Ascorbate, glutathione and related enzymes in chloroplasts of tomato leaves infected by Botrytis cinerea

The effect of Botrytis cinerea infection on the total pool sizes of ascorbate, glutathione and their redox status, the activities of ascorbate-glutathione cycle related enzymes, APX, DHAR, GR as well as GST and GSH-Px activities in chloroplasts isolated from tomato leaves were studied. An accelerated chlorophyll loss in chloroplasts from infected leaves was observed. The AA content was not changed considerably but a burst in DHA formation, up to 319% of control, and a significant prooxidative shift in the ascorbate redox status were found in chloroplasts from infected leaves. A massive progressive decrease in GSH and total glutathione contents as well as GR activity increase were found after infection. However, similar but less-pronounced glutathione-related changes were observed in control suggesting that they could be at least partly the result of B. cinerea induced promotion of senescence and not a specific response to pathogen infection. As shown by the analysis of ascorbate-glutathione cycle related enzyme activities as well as correlations between the two antioxidants and enzymes responsible for keeping them in the reduced state GSH is the limiting factor for the whole cycle operation in chloroplasts. This is in accordance with our previous results for the whole-cell extracts. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.