulting from the expression of a number of physiological and
metabolic adaptations to low temperature (Levitt 1980). Major
metabolic changes in carbohydrates, protein, nucleic acids,
amino acids, and growth regulators have been documented
during the acquisition of cold tolerance. Among these, water
soluble carbohydrates like the fructose polymers and fructans
were shown to accumulate during cold acclimatization of
grass species (Livingston 1991). Fructans are claimed to
enhance the cold tolerance in plants. The ability of plants to
synthesize fructans correlates their survival in colder climates.
Relationship between cold tolerance and fructan accumulation
has been noted in cereals (Suzuki and Nass 1988, Pontis 1989).
Evidence suggests that soluble sugars, such as sucrose and
oligosaccharides of the raffi nose family, in combination with
heat stable proteins could play a determinant role in cold stress
tolerance by protecting proteins and membranes against stress
(Gusta et al. 1996).
Cold stress induced major changes in amino acid levels
in over wintering crowns of the three ecotypes and the
highest contributions to total amino acid accumulation after
acclimatization at low temperatures came from proline,
glutamine and glutaric acid. Heat stable proteins have been
isolated from cold-acclimated plants and a correlation between
a heat-stable protein accumulation and cold induced tolerance
suggests that protein induced may act in combination with
soluble carbohydrates. During cold acclimation, homologs of
LEA proteins also accumulate in many plant species. During
cold water is drawn out of the cells, resulting in cellular
dehydration (Guy 1990). Thus, LEA protein homologs may
