Modified branched-chain amino acid pathways give rise to acyl acids of sucrose esters exuded from tobacco leaf trichomes

L. Kandra, R. Severson, G. J. Wagner

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

A major diversion of carbon from branched-chain amino acid biosynthesis/catabolism to form acyl moieties of sucrose esters (6-O-acetyl-2,3,4-tri-O-acyl-α-D-glucopyranosyl-β-D-fructofuranoside s) was observed to be associated with specialized trichome head cells which secrete large amounts of sucrose esters. Surface chemistry and acetyl and acyl substituent groups of tobacco (T.I. 1068) sucrose esters were identified and quantified by gas chromatography/mass spectrometry. Sucrose esters were prominent surface constituents and 3-methylvaleric acid, 2- and 3-methylbutyric acid, and methylpropionic acid accounted for 60%, 25% and 9%, respectively, of total C3-C7 acyl substituents. Radiolabeled Thr, Ile, Val, Leu, pyruvate and Asp, metabolites of branched-chain amino acid pathways, were compared with radioactively labeled acetate and sucrose as donors of carbon to sucrose, acetyl and acyl components of sucrose esters using epidermal peels with undisturbed trichomes. Preparations of biosynthetically competent trichome heads (site of sucrose ester formation) were also examined. Results indicate that 3-methylvaleryl and 2-methylbutyryl groups are derived from the Thr pathway of branched-chain amino acid metabolism, 3-methylbutyryl and methylpropionyl groups are formed via the pyruvate pathway, and that acetyl groups are principally formed directly via acetyl-CoA. Arguments are presented which rule out participation of fatty acid synthase in the formation of prominent acyl acids. Results suggest that the shunting of carbon away from the biosynthesis of Val, Leu and Ile may be due to a low level of amino acid utilization in protein synthesis in specialized glandular head cells of trichomes. This would result in the availability of corresponding oxo acids for CoA activation and esterification to form sucrose esters. Preliminary evidence was found for the involvement of cyclic reactions in oxo-acid-chain lengthening and for utilization of pyruvate-derived 2-oxobutyrate to form straight-chain acyl substituents.

Original languageEnglish
Pages (from-to)385-391
Number of pages7
JournalEuropean Journal of Biochemistry
Volume188
Issue number2
Publication statusPublished - 1990

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Trichomes
Branched Chain Amino Acids
Tobacco
Sucrose
Esters
Acids
Pyruvic Acid
Keto Acids
Carbon
Biosynthesis
Fatty Acid Synthases
Acetyl Coenzyme A
Esterification
Coenzyme A
Viperidae
Metabolites
Surface chemistry
Metabolism
Gas chromatography
Gas Chromatography-Mass Spectrometry

ASJC Scopus subject areas

  • Biochemistry

Cite this

Modified branched-chain amino acid pathways give rise to acyl acids of sucrose esters exuded from tobacco leaf trichomes. / Kandra, L.; Severson, R.; Wagner, G. J.

In: European Journal of Biochemistry, Vol. 188, No. 2, 1990, p. 385-391.

Research output: Contribution to journalArticle

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abstract = "A major diversion of carbon from branched-chain amino acid biosynthesis/catabolism to form acyl moieties of sucrose esters (6-O-acetyl-2,3,4-tri-O-acyl-α-D-glucopyranosyl-β-D-fructofuranoside s) was observed to be associated with specialized trichome head cells which secrete large amounts of sucrose esters. Surface chemistry and acetyl and acyl substituent groups of tobacco (T.I. 1068) sucrose esters were identified and quantified by gas chromatography/mass spectrometry. Sucrose esters were prominent surface constituents and 3-methylvaleric acid, 2- and 3-methylbutyric acid, and methylpropionic acid accounted for 60{\%}, 25{\%} and 9{\%}, respectively, of total C3-C7 acyl substituents. Radiolabeled Thr, Ile, Val, Leu, pyruvate and Asp, metabolites of branched-chain amino acid pathways, were compared with radioactively labeled acetate and sucrose as donors of carbon to sucrose, acetyl and acyl components of sucrose esters using epidermal peels with undisturbed trichomes. Preparations of biosynthetically competent trichome heads (site of sucrose ester formation) were also examined. Results indicate that 3-methylvaleryl and 2-methylbutyryl groups are derived from the Thr pathway of branched-chain amino acid metabolism, 3-methylbutyryl and methylpropionyl groups are formed via the pyruvate pathway, and that acetyl groups are principally formed directly via acetyl-CoA. Arguments are presented which rule out participation of fatty acid synthase in the formation of prominent acyl acids. Results suggest that the shunting of carbon away from the biosynthesis of Val, Leu and Ile may be due to a low level of amino acid utilization in protein synthesis in specialized glandular head cells of trichomes. This would result in the availability of corresponding oxo acids for CoA activation and esterification to form sucrose esters. Preliminary evidence was found for the involvement of cyclic reactions in oxo-acid-chain lengthening and for utilization of pyruvate-derived 2-oxobutyrate to form straight-chain acyl substituents.",
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