Since plants throughout their life time are frequently exposed to stresses such as high and low temperatures, drought, salinity, etc., the growth and distribution of plants in nature are affected by a variety of biotic and abitoic stresses. Cold temperatures like drought and salinity suppress metabolism and reduce the amount of water in the cells and because of this, they are called dehydration or osmotic stresses (Roberts 1988; Yamazaki et al. 2009).
Therefore, plants as non-moving organisms, in addition to being able to understand fluctuations and seasonal temperature changes, should also be able to respond to these changes (Went 1953; Browse and Xin 2001). At the time of stress, ROSs are produced, which are in fact reactive oxygen species and act in small amounts as stress signals but in large amounts, they are also stress factors in their cells (Chinnusamy et al., 2007). Some plants, such as Spinach and Arabidopsis thaliana, could be adapted to cold stress (Thomashow 2010), but rice, tomatoes and corn are sensitive to cold stress (temperatures of 0-12°C). Solanum Lycopersicum L. is an annual herb and a member of the Solanaceae family (Zhao et al. 2009).
Tomatoes are low in calories and contain vitamins such as A, C and E, minerals, lycopene, beta-carotene, about 95-93% water, 3-4% glucose and fructose (Etminan et al. 2014). S. Lycopersicum is a cultivar tomato, and at all vegetative reproductive growth stages is susceptible to cold (Venema et al.
2005; Foolad and Lin 2011). The researchers showed that physiological functions such as hormones and calcium signal molecules play an important role in the expression of genes in response to low temperatures (Liu et al. 2012; Lyons 1973), due to the oxidative stress, the viscosity of the membrane is impaired and the osmotic potential is reduced (Beck et al. 2004), and after several hours or a few days, cold affects the tomatoes’ photosynthesis and decreases the necessary carbohydrates to form seeds, so reduce the growth and yield (Allen et al. 2001; Naidu et al.
2005; Ort et al. 2002). Responses to stresses include the series of physiological and morphological functions such as decreasing the growth, increasing the ABA, changes the gene expression levels and amounts of compatible solutions; through antioxidant enzymes, non-enzymatic antioxidants and hormones (Browse and Xin 2001; Thomashow 2010; Alia et al. 1991; Ashraf et al. 2007; Chinnusamy et al.
2007). The first defense line of cells in plants against stresses is antioxidant enzymes such as catalase (CAT), ascorbate peroxidase (APX), peroxidase (POX), superoxide dismutase (SOD), etc. (Ruelland and Zachowski 2010). Superoxide dismutase (SOD: EC 1.15.
1.1) belonging to the metalloprotein class, converts superoxide into oxygen and peroxide. The produced peroxide should be removed later by catalase or peroxidase. FeSOD (iron SOD), MnSOD (manganese SOD) and Cu/Zn SOD (????/Zink SOD) are three SOD forms that they are different based on the type of metal co-factor in their catalytic site (Comba et al., 2010; Scandalios 2005).
The MnSOD type exists in the mitochondrial matrix and peroxisomes, Cu/Zn SOD is present in cytosol, chloroplast and extracellular space, and the FeSOD type is in chloroplasts (Scandalios 2005; Alsher et al.). The phylogenetic analysis shows that FeSOD and MnSOD are similar to each other, while Cu/Zn SOD is different, probably because they come from eukaryotes in response to biosphere oxygenation as a biological stress. The expression of antioxidant enzymes genes reflects the defense of plant cells. Three SOD isozymes are encoded in the nucleus by a large group of genes, which have been studied in corn (Fink et al. 2002), rice (Sakamato et al.
1992) and tomato (Perl-Treves et al. 1991). Osmotic stress can increase the expression of the SOD (FeSOD, MnSOD) genes in Cabbage (Hosseini et al.
2015; Baator et al. 2012) and Lycopersicum esculentum L. (SoaidomAydin et al., 2013). Against osmotic stresses, phytohormones such as abscisic acid (ABA), salicylic acid, jasmonate and ethylene, alone or in combination with each other are activated (Bao Yang et al. 2017). Increasing the level of ABA through the expression of genes leads to the establishment of a signal cascade, closure of stomata, seed sleeping, and inhibition of germination (Melcher et al.
2009; Rodrigo et al. 2006). AtNCED2 and AtNCED3 genes have been found in Arabidopsis stomatal guard cells, which showed that ABA is present during water stress (Garsimata et al. 2003; Kumar et al. 2008). ABA synthesis at the middle of the isoprenoid pathway, the phyton molecule (C40) is composed of two geranylgeranyl diphosphate (GGPP) (C20), and then the lycopene, ?&?-carotene are synthesized. After hydroxylation, ?-carotene is converted to zeaxanthin (Barrero et al.
2005), then the zeaxanthin epoxidase(ZEP) and neoxanthin synthase convert it to violaxanthin and neoxanthin, respectively (Koomneef et al. 1982; McAdam et al. 2015). Violaxanthin and neoxanthin are pressure to 9-cis-epoxycarotenoid dioxygenase (NCED) to form xanthoxin in plastids. Xanthoxin goes to cytosol and with C25 epoxy-apocarotenal produce ABA di-aldehyde and ultimately convert to ABA (Schwartz et al.
2003; Taylor et al. 2005).