Chlorsulfuron Modifies Biosynthesis of Acyl Acid Substituents of Sucrose Esters Secreted by Tobacco Trichomes

Abstract

Sucrose esters and duvatrienediol diterpenes are principal constituents formed in and secreted outside head cells of trichomes occurring on surfaces of Nicotiana tabacum. Using trichome-bearing epidermal peels prepared from midveins of N. tabacum cv T.l. 1068 leaves, we found that chlorsulfuron reduced and modified radiolabeling of sucrose ester acyl acids derived from branched-chain amino acid metabolism. The herbicide did not effect formation and exudation of diterpenes which are products of isoprenoid metabolism. Treatment with 1.0 micromolar chlorsulfuron affected 8.5-and 6.3-fold reductions in radiolabeling of methylvaleryl and methylbutyryl groups of sucrose esters, respectively, and concomitant increases of 9-and 9.8-fold in radiolabeling of straight chain valeryl and butyryl groups, respectively. These results and others indicate that inhibition of acetolactate synthase causes an accumulation of 2-oxo-butyric acid that is utilized by enzymes common to Leu biosynthesis to form 2-oxo-valeric acid. Coenzyme A (CoA) activation of this keto acid gives rise to butyryl CoA, which is utilized to form butyryl containing sucrose esters. Alternatively, reutilization of 2-oxo-valeric acid by the same enzymes followed by CoA activation leads to valeryl containing sucrose esters. We propose that in trichome secretory cells synthase, isomerase and dehydrogenase enzymes which catalyze Leu synthesis/degredation in most tissues, convert iso-branched, anteiso-branched and straight-chain keto acids in the formation of sucrose ester acyl groups. SE' and DVT are principal components produced and secreted by trichome head cells of tobacco species (9, 12). Trichome exudate can comprise about 10% of the dry weight of mature Nicotiana tabacum, T.I. 1068 leaves, and DVT and SE account for about 55 and 23% of exudate, respectively (our unpublished data). While the roles of these prominent constituents in the plant are only now being studied intensively, they are thought to be involved in plant-pest interactions (9, 25 and references therein).In N. tabacum species, SE are comprised of 6-0-acetyl-2,3,4-tri-O-acyl-a-D-glucopyranosyl-f-D-fructofuranosides, ' Abbreviations: SE, sucrose esters (6-0-acetyl-2,3,4-tri-O-acyl-a-

Mass spectrometry screening reveals widespread diversity in trichome specialized metabolites of tomato chromosomal substitution lines

“…The biosynthesis of acyl sugars is relatively poorly understood. Feeding studies demonstrated the involvement of branched chain amino acid pathway intermediates as a source of branched acyl chains ( Figure 7 ) ( Kandra and Wagner, 1990 ; Walters and Steffens, 1990 ). Previously published results are consistent with the hypothesis that these short acyl chains are then elongated to produce the variety of chain lengths observed in tomato acyl sugars ( van der Hoeven and Steffens, 2000 ; Kroumova and Wagner, 2003 ; Slocombe et al , 2008 ).…”

Secreting Glandular Trichomes: More than Just Hairs

“…In mature gland cells, pathways for synthesis of valine, leucine, and isoleucine appear to be diverted to form CoA-activated acids for esterification in sucrose ester formation. We have suggested that normal flow of carbon to amino acids is diverted somewhat in mature glands due to the lack of a sink for branched-chain amino acid (lack of protein synthesis) or a lack of transaminase to convert ketoacid intermediates to amino acids (14,15 (4,20). Clearly, further study is needed to define the metabolic capability of secreting gland cells but one can already begin to consider modification of isoprenoid metabolism, reactions which modify terpene skeletons, and branched-chain amino acid metabolism (in sugar ester producers) to alter exudate chemistry.…”

A pathway for the biosynthesis of straight and branched, odd- and even-length, medium-chain fatty acids in plants.

“…Lines under atoms of carbon skeletons at top indicate the position of label derived from [2-14C]acetate. The metabolic sequences from pyruvate through valeryl-CoA, methylbutyryl-CoA, and 3-methylvaleryl-CoA were concluded from previous work (6,7). Superscripted letters represent principal sugar ester alkyl groups formed (and labeled from [2-14C]acetate, shown here) in trichome glands of tomato (T), petunia (P), and Nicotiana glutinosa (G).…”

“…In contrast, metabolism leading to the biosynthesis of mcFAs is not well understood (4,5), particularly that catalyzing the formation of branched and odd-length mcFAs. Straight, iso-, and antiso-branched, oddand even-length scFAs are synthesized via modified branched-chain amino acid (bcAA) metabolism in tobacco trichome glands (6,7). It is possible that at least branched and odd-length mcFAs are formed in this tissue similarly.…”

“…Reaction 3 describes the first step in the catabolism of oxoacids derived from valine, leucine, and isoleucine by deamination (11). Threonine donates carbon to anteiso-and straight-chain CoA products via threonine-deaminase-catalyzed formation of 2-oxobutyric acid (6,7). Lines under atoms of carbon skeletons at top indicate the position of label derived from [2-14C]acetate.…”