Effects of Elevated Cytosolic Glutathione Reductase Activity on the Cellular Glutathione Pool and Photosynthesis in Leaves under Normal and Stress Conditions

Abstract

Tobacco (Nicotiana tabacum var Samsun) was transformed using the bacterial gor gene coding for the enzyme glutathione reductase. Transgenic plants were selected by their kanamycin resistence and expression of the bacterial gor gene. After separation by isoelectric focusing techniques, leaf extracts from transgenic plants having both native and bacterial glutathione reductase activity gave, in addition to the six bands of the native enzyme, two further closely running isoenzymes. These additional bands originating from the expression of the bacterial gor gene were nonchloroplastic. Leaves from transgenic plants had two-to 10-fold higher glutathione reductase activity than nontransgenic controls. The amount of extractable glutathione reductase activity obtained in transgenic plants was dependent on leaf age and the conditions to which leaves were exposed. Both light and exposure to methylviologen increased leaf glutathione reductase activity. Elevated levels of cytosolic glutathione reductase activity in transgenic plants had no effect on the amount or reduction state of the reduced glutathione/oxidized glutathione pool under optimal conditions or oxidative conditions induced by methylviologen. The glutathione pool was unaltered despite the oxidation-dependent loss of CO2 assimilation and oxidation of enzymes involved in photosynthesis. However, the reduction state of the ascorbate pool was greater in transgenic plants relative to nontransgenic controls following illumination of methylviologen-treated leaf discs. Therefore, we conclude that in the natural state glutathione reductase is present in tobacco at levels above those required for maximal operation of the ascorbateglutathione pathway.Glutathione and GR2 appear to be ubiquitous in the biosphere. Glutathione is the major low mol wt thiol-containing compound in all living organisms. It is present in millimolar concentrations in leaves (7-9), where it is a general reductant. It has, in addition, several important functions, including the detoxification of herbicides, the removal of toxic derivatives of oxygen in the ascorbate-glutathione cycle, the induction of enzymes, and it participates in sulfur metabolism and gene 'Present address: AECI Limited, Research and Development Department, PO Modderfontein 1645, South Africa.

Effects of Iron Excess on Nicotiana plumbaginifolia Plants (Implications to Oxidative Stress)

“…They are known for the close relative N. tabacum to be strongly reduced in unstressed leaf material (Foyer et al, 1991). Indeed, in the control plants used here, the GSH/GSSG couple was reduced to 96%, and for the AsA/DAsA the oxidized form could not even be detected (Table 111).…”

Comparative response on the accumulation of inorganic phosphate in leaf of Basella alba to low and high temperature

“…It has been shown that low temperature causes the higher oxidative stress inducing the synthesis of active oxygen species (AOS) (Lee and Lee 2000) and increases tolerance to AOS in cereals and with an increase in anti oxidative enzymes (Mahajan andTuteja 2005, Kuk 2003). Anti oxidative enzymes can neutralize AOS (Lee andLee 2000, Odaira et al 2000) and thereby prevents the cellular membranes and organelles from the damaging effects of AOS (Foyer et al 1991). Similarly, heat stress or high temperature is also involved in the synthesis of AOS (Mei and Song 2010).…”

Paraquat: An Oxidative Stress Inducer

“…These have involved the overexpression of enzymes associated with the Asada-Halliwell pathway including SOD (Arisi et al, 1998;Bowler et al, 1991;McKersie et al, 1999;Melchiorre et al, 2009;Perl et al, 1993;Pitcher et al, 1991;Sen Gupta et al, 1993;Tepperman et al, 1990;Van Camp et al,1996), and GR (Aono et al, 1991(Aono et al, , 1993Creissen et al, 1995;Foyer et al, 1991Foyer et al, , 1995Melchiorre et al, 2009). The tolerance to different oxidative stress conditions was dependent on the copy numbers and overexpression levels; the isoform overexpressed; the subcellular location where the overexpressions were targeted; and the induction of other antioxidant enzymes.…”