Lecture14Lecture14

Stress senescence tolerant Stress senescence tolerant plantsplants

Development of oxidative Development of oxidative stress tolerant plantsstress tolerant plants

• Under oxidative stress the enzyme Under oxidative stress the enzyme superoxide dismutase detoxifies super superoxide dismutase detoxifies super oxide anion to hydrogen peroxide and oxide anion to hydrogen peroxide and then to water and oxygenthen to water and oxygen

Development of oxidative Development of oxidative stress tolerant plantsstress tolerant plants

• tobacco plants transformed with a tobacco plants transformed with a superoxide dismutase gene superoxide dismutase gene

• under the control of the 35S under the control of the 35S promoter from cauliflower mosaic promoter from cauliflower mosaic virus virus

• reduced oxygen radical damage reduced oxygen radical damage under stress conditions compared under stress conditions compared with control plantswith control plants

Oxidative stress tolerant Oxidative stress tolerant plantsplants• Stress reduced if the level of oxidized Stress reduced if the level of oxidized

glutathione within a plant is increasedglutathione within a plant is increased

• a tobacco cDNA encoding an enzyme with both a tobacco cDNA encoding an enzyme with both glutathione S-transferase and glutathione glutathione S-transferase and glutathione peroxidase activity was isolatedperoxidase activity was isolated

• Glutathione peroxidase catalyzes the Glutathione peroxidase catalyzes the conversion of glutathione (GSH) to oxidized conversion of glutathione (GSH) to oxidized glutathione (GSSG) by reacting with organic glutathione (GSSG) by reacting with organic peroxides and reducing them to organic peroxides and reducing them to organic alcohols (Fig.2)alcohols (Fig.2)

Oxidation of GSH to GSSH and simultaneous Oxidation of GSH to GSSH and simultaneous reduction of organic peroxide to an organic reduction of organic peroxide to an organic alcohol, catalyzed by glutathione peroxidasealcohol, catalyzed by glutathione peroxidase

Oxidative stress tolerant Oxidative stress tolerant plantsplants• Transgenic tobacco plants that express Transgenic tobacco plants that express

glutathione peroxidase were createdglutathione peroxidase were created• using the isolated cDNA under the control using the isolated cDNA under the control

of the 35S promoterof the 35S promoter• the construct introduced into plants with the construct introduced into plants with

a binary Ti plasmid systema binary Ti plasmid system• transformed plant had approximately transformed plant had approximately

twice the level of enzyme activity found in twice the level of enzyme activity found in non transformed plantsnon transformed plants