Abiotic Stress in Plants and Metabolic Responses - Abiotic Stress: Plant Responses and Applications in Agriculture - page 26

2. Abiotic stresses and the impact on agriculture
Today, in a world of 7 billion people, agriculture is facing great challenges to ensure a sufficient
food supply while maintaining high productivity and quality standards. In addition to an ever
increasing demographic demand, alterations in weather patterns due to changes in climate are
impacting crop productivity globally. Warming and shifts in rainfall patterns caused an
historically high $10.3 billion in crop insurance payments to cover agriculture losses in 2011
in the U.S. [1]. Unfavorable climate (resulting in abiotic stresses) not only causes changes in
agro-ecological conditions, but indirectly affects growth and distribution of incomes, and thus
increasing the demand for agricultural production [2]. Adverse climatic factors, such as water
scarcity (drought), extreme temperatures (heat, freezing), photon irradiance, and contamina‐
tion of soils by high ion concentration (salt, metals), are the major growth stressors that
significantly limit productivity and quality of crop species worldwide. As has been pointed
out, current achievements in crop production have been associated with management practices
that have degraded the land and water systems [3]. Soil and water salinity problems exist in
crop lands in China, India, the United States, Argentina, Sudan, and many other countries in
Western and Central Asia. Globally, an estimated 34 million irrigated hectares are salinized [4],
and the global cost of irrigation-induced salinity is equivalent to an estimated US$11 billion
per year [5].
A promising strategy to cope with adverse scenario is to take advantage of the flexibility that
biodiversity (genes, species, ecosystems) offers and increase the ability of crop plants to adapt
to abiotic stresses. The Food and Agricultural Organization (FAO) of the United Nations
promotes the use of adapted plants and the selection and propagation of crop varieties adapted
or resistant to adverse conditions [6]. Global programs, such as the Global Partnership
Initiative for Plant Breeding Capacity Building (GIPB), aim to select and distribute crops and
cultivars with tolerance to abiotic stresses for sustainable use of plant genetic resources for
food and agriculture [7].
3. Plant responses to abiotic stress
Through the history of evolution, plants have developed a wide variety of highly sophisticated
and efficient mechanisms to sense, respond, and adapt to a wide range of environmental
changes. When in adverse or limiting growth conditions, plants respond by activating
tolerance mechanisms at multiple levels of organization (molecular, tissue, anatomical, and
morphological), by adjusting the membrane system and the cell wall architecture, by altering
the cell cycle and rate of cell division, and by metabolic tuning [8]. At a molecular level, many
genes are induced or repressed by abiotic stress, involving a precise regulation of extensive
stress-gene networks [9-11]. Products of those genes may function in stress response and
tolerance at the cellular level. Proteins involved in biosynthesis of osmoprotectant compounds,
detoxification enzyme systems, proteases, transporters, and chaperones are among the
multiple protein functions triggered as a first line of direct protection from stress. In addition,