Effects of frost‐hardening and salinity on glutathione and sulfhydryl levels and on glutathione reductase activity in spinach leaves

Abstract

In frost‐hardened spinach leaves (Spinucea oleracea L. ev. Vroeg Reuzenblad) an enhanced content of water‐soluble non‐protein sulfhydryl compounds was observed. The enhancement was due to higher levels of glutathione as well as to other non‐protein‐bound sulfhydryl compounds. In addition glutathione reductase activity was increased upon hardening. The affinity of the enzyme for oxidized glutathione was slightly lowered during hardening. The significance of glutathione accumulation during frost‐hardening is discussed. Exposure of spinach to NaCl‐stress did not affect the levels of glutathione and glutathione reductase of the leaves. In addition the kinetic properties of the enzyme remained unaltered by salinity. It is suggested that glutathione and glutathione reductase activity are not involved in adaptation of spinach to saline conditions.

Genetic study of glutathione accumulation during cold hardening in wheat

“…Under controlled conditions long-term hardening (4°C, 59 d) increased the GR activity in spinach (de Kok and Oosterhuis 1983), while short-term hardening (4°C, 7 d) resulted in greater GR activity in pre-emergent maize seedlings (Prasad 1997). The Activity of GR did not change during chilling in the leaves of tomato and maize (Walker and McKersie 1993;Kocsy et al 1996) but it decreased in rice (Fadzillah et al 1996).…”

Thermal Dependence of the Apparent Km of Glutathione Reductases from Three Plant Species

“…Thermal stress has been defined as a temperature-induced aberration in the metabolism of the plant that, under certain conditions, is expressed as a reduction in growth, yield, or value of the plant (7). Temperature-induced aberrations in metabolism are often related to changes in the activity of enzymes and thus the thermal dependence of enzyme function may prove to be a useful indicator of the onset of thermal stress.GR' is thought to play an important role in the protection of the plant from both high and low temperature stresses by preventing the oxidation of enzymes and membranes (5,8,13,16). In the light ofthis role, a temperature-induced decline in GR activity could adversely affect the metabolism of the plant and thereby increase its susceptibility to thermal stresses.…”

“…GR' is thought to play an important role in the protection of the plant from both high and low temperature stresses by preventing the oxidation of enzymes and membranes (5,8,13,16). In the light ofthis role, a temperature-induced decline in GR activity could adversely affect the metabolism of the plant and thereby increase its susceptibility to thermal stresses.…”

Temperature-Induced Protein Conformational Changes in Barley Root Plasma Membrane-Enriched Microsomes

“…Furthermore, any stress-induced increase in the exposure of protein sulfhydryl groups might also damage membrane proteins by allowing the binding of heavy metal cations (11). It has been suggested that the observed increases in plant cellular nonprotein sulfhydrylcontaining compounds, usually glutathione, induced by low temperatures could prevent stress-induced protein damage (7,11,12).Other than the increased glutathione levels, there is little direct evidence for Levitt's SH-hypothesis. The cold temperature inactivation of the cytosolic enzyme RuBPCase from tobacco resulted in increased exposure of protein sulfhydryl groups (6).…”

“…Furthermore, any stress-induced increase in the exposure of protein sulfhydryl groups might also damage membrane proteins by allowing the binding of heavy metal cations (11). It has been suggested that the observed increases in plant cellular nonprotein sulfhydrylcontaining compounds, usually glutathione, induced by low temperatures could prevent stress-induced protein damage (7,11,12).…”