Jerry W. McClure

The distribution of flavonoids in chloroplasts of twenty five species of vascular plants

Abstract A survey was made of the major flavonoids in whole leaf extracts and in chloroplast preparations from twenty five species of vascular plants including Anthophyta (20), Coniferophyta (1), Ginkophyta (1), Pterophyta (2), and Arthrophyta (1). The chloroplasts variously contained derivatives of flavones, C -glycosylflavones, flavonols, flavanones, isoflavones, 3-deoxyanthocyanidins, and anthocyanins. Twenty three species contain one or more flavonoids in isolated chloroplast, usually in a pattern quite similar to that found in whole-leaf extracts but occasionally showing enrichment of one or more flavonoids in the chloroplasts. Flavonoids are apparently absent from chloroplasts of Phaseolus aureus and Morus alba although whole-leaf extracts of these species are rich in quercetin derivatives.

Phenolic metabolism, growth, and uv–b tolerance in phenylalanine ammonia-lyase-inhibited red cabbage seedlings

Abstract Red cabbage seedlings were grown with or without the phenylalanine ammonia-lyase (PAL) inhibitor, 2-amino-indan-2-phosphonic acid (AIP), at concentrations ranging from 0.5 to 50 μ M. The I 50 for anthocyanin accumulation was μ M, with >99% inhibition at 10 μ M, but levels of sinapic acid esters were essentially unchanged by AIP. When grown with 50 μ M AIP, fresh and dry weights were increased slightly over controls, total chlorophylls were unchanged, and microscopic examination revealed no apparent effect of AIP on plant architecture. This suggests no toxic effect of AIP in red cabbage seedlings at levels highly effective in inhibiting PAL. At 50 μ M AIP, the cotyledon area was slightly increased but hypocotyls were significantly reduced in length, perhaps the result of enhanced blue light sensitivity in the absence of anthocyanins. Negative phloroglucinol reactions in AIP-grown plants are consistent with AIP inhibition of lignification. Plants grown with 50 μ M AIP were about twice as sensitive as control plant to UV–B damage of photosystem II, suggesting that phenylpropanoids carried over from the seed, as well as flavonoids, serve as UV screens in young red cabbage seedlings.

The Physiology of Phenolic Compounds in Plants

An Oriental fable tells of six blind men who found an elephant and did not know what it was. They described it as resembling a wall, a spear, a snake, a tree, a fan, or a rope; depending on which part each had touched. Each believed he knew just how the animal looked; and each called the others hard names because they did not agree with him. One finds similarly diverse opinions of how certain treatments, or environmental situations, influence phenolic enzymes or phenolic accumulations76, 112.

Phytochrome controlled phenylalanine ammonia lyase in Hordeum vulgare plastids

Abstract Chloroplasts isolated from 5-day-old barley shoots by differential centrifugation have l -phenylalanine ammonia lyase (PAL) activity. Based on chlorophyll/PAL ratios, the chloroplasts have about 29% of the PAL of the whole shoot. When plastid preparations are fractionated by discontinuous sucrose gradient centrifugation, highest PAL activity is found at the interface containing predominantly intact plastids. Continuous sucrose gradient centrifugation shows a correlation between chlorophyll content and PAL levels. PAL activity in 5-day-old etioplasts is increased ca 40% by giving the plants 4 min of red light 5 hr before harvest. Far-red light reverses the red light effect and demonstrates phytochrome control of barley plastid PAL.

Altered lignin composition in phenylalanine ammonia-lyase-inhibited radish seedlings: implications for seed-derived sinapoyl esters as lignin precursors

We earlier reported that when phenylalanine ammonia-lyase (PAL) activity in radish seedlings was inhibited by the competitive inhibitor 2-aminoindan-2-phosphonic acid (AIP), soluble sinapoyl esters carried over from the seed were converted to wall-bound esters in young cotyledons. We now report that these soluble sinapoyl esters may also be converted into lignin in the cotyledons. When radish seedlings were grown in the presence of 100 microM AIP, lignin formation (determined as lignothioglycolic acid) was inhibited ca. 74% in the cotyledons and ca. 80% in hypocotyls plus roots. The syringyl to guaiacyl (S/G) ratio in the lignin of AIP-grown plants, as determined by alkaline cupric oxidation and from Fourier-transform infrared (FT-IR) spectra, was higher in cotyledons, but lower in hypocotyls plus roots, as compared to plants grown on distilled water. These results support the view that soluble sinapoyl esters preformed in seeds may contribute to the syringyl moiety of lignin in cotyledons during early seedling development and that there is no appreciable transport of soluble sinapoyl esters from cotyledons to the hypocotyls and roots.

Lysine-methionine-threonine interactions in growth and development of Mimulus cardinalis seedlings.

SummaryPlants of Mimulus cardinalis Douglas (Scrophulariaceae) were grown in axenic culture from seed for 28 days on a minimal salts medium supple-mented with l-lysine, l-methionine, l-threonine, l-isoleucine, dl-or l-homoserine or dl-homocysteine, alone or in combinations ranging from 5 to 1000 μM. Abnormal growth was observed at the higher concentrations of all these aminoacidsexcept homocysteine. The lysine inhibition was significantly reduced by methionine, homocysteine or isoleucine. The threonine inhibition was significantly reduced by methionine or homocysteine. A combination of lysine and threonine at 1 MM was lethal. This synergistic effect was prevented when methionine, homoserine or homocysteine were added to the lysine-threonine combination. These results can be explained in terms of end-product control of aspartokinase and homoserine dehydrogenase by lysine and threonine, respectively, in the biosynthetic pathway to these aspartic-acid-derived amino acids.

Polyamine oxidase of primary leaves is apoplastic in oats but symplastic in barley

Abstract Peeling away the lower epidermis and vacuum-infiltrating six-day-old primary leaves with buffered 200 mM NaCl extracted an intercellular washing solution (IWS) containing up to 99% of the polyamine oxidase (PAO) activity from oats, none of the PAO activity from barley, and no cytoplasmic glucose-6-phosphate dehydrogenase (G6P-D) from either species. In barley, but not oats, PAO activity was recovered from either isolated mesophyll protoplast or leaves from which the IWS had been extracted. We conclude that PAO is apoplastic and weakly ionically bound to mesophyll cell walls of oat primary leaves, but symplastic in primary leaves of barley. Implications of this differential localization including the involvement of PAO in providing hydrogen peroxide for lignification are considered.

Photocontrol of C-glycosylflavones in barley seedlings☆

Abstract The sole flavonoid of etiolated barley plumules is saponarin, a C-glycosylflavone restricted to the primary leaves. Increased saponarin synthesis is under a typical low-energy phytochrome control in both etiolated plumules and in those grown in white light. Prolonged illumination with white light, or high levels of blue light followed by red light, greatly increases saponarin and initiates the synthesis of lutonarin; this response is characteristic of high-energy photoresponses (HER). Kinetic studies show a typical lag of about 4 hr for phytochrome control of saponarin in etiolated plumules. Surprisingly, during this lag-phase and within 2 min following a red-light (132 Kerg cm−2) treatment, there is a 25 per cent decrease in saponarin recovered from whole plumules. Within 1 hr the light-treated plants yield only about half as much saponarin as do the dark controls. After 1 hr apparent saponarin content increases and by the fourth hour the flavonoid content of the light-treated and dark-control plants is similar. The fate of this “lost” saponarin is not known; it may be in part translocated into other parts of the seedling as the apical 1 cm of the plumule shows a more rapid recovery under these conditions, a part may be complexed into forms not recoverable by our techniques. Mediatory aspects of changes in saponarin localization within the tissues are considered.

Fourier transform–IR determination of protein contamination in thioglycolic acid lignin from radish seedlings, and improved methods for extractive‐free cell wall preparation

Fourier transform (FT)–IR spectroscopy was used to characterize and check for contamination in lignothioglycolic acid (LTGA) preparations from radish seedlings. LTGA, prepared by the conventional technique of extracting plant material first with 50% (v/v) aqueous methanol, was so highly contaminated with proteins that lignin, based on absorptivity at 280 nm, was overestimated by as much as eight-fold. When samples were extracted first with buffer to remove soluble proteins, then with buffer plus 1 M sodium chloride to remove ionically-bound proteins, and finally digested with cellulase and pectinase, the FT–IR spectra of the LTGA samples so obtained were comparable to spectra of LTGA prepared from purified hardwood lignin. Lignin values estimated from benzaldehydes recovered after cupric oxide degradation were similar for both methods of sample preparation. FT–IR analysis of the cell wall material from which LTGA had been extracted showed that this procedure removed all detectable lignin. LTGA values provide an accurate and highly sensitive assay of lignin in radish seedlings and this procedure should be widely applicable to lignin analysis of other young herbaceous tissues, but only if proteins are removed during extractive-free cell wall preparation. Copyright

The occurrence and photoregulation of flavonoids in barley plastids

Abstract Whole-leaf extracts of etiolated or light-grown barley shoots contain the C-glycosylflavones saponarin, lutonarin and lutonarin 3′-methyl ether. Plastids isolated by aqueous techniques contain only saponarin. Contamination experiments using foreign flavonoids indicate that saponarin recovered from plastids is not a contaminant from other cellular fractions. In response to brief red light treatment 24 hr before harvest, saponarin levels are approximately doubled in whole-shoot extracts, but increased about 3.5 fold in plastids. This photocontrolled increase is far-red reversible. Thus saponarin is selectively accumulated in barley plastids and this accumulation is controlled by phytochrome.