Suitability of the Ratio Between Reduced and Oxidized Glutathione as an Indicator of Plant Stress

Abstract

It is generally assumed that plant stress is related to the release of reactive oxygen species (ROS) that need to be detoxified. Glutathione exists in reduced (GSH) and oxidized (GSSG) forms, and is involved in the detoxification of ROS during which GSH is oxidized to build GSSG. The glutathione status of the cell is thought to be a sensitive stress marker, and a change in the GSSG content or the GSH/GSSG ratio can indicate stress. However glutathione is also a very rapidly changing pool as an important interface between different metabolic pathways. Therefore whether the ratio between reduced and oxidized glutathione is a suitable indicator for stress under various experimental stress conditions is questionable. The early recognition of stress can be important in agriculture to be able to identify and counteract a special stress early enough to prevent yield losses. In this paper results are compiled from experiments where stress was triggered in greenhouse trials. Severe sulfur deficiency, drought, and elicitation of stress by methyljasmonate (MeJA) application and fungal infection as well as a disturbed mineral nutrition caused by high EDTA soil application were investigated as stress factors. The impact of plant part, age, and plant species was addressed. The results reveal that only under severe stress conditions does the GSH/GSSG ratio significantly decrease. Even under non-stress conditions, the ratio can be quite different depending on other factors such as plant part, age or species making the GSH/GSSG ratio alone unsuitable to be an early stress indicator.