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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TL;DR: There are unresolved difficulties inherent in the “cytokinin hypothesis” of phytochrome and gibberellin action that lead to increases in active cytokinin levels in seeds.
Abstract: Cytokinins overcome the inhibitory effect of abscisic acid on the germination of isolated embryos of Grand Rapids lettuce. We have used this fact to assess the content of cytokinins in embryos removed from intact seeds which have been supplied with these growth substances i.e. to determine hormonal uptake. The method has also been used to examine the hypothesis that phytochrome and gibberellin lead to increases in active cytokinin levels in seeds. Appreciable amounts of cytokinins enter intact seeds yet seem unable to promote germination. On the other hand, little or no cytokinin-like activity seems to result from light or gibberellin treatments. We conclude that there are unresolved difficulties inherent in the “cytokinin hypothesis” of phytochrome and gibberellin action.
35 citations
TL;DR: The basis for a mechanism of end-product control of HSDH activity in the 'physiological' direction (that is, ASA-+HS), as well as in the reverse direction, is provided by the observation that inhibition due to L-threonine is specifically reversed by either L-isoleucine or L-methionine.
Abstract: The HSDH of R. rubrum shows certain properties of considerable interest. In the absence of threonine, both L-methionine and L-isoleucine individually cause activation of the enzyme for the conversion of HS to ASA15 •16 • On the other hand, no activation is observed for the reverse reaction, that is, ASA + NADPH-+ HS + NADP15 • The nature of the kinetics of threonine inhibition in the two directions also differs, being competitive with HS and (apparently) non-competitive with respect to ASA14 •16 . The basis for a mechanism of end-product control of HSDH activity in the 'physiological' direction (that is, ASA-+HS), as well as in the reverse direction, is provided by the observation that inhibition due to L-threonine is specifically reversed by either L-isoleucine or L-methionine14• These observations, together with the fact that the effects of threonine and other amino-acid modifiers have been correlated16 with reversible 'monomer-polymer' interconversions of the enzyme, make the HSDH of R. rubrum an appealing experimental system for further exploration of the molecular aspects of enzyme regulation.
35 citations
TL;DR: The volatile compounds of two green algae, Scenedesmus sp. and Chlorella vulgaris, have been identified by GC and GC-mass spectrometry.
35 citations
TL;DR: Treatment of leaves of chinese cabbage plants with 2-thiouracil suppresses the production of infective TYMV nucleoprotein but the analog is not incorporated into the virus RNA in detectable amounts and has no effect on the infectivity of the virus that is formed in its presence.
35 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