Z-L-pyroglutamic acid dicyclohexylammonium salt

Silicon (Si) is generally considered a beneficial element for the growth of higher plants, especially under stress conditions, but the mechanisms remain unclear. Here, we tested the hypothesis that Si improves salt tolerance through mediating important metabolism processes rather than acting as a mere mechanical barrier. Seedlings of sorghum (Sorghum bicolor L.) growing in hydroponic culture were treated with NaCl (100 mm) combined with or without Si (0.83 mm). The result showed that supplemental Si enhanced sorghum salt tolerance by decreasing Na(+) accumulation. Simultaneously, polyamine (PA) levels were increased and ethylene precursor (1-aminocyclopropane-1-carboxylic acid: ACC) concentrations were decreased. Several key PA synthesis genes were up-regulated by Si under salt stress. To further confirm the role of PA in Si-mediated salt tolerance, seedlings were exposed to spermidine (Spd) or a PA synthesis inhibitor (dicyclohexylammonium sulphate, DCHA) combined with salt and Si. Exogenous Spd showed similar effects as Si under salt stress whereas exogenous DCHA eliminated Si-enhanced salt tolerance and the beneficial effect of Si in decreasing Na(+) accumulation. These results indicate that PAs and ACC are involved in Si-induced salt tolerance in sorghum and provide evidence that Si plays an active role in mediating salt tolerance.

1. 2-Hydroxypropylmercapturic acid, i.e. N-acetyl-S-(2-hydroxypropyl)-l-cysteine, has been isolated, as the dicyclohexylammonium salt, from the urine of rats dosed with 1-bromopropane. 2. The formation of the same metabolite from 1-chloropropane, 1-iodopropane, 1,2-epoxypropane and 1-chloropropan-2-ol has been demonstrated by chromatographic examination of the urine excreted by rats after they had been dosed with these compounds. 3. (+)- and (-)-Dicyclohexylammonium 2-hydroxypropylmercapturate have been prepared by fractional crystallization of the mixture of isomers obtained by two methods: the reaction of 1,2-epoxypropane with l-cysteine followed by acetylation, and the reduction of 2-oxopropylmercapturic acid. 4. The following compounds have also been prepared: S-(3-hydroxypropyl)-l-cysteine, (+)- and (-)-S-(2-hydroxypropyl)-l-cysteine, dicyclohexylammonium 3-hydroxypropylmercapturate, (+)- and (-)-dicyclohexylammonium 2-hydroxy-1-methylethylmercapturate, and (+)- and (-)-dicyclohexylammonium 1-(ethoxycarbonyl)ethylmercapturate.

1. Rabbits and rats dosed with 1-bromobutane excrete in urine, in addition to butylmercapturic acid, (2-hydroxybutyl)mercapturic acid, (3-hydroxybutyl)mercapturic acid and 3-(butylthio)lactic acid. 2. Although both species excrete both the hydroxybutylmercapturic acids, only traces of the 2-isomer are excreted by the rabbit. The 3-isomer has been isolated from rabbit urine as the dicyclohexylammonium salt. 3. 3-(Butylthio)lactic acid is formed more readily in the rabbit; only traces are excreted by the rat. 4. Traces of the sulphoxide of butylmercapturic acid have been found in rat urine but not in rabbit urine. 5. In the rabbit about 14% and in the rat about 22% of the dose of 1-bromobutane is excreted in the form of the hydroxymercapturic acids. 6. Slices of rat liver incubated with S-butylcysteine or butylmercapturic acid form both (2-hydroxybutyl)mercapturic acid and (3-hydroxybutyl)mercapturic acid, but only the 3-hydroxy acid is formed by slices of rabbit liver. 7. S-Butylglutathione, S-butylcysteinylglycine and S-butylcysteine are excreted in bile by rats dosed with 1-bromobutane. 8. Rabbits and rats dosed with 1,2-epoxybutane excrete (2-hydroxybutyl)mercapturic acid to the extent of about 4% and 11% of the dose respectively. 9. The following have been synthesized: N-acetyl-S-(2-hydroxybutyl)-l-cysteine [(2-hydroxybutyl)mercapturic acid] and N-acetyl-S-(3-hydroxybutyl)-l-cysteine [(3-hydroxybutyl)mercapturic acid] isolated as dicyclohexylammonium salts, N-toluene-p-sulphonyl-S-(2-hydroxybutyl)-l-cysteine, S-butylglutathione and N-acetyl-S-butylcysteinyl-glycine ethyl ester.