Sulfur assimilation in plants and weed control: Potential targets for novel herbicides and action sites of certain safeners

Abstract

Sulfur is an indispensable element for plants. It is found in sulfur-containing amino acids, cysteine and methionine, and in various other important biochemical components and processes. Inhibitors of sulfur assimilation, or cysteine and methionine synthesis, could be potential herbicides. In the present paper, the sulfur assimilation pathway in plants is described, followed by the introduction of several compounds (inhibitors and safeners) acting on this pathway. Uptake of inorganic sulfate through the roots is the first step of sulfur assimilation in plants. Sulfate is reduced mainly in chloroplasts to sulfide by a multistep process, and sulfide is then incorporated into cysteine. Cysteine is converted to cystathionine, homocysteine and methionine. Cysteine is incorporated into glutathione (GSH) by g -glutamylcysteine synthetase and GSH synthetase. Three enzymes involved in cysteine and methionine biosynthesis, cysteine synthase, cystathionine g -synthase and cystathionine b -lyase, have been investigated as target sites for herbicides. Several inhibitors of these enzymes (e.g. rhizobitoxine and propargylglycine) were also phytotoxic, suggesting that the synthetic pathway of sulfur-containing amino acids could be a new target site for herbicides. Some safeners for herbicides were found to act on the sulfur assimilation pathway and on GSH synthesis to increase GSH, which can be involved in herbicide metabolism and detoxification. Several safeners elevate GSH levels by increasing the activities of enzymes involved in sulfur assimilation and GSH synthesis. Further studies on plant sulfur metabolism may lead to the discovery of new herbicides and to the comprehensive understanding of the mode of action of safeners.

Effect of Seeds Dressingon the Initial Establishment of Irrigated Rice in Different Temperatures and Sowing Periods

“…The reduction of the growth suggests the existence of the sensibility of rice seeds to the protector studied, since the treatment that possessed dietholate inhibited the initial growth of the shoot of seedlings in two tested temperatures. Similar results were obtained in sorghum, using seeds protector flurazole, which induced the inhibition of the seedlings growth (Hirase & Molin, 2003), in rice, with the protector diethyl phenyl phosphorothioate (Mistura, 2008).…”

Effects on GSH synthesis in Chinese cabbage when the culturing solution is supplemented with ammonium sulfate or the constituent amino acids for glutathione

“…Though some environmental conditions, stresss or chemicals have been reported to increase GSH concentration in plants (Hirase and Molin, 2003;Kopriva and Rennenberg, 2004;Tausz et al, 2004). To increase the production of GSH in Chinese cabbage, we added its constituent amino acids -Glu, Cys, and Gly -~ to the culture solution.…”

Interactions and Effects on Cysteine Synthase Activity of Aminooxyacetate and Boc-Aminooxyacetate on the Bioherbicides <i>Colletotrichum truncatum</i> and <i>Alternaria cassia</i> and Their Weed Hosts

“…Furthermore, AOA effects on weed pathogen interactions have not been studied, and there is little or no biological data on Boc-AOA. [21]. Cysteine is synthesized from serine in two steps; serine transferase catalyzes acetylation of serine using acetyl-CoA to yield O-acetylserine, and then CS catalyzes addition of inorganic sulfide to O-acetylserine with release of acetate and cysteine.…”

“…The interactions of herbicides and safeners on CS as a potential target for new herbicidal compounds has also been examined [21] [26] [27] [28] [29]. CS has also been shown to be inhibited by AOA [28].…”