Occurrence and distribution of free flavonoid aglycones in plants

Wollenweber, Eckhard; Dietz, Volker

doi:10.1016/0031-9422(81)83001-4

Cited by 352 publications

(176 citation statements)

References 356 publications

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“…It has previously been reported that in several species found in arid environments a dense covering of wax and trichomes might help in decreasing water loss by lowering the amount of light absorbed by the leaf and the accompanying heat load (Ehleringer et al, 1976 ;Vogelmann, 1993). Flavonoids, especially flavonoid aglycones (Wollenweber, 1993), accumulate on the leaf surface of species from arid or semi-arid habitats and can act as filters for UV radiation (Wollenweber & Dietz, 1981 ;Fahn, 1988). In Olea europaea, another member of the Oleaceae that is widely distributed in the Mediterranean basin, the deposition of polyphenols in leaf hairs has been suggested to protect leaf cells from damage by UV radiation (Karabourniotis et al, 1998).…”

Section: mentioning

confidence: 99%

Flavonoids accumulate in leaves and glandular trichomes of Phillyrea latifolia exposed to excess solar radiation

Tattini¹,

Gravano²,

Pinelli³

et al. 2000

New Phytologist

195

174

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Experiments were conducted on Phillyrea latifolia plants grown under a dense overstorey of Pinus pinea (shade plants) or on seashore dunes (sun plants) in a coastal area of Tuscany (42m 46h N, 10m 53h E). Total integrated photon flux densities averaged 1n67 and 61n4 m mol m −# d −" for shade and sun sites, respectively. A leaf morphological-structural analysis, a qualitative and quantitative analysis of phenylpropanoids of leaf tissue and leaf surface, and a histochemical localization of flavonoids were conducted. The area of sun leaves reached 57% of that of shade leaves, whereas leaf angle (β), sclerophylly index (ratio of leaf d. wt : leaf area), and trichome frequency (trichome number mm −# ) were markedly greater in leaves exposed to full solar radiation than in leaves acclimated to shade. The total thickness of sun leaves was 78% higher than that of shade leaves, mostly owing to a greater development of both palisade parenchyma and spongy mesophyll. The concentration, but not the composition, of leaf tissue phenylpropanoids varied significantly between sun and shade leaves, with a marked increase in flavonoid glycosides in sun leaves. Flavonoids occurred almost exclusively in the upper epidermal cells of shade leaves. By contrast, flavonoids largely accumulated in the upper and lower epidermis, as well as in the mesophyll tissue of leaves that were acclimated to full sunlight. Flavonoid glycosides were found exclusively in the secretory products of glandular trichomes of P. latifolia leaves exposed to high levels of light ; luteolin 7-Oglucoside and quercetin 3-O-rutinoside were the major constituents. By contrast, verbascoside and an unidentified caffeic acid derivative constituted 72% of total phenylpropanoids secreted by glandular trichomes of shade leaves, whereas they were not detected in glandular trichomes of sun leaves. These findings suggest that the light-induced synthesis of flavonoids in glandular trichomes of P. latifolia probably occurs in situ and concomitantly inactivates other branch pathways of the general phenylpropanoid metabolism. This is the first report of the key role of glandular trichomes and of flavonoid glycosides in the integrated mechanisms of acclimation of P. latifolia to excess light.

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Section: mentioning

confidence: 99%

Flavonoids accumulate in leaves and glandular trichomes of Phillyrea latifolia exposed to excess solar radiation

Tattini¹,

Gravano²,

Pinelli³

et al. 2000

New Phytologist

195

174

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“…Lipophilic methylated flavonoids occur frequently in several eudicot families, such as the Lamiaceae, Asteraceae, and Rutaceae, but are also found in representatives of other plant families, including ferns and monocots (7,8). Hydroxylation at positions 6 and 8 of ring A and multiple regiospecific O-methylations appear to be common modifications underlying the high lipophilicity.…”

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confidence: 99%

The Roles of a Flavone-6-Hydroxylase and 7-O-Demethylation in the Flavone Biosynthetic Network of Sweet Basil

Berim

Gang

2013

Journal of Biological Chemistry

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Background: Late steps of lipophilic flavone biosynthesis in mints are unknown. Results: CYP82D monooxygenases catalyze 6-hydroxylation of 7-O-methylated precursor, whose 7-methyl group is subsequently removed by demethylation in basil but not in peppermint. Conclusion: Flavone biosynthesis in basil involves an unusual loop. Significance: Novel mechanisms elucidated in basil suggest a new hypothesis for similar metabolic networks in other plants.

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“…Newly synthesized flavonoids could be released directly into the rhizosphere or conjugated and stored in vacuoles. In many plants, flavonoids are stored in vacuoles as glycosides or related conjugates (14,19), while aglycones are the major form secreted (29). Movement from the vacuole to the external environment would require conversion from conjugate to aglycone.…”

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confidence: 99%

Concurrent Synthesis and Release of nod-Gene-Inducing Flavonoids from Alfalfa Roots

Maxwell

Phillips

1990

Plant Physiol.

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Flavonoid signals from alfalfa (Medicago sativa L.) induce transcription of nodulation (nod) genes in Rhizobium meliloti. Alfalfa roots release three major nod-gene inducers: 4',7-dihydroxyflavanone, 4',7-dihydroxyflavone, and 4,4'-dihydroxy-2'-methoxychalcone. The objective of the present study was to define temporal relationships between synthesis and exudation for those flavonoids. Requirements for concurrent flavonoid biosynthesis were assessed by treating roots of intact alfalfa seedlings with [U-14C]-L-phenylalanine in the presence or absence of the phenylalanine ammonia-lyase inhibitor L-2-aminoxy-3-phenylpropionic acid (AOPP). In the absence of AOPP, each of the three flavonoids in exudates contained 14C. In the presence of AOPP, 14C labeling and release of all the exuded nod-gene inducers were reduced significantly. AOPP inhibited labeling and release of the strongest nod-gene inducer, methoxychalcone, by more than 90%. Experiments with excised cotyledons, hypocotyls, and roots incubated in solution showed that the flavonoids could be synthesized in and released from each organ. However, the ratio of the three flavonoids in exudates from intact plants was most similar to the ratio recently synthesized and released from excised roots. A portion of recentiy synthesized flavonoid aglycones was found conjugated, presumably as glycosides, in root extracts and may have been involved in the release process. Data from root extracts showed that formononetin, an isoflavonoid which does not induce nod genes, was present in conjugated and aglycone forms but was not released by normal intact roots. In contrast, roots stressed with CuCI2 did release the aglycone formononetin. Thus, the release process responsible for exudation of nod-gene inducers appears to be specific rather than a general phenomenon such as a sloughing off of cells during root growth. The synthesis and specific concurrent release of flavonoid nod-gene inducers in this study is consistent with the physiological requirement for nodule formation of the 3-day-old seedlings used.Alfalfa (Medicago sativa L.), an important leguminous forage crop, forms N2-fixing root nodules in association with the soil bacterium Rhizobium meliloti. Early events of alfalfa nodule formation require expression of nodulation genes including nodDABC on the megaplasmid of R. meliloti (6,15). Transcription of nodABC is induced through the cooperative action of the protein product of the nodD gene and components of root and seed exudates (21). Luteolin, '

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Occurrence and distribution of free flavonoid aglycones in plants

Cited by 352 publications

References 356 publications

Flavonoids accumulate in leaves and glandular trichomes of Phillyrea latifolia exposed to excess solar radiation

Flavonoids accumulate in leaves and glandular trichomes of Phillyrea latifolia exposed to excess solar radiation

The Roles of a Flavone-6-Hydroxylase and 7-O-Demethylation in the Flavone Biosynthetic Network of Sweet Basil

Concurrent Synthesis and Release of nod-Gene-Inducing Flavonoids from Alfalfa Roots

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