generally, expression of enzymatic scavengers is transcriptionally upregulated initially as a cellular attempt to cope with oxidative stress. However, being proteins the enzymes themselves are susceptible to oxidative modifications (esp. cysteine thiol hyper-oxidation, nitration). Enzymes like SOD, peroxiredoxins do get inactivated by high amounts of ROS (e.g. lots of H2O2, peroxynitrite, HOCl).

For example, 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3757672/ 

http://www.ncbi.nlm.nih.gov/pubmed/24023284

At the same time, certain ROS/RNS sources also get inactivated by ROS/RNS that they produce. E.g. iNOS by peroxynitrite. 

Rahul,

It depends on the type of stressor, the cell type and duration of stress. For example during amino acid deprivation stress,  integrated stress response genes (such as Trb3, Asns, Chac1, Slc7a11  etc ) regulated by ATF4, CEBPg are induced in primary cells (MEFs) .

It depends of the stressor and also the tissue/cell you are analyzing. Which conditions are you interested in?

Hi Rahul,

Please take into consideration uncommon reaction of POX–SOD–CAT in some leaves, for instance, the data reported in 2004 by Brazilian team led by Joaquim Silveira. Thus  they suggested that the POX–SOD–CAT antioxidant system of cowpea leaves was not effective in scavenging superoxide and peroxide radicals generated by salt-induced osmotic stress, as indicated by the intense damage to membrane integrity seen in older leaves. It appears that the ability of cowpea plants to survive under high levels of salinity is not caused by an operating antioxidant system involving SOD, POX and CAT activities in the mature leaves.

Best wishes,

Ilya

thanks for your suggetions

i am using nanoparticles for stress in plant system

Plants are rich in antioxidant ,so if you use nanoparticels as a hazard these contents( as catalase, SOD, GSH) will be decreased and oxidative stress as (ROS, NO,MDA) will be increased.

It depends on type and level of stress. Generally, stress increase the production of Reactive Oxygen Species (ROS) and to minimise these toxic molecules, antioxidant enzyme activity also increase. However, higher concentration of ROS is also toxic for the enzymes. Therefore, external antioxidants are needed to minimise the toxicity.

Physico-chemical features, concentration of NPs and the type and nature of the plant (cells)  tissue involved in investigation should be considered to evaluate the redox homeostasis. Type and  rate of formation of reactive species by the NPs under consideration is another aspect to be considered. The NPs being investigated, are these engineered or natural in nature? Because engineered NPs have specific target while natural one may be or may not be target oriented. I feel the basics should not be ignored at any stage of investigation. The stress induced should be well defined,  l controlled qualitatively and quantitatively and its nature be well defined i.e., chemical stress, physical stress or hydrostatic, ionic stress or pesticidal stress. These factors may dictate  overall effect of the NPs on plant tissues under study.