Sumntmary. The oxygen consumption of a starved chlorophyll-free, yellow mutant of Chlorella vulgaris is enihanced by very smalq amounts of blue light (X 450 mu); a saturation level is reached at about 500 ergs cm 2 sec'l. At that intensity the respiration is about 3 times greater than in the dark. An action spectru-m for the enhancement of respiration shows 2 peaks around X 450 and 375 mju. Fliavins and cis-caroteno'ids are dis;cussed as the pigments involved.Fifteen years ago Voskresenskaja (13) reported that leaves of higher plants contain more protein after growth in blue ligh't thian after growth in red light and since then this restlt has been confirmed several times (1,2,5,9). I't was also exten(led to several green algae (6,11).WVhile looking for the primary photochemistry in this process we found recently that blue light enhanced the endogenous respiration of starved Chlorella markedly in a reversible manner (7,8).The first step in the search for the photochemically active pigment was to exclude chlorophyll by demonstrating the same effect in a chlorophyll-free, yellow mutant of Chlorella. Lacking an overlapp:ng chlorophyll absorption in the blue, this yellow organism was obviously the very object for measuring an action spectrum of the enhancement o,f respiration by light. The result we have obtained points to participation of either a cis-carotenoid or a flavin.
Materials and MethodsThe The oxygen sensor is inserted in one wall of a 2X2X2 cm plexiglass vessel which can be closecl air tight. Figure 1 illustrates the set ulp. The vessel with the sensor and the suspension (1) sits in a bigger plexiglass vessel (k) which serves as a water bath. The latter is connected to a thermostat and portable cooling bath. The vessel is placed on top of a magnetic stirrer (i) w-hich turns at 1000 rpm. Before closing the vessel (1) its contents can be equilibrated with a gas stream brought uip to temperature by passing it through
Crude extracts of dark-kept resting cells of a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris Beijerinck (211-11h/20) were found to convert 14.44±0.77 nmol PEP per min and mg protein into pyruvate by the action of pyruvate kinase (=PK; EC 2.7.1.40). When such cells were exposed to blue light (λ<550 nm, ∼300 μW cm(-2)) for 3 hrs the PK-activity/protein of their crude extracts rose to 21.47±1.30, i.e., it was enhanced by 43%. Poisoning with 10(-3) mol cycloheximide or with 150 μg actinomycin D/ml prevented the effect of blue light by 80-90% (Table 1). This result points to an induction of enzyme synthesis in blue light. Addition of 1% glucose in the dark resulted in an increase in PK-activity, too. Three hrs after application of glucose the PK-activity was 28.05±1.88 nmol/min and mg protein, which was 94% greater than in the control. The effect of glucose was also largely preventable by cycloheximide (10(-3) mol) or by actinomycin D (150 μg/ml) (Table 2). These results lead to the conclusion that blue light may induce the synthesis of PK by supplying free sugars at the site of enzyme synthesis. The assumption is supported by the observation that in hot water extracts of blue illuminated cells in which glucose oxidation had been poisoned by. 10(-2) mol monoiodoacetic acid there was 60% more glucose, glucose-6-phosphate, fructose-6-phosphate and sucrose detectable than in extracts of equally poisoned algae from darkness (Table 3). It is suggested that blue light activates a system for the transport of sugar out of the chloroplast, which results in the induction of respiratory enzyme synthesis and thus in enhanced respiration.
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