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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

et al., 2000). Most of the chaperone proteins are located in the ER, which

folds newly synthesized glycoproteins. They contain calreticulin, binding

immunoglobulin protein, calnexin, and the majority of heat shock proteins

(Williams, 2006). The expression of molecular chaperone proteins helps

the cell adapt to adverse environmental conditions by preventing protein

aggregation. Various studies have demonstrated that chaperone proteins are

regulated differently in response to abiotic stress (Ahsan et al., 2010b). The

expression of molecular chaperones in response to stress does not abide by

a set of rules. The expression of molecular chaperones is influenced by the

plant’s age, the consequence, and time of exposure could influence several

proteins which would be up or downregulated. Moreover, the expression of

molecular chaperones might differ between organelles. As a result, investiga­

tions on the molecular chaperone sub-proteome must be carefully designed

concerning the stressful circumstances as well as the cells and organelles

involved (Wang et al., 2004; Komatsu et al., 2009; Ahsan et al., 2010).

13.4.3 ROS SCAVENGER PROTEINS

Abiotic stress causes cells to produce reactive oxygen species (ROS), such

as hydroxyl radicals, hydrogen peroxide (H2O2), and superoxide anions,

which together induce oxidative stress. The stress response of the cell

varies depending on the degree of the oxidative stress and can vary from

antioxidant defense systems activation to programmed cell death. The major

defense against oxidative stress is the creation of ROS scavenger proteins.

The predominant scavenging proteins found in plant cells are superoxide

dismutase (SOD), ascorbate peroxidase (APX), glutathione peroxidase

(GPX), and catalase (CAT) (Blokhina et al., 2003; Apel et al., 2004; Hossain

et al., 2009). In organelles like mitochondria and chloroplasts, the production

of reactive oxygen species (ROS) is a common biological activity. Stress,

on the other hand, induces oxidative damage by increasing the generation

of reactive oxygen species (ROS). The presence of scavenger proteins in

different plant organelles and subcellular compartments during abiotic stress

has been documented, including the nucleus, mitochondria, chloroplasts,

plasma membrane, and cell wall. ROS may act as signaling molecules in

organelles and compartments, based on the distribution of scavenger proteins

throughout the cell (Bae et al., 2003; Qiu et al., 2004; Kotchoni et al., 2006;

Giacomelli et al., 2006; Komatsu et al., 2009; Nanjo et al., 2010).