?Changes in glutathione reductase activity and protein content in wheat leaves and chloroplasts exposed to photooxidative stress?

LASCANO, H.R.,; GÓMEZ, LD., ; CASANO, L.M.,; TRIPPI V.S

PLANT PHYSIOLOGY AND BIOCHEMISTRY

Elsevier

Año: 1998 vol. 36 p. 321 - 329

0981-9428

The effect of different extents of oxidative stress on total glutathione reductase (CR, EC I .6.4.2) activity, isozymic pattern, and chloroplastic GR protein content were studied in wheat (Trificum nesfi,~un? L. cv. Oasis) leaves exposed to increasing doses of paraquat (PQ). Low concentrations of PQ increased total GR activity, peaking at 0.25 PM. In 0.75 to 2 pM PQ total GR activity remained around 30 % lower than control, while at 3 yM PQ activity decreased to 54 c/o of control. TwoGR isoforms were detected in crude extracts, one chloroplastic and one extrachloroplastic. PQ, at 0.25 and 0.50 FM, increased chloroplastic GR; but, at higher concentrations,it markedly decreasedth e activity and protein content of this isoform. A photooxidative-inducedlo sso f GR protein was also observedi n chloroplastsis olatedf rom PQ pre-treatedl eavesa nd subsequently exposedt o light. ExtrachloroplasticG R was lessa ffected by treatmentsT. he influenceo f active oxygensa nd lastidic protease on photooxidative-inducedc hloroplasticC R degradationw as studied. While purified GR was not affected by treatments with H,O,, when exposed to an *OH-generating system, a dose- ependent inactivation and breakdown were observed. Chloroplastic GR showed to be hydrolysed by a sulphydryl- and metal-containing protease, active at acid pH in both stressed andn on-stressecdh loroplastsH. owever,t his proteased egraded*O H-pretreatedG R morer apidily than nativeC R. It is suggested that the rapid degradationo f chloroplasticG R under strong photooxidative stress could be mainly due to direct fragmentation and/or increaseds usceptibilityo f the enzymet o proteasea ttack. caused by higher levels of *OH radicals. 0 Elsevier, Paris