Superoxide production by thylakoids during chilling and its implication in the susceptibility of plants to chilling-induced photoinhibition

Abstract

Factors influencing the rate of superoxide (O 2 (-) ) production by thylakoids were investigated to determine if increased production of the radical was related to injury induced by chilling at a moderate photon flux density (PFD). Plants used were Spinacia oleracea L., Cucumis sativus L. and Nerium oleander L. grown at either 200° C or 45° C. Superoxide production was determined by electron-spin-resonance spectroscopy of the (O 2 (-) )-dependent rate of oxidation of 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidine (OXANOH) to the corresponding oxazolidinoxyl radical, OXANO ·. For all plants, the steady-state rate of O 2 (-) production by thylakoids, incubated at 25° C and 350 μmol photon · m(-2) · s(-1) (moderate PFD) with added ferredoxin and NADP, was between 7.5 and 12.5 μmol · (mg chlorophyll)(-1) · h(-1). Incubation at 5° C and a moderate PFD, decreased the rate of O 2 (-) production 40% and 15% by thylakoids from S. oleracea and 20° C-grown N. oleander, chillinginsensitive plants, but increased the rate by 56% and 5% by thylakoids from C. sativus and 45° C-grown N. oleander, chilling-sensitive plants. For all plants, the addition of either ferredoxin or methyl viologen increased the rate of O 2 (-) -production at 25° C by 75-100%. With these electron acceptors, lowering the temperature to 5° C caused only a slight decrease in O 2 (-) production. In the absence of added electron acceptors, thylakoids produced O 2 (-) at a rate which was about 45% greater than that when ferredoxin and NADP were present. The addition of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea reduced O 2 (-) production under all conditions tested. The results show that the rate of O 2 (-) production increases in thylakoids when the rate of electron transfer to NADP is reduced. This could explain differences in the susceptibility of thylakoids from chilling-sensitive and chilling-insensitive plants to chilling at a moderate PFD, and is consistent with the proposal that O 2 (-) production is involved in the injury leading to the inhibition of photosynthesis induced under these conditions.

Magnesium Deficiency and High Light Intensity Enhance Activities of Superoxide Dismutase, Ascorbate Peroxidase, and Glutathione Reductase in Bean Leaves

“…Photogeneration oftoxic 02 species can be intensified when plants grown at a high light intensity are exposed to an environmental stress that impairs the utilization of absorbed light energy for photosynthetic CO2 fixation (2,9,18). Such conditions may lead to a limited NADP+ pool for acceptance of electrons from PSI and, thereby, a higher potential for 02 activation (18).…”

“…Such conditions may lead to a limited NADP+ pool for acceptance of electrons from PSI and, thereby, a higher potential for 02 activation (18). Accordingly, in many instances, activities of SOD and enzymes of the H202 scavenging pathway are increased in response to environmental stress factors such as drought (33), chilling (30), and treatments with hyperbaric 02 levels ( 11) and air pollutants (34).…”

Involvement of Polyamines in the Chilling Tolerance of Cucumber Cultivars

“…Enhanced chilling tolerance was reported in transgenic tobacco into which a gene for glycerol-3-phosphate acyl transferases or chloroplastic fatty acid desaturases from Arabidopsis was introduced (Murata et al, 1992;Kodama et al, 1994). Another mechanism involves cellular defense against membrane lipid peroxidation caused by a chill-induced increase in the generation of reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radicals (Omran, 1980;Hodgson and Raison, 1991;Prasad et al, 1994). Chilling-tolerant plants are known to have more efficient antioxidant systems than chilling-sensitive ones (Walker and McKersie, 1993;Dipierro and Leonardis, 1997).…”

Purification of Two Superoxide Dismutase Isozymes and Their Subcellular Localization in Needles and Roots of Norway Spruce (Picea abies L.) Trees

“…During photosynthesis, superoxide radicals can be produced at a steady-state rate of 3.5 X 10-9 mol mg-' Chl s-1, even under low light intensities (12). Unfavorable environmental conditions such as low temperatures, desiccation stress, and air pollutants can enhance the production of toxic oxygen species in plant cells (7).…”

“…They catalyze the disproportionation of superoxide radicals (19) at a rate close to the diffusion limit (rate constant KsOD = 2 X 109 M-1 S-2 [12]) and, thus, prevent the oxidation of cellular components by the radical itself or by active oxygen ' Part of this study was financially supported by the Bayerisches Staatsministerium fur Landesentwicklung und Umweltfragen.…”