Environmental Changes In Plants

Plants in nature are constantly exposed to various abiotic stresses resulting from unfavorable environmental conditions which negatively affect their growth and development (Atkinson and Urwin, 2012). Most crops are exposed to stress during some stages of their life cycle (Bartels and Nelson, 1994). Changes in temperatures, starvation, drought, change in nutrients abundance, flooding, air pollution, soil pollution and osmotic alterations are some of the examples present in nature (Apel and Hirt, 2004).

In literatures, there are many definitions of the term stress. Koehn and Bayne (1989) defined the stress as the environmental changes that result in the reduction of the organism fitness and consequently decrease its growth and development.

In 2013, according to Food and Agriculture Organization of the United Nations (FAO) statistics, more than 800 million hectares of land throughout the world are currently salt-affected, including both saline and sodic soils equating to more than 6% of the world’s total land area. In addition it’s expected that continuing salinization of arable land will cause tremendous global impact, resulting in a 30% loss of agricultural land over the next 25 years and up to 50% loss by 2050. In general, the world is losing at least 3 ha of arable land every minute due to soil salinity. Some of the most severe effects of abiotic stresses occur in the arid and semiarid regions where rainfall, high evaporation low, native rocks, saline irrigation water, and poor water management all contribute in agricultural areas (Leslie, 2013).

Salinity is a major threat in agriculture. Accumulative effect of salinity by water irrigation adds up to the problem and inhibits agricultural productivity in many semi-arid and arid regions worldwide (Flowers et al., 1977; Qadir et al., 2000). Salinity, reduces seed germination, vegetative growth, flowering, and limits crop productivity. It results in water deficit, ion toxicity, and nutrient deficiency in plants, which causes cellular damage, growth reduction, and may lead into death (Wang,

(2009) summarized the number of affected genes and proteins of some model plants under salt stress and indicated that several genes related to ATP synthase, PSI and PSII were down-regulated under salt stress. Photosynthesis-related proteins were down-regulated in soybean seedling leaf under salt stress (Sobhanian et al., 2010). Sobhanian et al., 2011 reviewed the effects of salt stress on several plants, including rice, soybean, wheat, potato and Aleuropus lagopoides. The authors concluded that reducing photosynthesis activity under salt stress was the only common response in the plants. Using in vivo hydroponic rice seedling culture system, proteome of rice leaves under salt stress was evaluated. Among the photosynthesis related proteins, oxygen evolution proteins, a protein related to PSII, was up-regulated in response to salt stress (Kim et al., 2005). Salt stress alters the expression of proteins even after few hrs of stress exposure. It had been shown sodium ions accumulate quickly and excessively in chloroplast of maize during the initial phase of stress (up to 4 h). This could enhance the expression of polypeptides of PSII, ferredoxin NADPH and oxidoreductase, ATP synthase and chlorophyll a/b binding protein (Zörb et al., 2009). Since the water potential of the leaves remained unchanged, it can be assumed that the rapid response of plant to salinity is a reflecting mechanism to alleviate the detrimental effects of sodium ions on the photosynthetic