Amino Acid Metabolism of Lemna minor L.

Abstract

ABSTRACUChlorsulfuron, an inhibitor of acetolactate synthase (EC 4.13.18) (TB Ray 1984 Plant Physiol 75: 827-831), markedly inhibited the growth of Lemma minor at concentrations of 10' molar and above, but had no inhibitory effects on growth at 10' molar. At growth inhibitory concentrations, chlorsulfuron caused a pronounced increase in total free amino acid levels within 24 hours. Valine, leucine, and isoleucine, however, became smaller percentages of the total free amino acid pool as the concentration of chlorsulfuron was increased. At concentrations of chlorsulfuron of 10'8 molar and above, a new amino acid was accumulated in the free pool. This amino acid was identified as a-amino-n-butyrate by chemical ionization and electron impact gas chromatography-mass spectrometry. The amount of a-amino-n-butyrate increased from undetectable levels in untreated plants, to as high as 840 nanomoles per gram fresh weight (2.44% of the total free pool) in plants treated with 10 molar chlorsulfuron for 24 hours. The accumulation of this amino acid was completely inhibited by methionine sulfoximine. Chlorsulfuron did not inhibit the methionine sulfoximine induced accumulations of valine, leucine, and isoleucine, supporting the idea that the accumulation of the branched-chain amino acids in methionine sulfoximine treated plants is the result of protein turnover rather than enhanced synthesis. Protein turnover may be primarily responsible for the failure to achieve complete depletion of valine, leucine, and isoleucine even at concentrations of chlorsulfuron some 104 times greater than that required to inhibit growth. Tracer studies with "N demonstrate that chlorsulfuron inhibits the incorporation of '"N into valine, leucine, and isoleucine. The a-amino-nbutyrate accumulated in the presence of chlorsulfuron and ["NjR.+ was heavily labeled with "N at early time points and appeared to be derived by transamination from a rapidly labeled amino acid such as glutamate or alanine. We propose that chlorsulfuron inhibition of acetolactate synthase may lead to accumulation of 2-oxobutyrate in the isolencine branch of the pathway, and transamination of 2-oxobutyrate to a-aminon-butyrate by a constitutive transaminase utilizing either glutamate or alanine as a-amino-N donors.

Herbicidal Activity of an Isopropylmalate Dehydrogenase Inhibitor

“…A 50% decline in Leu was observed after 1 d, but the levels recovered, on a fresh weight basis, by the 2nd d. This recovery in free Leu is likely due to protein tumover and degradation, which are also ongoing processes in the pea sections. Similar levels of reduction in free branched-chain amino acids 1 d after treatment have been observed with sulfonylurea arid imidazolinone herbicides in other systems (Rhodes et al, 1987; Shaner and Singh, 1992). In addition to the decline in Leu, we also observed increases in the levels of Val, Ile, Tyr, and Phe.…”

Expression Profiles of <i>psbA, ALS, EPSPS</i>, and Other Chloroplastic Genes in Response to PSII-, ALS-, and EPSPS-Inhibitor Treatments in <i>Kochia scoparia</i>

“…An increase in the free amino acid pool after the application of ALS-inhibitors has been reported [38] [39] [40]. This increased protein pool was attributed to an increase in protein turnover rates in response to treatment with ALS-inhibitors [41]. The higher expression levels of KsALS gene observed in this study, may lead to increased protein turnover and free amino acid pools after application of ALS-inhibitors.…”

Preliminary Genetic Studies of the Phenotype of Betaine Deficiency in Zea mays L.

“…Gas chromatographic conditions were as follows: injector temperature, 250°C; detector temperature, 280°C; oven temperature program, 100°C (4 min) to 260°C at 6°C/min; carrier gas, N2 (20 psi at injector port); column carrier gas flow rate, 1 mL/min; split ratio at injector port, 20:1; air flow rate, 222 mL/min; H2 flow rate, 35 mL/min; N2 sweep gas flow rate, 20 mL/min; detector, flame ionization (see Ref. 19 for details of amino acid retention times on the latter system).…”

“…In the former trial (Tables III, IV, and V) no a-amino-n-butyrate was detectable in any of the genotypes evaluated; hence, the choice ofthis internal standard in subsequent work (but see Ref. 19 for evidence for endogenous accumulation of this amino acid in response to certain herbicides). Where an internal standard was included, amino acids were quantified by reference to the area of the internal standard and its reponse factors relative to the individual components of amino acid standard mixtures of known concentration.…”