Abiotic stress factors are the main limitation to plant growth and yield in agriculture. Among them, drought stress caused by water deficit, is probably the most impacting adverse condition and the most widely encountered by plants, not only in crop fields but also in wild environments. According to published statistics, the percentage of drought-affected land area in the world in 2000 was double that of 1970 [1].
Another major environmental factor that limits crop productivity, mainly in arid and semi-arid regions is high salinity. Approximately 19.5% of the irrigated soils in the world have elevated concentrations of salts either in the soil or in the irrigation water [2], damaging both the economy and the environment [3, 4]. The deleterious effects of salinity on plant growth are associated with low osmotic potential of soil solution (water stress), nutritional imbalance, specific ion effect (salt stress), or a combination of these factors [5].
Abiotic stress leads to a series of
morphological, physiological, biochemical, and molecular changes that adversely affect plant growth and productivity [6]. Drought, salinity, extreme temperatures, and oxidative stress are often interconnected, and may induce similar cellular damage (for more details see [7]).
During the course of its evolution, plants have developed mechanisms to cope with and adapt to different types of abiotic and biotic stress. Plants face adverse environmental conditions by regulating specific sets of genes in response to stress signals, which vary depending on factors such as the severity of stress conditions, other environmental factors, and the plant species [8].
The sensing of these stresses induces signaling events that activate ion channels, kinase cascades, production of reactive oxygen species, and accumulation of hormones [9].
These signals ultimately induce expression of specific genes that lead to the assembly of the overall defense reaction. In contrast to plant resistance to biotic stresses, which is mostly dependent on monogenic traits, the genetically complex responses to abiotic stresses are multigenic, and thus more difficult to control and engineer [10].
The conventional breeding programs are being used to integrate genes of interest from inter crossing genera and species into the crops to induce stress tolerance. However, in many cases, these conventional breeding methods have failed to provide desirable results [11].
In recent decades, the use of techniques based on in vitro plant tissue culture, has made possible the development of biotechnological tools for addressing the critical problems of crop improvement for sustainable agriculture. Among the available biotechnological tools for crop breeding, genetic engineering based on introgression of genes that are known to be involved in plant stress response and in vitro selection through the application of selective pressure in culture conditions, for developing stress tolerant plants, have proved to be the most effective approaches [12].
On the other hand, it is often difficult to analyze the response of plants to different abiotic stresses in the field or in greenhouse conditions, due to complex and variable nature of these stresses. In vitro tissue culture-based tools have also allowed a deeper understanding of the physiology and biochemistry in plants cultured under adverse environmental conditions [13].
In this work, the progress made towards the development of abiotic stress-tolerant plants through tissue culture-based approaches is described. The achievements in the better understanding of physiological and biochemical changes in plants under in vitro stress conditions are also reviewed.
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