Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta II. Aspects of Photoregulative Reaction

The photoregulation of carotenogenesis in Rhodotorula minutawas found to consist of tow phases, a temperature-independentphotochemical reaction (light process) and temperature-dependentbut light-independent biochemical reactions (dark process).These processes were separately examined by regulating the temperatureand were characterized as follows: 1) The quantity of carotenoid produced [C (µg g^–1)]and the rate of carotenoid production [Vc (µg g^–1hr^–1)] in the dark process were regulated by the lightdose [D (erg cm^–2)] to which cells were exposed in thelight process. These relationships were expressed by the equations:C=9.1 log D–62.0 and Vc=0.81 log D–5.60. This photoresponsefollowed the Roscoe-Bunsen reciprocity law. 2) The induced state toward carotenogenesis, once acquired inthe light process, was very stable, suggesting that the proposedphotochemical product is stable as an inducer of carotenogenesisand decreases only in conjunction with carotenoid biosynthesis. 3) The photochemical reaction was oxygen-independent, but subsequentdark reactions were completely dependent on oxygen. 4) Postulated compounds related to the photochemical reactionwere not metabolized in vivo. (Received September 12, 1981; Accepted February 20, 1982)     

Export, Mobilization, and Respiration of Assimilates in Uniculm Barley during Light and Darkness

The respiratory losses and the pattern of carbon supply froma leaf of unicuim barley were examined during a complete diurnalperiod using a steady state ¹⁴C-labelling technique. After a delay of c. 1 h a portion of the ¹⁴C exported from acontinuously assimilating leaf was lost in respiration in thelight. This respiratory loss amounted to c. 20% of the total¹⁴C fixed. A further 28% of the total ¹⁴C fixed was respiredduring the dark period. In the light, carbon was fixed at a rate of c. 8·9 mgC dm^{–2 h–1} and exported from the leaf at ^c. 5·3mg C dm^{–2 h–1}. Dark export averaged ^c. 31% of theday-time rate. Carbohydrate was stored in the leaf during the day and was almostcompletely remobilized during the dark. Sucrose, the major reservecarbohydrate, was exported first whilst the starch level remainedconstant. After some 9 h of darkness, sucrose declined to alow level and starch remobilization began.     

Removal by chemicals of photoperiodic light requirements of Lemna gibba G3

Both the initial and the terminal 1 hr portions of the subjectiveday fraction, namely the L1- arid L2-phases, of a 24 hr daymust be illuminated in order for the day to be perceived asa long day in the min-LD determination by the long-day plant,Lemna gibba G3 (9). The light requirement of the L1-phase wassatisfied by a 10 min red light pulse given at the beginningof the phase. The red light effect was erased by a subsequent10 min far-red light, indicating phytochrome-mediated processesoccurring in the L1-phase. The light requirement of the L2-phasewas satisfied by blue or far-red light given during the terminal10 min period of the phase; there was no indication of phytochromeinvolvement. The light action on the L1-phase was replaced by10^–5 M of cyclic AMP or 10^–7 M of DL-isoproterenol.The isoproterenol action was antagonized by 10^–7 M ofDL-propranolol. Cyclic AMP (10^–5 M) combined with salicylicacid (10^–6 M), which can remove the light requirementof the L2-phase (10), rendered a completely dark day physiologicallyequivalent to a long day. Acetylcholine (10^–5 M) exertednyctomimetic action on the L1-phase of the second light day.The action of acetylcholine was antagonized by cyclic AMP (10^–5M). The L2-phase required no light in the presence of 10^–7M of DL-propranolol, and this propranolol action was not affectedby isoproterenol. These findings suggest changes in membranepermeability caused by the light given during the L1- and L2-phases. (Received July 7, 1976; )     

A comparison of net and gross rates of oxygen production as a function of light intensity in some natural plankton populations and in a Synechococcus culture

In vitrorates of gross and net oxygen production were measuredas a function of light intensity in some plankton communitiescollected from Bedford Basin, Nova Scotia, and in a monoclonalculture of Synechococcus. The rate of gross oxygen productionwas measured by a technique in which the stable oxygen isotope,¹⁸O, serves as a photosynthetic tracer Net oxygen productionwas measured by automated Winkler technique. The rate of communityrespiration in the light was then determined by the differencebetween gross and net rates of oxygen production. In the naturalpopulations examined, neither gross nor net oxygen productionrates were significantly inhibited at the highest light intensitymeasured (500–800 µE m^–2 s^–1) In a samplein which the dark respiration rate was small relative to themaximal rate of production [P_max;sensu Platt et al (1980) JMar. Res., 38, 687–701] the rates of ‘light’respiration were 3 times greater. In two other communities,with high rates of dark respiration relative to P_maxthe ratesof ‘light’ respiration were closer to rates of darkrespiration. In the Synechococcus clone, both gross and netoxygen production rates were inhibited at high light intensities.Rates of ‘light’ respiration were found to varyas a function of light intensity. The greatest rates of respirationwere measured in samples incubated at light intensities thatwere just saturating (100 µE m^–2 s^–1). Therates of ¹⁴C production were also measured as a function oflight intensity The photosynthetic quotients, based on ¹⁴C productionrates and gross oxygen production rates, average 1 9     

Photoinhibition under Atmospheric O2, the Activation State of RuBP Carboxylase and the Content of Photosynthetic Intermediates in Soybean and Wheat

Ward, D. A. and Drake, B. G. 1987. Photoinhibition under atmosphericO₂, the activation state of RuBP carboxylase and the contentof photosynthetic intermediates in soybean and wheat.—J.exp. Bot. 38: 1937–1948. Associations between photosynthesis, the activation state ofRuBP carboxylase and the contents of photosynthetic intermediateswere compared in soybean and wheat leaves before and after exposureto photoinhibitory treatments in the presence of atmosphericO₂. Exposing attached leaves to a supra-saturating irradiance(3 800 µmol quanta m^{– 2} s^–1) for 2 h in CO_2-freeair decreased carboxylation efficiency and the light-saturatedphotosynthetic rate in air by approximately 50%. Exposure tothe photoinhibitory treatment for periods in excess of 2 h didnot cause a further decrease of photosynthesis in soybean. Althoughphotosynthesis was reduced, the initial and total (fully-activated)activities of ribulose 1,5-bisphosphate carboxylase (RuBPCase)in leaf extracts were unaltered in each species by the photoinhibitorytreatment. This was true for leaves sampled under both air andat a rate-limiting intercellular CO₂ partial pressure (C_i) of75 µPa Pa^–1. The contents of ribulose l,5-bisphosphate(RuBP) and 3-phosphoglyceric acid (3-PGA) were reduced by thephotoinhibitory treatment in soybean leaves sampled in air andat a rate-limiting C_i, although the RuBP/3-PGA ratio was unaffected.The relative reduction of RuBP content in soybean leaves atrate-limiting C₁ was similar to the corresponding reductionof carboxylation efficiency. For wheat,the relative reductionof RuBP content at rate-limiting C_i (–19%) caused by thephotoinhibitory treatment was considerably less than the correspondingdecrease of carboxylation efficiency (–49%).The RuBP/3-PGAratio of wheat was also increased significantly by the photoinhibitorytreatment The significance of these observations to the regulationof CO₂-limited photosynthesis in leaves experiencing photoinhibitionunder atmospheric oxygen is discussed. Consideration is alsogiven to the previous contention that contemporary measurementsof initial activity in crude extracts may provide a spuriousindication of the amount of the enzyme-CO₂-Mg_{2 +} form of RuBPcarboxylase present in the leaf. Key words: Carboxylation efficiency, RuBP carboxylase, photoinhibition, RuBP, 3-PGA     

Frond and flower production in Lemna gibba G 3 in presence of respiratory inhibitors

Effects of respiratory inhibitors on frond and flower productionin light culture of a long-day duckweed, Lemna gibba G 3, wereinvestigated. The inhibitors examined could be divided into3 groups based on their specific actions: (A) 2,4-Dinitrophenol(10^–6M), arsenate (10^–4M), malonate (10^–2M),o-phenanthroline (10^–6M), ,'-dipyridyl (10^–5M) andazide (10^–6M) inhibited flower production by suppressingthe rate of flower production without affecting the inductionperiod. Frond production, however, was promoted by these reagents.Effective time of application came one day after the end ofthe induction period. (B) Iodoacetate (10^–6M) and fluoride(10^–4M) inhibited both flower production and, less significantly,frond production. Reduced rate of flower production was responsiblefor the inhibition of flowering. Effective time of applicationpreceded by one day that of A group inhibitors. (C) Salicylaldoxime(10^–6M), diethyldithiocarbamate (10^–6M) and 8-hydroxyquinoline(10^–7M) enhanced flower production by reducing the lengthof the induction period, and simultaneously slightly inhibitedfrond production. Effective time of application was the latterhalf of the induction period. The implications of these findingsare discussed with special reference to the component processesinvolved in photoperiodic induction of flowering in duckweed. (Received March 27, 1969; )     

Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta I. Photocontrol of Carotenoid Production

Rhodotorula minuta cells, which have only traces of carotenoidswhen grown in the dark, started carotenoid production with theonset of illumination and the amount increased almost linearlyuntil 70 hr then remained constant thereafter when incubationwas continued under illumination, with the number of cells continuingto increase. The rate of carotenoid production [Vc (µgg^–1 hr^–1)] depended on the intensity of light [I(ergcm^–2 sec^–1)], with the relationship of Vc=0.74 logI–1.46. The final carotenoid content [C(µg g^–1)]of cells incubated under continuous light was also controlledby the light intensity [I], with the relationship of C=52 logI–81. Control of carotenoid production by light occursas a two-phase process consisting of a temperatureindependentphotochemical reaction and light-independent biochemical reactions. (Received September 12, 1981; Accepted February 20, 1982)     

Photoacclimation in the marine alga Nannochloropsis sp. (Eustigmatophyte): a kinetic study

Exponentially growing cultures of Nannochloropsis sp. were transferredfrom high light (650 µ.mol quanta m^–2 s^–1)to low light (30 (µrnol quanta m^–2 s^–1). Thekinetics of changes in the various parameters of the photoacclimationprocess were followed until steady state was reached. In thisorganism, the observed 4.25 increase in cellular chlorophylla in the low-light-acclimated cells was linearly correlatedwith an increase in the number of photosynthetic units (PSU),while the PSU size remained constant. The new steady state wasreached after a transition period of 87 h and following an initialovershoot in the chlorophyll a concentration. During the processof photoacclimation, harvested and utilized light was increaseddue to a combination of increased cellular chlorophyll and anincrease of the quantum yield. These improvements in efficiencywere coupled with the reduction of respiration. The overalleffect of photoacclimation, therefore, amounted to reducingthe impact of low light on the growth rate of the algae. Ourstudy demonstrates the importance of the photoacclimation processin the context of the planktonic way of life. An index of the'effectiveness of photoacclimation' is proposed.     

Evidence for Essential Maintenance Respiration of Leaves of Xanthium Strumarium at High Temperature

Mesophyll resistance to photosynthetic carboxylation (r'_m) wasused as a criterion for leaf integrity. It was measured, at25 °C, in the light, before and after periods of high temperature(3 h at 38 °C) in the dark. During the high temperatureperiods, respiration (R_D) of attached leaves of Xanthium strumariumwas suppressed from 27%-36% by either low [O₂] (1.04% or 0.21%v.v.) or high [CO₂] (840 µl 1^–1) in the ambientair. Neither treatment affected rates of R_D or photo-respirationduring the second period at 25 °C. There was no significant increase of r'_m when R_D was not suppressedduring the high temperature treatment. When R_D was suppressedat high temperatures, r'_m increased from about 3s cm^–1before, to about 26 s cm^–1 after the high temperaturetreatment. The increase depended upon the degree of suppression. It is concluded that increased R_D at high temperature in Xanthiumleaves is partly the result of an increase of energy demandingmaintenance. The subsequent rate of carbon dioxide fixationis reduced when this increase of maintenance-induced respirationis inhibited.     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.     

Environmental Anoxia is Unnecessary for Inhibiting Chloroplast Photomorphogenesis in Rice Coleoptiles (Oryza sativa L.)

High population densities of germinating rice seedlings in initiallyair-saturated sealed aquatic environments exhibited d^–seedling growth consisting solely of coleoptile emergence inlight and dark environments. Residual oxygen tensions of 17–23%of the initially air-saturated water containing the d^–seedlings were evident after 15 d in both the light and dark.Coleoptiles of all d^– seedlings were stark white in appearance,lacked protochlorophyllide, and contained proplastids and amyloplasts,there being no evidence of normal etioplast development in thelight or dark and no chloroplast development in the light. Thus,complete environmental anoxia was observed to be unnecessaryfor inhibiting normal chloroplast photomorphogenesis in coleoptilesof light-germinated rice seedlings. Increasing the oxygen tensionsof the 15-d-old aquatic environments of light- and dark-germinatedd^– seedlings placed in the light resulted in normal chloroplastphotomorphogenesis in coleoptiles, shoots, and roots. Key words: Oryza sativa, environmental anoxia, chloroplast photomorphogenesis, rice coleoptiles     

Diurnal regulation of NO3- uptake in soybean plants I. Changes in NO3- influx, efflux, and N utilization in the plant during the day/night cycle

The effect of light on NO₃^– utilization was investigatedin non-nodulated soybean (Clycine max L. Merr., cv. Kingsoy)plants during a 14/10 h light/dark period at a constant temperatureof 26C. A 30–50% decrease of net NO₃^– uptake ratewas observed 2–6 h after the lights were turned off. Thiswas specifically due to an inhibition of NO₃^– influx asmeasured by ¹⁵N incorporation during 5 min. The absolute valuesof NO₃^– efflux depended on whether the labelling protocolinvolved manipulation of the plants or not, but were not affectedby illumination of the shoots. Darkness had an even more markedeffect in lowering the reduction of ¹⁵NO₃^– in both rootsand shoots, as well as xylem transport of ¹⁵NO₃^– and reduced¹⁵N. Concurrently with this slowing down of transport and metabolicprocesses, accumulations of NO₃^– and Asn were significantlystimulated in roots during the dark period. These data are discussedin view of the hypothesis that darkness adversely affects NO₃^–uptake through specific feedback control, in response to alterationsin the later steps of N utilization which are more directlydependent on light. Key words: Glycine max, light/dark cycles, nitrate uptake, nitrate reduction     

Growth of Ryegrass (Lolium perenne L.) Exposed to SO2: III. EFFECTS ON FREE AND STORAGE CARBOHYDRATE CONCENTRATIONS

Exposure of ryegrass (Lolium perenne L.) cv. S23 to 0, 50, and400 µg m^–3 SO₂ for an initial 29 d (first harvest),and for an additional 22 d period of regrowth (second harvest),resulted in distinct alterations in carbohydrate metabolismat each harvest. At the first harvest, exposure to 50 µgm^–3 increased concentrations of free and total carbohydrates,whereas exposure to 400 µg m^–3 resulted in concentrationshardly different from those in control plants. At both SO₂ concentrations,more assimilate was retained as free carbohydrate rather thanas storage carbohydrate. Comparison of assimilate distributionat the end of the light, and at the end of the dark period atthe first harvest led to the conclusion that light-mediatedmetabolism is more sensitive to SO₂ exposure than dark metabolism,and that assimilate distribution might be controlled by at leasttwo processes exhibiting different SO₂ sensitivities.     

Effects of Preillumination on Dark Nitrogen Fixation and Respiration by Anabaena Cylindrica

In whole filaments of Anabaena cylindrica dark nitrogen-fixingactivity (measured as acetylene reduction) and respiration increasedwith the light intensity of a fixed period of preillumination,saturating at ca. 10,000 lux. With saturating light during preillumination,the amount and duration of dark nitrogen-fixing activity increasedwith length of preillumination, but respiration declined rapidlyin the dark. At dark respiration rates below 250 nmol O₂ uptake mg protein^–1?h^–1(State 1) no significant nitrogen-fixing activity is observed.From 250 to 550 nmol O₂ uptake?mg protein^–1?h^–1(State 2), nitrogen-fixing activity depends on O₂ uptake whileabove 550 nmol O₂ uptake?mg protein^–1?h^–1 (State3), nitrogen-fixing activity no longer increases with furtherincrease in O₂ uptake rate. (Received June 18, 1983; Accepted November 10, 1983)     

Diurnal Rb+ Transport from Roots to the Laminar Pulvinus in Phaseolus vulgaris L.

The primary leaves of kidney bean (Phaseolus vulgaris L.) openunder light and close in the dark by the deformation of thepulvinus resulting from diurnal distribution changes of K⁺,Cl^–, organic acid (or H⁺) and NO₃^–. When Rb⁺ was added as a tracer of K⁺ to the seedlings throughtheir roots, it was transported to the pulvinus cells duringthe light period but not during the dark period. Transpirationoccurred vigorously in the light but almost stopped in the dark.We concluded that Rb⁺ absorbed by the roots was carried to thepulvinus by the transpiration stream. Phaseolus vulgaris L., pulvinus, Rb⁺, diurnal transport transpiration stream     

In situ bacterial production and growth yield measured by thymidine, leucine and fractionated dark oxygen uptake

In situ bacterial net production and growth yield were measuredusing thymidine, leucine incorporation and dark oxygen consumptiontechniques in marine enclosures and in the Bay of Aarhus, Denmark.Bacterial respiration was significantly correlated with thymidine(r² = 0.42, P < 0.01, y = 0.l2x + 0.054) and leucine (r²= 0.45, P < 0.01, y = 0.09x + 0.043). The range of bacterialgrowth yield, calculated from the relationship net production/netproduction + respiration, was 0.07–0.77 with 74% of theobservations lying in the 0.15–0.45 growth yield interval.Substrate was an important determinant of growth yields. A significantdifference was found between growth yields obtained from anenclosure with added glycine (mean 0.32±0.096) and onewith added inorganic nutrients (mean 0.16±0.051) (P <0.01, t-test). Growth yield showed a weak but significant negativecorrelation with temperature (r² = 0.0.35, P < 0.001, y =–0.017 + 0.52). No correlation between chlorophyll a andgrowth yield was found (r² = 0.25, P > 0.05). The resultssuggest that thymidine and leucine techniques reflect the levelsof bacterial production to better than an order of magnitude.The variations found in the growth yield support the notionthat relying on fixed growth yields reduces the accuracy ofestimating gross bacterial production.     

Photosynthesis and primary production of Microcystis aeruginosa Kutz. in Lake Kasumigaura

Seasonal changes in the photosynthesis and primary productionof Microcystis aeruginosa Kütz. were investigated in LakeKasumigaura during 1981–1982. Microcystis always showeda light-saturated photosynthesis-light curve. Both P_max andthe initial slope of the photosynthesis-light curve of Microcystisin early summer were very high, so it was concluded that Microcystisutilized both low and high light intensities efficiently. TheP_max of Microcystis was found to be a function of the watertemperature except in August and September. The linear regressionon the temperature-P_max relationship discontinued at 11°C,where the P_max value dropped; Microcystis did not photosynthesizebelow 4°C. The initial slope of the curve was also descendingbelow 11°C. It is suggested that Microcystis changes itsphysiological properties below 11°C. The highest value ofgross production calculated for M. aeruginosa was 5.4 gC m^–2d^–1 in July; the annual gross production was estimatedto be 300 gC m^–2year^–1 (i.e., 40% of the total primaryproduction in this lake).     

Growth and Antithraquinone Biosynthesis by Galium mollugo L. Cells in Batch and Chemostat Culture

The kinetics of growth, nutrient uptake, and anthraquinone biosynthesisby suspension cultures of Galium mollugo L. cells were examinedin batch and continuous (chemostat) culture. In batch culture,although the initial growth rate was constant (minimum doublingtime = 35 h) characteristic changes in cell composition wereobserved during the growth cycle particularly cell dry weight(between 3.9 and 9.2 g/10⁹ cells), cell anthraquinone (22–80mg/10⁹ cells), and cell protein (0.7–1.6 g/10⁹ cells).Using a chemostat steady state growth was established at twodifferent specific growth rates with mean doubling times of40 h and 25 h. Phosphate was established as the growth-limitingnutrient in chemostat culture at a concentration of 11 µgP ml^–1. In steady state growth at a doubling time of 40h the cell composition remained constant although this was differentfrom any cells grown in batch culture. The cell anthraquinonelevel in steady state growth was between 7 and 30 times lowerthan in batch culture. This result raises the question of therelative importance of growth rate and the growth-limiting nutrientin determining accumulation of secondary products by culturedplant cells.     

Primary and bacterial production compared to growth and food requirements of Daphnia longispina in Lake Kvernavatnet, west Norway

Primary production, and bacterial production as measured byincorporation of [³H-methyl]thymidineinto ice cold TCA insolublematerial were investigated during 1984 in Lake Kvernavatnet,west Norway. Primary production averaged 222 mg C m^–2day^–1 and bacterial production averaged 163 mg C m^–2day^–1. The bacterial production in the euphotic pelagiczonecontributed -60% of the total pelagic bacterial production.The zooplankton was dominated byDaphnia longispina. From growthexperiments with animals fed only natural food in coarse filteredlake water, the population daily growth increments were calculated.The average production of D.longispina was 151 mg C m^–2day^–1 during the period investigated. The estimated primaryproduction was too low to sustain both the bacterial productionand the zooplankton food requirements. These results imply thatthe carbon cycle of the lake is dependent on the supply of allochtonousmaterial, or that the current methods for measuring productionrates in aquatic environments are systematical erratic.     

Intraspecific variation in the light/dark modulation of ribulose 1,5-bisphosphate carboxylase-oxygenase activity in soybean

A comparative study was made of the inhibition of ribulose-1,5-bisphosphatecarboxylase-oxygenase (Rubisco) amongst six cultivars of Glycinemax L. Merr., associated with synthesis of 2-carboxyarabinitol1-phosphate (CA1P) during darkness. Significantly lower meanvalues of dark inhibition of Rubisco were observed in soybeancv. Davis than in cvs Bragg, Cobb, Hardee, Gordon, and Kirby.The CA1P synthesis/degradation cycle during dark/light transitionsremained operational in cv. Bragg plants grown at low irradiance(40 µmol photons m–2 s–1). However, CA1P synthesisand degradation rates were slower in the dark (t_0.5 = 240 versus25 min), and light (t_0.5 = 20 versus 3.8 min) respectively,as compared to plants grown at higher irradiance (550 µmolphotons m^–2 s^–1). In addition, the activation stateof Rubisco in low-light-grown plants showed only a small declineafter a transition to darkness. We conclude that (a) cultivar-dependentvariation occurs amongst soybeans with respect to CAlP regulationof Rubisco, and (b) soybeans acclimated to low irradiance maydepend more on CA1P synthesis/degradation to regulate Rubisco,and less on changes in the enzyme activation state. Key words: Activation state, Glycine max, photosynthesis, Rubisco, 2-carboxyarabinitol 1-phosphate