Abiotic Stress in Plants and Metabolic Responses - Abiotic Stress: Plant Responses and Applications in Agriculture - page 29

strategies for improvement of plant tolerance involving the accumulation of those protective
osmolytes in plants by expression of core biosynthetic enzymes or their improved derivatives,
expression of related transporters, and deletion of osmolyte-consuming enzymes. These
numerous studies have provided evidence that enhanced accumulation of compatible solutes
correlates with reinforcement of plant resistance to adverse growth conditions.
5. Plant metabolomics and applications
The traditional approach of enhancing the accumulation of a specific compounds in response
to a determined stimulus, as done with compatible solutes, have resulted in some degree of
tolerance in plants, and also demonstrates that the ability to redirect nutrients to imperative
processes and the induction of adequate metabolic adjustments are crucial for plant survival
during conditions of stress. However, this is a sectioned view of how plants regulate their
entire metabolism in response to stressing conditions. In order to achieve a more comprehen‐
sive understanding, we must consider that plant metabolism is an intricate network of
interconnected reactions. Plants have a high degree of subcellular compartmentation, a vast
repertory of metabolites, and developmental stage strongly influences metabolism. Therefore,
metabolic responses are complex and dynamic and involve the modification of more than one
metabolite. Also, accumulation of a specific compound is not an absolute requirement
indicative of a tolerance trait; adjustment of the flux through a certain metabolic pathway might
be enough to contribute to stress tolerance [62]. Recently, it has been reported that plants
modulate stoichiometry and metabolism in a flexible manner in order to maintain optimal
fitness in mechanisms of storage, defense, and reproduction under varying conditions of
temperature and water availability [63]. Furthermore, time-series experiments in Arabidopsis
thaliana plants subjected to temperature and/or light alterations revealed that time-resolved
metabolic activities respond more quickly than transcriptional activities do [64].
Traditional molecular approaches for tracing metabolic phenotypes in plants responding to
abiotic stress have identified and manipulated specific genes or groups of genes in plant
models. These have primarily been genes involved in early responses or in down-stream
assembly of the response reaction. With the application of new powerful tools of molecular
biology and bioinformatics, large collections of genes have been subjected to complete analysis.
To arrive at a complete and comprehensive knowledge of physiology in the plant response to
abiotic stress, researchers are embracing ionomic profiling, transcriptomic, proteomic and
metabolomic analysis. A deep dissection of the biochemical pathways in plants facing stressing
conditions requires integrative and comprehensive analyses in order to identify all the
simultaneous metabolic responses and, more importantly, to be able to link these responses to
specific abiotic stress. In this sense, metabolomics could contribute significantly to the study
of metabolic responses to stress in plants by identifying diverse metabolites, such as the by-
products of stress metabolism, stress signal transduction molecules, and molecules that are
part of the acclimation response [65].
The metabolome is the entirety of small molecules present in an organism and can be regarded
as the ultimate expression of its genotype in response to environmental changes. Metabolomics