Explant Orientation and Polarity Determine the Morphogenic Response of Epicotyl Segments of Troyer Citrange

The morphogenic pathway of adventitious bud and shoot regenerationat the ends of Troyer citrange epicotyl cuttings is determinedby polarity and explant orientation. In explants planted verticallywith the basal end inserted in the medium, bud formation atthe apical end occurs by direct organogenesis. Bud growth andsubsequent shoot formation is markedly increased by the additionof 6-benzyladenine (BA) to the medium. This growth regulatoralso increases the number of buds formed. When they come intocontact with the culture medium, both the apical end and thebasal end of the cuttings form a vigorous callus with many xyllaryelements, more numerous in the calli from the basal end. Inthese calli, buds differentiate by a process of indirect organogenesis.This indirect regeneration pathway requires the addition of6-benzyladenine to the medium, and the number of buds formedis higher at the apical end than at the basal end of the cuttings.This pathway of regeneration is reduced as the position of thecuttings during incubation deviates from the normal uprightvertical position. Thus, for the basal end of the cuttings,the number of buds and shoots formed is higher when the explantsare placed vertically than when they lie on the surface of themedium. For the apical end, this number is higher in explantsplaced horizontally than when inserted vertically in the mediumin an inverted position. Copyright 1999 Annals of Botany Company Troyer citrange, Citrus sinensis x Poncirus trifoliata, explant orientation, histology, hormone dependence, morphogenesis, organogenesis, polarity, xylogenesis.     

Shoot, Stolon, and Tuber Formation on Potato (Solanum tuberosum L.) Cuttings in Response to Photoperiod

The intensity of “tuberization stimulus” in potato shoots (Solanum tuberosum L.) can be assessed from cuttings containing one or more leaves. Cuttings maintained in a mist chamber under long days will form tubers from underground buds if prior to taking the cutting the leaves received sufficient exposure to photoperiods less than the critical photoperiod. The greatest tendency to tuberize was found in cuttings that consisted of a single, fully expanded leaf and its subtended bud. Grafts showed that genetical differences in critical photoperiod resided in properties of the leaf. Short days before cutting tended to shift growth from above ground buds of two-node cuttings to below ground buds, even if the number of short days was insufficient for tuber induction. As few as 6 short days reduced growth of shoots at the upper bud and increased underground growth of shoots and stolons.     

Metabolomics Reveals Metabolically Healthy and Unhealthy Obese Individuals Differ in their Response to a Caloric Challenge

Objective

To determine if metabolically healthy obese (MHO) individuals have a different metabolic response to a standardized diet compared to lean healthy (LH) and metabolically unhealthy obese (MUO) individuals.

Methods

Thirty adults (35–70 yrs) were classified as LH, MHO, and MUO according to anthropometric and clinical measurements. Participants consumed a standardized high calorie meal (~1330 kcal). Blood glucose and insulin were measured at fasting, and 15, 30, 60, 90 and 120 min postprandially. Additional blood samples were collected for the targeted analysis of amino acids (AAs) and derivatives, and fatty acids (FAs).

Results

The postprandial response (i.e., area under the curve, AUC) for serum glucose and insulin were similar between MHO and LH individuals, and significantly lower than MUO individuals (p < 0.05). Minor differences were found in postprandial responses for AAs between MHO and MUO individuals, while three polyunsaturated FAs (linoleic acid, γ-linolenic acid, arachidonic acid) showed smaller changes in serum after the meal in MHO individuals compared to MUO. Fasting levels for various AAs (notably branched-chain AA) and FAs (e.g., saturated myristic and palmitic acids) were found to correlate with glucose and insulin AUC.

Conclusion

MHO individuals show preserved insulin sensitivity and a greater ability to adapt to a caloric challenge compared to MUO individuals.     

Pathways that Regulate Autophagy and their Role in Mediating Tumor Response to Treatment

Addenda to:

Rapamycin-Sensitive Pathway Regulates Mitochondrial Membrane Potential, Autophagy and Survival in Irradiated MCF-7 Cells

Paglin S, Lee N-Y, Nakar C, Fitzgerald M, Plotkin J, Deuel B, Hackett N, McMahill M, Sphicas E, Lampen N and Yahalom J.

Cancer Res 2005; 65:11061-70.

In addition to their role in cellular homeostasis, pathways that regulate autophagy affect both tumorigenesis and tumor response to treatment. Therefore, understanding regulation of autophagy in treated cancer cells is relevant to discovery of molecular targets for development of anti-cancer drugs. Our recent report points to radiation-induced inactivation of mTOR pathway as an underlying mechanism of radiation-induced autophagy in the human breast cancer cell line MCF-7. Most importantly, radiation-induced inactivation of this pathway was detrimental to cell survival and was associated with reversal of mitochondrial ATPase activity and mitochondrial hyperpolarization, decreased level of eukaryotic initiation factor 4G (eIF4G) and increased phosphorylation of p53. Future analysis of the interrelationship among these events and the role each of them plays in cell survival following radiation will increase our ability to employ the mTOR pathway in anti-cancer therapy.     

Stimulation of Shoot Regeneration on Linum Hypocotyl Segments by Thidiazuron and Its Response to Light and Calcium

The basal segment from hypocotyl of Linum usitatissimum L. seedling readily regenerates, to produce a large number of shoots, in a short period of 5 [ndash ] 7 d. This response was stimulated by a low concentration (0.1 [micro ]M) of thidiazuron (TDZ). TDZ was also effective in inducing regeneration in dark. A drastic reduction in regeneration response on hormone-free as well as TDZ-supplemented medium was found after inclusion of an inhibitor of calcium-uptake, lanthanum (La³⁺). An essentiality of calcium in the regeneration was also evidenced by an increased response with increasing concentration of calcium. At Ca²⁺ concentration insufficient for regeneration, inclusion of TDZ resulted in shoot formation.     

Propagation of Citrus reticulata via in vitro Seed Germination and Shoot Cuttings

Seeds of Citrus reticulata were germinated efficiently when they were sown directly after their extraction from fruits harvested in January, and incubated at constant temperature (25 °C). Seed drying decreased both the percentage of seed germination and the number of seedling per seed. Germination of seeds was better on Murashige and Skoog (MS) medium supplemented with 0.5 mg dm⁻³ benzylaminopurine (BAP) than in a soil. Shoot cuttings obtained from germinated seeds were subcultured on B5 medium supplemented with 1 mg dm⁻³ BAP, 0.5 mg dm⁻³ kinetin (KIN) and 0.5 mg dm⁻³ naphthalene acetic acid (NAA), where shoots grew and multiplied. They were rooted on half strength MS medium supplemented with 0.25 mg dm⁻³ BAP, 0.5 mg dm⁻³ NAA and 1 mg dm⁻³ isobutyric acid (IBA). Rooting under light was better than under dark. Seedlings and shoot cuttings with roots were transferred successfully to the soil after three weeks of acclimatization. This revised version was published online in July 2006 with corrections to the Cover Date.     

Indirect and Direct Energy Requirements of City Households in Sweden: Options for Reduction, Lessons from Modeling

The objective of this article is to explore the potential for lowering household energy use given existing local support systems, in this case in the Stockholm inner city with the aid of the Dutch energy analysis program (EAP) that was adapted to Swedish conditions and that portrays total energy use for 300 consumption categories. Previously such modeling for Sweden was carried out using only Dutch databases. Our case-study area is well equipped with food stores, local markets, public transportation, and entertainment, facilitating some energy-efficient consumption choices. With maintained expenditure levels but changed consumption patterns, current reduction potentials are on the order of 10–20%. Options concerning diet can lower food indirect energy use by up to 30%, whereas options in other areas have a lower potential. Further reductions will require enhanced local support systems, external as well as internal. The results indicate that it is risky not to use nationally adapted figures for energy efficiency in the production sectors when modeling household energy use, because potential for change may be overlooked. Future work should include foreign energy intensities when modeling imported goods; otherwise, results may be less reliable. The Swedish EAP needs further work before it can be put to use as a modeling tool for everyday behavior, but it is already generating important possibilities for producing reliable data that can be used by local energy counselors.     

Plasma Luteinizing Hormone Response to Increasing doses of Synthetic Gonadotrophin-Releasing Hormone in Heifers

The dosenresponse relationship for a synthetic gonadotrophin-releasing hormone (GnRH) was studied in normally cycling heifers using the area under the luteinizing hormone (LH) curve as a response parameter. Oestrus was synchronized by an injection of 0.5 mg cloprostenol before the experiment started and after the 3rd treatment with GnRH. Treatment with GnRH as assigned in a Latin square included 5 dose levels (0, 10, 50, 100, 250 μg) and 5 treatment days over a period of 22 days. GnRH was capable of inducing an increase of plasma LH within 30 min after injection. Plasma LH response increased with increasing doses of GnRH, the largest increase being observed when the dose was raised from 50 μg to 100 μg. One heifer did not respond to any of the doses applied. The existence of an individual treshold dose of GnRH is suggested.     

Shoot Elongation in Scots Pine: Diurnal Variations and Response to Temperature

Kanninen, M. 1985. Shoot elongation in Scots pine: Diurnal variationsand response to temperature.—J. exp. Bot. 36: 1760–1770. Time series analysis is used to study the diurnal variationsin the rate of shoot elongation of Scots pine (Pinus sylvestrisL.) seedlings, and its response to temperature. The shoot elongation of three 5-year-old Scots pine seedlingswas measured at 2 h intervals over a 12 d period in June 1979.Ambient temperature, measured with a thermocouple, was continuouslyrecorded during the same period. The measurements were carriedout in the field. Time series analysis of the data was carried out by estimatedauto-correlation and partial auto-correlation functions. A multiplicative‘seasonal’ model was applied to both the input andoutput series to ‘prewhiten’ the data set. Serialcross-correlation analysis of the prewhitened series was usedto identify the structure of the transfer function model betweentemperature and growth rate. There was a phase shift between the air temperature and shootextension. The cross-correlation function peaked at 2 h lagvalue. The influence of temperature on the growth rate was adequatelydescribed by a first-order transfer function model. The characteristicfeature of the model was a time constant of 3.3 h and a basetemperature of 6.3 °C for the response of shoot elongationto temperature. Key words: Scots pine, Pinus sylvestris L., shoot elongation, temperature response, time-series analysis     

Basal Plate Tissue in Narcissus Bulbs and in Shoot Clump Cultures: Its Structure and Role in Organogenic Potential of Single Leaf Cultures

Light microscopy demonstrated that the apparently amorphous,achlorophyllous tissue at the base of in vitro shoot clump cultureof Narcissus was comparable in structure to the basal plateof Narcissus bulbs. Both had very complex vascularisation andsmall, densely packed parenchymatous cells. In shoot clump cultures, primordia were produced by meristematiczones at the surface of this achlorophyllous tissue, very closeto the base of leaves. Single leaf units excised from the invitro shoot clump cultures with a wedge of basal achlorophylloustissue were highly organogenic when used as secondary explantsfor in vitro culture of Narcissus. No organogenesis occurredin the absence of the leaf base and achlorophyllous (basal plate)tissue and little organogenesis occurred unless the leaf baseand basal plate tissue were immersed in the culture medium (i.e.explants inoculated into liquid medium or upright in agar-solidifiedmedium). After two 5-week culture passages in liquid medium, more thanfive leaves were produced per leaf base inoculated. Thus rapidmicropropagation of Narcissus can be achieved using only thebase of single leaf units excised from shoot clump cultures.Copyright1993, 1999 Academic Press Anatomy, basal plate, bulb, in vitro, leaf culture, Narcissus, organogenesis     

Early- and Late-Emerging Drosophila melanogaster Fruit Flies Differ in Their Sensitivity to Light During Morning and Evening

The authors derived early and late populations of fruit flies showing increased incidence of emergence during morning or evening hours by imposing selection for timing of emergence under 12:12?h light/dark (LD) cycles. From previous studies, it was clear that the increased incidence of adult emergence during morning and evening hours in early and late populations was a result of evolution of divergent and characteristic emergence waveforms in these populations. Such characteristic waveforms are henceforth referred to as “evolved emergence waveforms” (EEWs). The early and late populations also evolved different circadian clocks, which is evident from the divergence in their clock period (τ) and photic phase response curve (PRC). Although correlation between emergence waveforms and clock properties suggests functional significance of circadian clocks, τ and PRCs do not satisfactorily explain the early and late emergence phenotypes. In order to understand the functional significance of the PRC for early and late emergence phenotypes, the authors investigated whether circadian clocks of these flies exhibit any difference in photosensitivity under entrained conditions. Such differences would suggest that the light requirement for circadian entrainment of the emergence rhythm in early and late populations is different. To test this, they examined if early and late flies differ in their light utilization behavior, first by assaying their emergence rhythm under complete photoperiod and then in three different skeleton photoperiods. The results showed that early and late populations require different durations of light during the morning and evening to achieve their EEWs, suggesting that for the circadian entrainment of the emergence rhythm, early and late flies utilize light from different parts of the day. (Author correspondence: vsharma@jncasr.ac.in or vksharmas@gmail.com)     

Light Response of Seedlings of a Central African Timber Tree Species,Lophira alata (Ochnaceae), and the Definition of Light Requirements

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many implications in forest management and restoration ecology. Most shade‐tolerance classification systems have been proposed based on empirical observations in a specific area and thus result in contradictions among categories assigned to a given species. In this study, we aimed to quantify the light requirements for seedling growth of a Central African timber tree, Lophira alata (Ochnaceae), taking into account effects of population origin. In two controlled experiments: a light response experiment and a comparative population experiment, conducted in southwestern Cameroon, using seeds collected from four populations (three from Cameroon and one from Gabon), we examined the quantitative responses to irradiance of seedlings. After 2 years, mortality was very low (<3%), even in extremely low irradiance. Growth and biomass allocation patterns varied in response to light, with intermediate irradiance (24–43%) providing optimal conditions. Light response differed between populations. The Boumba population in the northeastern edge of the species' distribution exhibited the highest light requirements, suggesting a local adaptation. As a result of positive growth at low irradiance and maximum growth at intermediate irradiance, we concluded that L. alata exhibits characteristics of both non‐pioneer and pioneer species. Implications of our results to propose an objective way to assign the light requirement for tropical tree species are discussed.     

Correlative Changes in Endogenous Hormone Levels and Shoot Growth Induced by Short Heat Treatments to the Root

Heat treatments of two minutes at 46 to 47°C to root systems of Nicotiana rustica and Phaseolus vulgaris affected roots and shoots. Xylem exudate of Phaseolus was collected, and it was found that heat treatment reduced cytokinin levels and increased abscisic acid levels in the exudate. Shoot and root growth of both species was reduced. Root membrane integrity of Nicotiana was measured and was found to be impaired. It is suggested that the changes in hormone activity due to heat treatment regulate the reduction in shoot growth. Cell wall metabolism and glucosyl transferases making β-glucans were investigated in Phaseolus leaves. Incorporation of ¹⁴C from ¹⁴CO₂ into wall constituents was slightly inhibited but neither photosynthesis nor extracted β-glucan synthetases were affected during the first 12 hours after treatment.     

Effects of Nutrients and Light on Growth and Root Formation in Pisum sativum Cuttings

Cuttings obtained from seedlings of Pisum sativum L. were rooted in water solution. Shoot growth continued after excision and shoot length increased considerably before roots emerged. Increase in dry weight was strongly dependent on light supply. Continued growth was dependent on supply of mineral nutrients to the rooting solution. Mineral nutrients had no or slight influence on the number of roots formed on cuttings from stock plants grown in fertilized soil, but the growth in length of the roots was dependent on the presence of calcium in the solution. Root formation was dependent on photosynthetic products formed after excision. No roots were formed on cuttings kept in the dark. The number of roots increased with increasing irradiance given to the leafy part of the cutting. At a low level of irradiance sucrose supply through the rooting medium increased the number of roots. Light given to the basal part of the cuttings had a strongly inhibitory effect on the number of roots formed. It is concluded that the carbohydrate level easily becomes a limiting factor for root formation in growing pea cuttings. Availability of mineral nutrients influences in the first place the growth of the shoots.     

Serpentine and Nonserpentine Achillea millefolium Accessions Differ in Serpentine Substrate Tolerance and Response to Organic and Inorganic Amendments

Subgrade serpentine substrates are exceptionally difficult to revegetate due to multiple limitations including low N, P, and K, low Ca:Mg molar ratios, high levels of heavy metals including Ni, Cr, and Co, low organic matter, low CEC, and low water holding capacity. To examine the influence of plant origin on the success of the revegetation of serpentine substrates, granite and serpentine accessions of Achillea millefolium were grown on subgrade serpentine substrate amended with yard waste compost, slow-release NPK fertilizer, and/or CaSO₄ · 2H₂O (gypsum). The goals of this study were to: (1) identify the substrate amendment combination that maximized establishment of A. millefolium on serpentine substrate, (2) compare seedling establishment, survival, and growth of the serpentine and granite A. millefolium accessions in order to determine if a serpentine edaphic ecotype of A. millefolium exists and if this ecotype is superior to the granite accession for the establishment of vegetation on serpentine substrate and (3) if a serpentine edaphic ecotype of A. millefolium does exist, what physiological features with respect to mineral nutrition convey a higher tolerance of serpentine for this ecotype than the nonserpentine ecotype. Seedling establishment, survival, and growth were greatest for A. millefolium when the subgrade serpentine substrate was amended with 30% (v/v) compost and 220 mg kg substrate⁻¹ each of N, P, and K. The serpentine A. millefolium accession displayed a greater tolerance of the subgrade serpentine substrate, serpentine topsoil, and the amended subgrade serpentine substrate than the granite accession. Higher capacity of the serpentine A. millefolium accession for selective Ca translocation from roots to the shoot resulted in a significantly higher shoot Ca:Mg molar ratio than the granite accession and appeared to be the most important physiological feature conveying greater tolerance of the serpentine accession for serpentine substrates.     

Separation of Direct and Indirect Responses of Stomata to Light: Results from a Leaf Inversion Experiment at Constant Intercellular CO2 Molar Fraction

Previous work has shown that stomata respond directly to light,but it was not clear whether the only additional response isthrough CO₂, or whether some other metabolite is involved inthis response. Gas exchange experiments were done with normallypositioned and inverted leaves of Hedera helix to investigatethis problem. The macroscopic optical properties of the leavesand their anatomical structure were also studied. These experimentssnowed that there is no need to postulate the existence of amessenger other than CO₂ to explain the indirect response ofstomata to light. The experiments also showed that leaf inversionaffects both stomatal conductance and photosynthesis, and highlightthe difficulties involved in the interpretation of the effectof leaf inversion on stomata when stomatal conductance measurementsare not done concurrently with measurements of CO₂ flux densityand intercellular CO₂ molar fraction Key words: Hedera helix, ivy, gas exchange, leaf inversion, stomatal conductance, light, CO₂ flux density, photosynthesis