摘要:

AbstractThe activity of the photosynthetic enzyme carboxydismutase (ribulose‐l,5‐diphosphate carboxylase) was measured in leaf extracts of a number of higher plant species from habitats with greatly contrasting light intensities. Plants occupying sunny habitats and capable of light saturated rates of photosynthesis several times higher than those growing in the deep shade of redwood forests also have a considerably higher carboxydismutase activity. Thus, when expressed on the basis of total chlorophyll or even fresh weight, the enzyme activity is several times greater among the sun than among the shade species.The comparatively low content of soluble protein in the shade plants indicates that their content of enzymes other than carboxydismutase also is low. Nevertheless, the activity of carboxydismutase even on the basis of soluble protein appears to be significantly higher in the sun than in the shade species.It is concluded that low carboxydismutase activity probably is one of the factors that limit the capacity for light saturated photosynthesis in the shade pla

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07225.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractCell‐free preparations ofChlorella pyrenoidosaChick, van Niel's strain, were assayed for oxidative enzymes, utilizing isotopic and spectrophotometric techniques. The enzyme activity of heterotrophic and autotrophic cells was compared.The study was divided into categories, one concerned with the spectrophotometric detection of enzymes involved in the initial reactions of glycolysis and the hexose monophosphate shunt, and the other with the direct oxidation of glucose as compared with that oxidized via glycolysis. The reduction of pyridine nucleotides in crude extracts was studied with glucose, glucose‐6‐phosphate, 6‐phosphogluconate, and fructose‐1‐6‐diphosphate as substrates. Enzymes detected in both heterotrophic and autotrophic cells were hexokinase, fructose‐diphosphate‐aldolase, NAD‐linked 3‐phosphoglyceraldchyde dehydrogenase, glucose‐6‐phosphate dehydrogenase, 6‐phosphogluconate dehydrogenase, and a NADP‐linked 3‐phosphoglyceraldchyde dehydrogenase.In addition to isotopic studies designed to make an appraisal of the hexose monophosphate shunt, a comparison of the rate of reduction of NADP by glucose‐6‐phosphate and 6‐phosphogluconate in relation to the reduction of NAD by 3‐phosphoglyceraldehyde was made in light‐ and dark‐grown cells. The rate of reduction of NADP appeared to be lowered in the light‐grown cells, suggesting, as did also the isotopic studies, that the hexose monophosphate shunt is less active in autotrophi

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07226.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractThe inability of several obligately thermophilic bacteria to grow at or below 37°C in common laboratory media was shown to be caused by inhibitors present in these media. The inhibitors could be removed by extraction with chloroform and by adsorption on ion exchange resins or starch. It was concluded that they were of organic nature, probably bile acids. Four laboratory strains ofBacillus stearothcrtno‐philusgrew readily at 37°C in detoxified media. With one of them (NCA 1503) growth was obtained at 34–35°C. A fresh soil isolate having a minimum growth temperature of 40°C in glucose nutrient broth grew at 30°C in this medium after the inhibitors had been

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07227.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractThe hydrolysis of inorganic pyrophosphate has been studied in cell‐free extracts prepared at different stages of development ofDictyostelium discoideum. Two enzyme reactions, pH optima 7.25 and 9.0, appear specific for inorganic pyrophosphate and have an absolute requirement for a divalent cation, preferably Mg2+. The enzyme specific activities do not change significantly during differentiation. Neither enzyme reaction is inhibited by orthophosphate and the presence of exogenous potassium phosphate does not affect the levels of pyrophosphalase at any stage. Exogenous glucose raises the pyrophosphatase levels in the sorocarp

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07228.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractThe pathway (s) of glucose degradation in detached senescent and non‐senescent tobacco leaves from plants approximately 100 days old were studied utilizing‘Relabeled carbohydrates. Comparable samples of each tissue were allowed to metabolize glucose‐1‐ and glucose‐6‐14C and C6/C1ratios were computed from the radioactivity of14CO2collected. Two methods of calculation were compared.Hexose monophosphate pathway activity was also compared in both ages of tissue by measuring14CO2respired from substrate ribose‐1‐, xylose‐1‐ and gluconic acid‐6‐14C.The results indicate that the hexose monophosphate pathway accounts for approximately 25 percent of the respired CO2in both senescent and non‐senescent tissues. Both types of tissue were equally efficient in degrading HMP s

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07229.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractThe formation of capture organs for nematodes in A. oligospora. and its dependence on substrate composition and additions of animal origin was studied in laboratory experiments. Variations in only the substrate composition did not give rise to capture organ formation. If nematodes were present, however, the medium composition was of great importance for the number of traps formed. Capture organs were not only formed in the presence of nematodes but also by addition of other taxonomically diverse animals such as earthworms, fly‐larvae and spring‐tails. The initialing factor is, for full effect, bound to the living state and not confined to nematodes. For biological control of nematodes with the aid of nematode‐trapping fungi, therefore, the effect of the other microfauna of the soil should also be taken into consider

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07230.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractThe diatomsDitylum brightwelliiandNitzschia turgidulawere grown in semi‐continuous culture under various combinations of light intensity, temperature and daylength (photoperiod). Growth was strongly limited by light intensities below 0.03 cal/em2. min in both species. Above this intensity, light saturation of growth was rapidly approached in Nitzschia but only gradually so in Ditylum. The growth rate in continuous light was never significantly higher than with 16 hours of light plus 8 hours of dark. In Ditylum, continuous light above 0.03 cal/cm2. min caused a strong inhibition of growth at all temperatures. The chlorophyll concentration in the cells was greater the shorter the photopceriod. In cultures synchronised by different combinations of light intensity and photoperiod, cell division generally took place in the light. Synchrony was best under short photoperiods of bright light. Time courses are shown for chlorophyll synthesis and photosynthesis in synchronised culture

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07231.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractThe senescent leaf disks fromBrassica rapaL. were floated on a medium containing14C‐L.‐leucine in the presence or absence of kinetin. The increase in radioactivity in protein fraction of kinetin‐treated disks was almost linear with time, while the increase in untreated disks incubated for 3 days started to slow down. The leaf disks were first incubated on the solution of14C‐L‐leucine and then transferred to either kinetin solution or water in order to study whether the slower incorporation is due to the decreased rate of protein synthesis or that of protein retention. The decrease in radioactivity of disks floated on kinetin was slower than that of disks floated on water. The slower decrease in radioactivity caused by kinetin was not due to an increased turnover rate, since the same phenomena were observed in the presence of cold leucine or casein hydrolysate solution. These results suggest that kinetin retards the decomposition of protein in leaf disks and does not stimulate the synthesis of the bulk o

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07232.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractMeasurements of the fraction of the incident light absorbed by diverseSolidagoleaves revealed that differences in light harvesting capacity cannot explain the differences in efficiency of utilization of weak light in photosynthesis that have previously been shown to exist between sun and shade ecotypes when these have been grown in strong light and between identical clones of shade ecotypes when grown at different light intensities. Photosynthesis measurements at low and normal oxygen concentrations, provided no evidence that a different degree of inhibition of photo‐synthetic CO2uptake by atmospheric oxygen is responsible for the observed differences in photosynthetic efficiency, at low or high light intensities. These results support the conclusion that the markedly less efficient use of weak light by shaded habitat clones grown in strong as compared with weak light is caused primarily by damage to the photosystems, or to a site close to them. Measurements of Emerson enhancement and of light‐induced absorbance changes provide some evidence that photoreaction II is more affected than I.Enzyme extracts prepared from clones native to an exposed habitat were found to contain considerably higher activities of carboxydismutase (ribulosc‐l,5‐diphos‐phate carboxylase) than from clones native to a shaded habitat when the plants were previously grown at a moderately high light intensity. Exposed habitat clones apparently have a genetically determined, higher capacity to produce the carboxyla‐tion enzyme than shaded habitat clones. The high degree of correlation found when the light‐saturated rate of CO2uptake invivoof a number of individual Solidago leaves is plotted against the carboxydismutase activities found in the extracts of these same leaves suggests that low carboxydismutase activity is one of the intrinsic properties responsible for the low capacity for light‐saturated photosynthesis of clones from shaded habitats.It is concluded from this and other investigations that differentiation between plants from habitats with contrasting light intensities, whether unrelated species or ecotypos of the same species, probably involves the capacity of several component steps of the photosy

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07233.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

AbstractThe effect of a range of externally supplied carbon Compounds on the growth ofPhaeodactylum tricornutumBohlin in the dark and in the light has been studied. No substance tested was capable of supporting growth of the diatom in The dark and it appears that the organism is obligately phototropic. P. tricornutum is able to respire glucose, mannitol and lactate without the energy released being apparently available for growth. Some slight stimulation of growth occurs in The light and this appears to be partly due to the occurrence of trace element impurities in the organic compounds.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1968.tb07234.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY