The glutathione system as a stress marker in plant ecophysiology: is a stress-response concept valid?

Abstract

Environmental stress impacts cause an increased formation of reactive oxygen species (ROS) in the chloroplasts (photo-oxidative stress). The role of glutathione in the antioxidative defence system provides a rationale for its use as a stress marker. However, responses of glutathione concentrations and redox states are not consistent among the large number of available publications. In the present review the hypothesis that stress responses of the glutathione system follow a general ecophysiological stress-response concept is investigated. In this view, an initial response phase would be followed by an acclimation phase where a new steady-state is established. Alternatively, if successful acclimation is not achieved, degradation of the system will follow. Recent publications dealing with responses to photochilling, salinity, and drought are analysed as to whether the results fit the concept. In general, an initial stress response was related to changes in the glutathione redox state, whereas acclimation was marked by increased glutathione concentrations, increased related enzyme activities, and/or a more reduced redox state of glutathione. The latter was interpreted as overcompensation leading to enhanced regeneration of glutathione. Deterioration effects upon strong stress impacts were related to progressive degradation and oxidation of the glutathione pool. A time-course analysis, which has rarely been done in the published literature, showed this sequence of events. When apple trees were subjected to progressing drought, the initial response was a slight oxidation of the glutathione pool, followed by increased glutathione concentrations. When the stress increased, glutathione concentrations dropped and redox state became more oxidized, which marked the degradation of the system. In spite of the general congruency of these results with the suggested stress-response concept, several limitations have to be highlighted: The importance of the glutathione system relative to other components of the photoprotective and antioxidative defence system, as well as relative to stress avoidance strategies, has to be established. It is suggested that a variety of parameters taking into account alternative protection pathways (e.g. photorespiration, light dissipation) and other components of the antioxidative systems should be measured. Within such response patterns the glutathione system is a valuable stress marker in ecophysiological studies.

Native halo-tolerant plant growth promoting rhizobacteria Enterococcus and Pantoea sp. improve seed yield of Mungbean (Vigna radiata L.) under soil salinity by reducing sodium uptake and stress injury

“…Accumulation of H 2 O 2 triggers the CAT (catalase), APO (ascrobate peroxidase) and POD (peroxidase) activities to reduce its concentration by converting it into oxygen and water (Tausz 2004). With salt stress, an increment in H 2 O 2 content (2.1-4.6 folds) occurred however; it decreased with the PGPR treatment.…”

Exogenous salicylic acid improves photosynthesis and growth through increase in ascorbate-glutathione metabolism and S assimilation in mustard under salt stress

“…10 In addition to its central task as an antioxidant, the role of GSH in plant metabolism concerns with the signaling of sulfur status, resistance to xenobiotics, heavy metal tolerance and pathogen response. 11,12 It also maintains redox homeostasis in cells. 13 The potential of GSH as antioxidant is related to the activity of glutathione reductase (GR), which catalyzes the regeneration of GSH from oxidized glutathione (GSSG).…”

Interactive effects of nitric oxide and glutathione in mitigating copper toxicity of rice (Oryza sativaL.) seedlings

“…7,8 It is also strongly involved in fine-tuning of redox signaling during environmental stresses and is therefore regarded as a stress marker in plant ecophysiological studies. 9 It is well established that not only GSH concentration, but also the GSH/GSSG ratio, is important in maintaining cell redox status. 8 Any imbalance in the cellular GSH level, both deficiency and excess, may adversely influence cellular metabolism.…”