Tissue localization of u.v.‐B‐screening pigments and of chalcone synthase mRNA in needles of Scots pine seedlings

Abstract

(Dedicated to Professor Klaus Hahlbrock on the occasion of his 60th birthday) SUMM.^RY Epidermal tissue was isolated from Scots pine {Pinus sylvestris L.) needles by enzymatic digestion in order to study tissue distribution of u.v,-B-screening pigments. Up to 90 "o ofthe needle content of a group of diacylated flavonoi glycosides tbat were structurally closely related was found in the epidermal layer. Among these metabolites. 3",6"-di-para-coumaroyl-isoquerfitrin and 3",6"-di-para-coum3roy]-astragal in were the main u.v.-B-induced compounds in cot\ ledons and primary needles, respectively. However, catechin and astragalin (kaempferol 3-glucoside), two non-acylated fla\'onoid metabolites, were only observed in total needle extracts, and at levels independent of u.v.-B treatment. According to this metabolite distribution, tbe mRNA of chalcone syntbase, the key enzyme to flavonoids, was found in epidermal and mesophyll as well as vascular tissues. The major alkaliextractable wall-hound phenolic metabolites, astragalin, 4-coumaric acid, and ferulic acid, a minor component of tbe cell wall, were also found exclusively in the epidermal layer. These compounds were not stimulated by u.v.-B irradiation within the experimental period. Staining of needle cross sections and epidermal layer preparations with NaturstofTreagenz A confirmed the specific localization of wall-bound astragalin in the outer wall of the epidermal layer. Model calculations of u.v.-B absorptions at 300 nm of soluble and cell-wall-bound metabolites of the epidermal layer revealed an almost complete shielding of the mesophyll tissue from u.v.-B radiation.

Enhanced biosynthesis of quercetin occurs as A photoprotective measure in Lycopersicon esculentum mill. under Acute UV-B exposure

“…Biosynthesis of flavonoids is often induced under the influence of UV-B radiation in the plants ( Li et al 1993;Jordan 1996;Caldwell et al 1999 andJenkins et al 2009), which may be due to the increased influx of precursor amino acids into their metabolic pathways. This can be seen as a strategy of the plants to overcome UV-B stress through effective absorption shown by the flavonoids in the UV-B spectral region (Reuber et al1996;Schnitzler et al 1996 andHoque andRemus 1999) and by overcoming the oxidative stress in cells (Dawar et al 1998). Despite these favourable effects in the plants, the increased level of flavonoids has been shown to interfere with vital physiological processes such as ATP synthesis and oxidative phosphorylation leading to disintegration of chloroplasts, causing chlorosis and necrosis (Kumari et al 2009).…”

Gene Expression and Metabolite Profiling of Developing Highbush Blueberry Fruit Indicates Transcriptional Regulation of Flavonoid Metabolism and Activation of Abscisic Acid Metabolism

“…For flavonol localization, cover slides were directly placed on slide-mounted tissue sections after the removal of paraffin with toluene. Flavonol autofluorescence (Schnitzler et al, 1996) was observed under green fluorescence (excitation filter, band pass 420-490; dichromatic mirror, 510; suppression filter, long pass 515) using a Leica DMRXA microscope in the fluorescence configuration, and micrographs were taken with a microscope-mounted Nikon camera controlled by ACT-1 software (Nikon). Tissue sections were also stained with the flavonol-specific stain DPBA, using the method of Peer et al (2001).…”

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

“…Trichome frequency was estimated by counting the number of glandular trichomes per unit leaf area at a magnification of i50 (Gravano et al, 1998). Histochemical localization of flavonoids was performed by modifying the protocol proposed by Schnitzler et al (1996). Transverse sections (30 µm) of fresh leaf tissue were stained for 1n5 min in 1% diphenylboric acid 2-amino-ethyl ester (Sigma) in ethanol (Naturstoff reagent).…”