Protective and defensive roles of non-glandular trichomes against multiple stresses:structure-function coordination

As superficial structures,non-glandular trichomes,protect plant organs against multiple biotic and abiotic stresses.The protective and defensive roles of these epidermal appendages are crucial to developing organs and can be attributed to the excellent combination of suitable structural traits and chemical reinforcement in the form of phenolic compounds,primarily fl avonoids.Both the formation of trichomes and the accumulation of phenolics are interrelated at the molecular level.During the early stages of development,non-glandular trichomes show strong morphological similarities to glandular ones such as the balloon-like apical cells with numerous phenolics.At later developmental stages,and during secondary wall thickening,phenolics are transferred to the cell walls of the trichomes.Due to the diff use deposition of phenolics in the cell walls,trichomes provide protection against UV-B radiation by behaving as optical fi lters,screening out wavelengths that could damage sensitive tissues.Protection from strong visible radiation is also aff orded by increased surface light refl ectance.Moreover,the mixtures of trichome phenolics represent a superfi-cial chemical barrier that provides protection against biotic stress factors such as herbivores and pathogens.Although the cells of some trichomes die at maturity,they can modulate their quantitative and qualitative characteristics during development,depending on the prevailing conditions of the external biotic or abiotic environment.In fact,the structure and chemical constituents of trichomes may change due to the particular light regime,herbivore damage,wounding,water stress,salinity and the presence of heavy metals.Hence,trichomes represent dynamic protective structures that may greatly aff ect the outcome of many plant–environment interactions.     

Validation of an extraction method for the quantification of soluble free and insoluble bound phenolic compounds in wheat by HPLC-DAD

Wheat is one of the three most widely grown grain crops and the most consumed in Europe. Wheat contains different phenolic compounds, mainly phenolic acids and flavonoids that are not evenly distributed in the wheat, being most abundant in the bran. These phenolic compounds are antioxidants against free radicals and other reactive oxygen species. Therefore, over the last few decades, there is a great interest to study and quantify these compounds present in wheat.This work proposes a HPLC-DAD method that allows a good separation of different phenolic compounds occurring as soluble free and insoluble bound compounds in wheat brand and flour. The extraction and the chromatographic conditions allowed the characterization of forty-two phenolic compounds, among phenolic acids (HBA, HCA, DFA and TFA), phenolic aldehydes, phenolic alcohols and flavonoids (flavones). This method is simple, sensitive, reproducible and accurate, and only a HPLC-DAD equipment is required. Thirty-four soluble and insoluble phenolic compounds can be quantified in wheat flour and brand. Hydroxytyrosol, a potent antioxidant compound, has been identified and quantified in wheat for the first time.     

Knotwood and bark extracts: strong antioxidants from waste materials

The antioxidant properties of hydrophilic extracts of knotwood of several industrially important tree species were evaluated by lipid-peroxidation inhibition and peroxyl-trapping capacity tests. The results were compared with the antioxidant properties of hydrophilic extracts of bark, and pure lignans and flavonoids isolated from knotwood extracts. The knot extracts from several tree species were stronger antioxidants than the bark extracts, which can, however, also be classified as strong antioxidants. In addition, the antioxidant properties of most of the knotwood extracts are stronger than the pure compounds. It is concluded that knotwood is a rich source of natural antioxidants.     

Two new chalcone glycosides from the stems of Entada phaseoloides

Two new chalcone glycosides 4′-O-(6″-O-galloyl-β-d-glucopyranosyl)-2′,4-dihydroxychalcone (1) and 4′-O-(6″-O-galloyl-β-d-glucopyranosyl)-2′-hydroxy-4-methoxychalcone (2) together with one known chalcone glycoside 4′-O-β-d-glucopyranosyl-2′-hydroxy-4-methoxychalcone (3) were isolated from the stems of Entada phaseoloides. The structures of the new compounds were elucidated on the basis of extensive spectroscopic analysis, including HSQC, HMBC, ¹H–¹H COSY, and chemical evidences. This is the first report of chalcone-type compounds isolated from the genus Entada.     

DPPH radical scavenging activity of two flavonol glycosides from Aconitum napellus sp. lusitanicum

The DPPH radical scavenging activity of two flavonol glycosides obtained from ethanolic extracts of Aconitum napellus sp. lusitanicum was studied. The results showed a high DPPH antiradical activity of compound 1 (quercetin 3-O-(6-trans-caffeoyl)-beta-glucopyranosyl-(1-->2)-beta-glucopyranosyl-7-O-alpha-rhamnopyranoside) when compared with compound 2 (quercetin-3-sophoroside-7-rhamnopyranoside), rutin and ascorbic acid. The relationship between the caffeoyl and rhamnopyranoside groups in the flavonol glycosides structures and the DPPH antiradical activity was also discussed.     

Antifeedant activity of flavonoids and related compounds against the subterranean termiteCoptotermes formosanus Shiraki

Antifeedant activity of some flavonoids and their related compounds against the subterranean termiteCoptotermes formosanus Shiraki was examined with nochoice tests and two-choice tests. The activities of these compounds were evaluated in relation to their chemical structures. All flavonoids tested showed antifeedant activity, whereas catechinic acid, possessing no A-ring or pyran ring in the molecule, showed feeding-preference activity. For the structure-activity relations, it was found that compounds containing two hydroxyl groups at C-5 and C-7 in A-rings showed high antifeedant activity. Furthermore, the presence of a carbonyl group at C-4 in the pyran rings of the compounds was necessary for the occurrence of high activity. 3-Hydroxyflavones and 3-hydroxyflavanones with 3,4-dihydroxylated B-rings exhibited higher activity than those with 4-hydroxylated B-rings.Part of this paper was presented at the 49th annual meeting of the Japan Wood Research Society, Tokyo, April 1999     

An iridoid and a flavonoid from Sideritis lanata L

A new iridoid diglucoside, 10-O-(E)-p-coumaroylmelittoside (1) and a new flavone glucoside, O-(6'-O-Acetyl-)-beta-glucopyranosylchrysoeriol (2), together with four known flavone glycosides, were isolated from the aerial parts of Sideritis lanata. The structures of the new compounds were elucidated by spectroscopic methods, 2D NMR and MS.     

A new dilactone from the seeds of Gaultheria yunnanensis

Gaultheriadiolide (1), a new compound, together with the known dauosterol (2), ginkgetin (3), myricetin (4), 6-ethyl-5-hydroxy-2,7-dimethoxy-1,4-naphthoquinone (5), ursolic acid (6), methyl salicylate 2-O-β-d-xylosyl(1→6)β-d-glucopyranoside (7), and methyl salicylate 2-O-β-d-glucopyranoside (8) were isolated from Gaultheria yunnanensis. The structure was elucidated on the basic of spectral analysis, especially 1D and 2D NMR. Primary bioassays showed that compound 1 had medium cytotoxic activity against HEp-2 and HepG2 Cells, with IC₅₀ of 23.337 μM and 29.4497 μM, respectively.     

甜茶植株不同部位总黄酮含量的测定

以广西甜茶为试材,用溶剂提取,利用高效液相色谱法,测定并分析了广西甜茶不同部位总黄酮含量的差异。试验结果表明:甜茶各部位总黄酮含量由高到低的排列顺序是:嫩叶、中茎皮、老茎皮、果实、嫩茎皮、老叶、中茎、老茎;根部和嫩茎的黄酮含量为零。茎皮的总黄酮含量普遍比茎中木质部高,形成由外向内递减趋势;嫩叶的含量最高,但老叶的含量却较低,叶子总黄酮含量形成了从上到下递减的趋势。