Factors influencing shoot regeneration from cotyledonary explants ofCucumis melo

Cotyledonary explants of 4-day-oldCucumis melo cv. Hale's Best Jumbo in vitro seedlings showed maximum initiation of shoot buds when cultured onto a revised Murashige & Skoog medium supplemented with 5 M indole-3-acetic acid and 5 M benzylaminopurine and cultured at 25–29°C under low light intensity (5–30 mol m^-2 s^-1). Subculture of the shoot buds onto the same medium without auxin and supplemented with 3 M benzylaminopurine caused the development of shoots from 30% of the buds. The presence of abscisic acid significantly increased the number of explants producing shoot buds. Bud initiation was affected by genotype, seedling age, light intensity, and temperature. Addition of gibberellic acid, thidiazuron or silver nitrate to regeneration medium did not improve either bud initiation or shoot regeneration.     

Phylogenetic and physiological characterization of a filamentous anoxygenic photoautotrophic bacterium ‘<Emphasis Type="Italic">Candidatus</Emphasis> Chlorothrix halophila’ gen. nov., sp. nov., recovered from hypersaline microbial mats

We report the phylogenetic and physiological characterization of a mesophilic and halophilic member of the filamentous anoxygenic phototrophic (FAP) bacteria, provisionally named Candidatus Chorothrix halophila gen. nov. sp. nov., that has been maintained in a highly enriched culture in our laboratory for over a decade. Phylogenetic analysis of small-subunit RNA-encoding sequences places Candidatus Chlorothrix halophila in a clade that includes cultivated members of the genera Chloroflexus and Oscillochloris. Physiological studies demonstrated sulfide-dependent photosynthetic uptake of ¹⁴C-labeled bicarbonate. Enzymatic assays for the activity of propionyl-coenzyme A synthase indicated that Candidatus Chlorothrix halophila does not use the 3-hydroxypropionate cycle of Chloroflexus aurantiacus OK-70-fl for autotrophic carbon assimilation. New concepts regarding the taxonomy and phylogeny of FAP bacteria have emerged from this work.Abbreviations MCLO Marine Chloroflexus-like organism - FAP Filamentous anoxygenic phototroph     

Aberrations in sexual behavior in some brewing and other industrial yeasts

Summary The mating behavior of a number of brewer's and distiller's yeasts was determined with a and haploid and aa and diploid tester strains. Mating frequencies were not high, ranging from one to (rarely) 2,000/10⁸ cells in the mating mixture. Sporulating hybrids were obtained in most matings, though the percentage spore viability initially obtained was often low. Notable the spore viability obtained in hybrids with the haploid tester strains and the brewing strains DIB and DICH was much higher than from the a haploid tester strain, and higher in hybrids between these strains and the aa diploid tester than in those from the tester strain. With the brewing strain NBA, the spore viability in hybrids with the a haploid tester strain was higher than in the case of strains DIB and DICH, but the spore viability in the hybrid of NBA x the haploid strain was higher still. The data are consistent with the hypothesis that with the a and aa tester strains, most of the industrial yeasts tested mate as diploids, and with the and testers, they mate as haploids, an hypothesis which is supported by the segregation of adenine markers in the progeny of these hybrids.Presented in part at the 6th International Specialized Symposium on Yeasts, Montpellier, France, 2–8 July, 1978     

Activities of growth inhibitors isolated from light-grown dwarf pea shoots

The growth inhibitory activities of 6 endogenous growth inhibitors isolated from light-grown dwarf peas (Pisum sativum cv. Progress No. 9) were examined in the epicotyl of dark-grown seedlings of the same cultivar in the dark in order to examine the possible contribution of these compounds to the growth inhibition brought about by red light. The activities of these natural inhibitors, including two A-2 and A-2 of as yet undetermined structure, were compared with those of synthetic growth retardants and benzyladenine. Samples were applied directly into the epicotyls via a glass capillary tube. In 24-h tests doses for a 25% inhibition (I₂₅) were: A-2, 4.3 × 10^-2: cis-xanthoxin, 1.2 × 10^-1 ; A-2, 1.6 × 10^-1; trans-xanthoxin, 1.2; R,S-dihydromaleimide, 3.5 × 10² and pisatin, 4.0 × 10² nmol plant^-1 . In 72-h tests, I₂₅'s were: benzyladenine, 1.5; AMO-1618 (ammonium-(5-hydroxycarvacryl)-trimethylchloride piperidine carboxylate), 2.4; R,S-dihydromaleimide, 4.0 × 10² and CCC (chlorocholine chloride), 1.1 × 10³ nmol plant^-1. -D-Glucosyl-R-dihydromaleimide had no activity at all. Benzyladenine caused the thickening as well as elongation inhibition of the epicotyls of intact plants. The possible involvement of A-2 and in the red light growth inhibition of dwarf peas is discussed.Abbreviations AMO-1618 ammonium-(5-hydroxycarvacryl)-trimethylchloride piperidine carboxylate - CCC chlorocholine chloride - G-DHMD -D-glucosyl-R-dihydromaleimide - I₂₅ dose required for a 25% growth inhibition - R red light author for correspondence     

Role of red light in hair-whorl formation induced by blue light in Acetabularia mediterranea

After a pre-treatment with red light, hair formation at the growing tip of the siphonaceous green alga Acetabularia mediterranea Lamour. (= A. acetabulum (L.) Silva) can be induced by a pulse of blue light. Red light is needed again after the inductive blue-light pulse if the new whorl of hairs is to develop within the next 24 h. In order to investigate the role of this red light, the duration of the red irradiation was varied and combined with periods of darkness. The response of hair-whorl formation was dependent on the total amount of red light, regardless of whether the red irradiation followed the blue pulse immediately or was separated from it by a period of darkness. Furthermore, periods of exposure to the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1-1dimethylurea had a similar effect to darkness. Both observations indicate that this red irradiation acts as a light source for photosynthesis. Whether or not the red light had an additional effect via phytochrome was tested in another type of experiment. The dependence of hair-whorl formation on red-light irradiance in the presence of simultaneous far-red irradiation was determined for the pre-irradiation period as well as for the irradiation period after the blue pulse. In both experiments, far-red light caused a small promotion of hair-whorl formation when low irradiances of red light were used. However, these differences were attributable to a low level of photosynthetic activity (which in fact was measurable) caused by red light reflected in the growth chamber. Furthermore, lowering the proportion of active phytochrome by far-red light would be expected to suppress hair-whorl formation. The influence of far-red light was also tested in a strain of Acetabularia mediterranea that developed hair whorls in about 20% of cells even when kept in complete darkness after the blue-light pulse. Far-red irradiation had no effect. These results strongly indicate that phytochrome is not involved in hair-whorl formation. Rather it is concluded that the effects of red light are caused by photosynthesis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Circadian oscillators,cell cycles,and singularities: light perturbations of the free-running rhythm of cell division inEuglena

Summary The free-running circadian rhythm of cell division in the algal flagellate,Euglena gracilis (Z) was perturbed by 3-h light signals of varying intensities imposed at different circadian times (CT). Light pulses within the range of 700 to 7,500 lux were found to yield the same strong (Type 0) phase response curve (PRC) comprising both advance and delaye phase shifts as great as 15 h. Dark signals generated a PRC of reduced amplitude with very little, if any, phase advance being observed. Light perturbations of lower intensity, however, elicited quite different responses if applied at a quite specific circadian time: A 40- to 400-lux pulse given at approximately CT 0 (late subjective night) induced total arrhythmicity, and the culture reverted to asynchronous, exponential growth. Different degrees of arryhtmicity were induced by the same low-intensity perturbations (I ^*) given slightly before or after this sensitive phase point (T ^*), but if imposed at other circadian times, they generated normal type 0 phase resetting. The demonstration of the existence of this critical pulse (T ^*,I ^*) provides further evidence that the cell division cycle ofEuglena (and presumably other microorganisms) is regulated by a circadian oscillator and, in particular, by one having limit cycle dynamics.Abbreviations LL continuous illumination - DD continuous darkness - LD light-dark cycle - LD x, y, light-dark cycle comprisingx h of light andy h of dark - t period of a LD cycle - CO circadian oscillator - CR circadian rhythm - period of a freerunning circadian rhythm in constant conditions (taken here to be the time between onsets of cell division in a population of cells - _R phase marker, or phase reference point (here, the onset of the division burst) - phase of the rhythm - change in phase (phase shift) - new phase attained after phase shift - CT circadian time (CT 0 indicates the phase point of a free-running rhythm that has been normalized to 24 h which corresponds to that occurring at the onset of light in aLD:12, 12 reference cycle) - PRC phase response curve (plot of phase shift engendered by a perturbation as a function of the circadian time of its application) - T ^*,I ^*) coordinates of an annihilating (light) stimulus given at a critical circadian time (T ^*, corresponding to the singularity point) and having a critical strength (I ^*) - CDC cell division cycle - average generation (doubling) time of a cell population - average step-size, or factorial increase in cell titer (plateau to plateau) after a phased division burst Dedicated to Prof. Colin S. Pittendrigh on only his 65th birthday     

Abnormal subcellular distribution of β-glucuronidase in mice with a genetic alteration in enzyme structure

Liver -glucuronidase is structurally altered in inbred strain PAC so that a peptide subunit with a more basic isoelectric point, GUS-SN, is produced. This allele of -glucuronidase was transferred to strain C57BL/6J by 12 backcross matings to form the congenic line B6 · PAC-Gus ⁿ. Liver -glucuronidase activity was halved in males of the congenic strain compared to normal males. The lowered activity was specifically accounted for by a decrease in the lysosomal component. There was no alteration in the concentration of microsomal activity. This alteration in the subcellular distribution of -glucuronidase in Gus ⁿ/Gus ⁿ mice was confirmed by two independent gel electrophoretic systems which separate microsomal and lysosomal components. -Glucuronidase activity was likewise approximately halved in mutant spleen, lung, and brain, organs which contain exclusively or predominantly lysosomal -glucuronidase. The loss of liver lysosomal -glucuronidase activity was shown by immunotitration to be due to a decrease in the number of -glucuronidase molecules in lysosomes of the congenic strain. The Gus ⁿ structural alteration likely causes the lowered lysosomal -glucuronidase activity since the two traits remain in congenic animals. Heterozygous Gus ⁿ/Gus ^b animals had intermediate levels of liver -glucuronidase. Also, the effect was specific, in that three other lysosomal enzymes were not reproducibly lower in Gus ⁿ/Gus ⁿ mice. Gus ⁿ is, therefore, an unusual example of a mutation which causes a change in the subcellular distribution of a two-site enzyme.This work was supported by National Institutes of Health Grants GM-33559 and GM-33160 and National Science Foundation Grant PCM-8215808.     

Hypoxia Tolerance of Two Haplochromine Cichlids: Swamp Leakage and Potential for Interlacustrine Dispersal

The ability to tolerate hypoxia in some haplochromine cichlid fishes contributes to the richness of habitats occupied by the lineage and may be important in interlacustrine dispersal through swampy channels. Lacustrine members of the genus Astatotilapia tend to be ecologically plastic but are rarely encountered in the interior of dense swamps. A notable exception is seen in the swamp corridor that joins Lake Kabaleka with Lake George, Uganda, where one species (Astatotilapia wrought-iron) is abundant, and a second species, A. aeneocolor, is rare. Both species are abundant in the open waters of the main lake. In this paper, we compare physiological (oxygen consumption) and behavioral indicators of hypoxia tolerance between A. wrought-iron from swamp and open-water habitats and between the two species of Astatotilapia. When exposed to progressive hypoxia, all fish used aquatic surface respiration (ASR); however, swamp-dwelling A. wrought-iron showed lower gill ventilation rates prior to the initiation of ASR, higher pre-ASR aggression rates, higher swimming speed during ASR, and a higher rate of bubble exchange than both the open-water group of A. wrought-iron and A. aeneocolor. These differences may reflect interpopulational variation in selection pressure for low-oxygen tolerance between swamp and open-water habitats. Several lines of evidence suggest that A. wrought-iron was in general more hypoxia tolerant than A. aeneocolor. These include a lower ASR₉₀ threshold, a drop in gill ventilation rate with the onset of ASR, and lower rate of equilibrium loss under extreme hypoxia in A. wrought-iron. The routine metabolic rate and critical oxygen tension did not differ between swamp-dwelling and open-water A. wrought-iron, or between A. wrought-iron and A. aeneocolor. Comparative data on the ASR thresholds and critical oxygen tensions of the Astatotilapia species from Lake Kabaleka and other East African cichlids suggest intermediate hypoxia tolerance. Nevertheless, our study suggests that some generalized lacustrine haplochromines may leak through swamp corridors even under relatively extreme conditions.     

High irradiance response promotion of a subsequent light induction response in Sinapis alba L.

Relative quantum responsivity curves for inhibition of hypocotyl elongation in Sinapis alba L. seedlings previously grown in white light confirm that a marked end of day inhibition response can be induced by a monochromatic light treatment (30 min) at the end of the light period. In dark grown seedlings, however, no growth inhibition can be induced by a 30 min monochromatic light treatment. A prerequisite for an induction response appears to be a pretreatment with continuous light. Far red light is most effective with blue and red light showing a lesser effectiveness. The light pretreatment also shows a marked fluence rate dependency with respect to its ability to allow an induction response to manifest itself. The pretreatment required shows all the characteristics of a classical HIR response. The appearance of the effect in plants treated with the herbicide SAN 9789 seems to exclude chlorophyll as being the photoreceptor.Abbreviations SAN 9789 4-chloro-5-(methylamino)-2-(, , -trifluoro-m-tolyl)-3(2H)-pyridazinone - RG9 light long wavelength far red light (Schott RG9 colour glass) - FR far red light - WL white light - BL blue light - RL red light - D darkness - P_tot total phytochrome - P_fr far red absorbing form of phytochrome - HSR high irradiance response     

Subcellular localization and topology of β(1→4)galactosyltransferase that elongates β(1→4)galactan side chains in rhamnogalacturonan I in potato

The subcellular localization and topology of rhamnogalacturonan I (RG-I) (14)galactosyltransferase(s) ([14]GalTs) from potato (Solanum tuberosum L.) were investigated. Using two-step discontinuous sucrose step gradients, galactosyltransferase (GalT) activity that synthesized 70%-methanol-insoluble products from UDP-[¹⁴C]Gal was detected in both the 0.5 M sucrose fraction and the 0.25/1.1 M sucrose interface. The former fraction contained mainly soluble proteins and the latter was enriched in Golgi vesicles that contained most of the UDPase activity, a Golgi marker. By gel-filtration analysis, products of 180–2,000 Da were found in the soluble fraction, whereas in the Golgi-enriched fraction the products were larger than 80 kDa and could be digested with rhamnogalacturonan lyase and (1,4)endogalactanase to yield smaller rhamnogalacturonan oligomers, galactobiose and galactose. The endogalactanase requires (14)galactans with at least three galactosyl residues for cleavage, indicating that the enzyme(s) present in the 0.25/1.1 M Suc interface transferred one or more galactosyl residues to pre-existing (14)galactans producing RG-I side chains in total longer than a trimer. Thus, the (14)GalT activity that elongates (14)-linked galactan on RG-I was located in the Golgi apparatus. This (14)GalT activity was not reduced after treatment of the Golgi vesicles with proteinase, but approximately 75% of the activity was lost after treatment with proteinase in the presence of Triton X-100. In addition, the (14)GalT activity was recovered in the detergent phase after treatment of Golgi vesicles with Triton X-114. Taken together, these observations supported the view that the RG-I (14)GalT that elongates (14)galactan was mainly located in the Golgi apparatus and integrated into the membrane with its catalytic site facing the lumen.Abbreviations GalT Galactosyltransferase - (14)GalT (14)-Galactosyltransferase - H ⁺ -ATPase Proton ATPase - HG Homogalacturonan - HSP70 ER resident Bip - mMDH Mitochondrial malate dehydrogenase - RG-I Rhamnogalacturonan I - RG-II Rhamnogalacturonan II - RGP Reversibly glycosylated polypeptide - RG-Lyase Rhamnogalacturonan lyase - Suc Sucrose - UDPase Uridine-5-diphosphatase     

Phototactic responses in Haematococcus lacustris and its modification by light intensity and the carotenoid biosynthesis inhibitor Norflurazon

At fluence rates below 45 W· m^-2 cells of the flagellate stage of Haematococcus lacustris react only positively phototactically with a rather high degree of orientation (indicated by r values up to 0.66 with the Rayleigh test). The directedness of orientation decreases with decreasing irradiance. The degree of directedness of the phototactic response depends on the intensity of preirradiation: Low light intensity applied after strong light application results in a dark reaction (low r values), low light given after darkness stimulates a rather high degree of directedness of positive phototaxis. Weak blue light (=483 nm; 0.4 W · m^-2) stimulates positive phototactic response, whereas comparable red light (=658 nm; 0.5 W · m^-2) does not.Cells which were grown in a medium containing 10^-4 M Norflurazon (effective in inhibition of carotenoid biosynthesis) although maintaining motility completely lose the ability to react positively phototactically. The possible role of carotenoids in the phototactic orientation is discussed.     

Phytochrome action in Oryza sativa L.

Summary In-vivo phytochrome determinations in totally etiolated rice seedlings with a dual-wavelength spectrophotometer showed that on a fresh weight basis phytochrome concentration was highest in the coleoptile apex (0.175 of mean) ( O.D.) g^-1 (fresh weight). The age of the seedlings had little effect on the pattern of phytochrome distribution in the coleoptiles.The extent of growth inhibition observed 2 days after the irradiations was proportional to the logarithm of P _fr amount in the coleoptiles at the time of initial exposure to either red or blue light. Ultraviolet irradiation, however, did not induce either reversible growth inhibition or optically detectable phytochrome changes in vivo.After the conversion of P _r to P _fr bya brief red irradiation, non-photochemical transformation of phytochrome was observed in intact coleoptile tissues. Most of the optically measurable P _fr disappeared within 6 hours at 27°, when the total ( O.D.) decreased to about one fifth of the original level. The optical data did not agree with the fact that 50% of the initial physiological reversibility was still observed 9 hours later. No significant difference in dark transformation rate was seen between intact and excised coleoptile tissues.Abbreviations P _r red light absorbing form of phytochrome - P _fr far-red light absorbing form of phytochrome - ( O.D.) the change in the optical density difference reading at two wavelengths, following irradiation of the sample with actinic sources of red and far-red light - UV ultraviolet light     

Use of resorufin-labelled N-glycopeptide in a high-performance liquid chromatography assay to monitor endoglycosidase activities during cultivation ofFlavobacterium meningosepticum

Peptide-N ⁴-(N-acetyl--glucosaminyl) asparagine amidase F (PNGase F) and endo--N-acetyl glucosaminidase F (Endo F) activities were monitored during cultivation ofFlavobacterium meningosepticum using a new fluorescence-HPLC procedure based on a commercially available substrate. The PNGase F activity reached a maximum level at the end of the log phase and remained constant during the stationary phase, while Endo F continuously increased until late stationary phase. PNGase F obtained at the end of the log phase was less contaminated by other proteins compared with late stationary phase.Abbreviations Con A concanavalin A - Endo F endo--N-acetyl glucosaminidase F (EC 3.2.1.96) - GlcNAc N-acetylglucosamine - PNGase F peptide-N ⁴-(N-acetyl--glucosaminyl) asparagine amidase F (EC 3.5.1.52).     

Correlation between 5-aminolaevulinate accumulation and protochlorophyll photoconversion

A 1-min light pulse delivered to mustard seedlings (Sinapis alba L.) 60 h after sowing initiates the release of cotyledonary 5-aminolaevulinate (ALA) accumulation which continues for at least 2 h in the dark. Phytochrome (P _fr) increases the rate of ALA accumulation after a 24-h red light pretreatment but is not the trigger for this release. It is shown that the rate of ALA accumulation varies with the wave-length and fluence rate of the 1-min light pulse and can be predicted from the degree of protochlorophyll-(ide) photoconversion. There is a linear correlation between the rate of ALA accumulation and the degree of protochlorophyll(ide) (PChl)chlorophyll(ide) a (Chl a) photoconversion in etiolated seedlings. In seedlings pretreated with red light this correlation is non-linear and the rate increases more rapidly with increasing degrees of PChlChl a photoconversion. It is suggested that there may exist an interaction between P _fr and PChlChl a photoconversion in controlling ALA accumulation.Abbreviations ALA 5-aminolaevulinate - Chl chlorophyll(ide) - PChl protochlorophyll(ide) - cp cotyledon pair - LA laevulinate     

The catalysis of nucleotide polymerization by compounds of divalent lead

Summary Soluble lead salts and a number of lead-containing minerals catalyze the formation of oligonucleotides from nucleoside 5-phosphorimidazolides. The effectiveness of lead compounds correlates strongly with their solubility. Under optimal conditions we were able to obtain 18% of pentamer and higher oligomers from ImpA. Reactions involving ImpU gave smaller yields.Abbreviations A adenosine - U uridine - Im imidazole - MeIm 1-methyl-imidazole - EDTA ethylenediaminetetraacetic acid - pA adenosine 5-phosphate - pU uridine 5-phosphate - Ap adenosine cyclic 2:3-phosphate - ATP adenosine 5-triphosphate - AppA P₁,P₂-diadenosine 5-diphosphate - pNp (N = A,U) nucleotide 2(3), 5-diphosphate - ImpA adenosine 5-phosphoreimidazolide - ImpU uridine 5-phosphorimidazolide - A ²pA adenylyl-[25]-adenosine - A ³pA adenylyl-[35]-adenosine - pA ²pA 5-phospho-adenylyl-[25]-adenosine - pA ³pA 5-phospho-adenylyl-[35]-adenosine - pUpU 5-phospho-uridylyl-uridine - pApU 5-phospho-adenylyl-uridine - pUpA 5-phospho-uridylyladenine - (pA)n (n, 2,3,4,) oligoadenylates with 5 terminal phosphate - ImpApA 5-phosphorimidazolide of adenylyl adenosine - (pA) ₅₊ pentamer and higher oligoadenylates with 5 terminal phosphate - (Ap)nA (n = 2,3,4) oligoadenylates without terminal phosphates In the following we do not specify the nature of the internucleotide linkageIn the following we do not specify the nature of the internucleotide linkage     

Light and GTP dependence of transducin solubility in retinal rods

The physical origin and functional significance of the near infra-red light scattering changes observable upon flash illumination of diluted suspensions of magnetically oriented, permeabilised frog retinal rods has been reinvestigated with particular attention paid to the degree with which transducin remains attached to the membrane. In the absence of GTP, the so called binding signal is shown to include two components of distinctive origins, widely different kinetics, and whose relative amplitudes depend on the dilution of the suspension and resulting detachment of transducin from the disc membrane. The fast component is a consequence of the fast interaction between photoexcited rhodopsin (R^*) and the transducin remaining on the membrane. Its kinetics monitors a structural modification of the discs caused by a change in electrostatic interaction between closely packed membranes upon the formation of R^*-T complexes. The slow component monitors the slow rebinding to the membrane and possible subsequent interaction with excess R^* of T-GDP which, in spite of its low solubility, had eluted into solution given the high dilution of the permeated rods. In the presence of GTP, the so called dissociation signal includes a fast, anisotropic release component that specifically monitors the release into the interdiscal space of T -GTP formed from the membrane-bound pool, and a slower isotropic loss component monitoring the leakage from the permeated rod of the excess T -GTP which did not interact with the cGMP phosphodiesterase. The amplitudes of both components depend exclusively on the membrane bound T-GDP pool. The kinetics of the loss component is limited by the size and degree of permeation of the rod fragments, rather than by the dissociation rate of T -GTP from the membrane.Abbreviations ROS rod outer segment - R rhodopsin - R^* photoactivated rhodopsin - T, T-GDP, T -GDP, T -GTP, T transducin and its various forms - T _mb, T _sol: T bound to membrane or soluble - PDE cGMP-phosphodiesterase - GTP guanosine 5-triphosphate - GDP guanosine 5-diphosphate - GDP S guanosine 5-O-(2-thiodiphosphate) - cGMP guanosine-3-5 cyclic-monophosphate - DTT dithiothreitol - HEPES 4-(2-hydroxyethyl)-1-piperazine-ethane sulfonic acid - TRIS Tris (hydroxymethyl)aminomethane - SDS sodium dodecyl sulfate     

The polarized UV-absorption spectra and the crystal structure of two different monoclinic crystal forms of the retinal homologue β-8′-apocarotenal

During the visual process, light absorption in the 11-cis retinylidene chromophore leads to a rapid cis-trans-isomerization which initiates the phototransduction step. Important spectroscopic properties of this chromophore can be derived from polarized UV-absorption spectra of crystalline 11-cis-retinal if a parallel X-ray structure analysis is performed. Several questions about the relation between molecular geometry and spectroscopic behavior could not be answered from these spectra. All crystal forms of 11-cis-retinal contain this molecule in its 6-s-cis-ring conformation. For the retinal homologue, -8-apocarotenal (APC), however, two crystal forms with different ring conformation can be grown. The spectrum of -APC (6-s-cis) shows a vibronic structure whereas that of -APC (6-s-trans) is diffuse but has a distinct shoulder on the low energy side of the main band. This S-band is typical for retinal spectra and has been ascribed to a transition into a ¹A _g ^-* -state. The appearance of the S-band is not correlated with a 6-s-cis-conformation as suggested by the retinal spectra but is due to intermolecular interactions: -APC has a dense dimer packing and a strong electrostatic interaction between the -electron systems. This might cause the forbidden ¹A _g ^-* -transition. On the other hand, this interaction is missing in the loose and polar packing of -APC which favors vibration in the polyene chain. This finding is remarkable in view of the photodynamic behavior of the visual chromophore for which strong electrostatic interactions with the protein helices of its binding site have to be postulated.Abbreviations APC 8--Apocarotenal - -APC/-APC /-form of crystallized APC - -CIS/-CIS /-form of crystallized 11-cis-retinal - ATR all-trans retinal - UV ultraviolet light - CI quantum-mechanical calculation employing configuration interaction - PPP-MRD quantum-mechanical calculations after Pariser, Parr, Pople employing multireference determinants - S-bands shoulder on main absorption band - R, S right, left enantiomer - EtOH ethyl alcohol - PE petroleum ether - E direction of electric vector of incident light - b crystallographic b-axis     

Holling's “hungry mantid” model for the invertebrate functional response considered as a Markov process. Part II: Negligible handling time

In this paper we analyse a stochastic model for invertebrate predation taking account of the predator's satiation. This model approximates Holling's hungry mantid model when handling time is negligible (see Part I). For this model we derive equations from which we can calculate the functional response and the variance of the total catch. Moreover we study a number of approximations which can be used to calculate these quantities in practical cases in a relatively simple manner.List of Notation a rate constant of digestion - b maximum of rate constant of prey encounter in the mantid - c satiation threshold for search - c satiation threshold for pursuit in the mantid - c _i (w^1/2(N- N)ⁱ) - expectation operator - f rate of change of satiation during search - F functional response: mean number of prey eaten per unit of time - g rate constant of prey capture - h probability generating function of N conditional on S = s times p - H probability generating function of N - m_i ¹ - n, N number of prey caught - p probability density of S - p_n simultaneous probability (density) of N and S - q probability of strike success - r dummy variable in generating function - s, S satiation - T _s search time - T _d digestion time - v asymptotic rate of increase of var v - V asymptotic rate of increase of var N - w weight of edible part of prey - W standard Wiener process - x prey density - z (N{S = s}-N)p - rate constant of prey escape time maximum pursuit time - (v{S = + w ^1/2}-v) - present time as a fraction of the time from the start to the end of the experiment - hazard rate of T _s - mean time between (downward) passages of S through c - v w_–1/2(N-) - edible prey biomass density - probability density of , number pi - parameter of Weibull distribution of T _s = (1/2acx(-g(c)))_1/2 - w_–1/2(S -) - satiation in the guzzler approximation: solution to d/dt = f() + g(), (0)=S(0). - biomass functional response: wF - total biomass catch in the guzzler approximation: solution to d/dt = g(), (0) = 0     

Absence of red-light enhancement of phototropism in pea seedlings at limiting irradiances of blue light

The effect of different light qualities (blue, green, white, red and far-red) on ethylene production in leaf discs and flower petal discs of Begonia × hiemalis cv. Schwabenland Red was studied. All the light qualities, except far-red, reduced the ACC-conversion to ethylene in leaf discs by about 70% at a photosynthetic photon flux density (PPFD) of 20 mol m^–2s^–1.Blue and green light were less inhibitory than white and red light at lower PPFD. In all treatments far-red light at 0.5 mol m^–2s^–1 of photon flux density (PFD) stimulated the ACC-conversion to ethylene in leaf discs by about 60–90% compared to the dark-incubated control. White and red light strongly inhibited the -naphthalene-acetic acid (NAA) stimulated ethylene synthesis in leaf discs. The results may suggest that the ethylene production is controlled by phytochrome in the leaves but not in the petals. Lack of coaction of any light quality with silver ions on ethylene production in leaf and petal discs was also observed.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene forming enzyme - NAA -naphthalene-acetic acid - PFD photon flux density - PPFD photosynthetic photon flux density - RH relative air humidity - SAM S-adenosylmethionine - STS silver thiosulphate