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Summary Traditional models of geriatric assessment have not considered the cultural and demographic changes that have affected women's ability to provide parent care in the 21st century. The United States has the world's highest fulltime employment rate and the longest workweek. These factors have an important impact on women's ability to provide care for aging parents. A life course assessment and intervention model currently employed at the US Army and Air War Colleges that helps female and male officers prepare proactively for parent care is described. The usefulness of the model is supported by data from a longitudinal survey of the needs of military families. The life course model provides a unique framework to guide social workers who help women within and outside the armed forces to manage 21st century commitments to family and work.

The glutathione S-transferases (FhGST) of the liver fluke Fasciola hepatica have been identified as novel vaccine candidates that protect sheep against a fluke infection. With the use of overlapping peptides covering the predicted amino acid sequences of four FhGST cDNAs, we have defined the linear epitopes recognized by polyclonal antibody from sheep vaccinated with FhGST. Dominant and minor epitopes were found to be present on all four of the sequences although some epitopes were shown to be specific to particular FhGST. A high percentage of the FhGST peptides were found to be antigenic although considerable variability in response to the peptides was observed among the animals. This analysis was extended to the IgG1 and IgG2 response at the peptide level. Based on the recently solved crystal structure of the rat mu-class GST 3-3, a three-dimensional model of one of the FhGST sequences was generated that allowed the predicted spatial localization of defined epitopes. Most epitopes were localized on regions of high flexibility and accessibility. A comparison of epitopes on FhGST with the B cell epitopes on Sm28, a 28-kDa GST from Schistosoma mansoni, has found few similarities. There was no correlation between an antibody response to linear peptide epitopes and the level of protection induced in sheep by vaccination with FhGST.

A successful unified pharmacophore/receptor model which has guided the synthesis of subtype selective compounds is reviewed in light of recent developments both in ligand synthesis and structural studies of the binding site itself. The evaluation of experimental data in combination with a comparative model of the alpha1beta2gamma2 GABA(A) receptor leads to an orientation of the pharmacophore model within the Bz BS. Results not only are important for the rational design of selective ligands, but also for the identification and evaluation of possible roles which specific residues may have within the benzodiazepine binding pocket.

As an alternative to the current Department of Defense approach to health promotion and related research, which is critiqued in Part I of this article, the authors present a new, integrative health promotion and wellness model. This age-graded model incorporates successful aging, targeted health promotion, and spirituality in the context of the developmental perspective provided by life course constructs. By using an age-graded, multidisciplinary system of assessment, intervention, and follow-up in the context of preparing military personnel and families for the next season of life, this model advocates the prevention of disease and disability, active engagement with life, the maximization of high cognitive and physical functioning, and positive spirituality. Preliminary, selected illustrations from a variation of this model at the U.S. Army War College are provided. Progressive extrapolation of the model to other military leadership schools is proposed as a more efficacious health promotion strategy for the Department of Defense.

Methylobacterium dichloromethanicum DM4 is able to grow with dichloromethane as the sole carbon and energy source by using a dichloromethane dehalogenase/glutathione S-transferase (GST) for the conversion of dichloromethane to formaldehyde. Mammalian homologs of this bacterial enzyme are also known to catalyze this reaction. However, the dehalogenation of dichloromethane by GST T1-1 from rat was highly mutagenic and toxic to methylotrophic bacteria. Plasmid-driven expression of rat GST T1-1 in strain DM4-2cr, a mutant of strain DM4 lacking dichloromethane dehalogenase, reduced cell viability 10(5)-fold in the presence of dichloromethane. This effect was exploited to select dichloromethane-resistant transconjugants of strain DM4-2cr carrying a plasmid-encoded rGSTT1 gene. Transconjugants that still expressed the GST T1 protein after dichloromethane treatment included rGSTT1 mutants encoding protein variants with sequence changes from the wild-type ranging from single residue exchanges to large insertions and deletions. A structural model of rat GST T1-1 suggested that sequence variation was clustered around the glutathione activation site and at the protein C-terminus believed to cap the active site. The enzymatic activity of purified His-tagged GST T1-1 variants expressed in Escherichia coli was markedly reduced with both dichloromethane and the alternative substrate 1,2-epoxy-3-(4'-nitrophenoxy)propane. These results provide the first experimental evidence for the involvement of Gln102 and Arg107 in catalysis, and illustrate the potential of in vivo approaches to identify catalytic residues in GSTs whose activity leads to toxic effects.

In view of the recent studies on the CDCs, a reasonable schematic of the stages leading to membrane insertion of the CDCs can be assembled. As shown in Fig. 3, we propose that the CDC first binds to the membrane as a monomer. These monomers then diffuse laterally on the membrane surface to encounter other monomers or incomplete oligomeric complexes. Presumably, once the requisite oligomer size is reached, the prepore complex is converted into the pore complex and a large membrane channel is formed. During the conversion of the prepore complex to the pore complex, we predict that the TMHs of the subunits in the prepore complex insert into the bilayer in a concerted fashion to form the large transmembrane beta-barrel, although this still remains to be confirmed experimentally. Many intriguing problems concerning the cytolytic mechanism of the CDCs remain unsolved. The nature of the initial interaction of the CDC monomer with the membrane is currently one of the most controversial questions concerning the CDC mechanism. Is cholesterol involved in this interaction, as previously assumed, or do specific receptors exist for these toxins that remain to be discovered? Also, the trigger for membrane insertion and the regions of these toxins that facilitate the [figure: see text] interaction of the monomers during prepore complex formation are unknown. In addition, the temporal sequence of the multiple structural changes that accompany the conversion of the soluble CDC monomer into a membrane-inserted oligomer have yet to be defined or characterized kinetically.

The primary purposes of this article are to (1) highlight current challenges facing health promotion advocates within the military and civilian culture; (2) present the strengths and weaknesses of the current Army approach to health promotion and preventive medicine; and (3) present several unifying themes that contribute to enhanced progress within the field of health promotion. A conceptual model that links common goals across the fields of successful aging, health promotion, spirituality and health, and life course is advocated to maximize efficacious interventions and to transform the current Army approach to health promotion. A companion article will describe an integrative model of health promotion and wellness that responds to the challenges and incorporates the unifying themes described in this article.

Glutathione S-transferases (GSTs) normally use hydroxy-group-containing residues in the N-terminal domain of the enzyme for stabilizing the activated form of the co-substrate, glutathione. However, previous mutagenesis studies have shown that this is not true for Beta class GSTs and thus the origin of the stabilization remains a mystery. The recently determined crystal structure of Proteus mirabilis GST B1-1 (PmGST B1-1) suggested that the stabilizing role might be fulfilled in Beta class GSTs by one or more residues in the C-terminal domain of the enzyme. To test this hypothesis we mutated His(106) and Lys(107) of PmGST B1-1 to investigate their possible role in the enzyme's catalytic activity. His(106) was mutated to Ala, Asn and Phe, and Lys(107) to Ala and Arg. The effects of the replacement on the activity, thermal stability and antibiotic-binding capacity of the enzyme were examined. The results are consistent with the involvement of His(106) and Lys(107) in interacting with glutathione at the active site but these residues do not contribute significantly to catalysis, folding or antibiotic binding.

An N-capping box motif (Ser/Thr-Xaa-Xaa-Asp) is strictly conserved at the beginning of helix alpha6 in the core of virtually all glutathione transferases (GST) and GST-related proteins. It has been demonstrated that this local motif is important in determining the alpha-helical propensity of the isolated alpha6-peptide and plays a crucial role in the folding and stability of GSTs. Its removal by site-directed mutagenesis generated temperature-sensitive folding mutants unable to refold at physiological temperature (37 degrees C). In the present work, variants of human GSTP1-1 (S150A and D153A), in which the capping residues have been substituted by alanine, have been generated and purified for structural analysis. Thus, for the first time, temperature-sensitive folding mutants of an enzyme, expressed at a permissive temperature, have been crystallized and their three-dimensional structures determined by X-ray crystallography. The crystal structures of human pi class GST temperature-sensitive mutants provide a basis for understanding the structural origin of the dramatic effects observed on the overall stability of the enzyme at higher temperatures upon single substitution of a capping residue.

Potentiometric, spectroscopic and stopped-flow experiments have been performed to dissect the binding mechanism of GSH to selected glutathione S-transferases (GSTs), A1-1, M2-2 and Lucilia cuprina GST, belonging to Alpha, Mu and Delta classes respectively. Both Alpha and Mu isoenzymes quantitatively release the thiol proton of the substrate when the binary complex is formed. Proton extrusion, quenching of intrinsic fluorescence and thiolate formation, diagnostic of different steps along the binding pathway, have been monitored by stopped-flow analysis. Kinetic data are consistent with a multi-step binding mechanism: the substrate is initially bound to form an un-ionized pre-complex [k(1)>/=(2-5)x10(6) M(-1).s(-1)], which is slowly converted into the final Michaelis complex (k(2)=1100-1200 s(-1)). Ionization of GSH, fluorescence quenching and proton extrusion are fast events that occur either synchronously or rapidly after the final complex formation. The Delta isoenzyme shows an interesting difference: proton extrusion is almost stoichiometric with thiolate formed at the active site only up to pH 7.0. Above this pH, at least one protein residue acts as internal base to neutralize the thiol proton. These results suggest that the Alpha and Mu enzymes retain not only a similar catalytic outcome and overall three-dimensional structure but also share a similar kinetic mechanism for GSH binding. The Delta GST, which is closely related to the mammalian Theta class enzymes and is distantly related to Alpha and Mu GSTs in the evolutionary pathway, might display a different activation mechanism for GSH.

Perfringolysin O (PFO), a water-soluble monomeric cytolysin secreted by pathogenic Clostridium perfringens, oligomerizes and forms large pores upon encountering cholesterol-containing membranes. Whereas all pore-forming bacterial toxins examined previously have been shown to penetrate the membrane using a single amphipathic beta hairpin per polypeptide, cysteine-scanning mutagenesis and multiple independent fluorescence techniques here reveal that each PFO monomer contains a second domain involved in pore formation, and that each of the two amphipathic beta hairpins completely spans the membrane. In the soluble monomer, these transmembrane segments are folded into six alpha helices. The insertion of two transmembrane hairpins per toxin monomer and the major change in secondary structure are striking and define a novel paradigm for the mechanism of membrane insertion by a cytolytic toxin.

Pneumolysin, an important virulence factor of the human pathogen Streptococcus pneumoniae, is a pore-forming toxin which also possesses the ability to activate the complement system directly. Pneumolysin binds to cholesterol in cell membrane surfaces as a prelude to pore formation, which involves the oligomerization of the protein. Two important aspects of the pore-forming activity of pneumolysin are therefore the effect of the toxin on bilayer membrane structure and the nature of the self-association into oligomers undergone by it. We have used analytical ultracentrifugation (AUC) to investigate oligomerization and small-angle neutron scattering (SANS) to investigate the changes in membrane structure accompanying pore formation. Pneumolysin self-associates in solution to form oligomeric structures apparently similar to those which appear on the membrane coincident with pore formation. It has previously been demonstrated by us using site-specific chemical derivatization of the protein that the self-interaction preceding oligomerization involves its C-terminal domain. The AUC experiments described here involved pneumolysin toxoids harbouring mutations in different domains, and support our previous conclusions that self-interaction via the C-terminal domain leads to oligomerization and that this may be related to the mechanism by which pneumolysin activates the complement system.SANS data at a variety of neutron contrasts were obtained from liposomes used as model cell membranes in the absence of pneumolysin, and following the addition of toxin at a number of concentrations. These experiments were designed to allow visualization of the effect that pneumolysin has on bilayer membrane structure resulting from oligomerization into a pore-forming complex. The structure of the liposomal membrane alone and following addition of pneumolysin was calculated by the fitting of scattering equations directly to the scattering curves. The fitting equations describe scattering from simple three-dimensional scattering volume models for the structures present in the sample, whose dimensions were varied iteratively within the fitting program. The overall trend was a thinning of the liposome surface on toxin attack, which was countered by the formation of localized structures thicker than the liposome bilayer itself, in a manner dependent on pneumolysin concentration. At the neutron contrast match point of the liposomes, pneumolysin oligomers were observed. Inactive toxin appeared to bind to the liposome but not to cause membrane alteration; subsequent activation of pneumolysin in situ brought about changes in liposome structure similar to those seen in the presence of active toxin. We propose that the changes in membrane structure on toxin attack which we have observed are related to the mechanism by which pneumolysin forms pores and provide an important perspective on protein/membrane interactions in general. We discuss these results in the light of published data concerning the interaction of gramicidin with bilayers and the hydrophobic mismatch effect.

A manual threading approach is used to model the human glutathione transferase T1-1 based on the coordinates of the related Theta class enzyme T2-2. The low level of sequence identity (about 20%), found in the C-terminal extension in conjunction with a relative deletion of about five residues makes this a challenging modeling problem. The C-terminal extension contributes to the active site of the molecule and is thus of particular interest for understanding the molecular mechanism of the enzyme. Manual docking of known substrates and non-substrates has implicated potential candidates for the T1-1 catalytic residues involved in the dehalogenation and epoxide-ring opening activities. These include the conserved Theta class residues Arg 107, Trp 115, and the conserved GSTT1 subclass residue His 176. Also, the residue at position 234 is implicated in the modulation of T1-1 activity with different substrates between species.

Pneumolysin, a member of the thiol-activated cytolysin family of toxins, is a virulence factor from the Gram-positive bacterium Streptococcus pneumoniae. The toxin forms large oligomeric pores in cholesterol-containing membranes of eukaryotic cells. A plethora of biochemical and mutagenesis data have been published on pneumolysin, since its initial characterization in the 1930s. Here we present an homology model of the monomeric and oligomeric forms of pneumolysin based on the recently determined crystal structure of perfringolysin O and electron microscopy data. A feature of the model is a striking electronegative surface on parts of pneumolysin that may reflect its cytosolic location in the bacterial cell. The models provide a molecular basis for understanding the effects of published mutagenesis and biochemical modifications on the toxic activity of pneumolysin. In addition, spectroscopic data are presented that shed new light on pneumolysin activity and have guided us to hypothesise a detailed model of membrane insertion. These data show that the environment of some tryptophan residues changes on insertion and/or pore formation. In particular, spectroscopic analysis of a tryptophan mutant, W433F, suggests it is the residue mainly responsible for the observed effects. Furthermore, there is no change in the secondary structure content when the toxin inserts into membranes. Finally, the basis of the very low activity shown by a pneumolysin molecule from another strain of S. pneumoniae may be due to the movements of a key domain-domain interface. The molecular basis of pneumolysin-induced complement activation may be related to the structural similarity of one of the domains of pneumolysin to Fc, rather than the presumed homology of the toxin to C-reactive protein as previously suggested.

Glutathione S-transferases (GSTs) represent the major class of detoxifying enzymes from parasitic helminths. As a result, they are candidates for chemotherapeutic and vaccine design. Indeed, GSTs from Fasciola hepatica have been found to be effective for vaccinating sheep and cattle against fasciolosis. This helminth contains at least seven GST isoforms, of which four have been cloned. The cloned isoforms (Fh51, Fh47, Fh7 and Fh1) all belong to the mu class of GSTs, share greater than 71% sequence identity, yet display distinct substrate specificities. Crystals of Fh47 were obtained using the hanging drop vapour diffusion technique. The crystals belong to space group I4122, with one monomer in the asymmetric unit, which corresponds to a very high solvent content of approximately 75%. The physiological dimer is generated via a crystallographic 2-fold rotation. The three-dimensional structure of Fh47 was solved by molecular replacement using the Schistosoma japonicum glutathione S-transferase (Sj26) crystal structure as a search model. The structure adopts the canonical GST fold comprising two domains: an N-terminal glutathione-binding domain, consisting of a four-stranded beta-sheet and three helices whilst the C-terminal domain is entirely alpha-helical. The presence of Phe19 in Fh47 results in a 6 degrees interdomain rotation in comparison to Sj26, where the equivalent residue is a leucine. Homology models of Fh51, Fh7 and Fh1, based on the Fh47 crystal structure, reveal critical differences in the residues lining the xenobiotic binding site, particularly at residue positions 9, 106 and 204. In addition, differences amongst the isoforms in the non-substrate binding site were noted, which may explain the observed differential binding of large ligands. The major immunogenic epitopes of Fh47 were surprisingly found not to reside on the most solvent-exposed regions of the molecule.

Spectroscopic and kinetic studies have been performed on the Australian sheep blowfly Lucilia cuprina glutathione S-transferase (Lucilia GST; EC 2.5.1.18) to clarify its catalytic mechanism. Steady state kinetics of Lucilia GST are non-Michaelian, but the quite hyperbolic isothermic binding of GSH suggests that a steady state random sequential Bi Bi mechanism is consistent with the anomalous kinetics observed. The rate-limiting step of the reaction is a viscosity-dependent physical event, and stopped-flow experiments indicate that product release is rate-limiting. Spectroscopic and kinetic data demonstrate that Lucilia GST is able to lower the pKa of the bound GSH from 9.0 to about 6.5. Based on crystallographic suggestions, the role of two hydroxyl residues, Ser-9 and Tyr-113, has been investigated. Removal of the hydroxyl group of Ser-9 by site-directed mutagenesis raises the pKa of bound GSH to about 7.6, and a very low turnover number (about 0.5% of that of wild type) is observed. This inactivation may be explained by a strong contribution of the Ser-9 hydroxyl group to the productive binding of GSH and by an involvement in the stabilization of the ionized GSH. This serine residue is highly conserved in the Theta class GSTs, so the present findings may be applicable to all of the family members. Tyr-113 appears not to be essential for the GSH activation. Stopped-flow data indicate that removal of the hydroxyl group of Tyr-113 does not change the rate-limiting step of reaction but causes an increase of the rate constants of both the formation and release of the GSH conjugate. Tyr-113 resides on alpha-helix 4, and its hydroxyl group hydrogen bonds directly to the hydroxyl of Tyr-105. This would reduce the flexibility of a protein region that contributes to the electrophilic substrate binding site; segmental motion of alpha-helix 4 possibly modulates different aspects of the catalytic mechanism of the Lucilia GST.

A tertiary model of the human GSTT2 Theta class glutathione transferase is presented based on the recently solved crystal structure of a related thetalike isoenzyme from Lucilia cuprina. Although the N-terminal domains are quite homologous, the C-terminal domains share less than about 20% identity. The model is used to consolidate the role of Ser 11 in the active site of the enzyme as well as to identify other residues and mechanisms of likely catalytic importance. The T2 subfamily of theta class enzymes have been shown to inactivate reactive sulfate esters arising from arylmethanols. A possible reaction pathway involving the conjugation of glutathione with one such sulfate ester, 1-menaphthyl-sulfate, is described. It is also proposed that the C-terminal region of the enzyme plays an important role in allowing substrate access to the active site.

The myosin-associated giant protein kinases twitchin and titin are composed predominantly of fibronectin- and immunoglobulin-like modules. We report the crystal structures of two autoinhibited twitchin kinase fragments, one from Aplysia and a larger fragment from Caenorhabditis elegans containing an additional C-terminal immunoglobulin-like domain. The structure of the longer fragment shows that the immunoglobulin domain contacts the protein kinase domain on the opposite side from the catalytic cleft, laterally exposing potential myosin binding residues. Together, the structures reveal the cooperative interactions between the autoregulatory region and the residues from the catalytic domain involved in protein substrate binding, ATP binding, catalysis and the activation loop, and explain the differences between the observed autoinhibitory mechanism and the one found in the structure of calmodulin-dependent kinase I.

Glutathione transferase P1-1 (EC 2.5.1.18) is a dimeric enzyme composed of identical subunits each containing one binding site for GSH and a second for the co-substrate e.g. 1-chloro-2,4-dinitrobenzene. Steady-state kinetics are strictly hyperbolic toward both these substrates. Replacement of Cys-47 with alanine or serine decreases the affinity for GSH and triggers a positive kinetic cooperativity with respect to the substrate. Hill coefficients were 1.31 and 1.43 for the C47A and C47S mutants. C47A/C101S and C47S/C101S double mutants display lower affinity for GSH and higher Hill coefficients (1.57 and 1.56, respectively) when compared with C47A and C47S single mutants. Conversely, replacement of Cys-101 with alanine or serine does not yield any cooperativity and any marked change of kinetic parameters. Fluorometric experiments gave sigmoidal isothermic GSH binding curves for all the Cys-47 mutants, with Hill coefficients similar to that obtained by the kinetic approach. These data, together with the activation experiments performed in the presence of S-hexylglutathione, suggest that the substitution of Cys-47 yields a dimeric low-affinity enzyme which may be revealed by the lack of a peculiar electrostatic bond between the thiolate form of Cys-47 and the protonated amino group of Lys-54.

One hundred ten patients complaining of nondental orofacial pain of more than 3 months' duration were psychologically evaluated with the Minnesota Multiphasic Personality Inventory. Four distinct personality profiles were found: psychophysiologic reaction, in 52% of the patients; depressed reaction, in 11% of the patients; defensive reaction, in 12% of the patients; and "no diagnosis" (normal), in 24% of the patients. These results indicate that chronic temporomandibular pain patients present personality characteristics that are similar to those of other chronic pain patients according to the Minnesota Multiphasic Personality Inventory. The diagnostic and therapeutic implications of each profile are reviewed and discussed in terms of a medical model of temporomandibular disorders.

Acromegaly was diagnosed in a 37-year-old woman with classical physical and biochemical findings; an enlarged sella on computed tomography suggested the presence of a pituitary macroadenoma. Radiologic evidence of a lung mass prompted radioimmunoassay of plasma growth hormone-releasing factor (7,500 pg/ml; normal less than 100 pg/ml). After resection of a bronchial carcinoid, which stained positive for growth hormone-releasing factor, circulating growth hormone-releasing factor levels normalized. Subsequently, her clinical, biochemical, and radiologic evidence for acromegaly resolved. This case represents the first reported use of the human pancreatic growth hormone-releasing factor 1-40 radioimmunoassay to preoperatively diagnose this rare etiology of acromegaly.

This article reviews the recent literature related to occlusal considerations in restorative dentistry. The major topics include the assessment and treatment of occlusal wear, the controversies surrounding treatment position of the mandibular condyles, occlusal considerations in osseointegrated prostheses, the two-way relationship between occlusal factors and temporomandibular disorders, design criteria and longevity studies in resin-bonded, fixed-partial dentures, and a potpourri of articles on other topics of interest. Five textbooks and 32 journal articles are cited.

1. Four lots of barley seedlings were grown on 16-hour photoperiod to ages of 5, 10, 15, and 20 days, respectively, at 65⚬ F. Each lot was then divided into three groups and all were grown for another week under the same conditions of light and photoperiod. One group of each lot, however, was continued during the week at 65⚬ F., one was transferred to 45⚬ F., and the third to 35⚬ F. The plants were then removed from the control rooms and transplanted out of doors for final differential photoperiodic treatment. 2. At the beginning and end of the temperature treatments representative plants from each lot were photographed and dissected. The total number of nodes in the main axis of each was determined, and enlarged photographs of the terminals of the main axes were made. 3. Ten plants from each age and temperature group were subjected to 12,- 16-, 20-, and 24-hour photoperiods after they were moved outside and remained on these photoperiods at natural temperatures for the duration of the experiment. 4. Numb...

1. When whole plants of Biloxi soy beans are subjected to 8 hour photoperiods, initiation occurs if the intensity of light during the photoperiod is above 100 foot candles. Below 100 foot candles no flower primordia are initiated. 2. When plants are given an 8 hour photoperiod of natural light supplemented by 8 hours of Mazda light, initiation occurs if the intensity of the supplemental light is below 0.5 foot candle, but does not occur if the intensity is above 0.5 foot candle. 3. The stimulus that causes initiation of flower primordia at the growing points arises in the leaves and moves to the growing plants. 4. Flower primordia may be initiated at growing points that are kept, either in complete darkness or on photoperiods above the critical, provided the leaves are kept on short photoperiods. 5. Photoperiods shorter than the critical, applied directly to growing points, have no effect on flower bud initiation. Control of initiation is exercised only through application of photoperiods of proper length...

1. In a study of the effects of photoperiod and nitrogen nutrition on the expression of certain morphological characteristics of soybean, plants of Morse, Virginia, Lincoln, and T-48 varieties were grown either in controlled-environment rooms or in the greenhouse and in either soil or sand cultures. 2. In experiments in which nitrogen nutrition was not a factor, all varieties flowered on all durations of photoperiod, but first-flower primordia were formed at a higher node on the plant axis with the longer photoperiods. 3. Position of first-flower primordia did not vary with nitrogen treatment when the plants were grown with short photoperiods. When grown with long photoperiods, however, plants of certain varieties initiated first-flower primordia at higher nodes as the amount of nitrogen in the nutrient solution was increased. Variety T-48 was outstanding in this respect, Lincoln was intermediate, while Morse and Virginia were least responsive. 4. Plants of Lincoln and Morse grown on long photoperiods sho...

1. A study was made of the several effects of photoperiod and nitrogen nutrition upon the bulb and flower-stalk development of onion. Plants were grown from seed, sets, and mature bulbs, and with soil and in sand culture. 2. Plants grown on photoperiods substantially longer than that critical for bulb formation showed no difference in bulb development when supplied different amounts of nitrogen. 3. Plants grown on a photoperiod at or near that critical for bulb formation exhibited the greatest bulb development with the lowest nitrogen concentration and the least with the highest concentration. 4. Under certain environmental conditions nitrogen and photoperiod can interact to influence bulb development of certain onion varieties. 5. Onion plants of sister lines gave similar bulbing response on photoperiods of identical duration. However, the two lines differed in their production and development of visible floral stalks, especially on the shorter of the photoperiods. Development of floral stalks was favore...

1. The purposes of this investigation were to obtain quantitative data on the photoreactions that prevent flowering of short-day plants, from which an action spectrum relating wave length to photoperiodic effectiveness of light could be derived, and to draw such inferences concerning the nature of the photoreactions as the action spectrum would permit. 2. Experiments designed to give the action spectrum made use of a specially designed prism spectrograph having a dispersion of 15 A. per cm. at 5000 A. At this wave length and with an effective slit width of 100 A. the energy was about 3000 ergs per sq. cm. per second with the slit illuminated by a carbon arc operated at 12 kw. input. 3. Plants investigated were soybean, Soja max (L.) Piper var. Biloxi, and cocklebur, Xanthium saccharatum Wallr. To facilitate irradiation, the foliar surface of the plants of each species at the beginning of an experiment was reduced to a single leaflet or leaf, respectively. 4. The experimental treatment was based on the fac...

1. Tomato seedlings were decapitated above the second lobed leaf and a mixture of 20 mg. of indoleacetic acid in 1 gm. of lanolin was applied to the cut surface. Similarly, decapitated plants were kept as controls, either untreated or with pure lanolin applied to the cut surface. 2. Gross observations and histological and microchemical studies were made of treated and control material collected at frequent regular intervals for a period of 216 hours after treatment. 3. The internode terminated by the cut surface fails to enlarge after decapitation unless the cut surface is treated with indoleacetic acid-lanolin mixture. The internodes so treated enlarge at about the same rate as do the internodes below. 4. The first change observed after treatment was enlargement of cells of the epidermis and cortex. 5. Many of the tissues of the stem became meristematic in response to the treatment, although most of this activity was confined to a zone 0.5 to 2 mm. from the treated surface. Most parenchymatous cells in t...

1. Biloxi plants or parts of Biloxi plants, subjected continuously to daily photoperiods of 17 or more hours, were used as one component of all grafts reported in this work. Plants of this variety do not develop sufficient flower-forming stimulus on long photoperiods to cause floral initiation. They therefore served to determine whether or not a flower-inducing stimulus was transmitted across the graft unions. They are referred to as receptors and the plant or plant parts grafted to them as the donors. 2. The donor components were from Agate, Batorawka, or Biloxi varieties of Soja max, or from Red Kidney, Plentiful, Black Valentine, or Dwarf Horticulture varieties of Phaseolus vulgaris. 3. Methods of grafting employed were approach grafting of stems, splice grafting of petioles, splice grafting of stems, and bud grafting. 4. A total of 490 Agate-Biloxi approach grafts were made and all formed strong unions. Approximately 50 per cent of the Biloxi receptors formed flower primordia. This percentage was some...

1. The influence of low temperature in suppressing flower-bud initiation in Biloxi soybean has been considered from three points of view: its influence upon the differentiation of flower buds from the meristems; its influence on translocation of a flower-forming stimulus from the leaves to the growing points; and its influence upon those processes in the leaf that bring about flower-bud formation. Data are presented on the first two of these points; the last is being subjected to further investigation. 2. Fewer flower buds were formed in response to a 4-day induction treatment on plants bearing a single leaf if the terminal buds or the petioles were cooled to 3⚬ C. than if they were not cooled. When the temperature was raised to 10⚬ C. the inhibiting effect on flowering decreased in both types of experiments, but even at this temperature only slight growth of the terminals occurred during the induction treatment. 3. Petiole-cooling experiments involving plants with two leaves indicate that inhibition of f...

1. Initiation of flower primordia in Biloxi soybean was limited by controlling photosynthesis during induction. This was done in one case by controlling the CO2 supplied to the plants and in another by controlling the duration of high-intensity light. 2. When no CO2 was supplied during 8-hour photoperiods, no initiation of primordia occurred. Plants that received the CO2 contained in natural air during 2, 4, 6, and 8 hours of each photoperiod produced flower primordia in proportion to the duration of time the natural air was supplied. 3. Plants that received only 1 hour of high-intensity light during an 8-hour photoperiod formed no flower primordia. Those that received 2 hours or more of high-intensity light during the photoperiod produced increasingly larger numbers of flower primordia as the duration of high-intensity light increased. 4. Increased concentration of CO2 in natural air resulted in increased floral initiation.

1. Flower primordia were present on plants of Taraxacum kok-saghyz collected from several localities in the central or northern parts of the United States during the late fall or winter months. Photoperiods of 8, 10, 12, 14, 16, and 18 hours did not inhibit the development of these primordia into mature flowers when the plants were transplanted in the greenhouses. 2. Wide variability of leaf pattern was observed in the seedlings, but morphological characteristics of the flowers indicated that almost all were kok-saghyz plants. Seedling plants subjected to six different lengths of photoperiods varying from 8 to 18 hours flowered under all conditions, but more of them flowered with photoperiods of 12 hours or longer than with shorter photoperiods. 3. Plants that received low temperatures during their early development flowered more abundantly than those that received no low temperature. Ninety-eight per cent of one lot of seedlings that had received several weeks of cold weather during the spring flowered, ...

1. Wintex barley grown with an 11.5-hour photoperiod and a 12.5-hour dark period remained vegetative. If the dark period was interrupted with a brief period of irradiation of sufficient intensity, spikelet formation was stimulated. 2. By use of this technique of interrupting the dark period, quantitative data on the photoreaction that promoted flowering were obtained, and action spectra relating wave-length to photoperiodic effectiveness of light were derived. 3. The most effective time to apply the dark-period interruptions was the 2-hour period beginning 6.5 hours after the start of the dark period. Within this time and with the intensities used, the reciprocity law held. Energy required to promote flowering, if applied continuously throughout the 12.5-hour dark period, was about tenfold greater than if applied within the 2 hours near the middle of the dark period. 4. The action spectrum for the production of spikes in barley was very similar to the action spectra for the prevention of floral initiation...

1. Biloxi soy bean plants with flower primordia initiated upon them were transferred to photoperiods of 8, 10, 12, 13, 14, 15, 16, and 18 hours. The development of these primordia and the flowering and fruiting responses of the plants were determined. 2. The plants transferred to photoperiods of 8 to 13 hours bloomed nearly simultaneously and all produced fruits. The yield of fruits on the 8 hour lot was somewhat less than on the 10, 12, and 13 hour lots. 3. Flowering on the 14 and 15 hour plants was later than on those of shorter photoperiod, the flowers were less numerous, and no fruits were formed. 4. No flowers opened on the 16 and 18 hour plants during the experiment. 5. When plants were transferred to a range of photoperiods after flower primordia were initiated it was found that the longest photoperiod on which fruit formation occurred was 13 hours and the shortest one on which no flowering took place was 16 hours. 6. Plants were grown for biochemical studies on 8, 13, and 16 hour photoperiods afte...

LIGHT TAKES part in a number of distinct physiological reactions in plants. Among these are chlorophyll formation, photosynthesis, photoperiodism, phototropism, and cell elongation. Pigments are necessarily involved in the initial absorption of light in each process. Measurement of the effectiveness of different wave lengths of light gives information about the pigment and possible basic similarity of the initial steps in different physiological processes. This method is here applied to establish a relationship between growth of etiolated seedlings and floral initiation in photoperiodically responsive plants. Spectral sensitivities or action curves have been obtained for floral initiation in both longand short-day plants by Parker et al. (1946, 1948). The response to light shows that the same pigment or same class of pigments is effective in both tvpes of plants and that the most effective absorption is in the red portion of the spectrum. Effects of light on stem and leaf growth of etiolated pea seedlings have been measured by Went (1941). Here too the red portion of the visible spectrum is most effective, the response being an increase in leaf area and suppression of internode elongation, while the blue is relatively ineffective. The spectrographic arrangement of Parker et al. (1946), which affords high dispersion, large irradiation area, and high intensity of a given wave length region but with low intensities of other wave lengths as impurity, meets the necessary conditions for use in a detailed study of the action curve for etiolated peas. MATERIALS AND METHODS.-Spectrograph apparatus.-The description of the spectrograph which has previously been given in detail (Parker et al., 1946) is repeated here for immediate reference and to indicate required modifications. The energy source is the crater of a high-intensity arc with rotating cathode (fig. 1). A diaphragm essentially serving as the slit of the spectrograph is placed in the convergent beam from the condensing lens. The essential focusing element is a front-aluminized concave spherical mirror of 2-m. focal length, conjugate foci of which are the slit and focal plane. Two large glass prisms, set for minimum deviation at 5780 A, are placed in the convergent beam from the mirror and the emergent light is reflected from a flat front-silvered mirror that can be rotated by a tangent screw. In experiments with etiolated pea seedlings the instrument was used essentially as a monochromator to throw a narrow wave length region on a slit in the focal plane. This narrow band of the spectrum 1 Received for publication September 8, 1948. had to be spread out to permit radiatinig the seedlings in the 35 cm. boxes and to give variation of intensity. This was accomplished by use of an achromatic lens as shown in the diagram. The F7 lens had previously been used for collimation on a large Steinheil Spectrograph and had a focal length of 195 mm. A 5.5-m. I beam was used as an optical bench in the diverging beam from the achromatic lens. Boxes of peas could be placed along this beam at predetermined distances from the lens corresponding to given magnifications. The bench was housed in black cloth to eliminate all light except that entering through the lens. A side opening in the housing led to the dark room in which the peas were held before treatment and to which they were returned. Intensity could be reduced as much as 1000-fold by the divergence and transmission of the lens (68 per cent). It was further reduced when desired by introducing neutral screens (blackened wire gauze) of known transmissions between the slit and the concave mirror, a more than 100-fold factor being obtainable in this way. Wave length calibration was carried out by use of a low-pressure mercury arc to illuminate the slit. Energy values for definite wave bands were measured with a ten-junction thermopile that was standardized with an N. B. S. certified lamp. Spectrographic procedure.-An action curve can be considered as expressing the energy required to give a definite effect as a function of wave length. This can be obtained in several ways for response of etiolated pea seedlings. The method adopted required two different types of treatment. It avoided investigation of variation of response with duration of illuminations which is intrinsically of interest but not immediately pertinent to the objective. In the first instance the variation of response was measured at different energies given in constant time. A 4-min. daily interval for illumination on 4 successive days was adopted on the basis of previous work by Went (1941). Energies were varied by approximately 20,000-fold for a given wave length band. Sufficient points were taken to give the response, change in leaf length, as a function of energy. These measurements were made for five regions varying from the blue to the red portion of the spectrum. Experiments, were performed as follows. Three stations were established on the optical bench in the diverging radiation from the lens in the focal plane to give relative energies of 18.5, 4.30, and 1.0. Two boxes of peas were irradiated at each of these stations. Neutral screens were then placed in the light beams to reduce the intensity to 1/80 of

1. Biloxi soybeans were grown in the greenhouse for four to five weeks and transferred to a series of control rooms where various combinations of temperature during the photoperiod and the dark period were applied for five days. Photoperiods of both 8 and 16 hours were used. 2. The effect of these various temperatures on the initiation of flower primordia has been determined. 3. Initiation of flower primordia was influenced to a much greater extent by variation in temperature during the dark period than by variation during the photoperiod. 4. When the temperature during the photoperiod was constant, a 55⚬ temperature during the dark period limited the amount of initiation that occurred. At 65⚬ initiation was much more extensive. This rise of 10⚬ in temperature during the dark period produced a greater difference in initiation than any other temperature variation of the same amount. 5. Variation in temperature resulted in the formation of different numbers of nodes. These differences, however, were not gre...

1. Vegetative plants of Hyoscyamus niger can be induced to flower by application of relatively small amounts of radiant energy near the middle of dark periods that would prevent flowering if uninterrupted. 2. Interruptions of 12-hour dark periods with energies corresponding to about 100 foot-candle-minutes of light were effective in causing initiation of flower primordia. Minimum energy to cause a given effect was relatively constant if the interruption was made during the 2-hour period following the middle of the dark period. 3. The action curve for floral initiation of H. niger was readily established in the region from 7300 A to 5600 A. Limitation of energy from 5600 A to 4000 A made it impossible to establish a continuous response curve for this region, but sufficient points were obtained to establish the limits of effectiveness. This curve is essentially the same as those for control of flowering in soybean, cocklebur, and barley, and for regulation of leaf size in etiolated peas. 4. Similarity of th...

1. Individual leaves on a Biloxi soybean when subjected to photoperiodic stimulation differ in their capacities to cause floral initiation. 2. The most effective leaf on the plant is the one that has most recently attained its full size. Young leaves increase in their capacity to effect floral initiation until they attain full size, after which they gradually decline in effectiveness. 3. The most active leaf, operating alone, is able to cause initiation of as many flower buds per plant as are formed when all leaves function simultaneously. 4. The capacities of different leaves to supply a flower-forming stimulus is correlated with their relative states of maturity and not with their distances from the growing points where flowers are formed. When the flower-forming stimulus from the third compound leaf passes downward through two internodes to the bud in the axil of the first compound leaf, it induces the formation of more flower primordia there than does the stimulus from the first compound leaf which is...

1. Apparatus was devised that made possible the application of controlled temperature to individual leaves of Biloxi soybean plants during the dark periods of a photoperiodic treatment, while the remainder of the plant received greenhouse temperatures and long photoperiods. 2. When a leaf was held at 50⚬F. or lower during a 5-day induction period, floral initiation was greatly inhibited. At 70⚬-90⚬, such initiation was in general equal to that of the controls held at greenhouse temperatures, but at 90⚬ or higher the extent of the initiation again was less. 3. On the basis of the data presented in this and two preceding papers, the inhibiting effect of low temperature on floral initiation in Biloxi soybean plants appears to be the result of its effect on the photoperiodic reactions occurring in the leaf blade during the dark period, rather than through its effect on translocation of a flower-inducing stimulus from the leaf to the terminal meristems or its effect at the terminal meristems upon the different...

1. Young Biloxi soy beans were grown for about a month on a long photoperiod. These long-day plants were divided into eight series, each receiving a different short photoperiod. Plants from each series were returned to natural day after 1, 2, 3, 4, 5, 6, 8, and 10 days. 2. Stimulation of two short photoperiods was sufficient to alter the course of development of the growing points in such a way that differentiation of flower primordia resulted. 3. The length of the photoperiod influenced the time of blossoming, since the plants receiving intermediate photoperiods blossomed earlier than those receiving either the extremely long or short photoperiods used in this experiment. 4. The number of days that the plants received these various treatments influenced the time of blossoming. Plants treated for 8 days blossomed earlier than those treated for only 6 days. 5. Meristems of plants growing on long day are described and compared with the meristems of those growing on short day. 6. The first visible response t...