Daniel I. Arnon

Bio: Daniel I. Arnon is an academic researcher from University of Cambridge. The author has contributed to research in topics: Thylakoid & Photosynthesis. The author has an hindex of 1, co-authored 1 publications receiving 18362 citations.

Copper enzymes in isolated chloroplasts. polyphenoloxidase in beta vulgaris

Abstract: The chloroplast, as the seat of chlorophyll pigments in plants, occupies a unique position in the economy of the green cell. In recent years there has been a renewed interest in the reactions and properties of chloroplasts as a result of the work of Hill (11, 12) and Hill and Scarisbrick (13, 14) who demonstrated that the reaction characteristic of photosynthesis in green plants, the evolution of oxygen, occurs in appreciable quantities in isolated chloroplasts under the influence of light and in the presence of suitable oxidants (2, 7, 8, 26). In the course of an investigation of oxygen evolution by isolated chloroplasts it was deemed important to explore their enzymatic composition. Of special interest were considered enzymes capable of participating in oxidation-reduction reactions, and more particularly, those localized principally, if not entirely, in the chloroplasts. This paper presents evidence that a copper enzyme, polyphenoloxidase (otherwise known as tyrosinase or catecholase), is localized in the chloroplasts of spinach beet (chard), Beta vu?garis.

Fixing the Kawarabayashi-Thomas-Wollan Flat Wall

Abstract: Two recent papers by Kawarabayashi, Thomas and Wollan,"A New Proof of the Flat Wall Theorem"(arXiv:1207.6927) and"Quickly Excluding a Non-Planar Graph"(arXiv:2010.12397) provide major improvements over Robertson and Seymour's original proof of the structure theorem for finite graphs that exclude a given graph. The first paper redefines the notion of a flat wall. Unfortunately, this new notion is too strong. As a result, the new Flat Wall Theorem in that paper is incorrect. A counterexample is given in Appendix A. A follow-on lemma in the first paper, about the transitivity of flatness, is also incorrect, a fact that was noticed by Dimitrios Thilikos et al in arXiv:2102.06463. However, that error is derivative and not the main issue. This paper provides a weaker definition of the notion of a flat wall, provides a correction to the proof of the new Flat Wall Theorem and a new proof of flatness transitivity. The notion of a tight rendition as presented here differs from Thilikos' definition but is defined much more simply, and the notion of a proper cycle is introduced. The notions of certificates and tilted walls used by Thilikos turn out of be unnecessary and transitivity is preserved in its original simplicity and generality. Most importantly, it looks like the new weaker definition of flatness is all that is really necessary to carry through the proof of the structure theorem in the second paper of Kawarabayashi, Thomas and Wollan.

Chlorophylls and carotenoids: Pigments of photosynthetic biomembranes

Abstract: Publisher Summary This chapter presents detailed information on chlorophylls and carotenoids to give practical directions toward their quantitative isolation and determination in extracts from leaves, chloroplasts, thylakoid particles, and pigment proteins. The chapter focuses on the spectral characteristics and absorption coefficients of chlorophylls, pheophytins, and carotenoids, which are the basis for establishing equations to quantitatively determine them. Therefore, the specific absorption coefficients of the pigments are re-evaluated. This is achieved by using a two-beam spectrophotometer of the new generation, which allows programmed automatic recording and printing out of the proper wavelengths and absorbancy values. Several procedures have been developed for the separation of the photosynthetic pigments, including column (CC), paper (PC), and thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC). All chloroplast carotenoids exhibit a typical absorption spectrum that is characterized by three absorption maxima (violaxanthin, neoxanthin) or two maxima with one shoulder (lutein and β-carotene) in the blue spectral region.

Some relationships between the biochemistry of photosynthesis and the gas exchange of leaves.

Abstract: A series of experiments is presented investigating short term and long term changes of the nature of the response of rate of CO2 assimilation to intercellular p(CO2). The relationships between CO2 assimilation rate and biochemical components of leaf photosynthesis, such as ribulose-bisphosphate (RuP2) carboxylase-oxygenase activity and electron transport capacity are examined and related to current theory of CO2 assimilation in leaves of C3 species. It was found that the response of the rate of CO2 assimilation to irradiance, partial pressure of O2, p(O2), and temperature was different at low and high intercellular p(CO2), suggesting that CO2 assimilation rate is governed by different processes at low and high intercellular p(CO2). In longer term changes in CO2 assimilation rate, induced by different growth conditions, the initial slope of the response of CO2 assimilation rate to intercellular p(CO2) could be correlated to in vitro measurements of RuP2 carboxylase activity. Also, CO2 assimilation rate at high p(CO2) could be correlated to in vitro measurements of electron transport rate. These results are consistent with the hypothesis that CO2 assimilation rate is limited by the RuP2 saturated rate of the RuP2 carboxylase-oxygenase at low intercellular p(CO2) and by the rate allowed by RuP2 regeneration capacity at high intercellular p(CO2).