D-LACTATE UTILIZATION BY GONIUM (CHLOROPHYCEAE)1

Acetate, glucose, pyruvate, and lactate utilization as Carbon sources have been investigated in 3 strains of Gonium multicoccum, 2 of G. octonarium, and 1 of G. quadratum. In all strains, growth was supported with acetate, pyruvate and dl -lactate in continuous light. These species commonly utilized d -lactate for growth as a carbon source in the light, but there was no effect in the dark. However, they could not utilize l -lactate for growth in light or darkness.     

GROWTH,PHYSIOLOGY, AND ULTRASTRUCTURE OF A DIAZOTROPHIC CYANOBACTERIUM,CYANOTHECE SP. STRAIN ATCC 51142, IN MIXOTROPHIC AND CHEMOHETEROTROPHIC CULTURES1

The growth, physiology, and ultrastructure of the marine, unicellular, diazotrophic cyanobacterium, Cyanothece sp. strain ATCC 51142, was examined under mixotrophic and chemoheterotrophic conditions. Several organic substrates were tested for the capacity to support heterotrophic growth. Glycerol was the only substrate capable of enhancing mixotrophic growth in the light and supporting chemoheterotrophic growth in the dark. Dextrose enhanced mixotrophic growth but could not support chemoheterotrophic growth. Chemoheterotrophic cultures in continuous darkness grew faster and to higher densities than photoautotrophic cultures, thus demonstrating the great respiratory capacity of this cyanobacterial strain. Only small differences in the pigment content and ultrastructure of the heterotrophic strains were observed in comparison to photoautotrophic control strains. The chemoheterotrophic strain grown in continuous darkness and the mixotrophic strain grown in light/dark cycles exhibited daily metabolic oscillations in N₂ fixation and glycogen accumulation similar to those manifested in photoautotrophic cultures grown in light/dark cycles or continuous light. This “temporal separation” helps protect O₂-sensitive N₂ fixation from photosynthetic O₂ evolution. The rationale for cyclic glycogen accumulation in cultures with an ample source of organic carbon substrate is unclear, but the observation of similar daily rhythmicities in cultures grown in light/dark cycles, continuous light, and continuous dark suggests an underlying circadian mechanism.     

Photo-Assimilation of Acetate by an Obligate Phototrophic Strain of Euglena gracilis

SYNOPSIS. Light-dependent incorporation of acetate occurs in an obligate phototrophic strain of Euglena gracilis (strain L). Assimilation is into all major biochemical fractions. Acetate does not induce operation of the glyoxylate by-pass as it does in heterotrophic strains; neither does it stimulate oxygen consumption. Acetate will not replace CO₂ in phototrophic growth. A number of carbon sources tested would not support growth in the dark, and glucose was not incorporated either in the light or the dark.     

Acetate Metabolism by an Obligate Phototrophic Strain of Pandorina morum1

SYNOPSIS. Acetate metabolism was studied in 2 strains of the green alga Pandorina morum. Both strains were capable of mixotrophic growth in the light, but only one strain was capable of heterotrophic growth in the dark. ¹⁴C-2-acetate uptake by both strains was studied in the light and dark, in the presence and absence of CO₂ and 3(3,4-dichlorophenyl)-1,1-dimethylurea (10^?5M). The distribution of radioactivity incorporated into the insoluble, aqueous and chloroform soluble fractions of the cells was determined. The strain incapable of heterotrophic growth in the dark was found to incorporate very little acetate in the dark, and its ability to incorporate acetate into the insoluble fraction was severely limited under all conditions. Incorporation into the aqueous and chloroform-soluble fractions in the light was similar in both strains. The reduced incorporation into the insoluble fraction was almost totally the result of limited incorporation of acetate into polysaccharides by the obligate phototrophic strain.     

On the physiology of the red alga Asterocytis ramosa in axenic culture

The red alga Asterocytis ramosa has been cultivated aseptically in artificial seawater ASP6 F. The alga shows optimal growth at 22·5–25° C. Optimal light conditions as well as phosphorus and nitrogen requirements were investigated. Nitrate and ammonium salts as well as organic nitrogen can be used as a nitrogen source. Arginine was an extremely good source of nitrogen, presumably because it splits off urea. Asterocytis is vitamin B₁₂ heterotrophic and growth is obtained with cyanocobalamin, Factor III and Factor Z₁. A mixture of other vitamins gives further stimulation. In the newly isolated culture, hexoses and pentoses enhanced growth. Acetate increased growth in an old axenic culture. In darkness no growth was obtained.     

Influence of gibberellin biosynthesis inhibitors on stem elongation and floral initiation on in vitro chicory root explants under dark and light conditions

Root explants of chicory (Cichorium intybus L.) were cultured in vitro under continuous light or darkness. On a standard medium (no plant growth regulators added), flowering-stems were initiated under continuous light while under continuous dark, vegetative-stems were formed. Different types of GA (gibberellin) biosynthesis inhibitors were added to the culture medium. Paclobutrazol and compounds belonging to the group of cyclohexanetriones clearly reduced flowering-stem growth under light conditions and vegetative-stem growth under dark conditions. Under light conditions, flower bud initiation was not affected. These and other results suggest that GA₁ may be synthesized during the in vitro culture period and that it controls flowering-stem growth but not floral initiation.Abbreviations CCC chlormequat chloride - GA gibberellin - LAB 198 999 3,5-dioxo-4-butyryl-cyclohexane carboxylic acid ethyl ester - BAS 111..W 1-phenoxy-3-(1H-1,2,4-triazol-1-yl)-4-hydroxy-5,5-dimethylhexane     

CIRCADIAN GROWTH RHYTHM IN JUVENILE SPOROPHYTES OF LAMINARIALES (PHAEOPHYTA)1

A circadian rhythm in growth was detected by computer-aided image analysis in 3–4-cm-long, juvenile sporophytes of the kelp species Pterygophora California Rupr. and in seven Laminaria spp. In P. californica, the free-running rhythm occurred in continuous white fluorescent light, had a period of 26 h at 10°or 15°C, and persisted for at least 2 weeks in white or blue light. The rhythm became insignificant in continuous green or red light after 3 cycles. Synchronization by white light-dark regimes, e.g. by 16 h light per day, resulted in an entrained period of 24 h and in a shift of the circadian growth minimum into the middle of the light phase. A morning growth peak represented the decreasing portion of the circadian growth curve, and an evening peak the increasing portion. The circadian growth peak was not visible during the dark phase, because growth rate decreased immediately after the onset of darkness. At night, some growth still occurred at 16 or 12 h light per day, whereas growth stopped completely at 8 h light per day, as in continuous darkness. During 11 days of darkness, the thallus area became reduced by 3.5%, but growth rate recovered in subsequent light–dark cycles, and the circadian growth rhythm reappeared in subsequent continuous light.     

The early stages of mildew colony development on susceptible oats

The chronology of primary infection by Erysiphe graminis f. sp. avenae on detached leaves of a susceptible host, and growth patterns of the primary haustorium and secondary hyphae, proved similar to those of wheat and barley mildew found by other workers. The timing of formation and subsequent growth of the primary haustorium was not affected by the light regime, but the formation of subsequent haustoria was highly synchronous under an alternating dark/light cycle, and far less so under continuous illumination. Five days after inoculation almost twice as many secondary and tertiary haustoria were formed per colony under the dark/light treatment than under continuous light. Because of the synchronous formation of haustoria subsequent to the primary, haustoria selected at random from leaves of susceptible host cultivars showed a bimodal distribution in length, the less well developed tertiary haustoria being distinguished from earlier formed primary and secondary haustoria. There was also a significant positive correlation between length and the number of digitate processes/haustorium. The energy required to produce one secondary haustorium was calculated to be equivalent to that required to produce approximately 4–7 hyphal cells.     

Occurrence of cytochrome c-554 in a facultative methylotroph,Protaminobacter ruber strain NR-1, during bacteriochlorophyll formation

A facultative methylotroph, Protaminobacter ruber was grown under two different conditions (aerobically grown under light, and aerobically in the dark after a light period). Bacteriochlorophyll was synthesized inducibly in the cells which were initially grown in the ligt and then grown in the dark, while bacteriochlorophyll was not found in the cells cultured under continuous light. Cytochrome c-554 was solely synthesized parallel to bacteriochlorophyll after switching from light to dark conditions. Both cytochrome c-554 and bacteriochlorophyll levels in the membrane preparation reached to a plateau in 24 h after switching from light and dark conditions. This cytochrome was membrane-bound and its M _r was 45,000 by sodium dodecylsulfate polyacrylamide gel electrophoresis. The midpoint potential was 358 mV at pH 7. Other major membrane-bound cytochromes and two soluble cytochromes were present in both types of cells and their content did not change irrespective of growth conditions.Abbreviations SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis - Bchl bacteriochlorophyll     

INDUCTION OF SPORE GERMINATION IN SCHIZAEA PUSILLA (SCHIZAEACEAE)

Requirements for spore germination in the rare and native New Jersey fern, Schizaea pusilla Pursh., were examined. Spores did not germinate in darkness and gibberellins (GA) did not induce germination in the dark. However, a dark pretreatment promoted germination in a subsequent light treatment and low temperatures during the dark pretreatment greatly enhanced germination in culture. Three wks of dark pretreatment were required for maximum germination. GA₃ promoted germination in red light more effectively than GA₄₊₇. Greater than ten days of continuous illumination was necessary for germination. Spores given red light reached half-maximum germination six days earlier than spores under white light. Red light promoted germination while blue light did not. Far-red light alone could stimulate germination and enhanced the promotive effect of red light; typical phytochrome photoreversibility was not observed. Blue light reduced the effect of red light.     

The effect of light on the endogenous levels of cytokinins and gibberellins in seeds of sitka spruce (Picea sitchensis Carriere)

Abstract Maximum germination of Sitka spruce seed was obtained at 22°C under continuous fluorescent light or following a single 10 min exposure to red light (RL) given after 48 h of dark imbibition. The levels of endogenous cytokinins and gibberellins were examined in seeds which were exposed to different light regimes. Cytokinin levels in Sitka spruce seeds increased approximately 1.7–fold during exposure to continuous white light, during dark stratification, or within 1 h or a 30 min exposure to RL. A single peak of activity could be eluted from the LH^?20 Sephadex column which appeared in the same volume as authentic zeatin riboside. Gibber-ellin activity in Sitka spruce seeds increased rapidly during exposure to 30 min of RL and then declined during subsequent dark incubation. Similarly, under continuous white light, gibberellin activity was at least twice as high as in the dark. Two gibberellm-like substances were found in Sitka spruce seeds which appeared to be similar to GA₇ and GA₉ on the basis of their chromato-graphic properties. The zone of gibberellin activity directly associated with photo-excitation of Sitka spruce seeds contains conjugate gibberellins, possibly glucosyl esters, which when hydrolysed with β-glucosidase form two products which are similar to the free gibberellins which were detected. The light response in Sitka spruce seed is compared to a similar response in Scots pine (Pinus sylvestris L.) seeds.     

Effects of Kinetin, Gibberellins and (±) Abscisic acid on the Germination of Lettuce (Lactuca sativa)

Germination responses of achenes of lettuce (Lactuca sativa L, cv. Arctic King) to treatment with kinetin, gibbe-rellins and abscisic acid were examined over a range of temperatures: in both light and dark. Kinetin (0.1–10 mg/l) strongly promoted germination at temperatures above 27±C in continuous light or after short periods of illumination during the early stages of imbibition. It also relieved the inhibitory affects of abscisic acid in these conditions. In total darkness however kinetin treatment resulted in only a minor promotive effect. Treatment with gibberellic acid (A₃) or a mixture of gibberellins A₄ and A₇ were much less effective in promoting germination at higher temperatures of lettuce achenes exposed to light but were strongly promotive in the dark.     

Investigation of the dark metabolism of acetate in photoheterotrophically grown cells ofRhodospirillum rubrum

The mechanism of the aerobic dark assimilation of acetate in the photoheterotrophically grown purple nonsulfur bacteriumRhodospirillum rubrum was studied. Both in the light and in the dark, acetate assimilation inRsp. rubrum cells, which lack the glyoxylate pathway, was accompanied by the excretion of glyoxylate into the growth medium. The assimilation of propionate was accompanied by the excretion of pyruvate. Acetate assimilation was found to be stimulated by bicarbonate, pyruvate, the C₄-dicarboxylic acids of the Krebs cycle, and glyoxylate, but not by propionate. These data implied that the citramalate (CM) cycle inRsp. rubrum cells can function as an anaplerotic pathway under aerobic dark conditions. This supposition was confirmed by respiration measurements. The respiration of cells oxidizing acetate depended on the presence of CO₂ in the medium. The fact that the intermediates of the CM cycle (citramalate and mesaconate) markedly inhibited acetate assimilation but had almost no effect on cell respiration indicated that citramalate and mesaconate were intermediates of the acetate assimilation pathway. The inhibition of acetate assimilation and cell respiration by itaconate was due to its inhibitory effect on propionyl-CoA carboxylase, an enzyme of the CM cycle. The addition of 5 mM itaconate to extracts ofRsp. rubrum cells inhibited the activity of this enzyme by 85%. The data obtained suggest that the CM cycle continues to function inRsp. rubrum cells that have been grown anaerobically in the light and then transferred to the dark and incubated aerobically.     

NUTRITION OF PLATYDORINA CAUDATA KOFOID

The vitamins p-aminobenzoic acid, thiamine, biotin, nicotinamide, and B₁₂ were tested for their ability to stimulate growth. Only vitamin B₁₂ was required. Urea and NaNO₂ supported excellent growth, although sodium nitrite, ammonium nitrate, and the Casamino acids supported only fair growth. Platydorina grew aerobically in the absence of an exogenous source of carbon; however a carbon source was required for anaerobic growth. Of 25 carbon compounds examined, isocitrate supported anaerobic growth in the light equalling the aerobic controls. Growth did not occur aerobically or anaerobically in the dark with any carbon source examined. Growth was excellent at pH values in excess of 7.0. Growth at pH 10.0 was 4 times that at 7.0 in strain I.U. 850 and twice that at 7.0 in strain Kan-3E. Growth was accelerated with the increase in temperatures but this increase may well be due to the increased intensity of light to which the cultures were exposed at the higher terperatures.     

Germination ecology of invasive alien Anthemis cotula helps it synchronise its successful recruitment with favourable habitat conditions

Anthemis cotula is a widespread invasive alien species in Kashmir Himalaya. Being a winter annual, the species reproduces entirely by achenes and synchrony between germination requirements of the species and the habitat conditions must be of critical importance in its invasiveness. To examine how the achenes of different ages respond to different environmental cues, two laboratory experiments were performed wherein effects of different nitrogen applications and growth hormones under continuous light and dark conditions were explored. Results show that the achenes are positively photoblastic and have requirement for after‐ripening. Nitrogen applied either as potassium nitrate or as thiourea significantly improved achene germination both under continuous light and dark conditions. Although kinetin (6‐furfurylaminopurine) did not influence achene germination, gibberellic acid (GA₃) applied at 1.0 mM concentration had the most significant effect on the final percentage germination under both light and dark conditions. These results suggest that the achenes have an elaborate mechanism of sensing the habitat conditions that helps them to synchronise their germination with favourable environmental conditions – a strategy that aids the species in ensuring recruitment, survival and its spread in Kashmir Himalaya.     

The Effect of the Plant Growth Retardants Amo 1618 and CCC on Gibberellin Production in Fusarium monili-forme: Light Stimulated Biosynthesis of Gibberellins

Through the use of a single gene dwarf mutant of Zea mays L., dwarf-1, the interaction of growth retardants with gibberellin biosynthesis was studied in Fusarium monitiforme. It was demonstrated that the growth retardants 2-isopropyl-4-dimcthylamine-5-methyphenyl-1-piperidine-cai'boxylate methyl chloride (Amo 1618) and (2-chloroethyl) trimethylammonium chloride (CCC) are more effective inhibitors of gibberellin biosynthesis in cultures maintained under continuous illumination. Light grown cultures produced significantly more biologically active gibberellin-like materials than dark grown cultures. Stock cultures exposed to light also promoted the subsequent biosynthesis of gibberellins in the dark. Chromatographical analysis of the soluble gibberellins extracted from the culture medium revealed that large amounts of chromatographically detectable A₃ and A₇ were produced in light cultures with only A₇ produced in the dark. Light also induced a greater incorporation of acelate-2-¹⁴C into the gibberellins A₇, A₃ and an unidentified gibberellin. Growth returdants occasionally caused a complete disappearance of chromatographically detectable gibberellins in the dark; however, in the light at no concentration tested was it possible to detect the complete disappearance of gibberellin-like material. A₃ was always detectable. Like higher plants, different strains of F. moniliforme exhibit variation which makes them more or less sensitive to the growth retardants. This variation is interpreted to mean that there may be more than one pathway leading to the synthesis of the gibberellins.     

Physiological characterisation of Colletotrichum gloeosporioides,the incitant of anthracnose disease of noni in India

Ten isolates of Colletotrichum gloeosporioides were collected from different noni growing areas of Tamil Nadu, Karnataka and Kerala in India and their pathogenicity was proved under glass house conditions. Effect of different pH levels, temperature, light intensity and media were tested against the growth of C. gloeosporioides under in vitro. The results indicated that the growth of C. gloeosporioides was maximum in pH range of 6.50–7.00 and temperature range of 25–30°C. Exposure of the fungus to alternate cycles of 12 h light and 12 h darkness resulted in the maximum mycelial growth of C. gloeosporioides compared to the 24 h exposure to continuous light and 24 h exposure to continuous dark. Among the different media tested, host leaf extract medium supported significantly the maximum growth of all the 10 isolates of C. gloeosporioides followed by potato dextrose agar. Further, the strains were found to vary morphologically between the isolates under the study.     

Possible control of gibberellin-induced release of temperature-dependent primary dormancy in seeds of celery (Apium graveolens L.) by transmembrane ion fluxes

The temperature-dependent primary dormancy of cv Florida 683 celery seeds in darkness was broken by GA_4/7 (2 × 10^-4 M) alone but other growth regulators such as BA, ethephon or daminozide were necessary to break dormancy of cv Lathom Blanching seeds in the presence of GA_4/7 at this concentration. Although AgNO₃ partially inhibited both the ethephon- and BA- induced germination of cv Lathom Blanching seeds in the presence of GA_4/7 in the dark it did not affect the promotive action of daminozide. Ethephon did not overcome the inhibitory action of high concentrations of AgNO₃ in the light. The ethylene synthesis inhibitor aminoethoxyvinylglycine (AVG) did not inhibit the germination of cv Lathom Blanching seeds induced by growth regulators in the dark or in the absence of growth regulators in the light. Fusicoccin (FC) did not break celery seed dormancy unless applied in the presence of GA_4/7. Germination of cv Lathom Blanching celery seeds treated with GA_4/7 at 16°C in the dark was inhibited by the K⁺ ionophore benzo-18-crown-C-6 (18-C-6) and in the presence of Ca²⁺ by the Ca²⁺ ionophore A23187; the 18-C-6 inhibition was reversed by BA.It is concluded that the involvement of gibberellin in celery seed dormancy is not dependent on endogenous ethylene and is directly or indirectly controlled through the action of other hormones on transmembrane ion fluxes.     

CO2-Fixation and ATP synthesis in continuous cultures of Chlorella fusca

In continuous cultures of Chlorella fusca under steady state conditions, the CO₂-fixation rate, the ATP-level, the apparent rate of photophosphorylation as calculated from the changes in the ATP-level during light to dark or dark to light transients and the energy charge were measured at various environmental conditions. During growth the energy charge was around 0.64. CO₂-assimilation and the apparent ATP-synthesis were strongly dependant on light intensity, however the ATP-level was independant on it. Since the rates of apparent ATP-synthesis and of the CO₂-fixation do not seem to be strictly correlated in a logic way when environmental factors are changed and furthermore the stoichiometry of 3 ATP necessary per CO₂ fixed was never achieved, the described method frequently used for procaryotes to determine the in vivo rate of phosphorylation does not give valid results in highly compartimented eukaryotic cells.