Role of the Ascorbate–Glutathione Cycle in Paraquat Tolerance of Rice

Abstract

Out of 1,343 mutant lines of rice mutated by sodium azide from the parental Japonica-type variety ‘Tainung 67’ (TNG67), a paraquat-susceptible line 1192 and a paraquat-tolerant line 72 were selected using whole seedlings at the four-leaf stage and leaf segments at the tillering stage as test materials. Further selection from progenies of these two mutant lines yielded the susceptible 1192-11 (S) and tolerant 72-16 (T), which were studied herein. Chlorophyll fluorescence, electrolyte leakage, and lipid peroxidation were measured for leaf segments of rice following treatment with 0.1 mM paraquat. A comparison of these responses among the three rice lines (TNG67, 72-16, and 1192-11), revealed a higher tolerance to paraquat in the tolerant mutant line 72-16 and the parental variety TNG67 than in the susceptible mutant 1192-11. Analysis of the antioxidative system in paraquat-treated leaf segments showed that the reduced form of glutathione (GSH) and the ratio of GSH to total glutathione increased by 3.5-fold within 6 h after treatment (HAT) and up to 5-fold 9 HAT in the T line, as compared with the S line. In view of the high activities of both dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in paraquat-treated leaves of TNG67 and the T line, the antioxidative effect of the ascorbate–glutathione cycle is hereby proposed to play an essential role in paraquat tolerance of rice. Pretreatment of rice segments with spermine enhanced DHAR and GR activities as well as paraquat tolerance of the S line. These results suggest that the activity of ascorbate–glutathione cycle induced by spermine is involved in rice tolerance to this herbicide. Although kinetics studies showed no significant difference among the three rice lines in paraquat inhibition of GR, a lower affinity of enzyme to substrate (Km) in TNG67 and the T line and a higher maximal reaction rate (Vmax) in the T line for the oxidized glutathione substrate (GSSG) were detected. These observations further implicate the importance of glutathione reductase in paraquat tolerance of rice

A Paraquat Tolerance Mutant in Rice (<i>Oryza sativa</i> L.) Is Controlled by Maternal Inheritance

“…A mutant pool of rice variety TNG67 contains more than 3000 mutants with many desirable traits were developed by sodium azide mutagenesis at the Taiwan Agricultural Research Institute [16]. In our previous study, two pure mutant lines, the paraquat tolerant 72 (T, Pq72) and susceptible 1192 (S, Pq1192), have been screened from this mutant pool [17], and the physiological mechanism study on the paraquat tolerance mutants revealed no difference in uptake, translocation, and metabolism of paraquat between T and S lines (C. S. Wang, unpublished data). However, the induction of enzymatic activities for free radical scavenging played a critical role in paraquat tolerance [15].…”

“…81, 802, 875, 948, 1081 and 1192) and 7 tolerant (T) lines (No. 72, 713, 881, 882, 883, 986 and 1067) have been selected from 1343 pure mutants at M7 generation from the mutant pool of TNG67 rice variety [17]. After further identification of paraquat tolerance was conducted for three selfed generations, two most stable pure lines, the tolerant 72 (T, Pq72) and susceptible 1192 (S, Pq1192), were confirmed in the M10 generation and selected as the materials for studying the inheritance of paraquat tolerance.…”

Photochemical changes and oxidative damage in the aquatic macrophyte Cymodocea nodosa exposed to paraquat-induced oxidative stress

“…Studies on Pq mode of action on non-target terrestrial plants are several [3,6,8,[17][18][19]. Recently it was proposed that the non-target organism Arabidopsis thaliana is protected from exposure to 1000 μM Pq by increasing NPQ that dissipates light energy and decreases the efficiency of photochemical reactions of photosynthesis (down-regulation of PSII) via the "waterwater cycle" [3].…”

Differences of endogenous polyamines and putative genes associated with paraquat resistance in goosegrass (Eleusine indica L.)

“…Paraquat is a haloid salt [1] that is widely used as a non-selective herbicide to control weeds throughout the world [2-4]. Paraquat resistance in plant cells is determined by the uptake, efflux, sequestration, detoxification, and catabolism of the reactive oxygen species (ROS) generated by paraquat.…”

“…Polyamines, including putrescine, spermidine and spermine, are small aliphatic polycations that are classified as growth regulators, although the specific mechanisms have not been well elucidated [9]. Exogenous application of polyamines provides high-level resistance against paraquat toxicity in a range of plant organs [4], such as the roots of intact maize seedlings [10], leaf discs of sunflower [11], and leaves of rice [12]. Endogenous polyamine probably plays a vital role in paraquat resistance in plants.…”