Chapter 4 – SOLAR UV IRRADIATION AND THE GROWTH AND DEVELOPMENT OF HIGHER PLANTS

Summary
Coumarins are derived via the phenylpropanoid pathway in plants. The 2H-1-benzopyran-2-one core structure of coumarins is formed via the ortho-hydroxylation of cinnamates, trans/cis isomerization of the side chain, and lactonization. Ortho-hydroxylation is a key step in coumarin biosynthesis as a branch point from lignin biosynthesis; however, ortho-hydroxylation of cinnamates is not yet fully understood. In this study, scopoletin biosynthesis was explored using Arabidopsis thaliana, which accumulates scopoletin and its β-glucopyranoside scopolin in its roots. T-DNA insertion mutants of caffeoyl CoA O-methyltransferase 1 (CCoAOMT1) showed significant reduction in scopoletin and scopolin levels in the roots, and recombinant CCoAOMT1 exhibited 3′-O-methyltransferase activity on caffeoyl CoA to feruloyl CoA. These results suggest that feruloyl CoA is a key precursor in scopoletin biosynthesis. Ortho-hydroxylases of cinnamates were explored in the oxygenase families in A. thaliana, and one of the candidate genes in the Fe(II)- and 2-oxoglutarate-dependent dioxygenase (2OGD) family was designated as F6′H1. T-DNA insertion mutants of F6′H1 showed severe reductions in scopoletin and scopolin levels in the roots. The pattern of F6′H1 expression is consistent with the patterns of scopoletin and scopolin accumulation. The recombinant F6′H1 protein exhibited ortho-hydroxylase activity for feruloyl CoA (Km = 36.0 ± 4.27 μm; kcat = 11.0 ± 0.45 sec−1) to form 6′-hydroxyferuloyl CoA, but did not hydroxylate ferulic acid. These results indicate that Fe(II)- and 2-oxoglutarate-dependent dioxygenase is the pivotal enzyme in the ortho-hydroxylation of feruloyl CoA in scopoletin biosynthesis.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2008.03568.x

Scopoletin is biosynthesized via ortho-hydroxylation of feruloyl CoA by a 2-oxoglutarate-dependent dioxygenase in Arabidopsis thaliana.

Electronically excited states of organic molecules are formed in many chemical reactions. Such chemically produced excited states are (with one exception) identical to light produced excited states, and they undergo the molecular transformations expected of such states (“photochemistry without light”). The excited states can also be used in energy transfer experiments. This review covers the generation of chemically produced excited states, the chemical reactions they undergo, and the possible role of chemically produced excited states in biology.

Chemically Produced Excited States

Trans-cis-equilibrium of hydroxycinnamic acids during irradiation of aqueous solutions at different pH

Combinatorial biosynthesis of plant-specific coumarins in bacteria

Light-Induced Trans to Cis Conversion of β-d-Glucosyl o-Hydroxycinnamic Acid in Melilotus alba Leaves

COUMARINIC and o-coumaric acids (respectively the cis and irons isomers of o-hydroxycinnamic acid) occur almost entirely as glucosides in intact sweetclover plants (5, 6). These compounds are most abundant in leaves, intermediate in level in stems, and least abundant in roots (1). Even in roots, however, total o-hydroxycinnamic acid contents of 0.5% (dry weight basis) are not uncommon. Sweetclover tissues also possess a /2-glucosidase which removes glucose from coumarinyl glucoside when the plant tissue is disrupted (5, 8, 9). The resulting coumarinic acid spontaneously lactonizes yielding coumarin. Other studies have shown that both o-hydroxycinnamic acid content and /3-glucosidase activity are influenced by genetic factors (2,9). Investigations employing C-labeled sh ik imic acid, phenylalanine, and trans-tinna.mic acid have shown that in excised shoots of white-flowered sweetclover (Melilotus alba Desr.) the biosynthesis of o-coumaryl glucoside and coumarin involves the shikimic acid pathway (7). A similar biosynthetic pathway in root cultures of yellow-flowered sweetclover (M. officinalis (L.) Lam.) is suggested

/pdf/culture-and-o-hydroxycinnamic-acid-content-of-excised-5ahvpjr7au.pdf

Larry G. Williams

Papers

Light-Induced Trans to Cis Conversion of β-d-Glucosyl o-Hydroxycinnamic Acid in Melilotus alba Leaves

Culture and ο-Hydroxycinnamic Acid Content of Excised Melilotus Roots 1