Fluorescence methods are being used increasingly in biochemical, medical, and chemical research. This is because of the inherent sensitivity of this technique. and the favorable time scale of the phenomenon of fluorescence. 8 Fluorescence emission occurs about 10- sec (10 nsec) after light absorp tion. During this period of time a wide range of molecular processes can occur, and these can effect the spectral characteristics of the fluorescent compound. This combination of sensitivity and a favorable time scale allows fluorescence methods to be generally useful for studies of proteins and membranes and their interactions with other macromolecules. This book describes the fundamental aspects of fluorescence. and the biochemical applications of this methodology. Each chapter starts with the -theoreticalbasis of each phenomenon of fluorescence, followed by examples which illustrate the use of the phenomenon in the study of biochemical problems. The book contains numerous figures. It is felt that such graphical presentations contribute to pleasurable reading and increased understand ing. Separate chapters are devoted to fluorescence polarization, lifetimes, quenching, energy transfer, solvent effects, and excited state reactions. To enhance the usefulness of this work as a textbook, problems are included which illustrate the concepts described in each chapter. Furthermore, a separate chapter is devoted to the instrumentation used in fluorescence spectroscopy. This chapter will be especially valuable for those perform ing or contemplating fluorescence measurements. Such measurements are easily compromised by failure to consider a number of simple principles."

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Principles of fluorescence spectroscopy

Vesicular-arbuscular mycorrhizal fungi can affect the water balance of both amply watered and droughted host plants. This review summarizes these effects and possible causal mechanisms. Also discussed are host drought resistance and the influence of soil drying on the fungi.

Water relations, drought and vesicular-arbuscular mycorrhizal symbiosis

http://utsc.utoronto.ca/%7Ebritto/publications/amtox.pdf

NH4+ toxicity in higher plants: a critical review

1,2-Amino Alcohols and Their Heterocyclic Derivatives as Chiral Auxiliaries in Asymmetric Synthesis

— Fluorescence spectra of a number of native and denaturated proteins have been analysed, using spectral band width (ΔΛ), spectral maximum position (Λm), fluorescence quenching by external ionic quenchers, lifetime (b), and quantum yield (q) and its changes upon denaturation. The results enabled a model of fluorescence properties of tryptophan residues in the proteins to be substantiated by considering the existence of three discrete spectral classes, one buried in nonpolar regions of the protein (Λm 330–332 nm, ΔΛ= 48–49nm, q 0.11, τ= 2.1 ns) and two on the surface. One of the latter is completely exposed to water (Λm# 350–353 nm, ΔΛ= 59–61 nm, q# 0.2, τ= 5.4 ns); the other is in limited contact with water which is probably immobilized by bonding at the macromolecular surface (Λm# 340–342 nm, ΔΛ= 53–55 nm, q# 0.3, = 4.4 ns). Some quantitative predictions from the model, for (a) the fraction of fluorescence that is quenched by ionic quenchers, (b) the mean values of quantum yield, and (c) the mean values of fluorescence lifetime for various proteins, show good concordance with independent experimentally determined values.

Fluorescence and the location of tryptophan residues in protein molecules

The polarized absorption spectra of crystals of indole derivatives have been measured in order to confirm the presence of two types of electronic transitions, 1Lb and 1La, in the long-wavelength absorption region, and in order to determine the direction of their transition moments. The polarization spectra show that the 1A–1Lb electronic transition forms a sharp absroption band with vibrational structures lying below a broader absorption band of the 1A—1La transition. The transition memont direction of the 1Lb makes an angle of 54° to the long axis of the molecule, while that of the 1La lies at an angle of −38° to the same axis. These results were compared with the results of theoretical calculations of the P–P–P SCF MO–CI method.

Polarized Absorption Spectra of Crystals of Indole and Its Related Compounds

The uptake of nitrate and ammonium by rice (Oryza sativa) seedlings was compared under various conditions. Nitrate uptake showed a 1-hour lag phase and then a rapid absorption phase, whereas ammonium uptake showed passive absorption during the first hour, then a shoulder of absorption, followed by a rapid metabolism-dependent absorption phase. Light did not affect the uptake of nitrate or ammonium. The uptake of nitrate and ammonium was markedly suppressed by removal of the endosperm. After removal of the endosperm, the uptake was restored by exogenous supply of 30 mm sucrose. No appreciable nitrate uptake was detected at temperatures below 15 C, whereas appreciable ammonium uptake occurred at 15 C, although lowered passive absorption and complete inhibition of the rapid metabolism-dependent absorption phase were observed at 5 C.Nitrate uptake was decreased by aeration and also by bubbling the mixture with O(2). It was greatly depressed by bubbling the mixture with N(2). These results suggest that there is a low optimal O(2) concentration for nitrate uptake. In contrast, ammonium uptake was increased by aeration, not influenced by bubbling with O(2), and slightly decreased by bubbling the mixture with N(2).Nitrate uptake was almost entirely inhibited by addition of cycloheximide, KCN, or arsenate. These compounds had scarcely any effect on the passive absorption of ammonium, but entirely depressed its successive metabolism-dependent absorption. Ammonium uptake occurred before nitrate uptake in solution containing both nitrate and ammonium.

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Comparison of the uptake of nitrate and ammonium by rice seedlings: influences of light, temperature, oxygen concentration, exogenous sucrose, and metabolic inhibitors.

Distribution and change in the contents of allantoin and allantoic acid in developing nodulating and non-nodulatng soybean plants

The present investigation was undertaken in order to examine the influence on nitrogen fixation of the accumulation of nitrite, as result of the supply of exogenous nitrate, in soybean nodules, and to clarify the relationship between the inhibition of nitrogen fixation, the formation of nitrite in the nodule cytosol, and the decrease in leghemoglobin function due to the formation of LbNO under such conditions

Yukio Yamamoto

Papers

Polarized Absorption Spectra of Crystals of Indole and Its Related Compounds

Comparison of the uptake of nitrate and ammonium by rice seedlings: influences of light, temperature, oxygen concentration, exogenous sucrose, and metabolic inhibitors.

Distribution and change in the contents of allantoin and allantoic acid in developing nodulating and non-nodulatng soybean plants

Inhibition of Nitrogen Fixation in Soybean Plants Supplied with Nitrate I. Nitrite Accumulation and Formation of Nitrosylleghemoglobin in Nodules

Enzymes of purine catabolism in soybean plants