Hi,

When tomato plants are grown at high

temperatures (35°C), H2O2 accumulates and cannot be

eliminated even by the glutathione/ascorbate cycle, as its main enzymes as peroxidase are possibly inactivated by the same high temperatures. This H2O2 accumulation would, first,

reduce foliar biomass and, afterwards, kill the plant.

see this article 

POX activity in the case of temperature stress may be associated with the effects related to the metabolism of ROS from lipid peroxidation. The concentration of MDA could explain this effect, since a high concentration is associated with increased structural instability of membranes.

Tomato plants (Lycopersicon esculentum L. cultivar Tmknvf2 were grown for 30 d at two temperatures (25°C, optimal temperature, and 35°C) with the objective of determining the effect of heat stress on oxidative metabolism. The leaf

concentrations of the antioxidant compounds ascorbate (AsA) dehydroascorbate (DHA), reduced glutathione (GSH), oxidized glutathione (GSSG) and the activities of the enzymes superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), as well as total hydrogen peroxide (H2O2) concentration and shoot dry weight, were determined. High temperature stress caused: (1) decreased shoot weight, (2) accumulation of H2O2, (3) increased SOD activity, (4) decreased activities of CAT, GPX, APX, DHAR, GR (associated with detoxifying H2O2), and (5) increased levels of the antioxidant compounds AsA, DHA, GSSG, and GSH. In addition, our data demonstrated that heat stress

occurred in tomato plants at 35°C, and this temperature may have initially inhibited the ascorbate/glutathione cycle and then provoked an oxidative burst, indicated by foliar H2O2 accumulation.

Dear dr.

Peroxidase is one of an enzymatic antioxidant to improve heat stress tolerance in tomato plants.

Plants under heat stress produce  some enzymatic antioxidant such as peroxidase, catalase, superoxide dismutase....