Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Sokawa et al. suggest that rel^- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.     

EFFECT OF LIGHT ON THE CHLOROPHYLL FORMATION IN THE "GLUCOSE-BLEACHED" CELLS OF CHLORELLA PROTOTHECOIDES

1. Previous studies have shown that when Chlorella protothecoidesis grown in a medium rich in glucose and poor in nitrogen source(urea), apparently chlorophyll-less cells with profoundly degeneratedplastids—referred to as "glucose-bleached cells—areproduced either in the light or in darkness. When the glucose-bleachedcells are incubated in a medium enriched with the nitrogen sourcebut without added glucose, an active formation of chlorophylloccurs after a certain lag period under illumination, whilein darkness a very small amount of chlorophyll is formed atabout the same time as in the light. The stimulating effectof light on the chlorophyll formation is not appreciably affectedwhen the photosynthetic CO₂-fixation of greening algal cellsis blocked by the addition of CMU. In the present study, itwas further found that the light-enhanced chlorophyll formationproceeds, although at a somewhat lower rate, under aerationof CO₂-free air. All the experiments in this work were doneunder these non-photosynthetic conditions to exclude any influenceof photosynthates.
2. The effect of light (from daylight fluorescentlamps) on thechlorophyll formation in the glucose-bleachedalgal cells wassaturating at about 1,000 lux. Blue light wasfound to be mosteffective; yellow, green and red light followingin the orderof decreasing effectiveness.
3. When the bleachedalgal cells were illuminated for a short periodin the lag phaseof chlorophyll formation and subsequently incubatedin darkness,there occurred an appreciable enhancement of chlorophyllformationin the dark. When the short illumination was appliedat differenttimes of the lag phase, the enhancement was inducedto almostthe same extent. But the longer the duration of theilluminationduring the lag phase, the greater was the enhancementof chlorophyllformation in the subsequent dark incubation.In such experimentsblue light was most effective and red lightleast, as it wasthe case in the experiments of continuous illumination.An intervenientillumination of the bleached cells at lowertemperatures orunder the atmosphere of N2 produced little orno enhancementof the chlorophyll formation in the subsequentdark incubation.
4. Based on these results, it was concluded that the light enhancementof chlorophyll formation in the glucose-bleached algal cellsis mediated by a non-chlorophyllous photoreceptor(s), absorbingmaximally blue and yellow light, and that a light-induced changeof the photoreceptor is immediately followed by a certain dark(temperaturedependent and aerobic) process(es) which is connected,directly or indirectly, to the chlorophyll synthesis.

(Received August 10, 1967; )     

EFFECTS OF LIGHT ON THE DEOXYRIBONUCLEIC ACID FORMATION AND CELLULAR DIVISION IN CHLORELLA PROTOTHECOIDES

1. It has been demonstrated previously that when Chlorella protothecoidesis grown in a medium rich in glucose and poor in nitrogen source(urea), chlorophyll-less cells with markedly degenerated plastids—called "glucose-bleached" cells—are produced eitherin the light or in darkness. When the glucose-bleached cellsare incubated in a medium enriched with the nitrogen sourcebut without added glucose, normal green cells with fully organizedchloroplasts are obtained in the light, and pale green cellswith partially organized chloroplasts in darkness. During theseprocesses of chloroplast development in the glucose-bleachedcells, there occurs, after a certain lag period, an active DNAformation followed by a more or less synchronous cellular division.In the present study the effects of light on the DNA formationand cellular division were investigated in the presence of CMUor under aeration of CO²-free air to exclude the interveninginfluence of photosynthetic process.
2. It was revealed thatlight severely suppresses the DNA formationand cellular divisionof the glucose-bleached cells while enhancingremarkably theirgreening. The suppression was saturated atthe light intensityof about 1,000 lux. Blue light was mosteffective, being followedby green, yellow and red light inthe order of decreasing effectiveness.
3. Further experiments unveiled that light exerts two apparentlyopposing effects on the DNA formation depending upon the timeof application during the incubation of algal cells. When thealgal cells were illuminated only during the lag period beforethe active DNA synthesis, there occurred an enhancement of theDNA synthesis occurring during the subsequent dark incubation.When, on the other hand, the cells were transferred to the lightfrom darkness at or after the start of the DNA synthesis, itcaused an almost complete abolition of the subsequent synthesisof DNA in the algal cells. No such effects of light were observedwith RNA and protein (total)
4. These findings were discussedin relation to the process ofchlorophyll formation occurringconcurrently in the algal cells.

(Received August 10, 1967; )     

Suppressive effect of light on the formation of DNA and on the increase of deoxythymidine monophosphate kinase activity in Chlorella protothecoides

As previously demonstrated, chlorophyll-less cells of Chlorellaprotothecoides are obtained when the alga is grown in a mediumrich in glucose and poor in a nitrogen source (urea). When thesecells are incubated in a medium enriched with a nitrogen source,there occurs, besides greening of algal cells, an active formationof DNA followed by synchronous cellular division. The DNA formationand cellular division are markedly suppressed by light of acomparatively low intensity. Blue light is most effective andred light least effective in suppression. The effect of light on the level of dTMP kinase activity inthe algal cells was investigated in relation to the photoinhibitionof DNA formation. It was found that light suppresses the increaseof dTMP kinase activity in the algal cells which starts in advanceof active DNA synthesis, and that blue light has a strongersuppressive effect than red light. ¹Present address: Institute of Medical Science, University ofTokyo, Tokyo.