Modern methods of plant analysis
01 Jan 1964-
About: The article was published on 1964-01-01 and is currently open access. It has received 1991 citations till now.
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01 Jan 1974-Progress in the chemistry of organic natural products. Progrès dans la chimie des substances organiques naturelles
TL;DR: In the present article, an attempt will be made to give a much briefer, although up-to-date review of the structure, chemistry, and biosynthesis of melanins.
Abstract: The term “melanin” (μέλας = black) is a purely descriptive one, which conveys no chemical information and merely denotes a black pigment of biological origin, although in fact some melanins are brown or even yellow. Different authors have accepted various definitions of exactly what constitutes a melanin; and melanins are sometimes loosely described as pigments of high molecular weight formed by the enzymic oxidation of phenols. The latter is not however a satisfactory definition. According to Thomson (149), who has written admirable reviews on the chemistry of melanins (149, 150), the term melanin appears to have been used first with some precision in 1902 by Furth and Schneider, in respect of the black precipitate they obtained by the action in vitro of insect tyrosinase on tyrosine. The fact that the general properties and the carbon, hydrogen, and nitrogen analyses of this material were in approximate agreement with those reported for natural pigments from animal hair, melanoma, Sepia black, etc., implied that these natural pigments also were products of the tyrosine-tyrosinase reaction. An excellent, comprehensive, and detailed account of these pigments has been given by Nicolaus (107) in his book, which includes references up to 1967, and in which he has classified the pigments into eumelanins, phaeomelanins, and allomelanins. In the present article, an attempt will be made to give a much briefer, although up-to-date review of the structure, chemistry, and biosynthesis of melanins. A number of other useful reviews on melanin, and on the chemistry and biochemistry of melanogenesis are also available (42, 53, 85, 86, 94, 95, 106, 130, 137, 148).
120 citations
120 citations
TL;DR: The effect of water deficits on leaf conductance and photosynthesis occurred later in the drying cycle in Bragg than Ruse, and the relationships among leaf water potential, osmotic potential, turgor potential, and leaf relative water content did not change with season or soil water depletion.
Abstract: Concurrent measurements of leaf water potential, leaf osmotic potential, leaf relative water content, quantum flux density, leaf conductance, 14CO2 photosynthesis, soluble and insoluble sugars, starch and potassium concentrations were made diurnally on six occasions between flowering and maturity on upper leaves of irrigated and rainfed crops of soybean (cvv. Ruse and Bragg) and a rainfed crop of sorghum (cv. TX 610). With adequate soil water, sorghum had lower values of leaf conductance than did soybeans at high light and yet had higher rates of photosynthesis. Stage of plant development had no effect on either leaf conductance or photosynthesis of the youngest fully expanded leaves of both sorghum and soybean, but starch accumulation in the leaf over the day was less at grain-filling than at flowering in the soybean. Starch and sugar levels in the leaf had no apparent effect on photosynthesis. The daily minimum leaf water potential decreased in Ruse soybean from - 1.5 to -2.7 MPa as soil water was depleted. Late in the drying cycle, the daily minimum leaf water potential was higher in Bragg than in Ruse. In both cultivars, stomatal closure and decrease in 14CO2 photosynthesis commenced at leaf water potentials below - 1.5 MPa. Thus, the effect of water deficits on leaf conductance and photosynthesis occurred later in the drying cycle in Bragg than Ruse. As photosynthesis decreased with the depletion of soil water, starch accumulation in leaves of both cultivars of soybean decreased; changes in soluble and insoluble sugars and in potassium were small. The relationships among leaf water potential, osmotic potential, turgor potential, and leaf relative water content did not change with season or soil water depletion. Bragg and Ruse soybeans showed a similar response and both approached zero turgor at the same relative water content (82-83 %) and the same leaf water potential (- 1.5 to - 1.7 MPa). No evidence ofr osmotic adjustment was found in either soybean cultivar.
119 citations
TL;DR: Southern blot analysis of genomic DNA indicated that the P34 gene has a low copy number, and a comparison of the nucleotide and deduced amino acid sequences in the GenBank Data Bank with the sequence of P34 has shown considerable sequence similarity to the thiol proteases of the papain family.
118 citations
TL;DR: The spectral absorption properties of fully deuteriated chlorophylls a and b, ordinary chlorophylla a andb, and methyl chlorophyLLides a andB, isolated in a state of high purity, have been compared.
118 citations
References
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01 Jan 1963
TL;DR: In this article, a physiologischer Vorgang auf eine enzymatische Wirkung zuruckgefuhrt werden (vgl. S. 301), besteht die folgende Aufgabe darin, Naheres uber die Eigenschaften des beteiligten Enzyms zu ermitteln.
Abstract: Kann ein physiologischer Vorgang auf eine enzymatische Wirkung zuruckgefuhrt werden (vgl. S. 301), so besteht die folgende Aufgabe darin, Naheres uber die Eigenschaften des beteiligten Enzyms zu ermitteln. Hierzu gehoren die Bestimmung der Reaktions- und Substratspezifitat sowie die Ermittlung der Bedingungen, unter denen eine optimale Wirkung des Enzyms gegeben ist. Wesentlich zur Charakterisierung ist ferner die Untersuchung der Stabilitat des Enzyms und dabei insbesondere die Feststellung, ob es sich um ein Ferment handelt, das zur vollen Aktivitat dialysable Cofaktoren benotigt. Falls diese Frage bejaht wird, ist auch die Bestimmung der unerlaslichen Cofaktoren anzuschliesen. Uberdies bietet auch der Nachweis der Lokalisation des Enzyms in der Zelle (oder im Zellverband) eine entscheidende Moglichkeit zur Charakterisierung des Fermentes. Hinzu kommt schlieslich noch die Untersuchung der Wirkung einzelner Inhibitoren1 auf das Enzym, die zu weitgehender Klarung des Reaktionsmechanismus beitragen kann und eine Abgrenzung der Eigenschaften des untersuchten Fermentes gegenuber ahnlichen Enzymen erlaubt.
2 citations
01 Jan 1962
TL;DR: Optical rotation has been found to be one of the most convenient methods of following the denaturation of proteins and rotatory dispersion is capable of providing information on the folding of the polypeptide chain in proteins and the changes accompanying denaturation.
Abstract: Optical rotation has been found to be one of the most convenient methods of following the denaturation of proteins. Generally speaking denaturation can be defined as a process or sequence of processes in which the spatial arrangement of the polypeptide chains within the molecule is changed from that typical of the native protein to a more disordered arrangement (Kauzmann 1959). The terms “configuration”, “conformation” and “state of folding” are widely used for spatial arrangement. It is probably best to follow the suggestion of Blout (1960) and restrict the use of “configuration” to its original sense, i.e. the spatial arrangement around an asymmetric carbon atom, and to use “conformation” for the shape of the molecule in its entirety. The properties discussed in the previous Chapter i.e., viscosity, diffusion, sedimentation, and light scattering — can all furnish information on the overall shape of proteins or other macromolecules and changes in this shape with environment. Thus Doty, Bradbury and Holtzer (1956) were able to show using these methods, together with streaming birefringence, that poly-γ-benzyl-L-glutamate could exist in two conformations, the α-helix and the solvated randomly coiled form, depending on the solvent. The change from α-helix to random coil was accompanied by marked changes in the optical rotatory properties of the polypeptides. It is to be expected that an α-helical structure should contribute to the rotatory power of a polypeptide since helices are asymmetric and not superimposable on their mirror images. The work on polypeptides has shown that rotatory dispersion is capable of providing information on the folding of the polypeptide chain in proteins and the changes accompanying denaturation.
1 citations