Phytochrom-induzierte Enzymbildung (Phenylalanindesaminase), ein schnell ablaufender Prozeß

Zusammenfassung Bei Erstbelichtung des Senfkeimlings mit Dauer-Dunkelrot tritt der P₇₃₀-abhängige Anstieg der Phenylalanindesaminase-Aktivität erst mit einer lag-Phase von 1,5 Std ein (Abb. 3, 4 unten). Bei einer Zweitbelichtung (Programm: Erstbelichtung — längere Dunkelperiode — Zweitbelichtung) fehlt die lag-Phase (Abb. 4, oben). Die Enzymaktivität steigt sofort linear an. Da der Anstieg der Enzymaktivität wahrscheinlich auf eine de novo Synthese von RNS und Enzymprotein zurückzuführen ist (Tabelle), so erscheint der Schluß berechtigt, daß P₇₃₀ sehr rasch eine differentielle Genaktivierung mit anschließender Enzymsynthese bewirken kann, falls die Gene der Aktivierung durch P₇₃₀ zugänglich sind. Die relativ lange lag-Phase nach Einsetzen der Erstbelichtung benötigt das P₇₃₀ offenbar dazu, die potentiell aktiven Gene (P₇₃₀) für das P₇₃₀ zugänglich zu machen. Das Problem der primären lag-Phase ist in einer vorangegangenen Arbeit zur P₇₃₀-abhängigen Anthocyansynthese ausführlich diskutiert worden (vgl. Lange, Bienger und Mohr, 1967).

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Phytochrome-mediated enzyme formation (Phenylalanine deaminase) as a rapid process

Summary In previous papers we have reported (Mohr and Durst, 1966a, b) that synthesis of phenylalanine deaminase (EC 4.3.1.5), an important enzyme of phenolic metabolism, can be stimulated by the physiologically active phytochrome (=P₇₃₀) in the mustard seedling. The data of the present paper suggest that induction of this enzyme is a rapid process if the gene in question is easily accessible for the activating action of P₇₃₀.The seedlings were irradiated with continuous standard far-red light. Longtime irradiation with far-red will maintain a low but virtually constant level of P₇₃₀ in the seedling over an extended period of time. At the moment when the far-red light is turned off the action of P₇₃₀ will virtually cease. — Fig. 3 and Fig. 4, lower part, show the kinetics of enzyme induction by P₇₃₀ in an etiolated seedling. The initial (or primary) lag-phase after the onset of far-red is 1.5 hours. If, however, a seedling which has been pre-irradiated with 12 hours of far-red is kept in darkness for 6 hours and is then re-irradiated with far-red no lag-phase for the action of the second irradiation can be found. Enzyme activity increases immediately after the onset of far-red. Since the action of the second irradiation as measured by increase of enzyme activity can be inhibited by relatively low doses of Puromycin and Cycloheximide (table) we conclude that the re-appearance of P₇₃₀ leads to de novo synthesis of enzyme protein. — Application of Actinomycin D (10 g/ml) only partially inhibits the action of the second irradiation as measured by increase of enzyme activity. This finding was to be expected. In preceding papers (e.g. Mohr and Bienger, 1967) it has been concluded that genes which have once been activated by P₇₃₀ remain less sensitive towards Actinomycin D even when P₇₃₀ has disappeared. Taking into account all available data the conclusion seems to be justified that the induction of enzyme synthesis by P₇₃₀ (i.e. differential gene activation followed by enzyme synthesis) is a rapid process if the genes are accessible for the action of P₇₃₀. The relatively long initial lag-phase (1.5 hours) is needed to make the potentially active genes (P₇₃₀) accessible for the action of P₇₃₀. The problem of how the initial lag-phase can be understood has been dealt with more in detail in a previous paper on phytochrome-mediated anthocyanin synthesis (Lange, Bienger and Mohr, 1967).

     

Quantum Requirement for Photosynthesis in Chlorophyll-Deficient Plants with Unusual Lamellar Structures

Neither an over-all deficiency of chlorophyll, nor an increased enzymatic capacity for maximal rates, nor an unusual lamellar structure was found to change the number of quanta required for the evolution of one molecule of oxygen in healthy aurea mutants of tobacco. The average minimal quantum number remains 10 (efficiency 0.1) as in many algae and typical higher plants. Most of the time the optimal efficiency depends on the availability of some far-red radiation, particularly in the blue region of the spectrum where blue light alone is rather inefficient. These results fit an explanation offered earlier in connection with the hydrogen or acetate photometabolism of algae in far-red light.     

DEVELOPMENTAL STUDIES OF THE DIPTERAN SALIVARY GLAND : II. DNase Activity in Chironomus thummi

The deoxyribonuclease (DNase) activity of the dipteran (Chironomus thummi) salivary gland, measured both enzymatically and immunochemically, increases about 7-fold with the onset of metamorphosis. The increase in DNase activity occurs at a time when the activities of other enzymes and the total protein content are decreasing. The increased DNase activity is followed by glandular destruction. It is suggested that the alterations of this activity may be regulated by the activities of specific chromosomal sites, and that the enzyme may, at least in part, account for the glandular destruction observed at the time of increased enzyme activity.     

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