Effects of exogenous cytokinins on flowering of the short-day plantChenopodium rubrum L.

Kinetin at a concentration from 3.10^-6 M to 1.10^-3 M was applied to the plumule ofChenopodium rubrum plants during photoperiodic induction. Different levels of induction were compared (one and three short days). The higher concentrations of kinetin applied to induced plants inhibited flower formation. The rate of leaf initiation was increased under these treatments. Lower concentrations of kinetin (from 3.10^-6 M to 1.10^-5 M) usually promoted lateral bud formation and flowering. The step-wise application of kinetin revealed that the inhibitory effect on flowering had been restricted to the inductive period. The effects of kinetin, benzyladenine and trans-zeatin were compared in plants partially induced by two short days. High concentrations always inhibited flowering. Benzyladenine was the most effective in this respect. Root removal diminished the inhibitory effects of cytokinins on flowering as was stated with benzyladenine. It is assumed that endogenous cytokinins play a role in the regulation of organogenetic activity of the stem apical meristem. Depending on the photoperiodic conditions, they presumably exert their activity by maintaining the vegetative functions of the apex.     

EFFECT OF IONS ON STIMULUS-INDUCED RELEASE OF AMINO ACIDS FROM MAMMALIAN BRAIN SLICES

Slices of mammalian brain accumulate amino acids contained in physiological medium. When such tissues were subjected to mild electrical stimulation of short duraation capable of depolarizing neural membranes, there occurred a striking increase in the efflux of exogenous amino acids. The effects on representative acidic, neutral, and basic amino acids were similar. Elevated levels of potassium chloride evoked release of amino acids comparable to electrical stimulation. Electrically stimulated release of [³H]γ-aminobutyric acid was not inhibited by the presence of reduced concentrations of calcium ions. Although amino acids are actively accumulated by liver and kidney slices, electrical stimulation of these tissues failed to release these compounds. Stimulation-induced release was significantly diminished by the presence of small amounts of lithium in the perfusing medium.     

光周期对环青春期雄性根田鼠繁殖发育的作用与光周期信息的母体传递模式

在实验室条件下,采用析因设计,分别以长光照及短光照水平,测定根田鼠母体怀孕期、哺乳期及幼体断乳期光周期信息对环青春期雄性子代繁殖发育的作用,探讨雄性子代对光周期信息的反应及光周期信息的母体传递模式。检验的特定假设为,光周期能刺激和调节田鼠类动物雄体的繁殖发育;在其亲代与子代间存在光周期信息的母体传递。研究结果表明,在根田鼠亲代母体与子代幼体间具有光周期信息的母体传递。雄体的繁殖发育,不仅受母体传递光周期信息的作用,亦受断乳期光周期的影响。断乳后的光周期信息是影响雄体繁殖发育的主要信息。在长期的适应和进化过程中,根田鼠对高寒环境形成特殊的光周期信息传递格局和繁殖策略。     

Floral Induction in a Photoperiodically Insensitive Duckweed, Lemna paucicostata LP6 : Role of Glutamate, Aspartate, and Other Amino Acids and Amides

The effects of 20 amino acids and two amides were studied on the flowering of a photoperiodically insensitive duckweed, Lemna paucicostata LP6. Alanine, asparagine, aspartate, cystine, glutamate, glutamine, glycine, lysine, methionine, proline, serine, and threonine induced flowering under a photoperiodic regime of 16 hours light and 8 hours darkness. Among these, glutamate and aspartate were found to be the most effective for flower induction. These acids could initiate flowering even at 5 × 10⁻⁷ molar level, though maximal flowering (about 80%) was obtained at 10⁻⁵ molar. Change in the photoperiodic schedule or the pH of the nutrient medium did not influence glutamate- or aspartate-induced flowering. The low concentrations at which glutamate and aspartate are effective suggests that they may have a regulatory role rather than simply acting as metabolites.     

EFFECTS OF EXOGENOUS AMINO ACIDS ON THE DEVELOPMENT OF MARCHANTIA POLYMORPHA GEMMALINGS

The effects of various nitrogenous compounds in concentrations ranging from 10^-4 to 10^-3 m on the growth and morphology of gemmae of Marchantia polymorpha L. were investigated under axenic conditions. Only nine of the 24 compounds tested were effective in altering the normal developmental pattern of this plant. l -Isoleucine, l -leucine, l -methionine or l -threonine resulted in a disruption of the apical regions at concentrations of 10^-3 m . The addition of lower concentrations of l -arginine, l -histidine, l -hydroxyproline, l -lysine or l -tryptophan to the nutrient medium resulted in morphological irregularities. These latter abnormal growth patterns were highly specific for the individual amino acids and ranged from lack of air chamber development to complete thallus disorganization. Both the formation and duration of abnormal developmental patterns were dependent upon the concentration of the amino acids employed. Although the experimental results are inconsistent with certain physiological mechanisms such as a general nitrogen toxicity, alternative possibilities are discussed.     

Dynamics of amino acids in pea stem sections during root formation and its inhibition by kinetin and ethionine

An investigation was conducted to study the interrelation of free amino acid metabolism and root formation in etiolated pea stem sections as dependent on time and on inhibition of root formation by kinetin and ethionine. The rise in the level of aspartic acid and increase in the rate of conversion of¹⁴C-labeled glucose to free amino acids were found to be characteristic features of the formation of foci of meristematic cells in pericyclo region. The formation of roots was reflected, in general, much more in the rate of conversion of labeled glucose to free amino acids than in the levels of corresponding amino acids. The total amount of free amino acids was not significantly changed during incubation of stem sections in a solution of kinetin (5×10^?5 m). A rapid fall in their level was recorded in the next 24 hours. The incorporation of¹⁴C from glucose into a precursor of lignin, phenylalanine, was completely inhibited by kinetin which stimulated simultanously the growth of adjacent buds. Stimulation of secondary xylem formation, which appeared later, was accompanied by the resumption of¹⁴C-incorporation into phenylalanine. Inhibition of root formation by ethionine resulted in the rapid fall of the level of most amino acids and in a significant decrease in the rate of incorporation of¹⁴C from glucose into amino acids. A decreasing level of ethionine in tissues during cultivation of ethionine-treated stem sections was accompanied by a gradual rise in the individual amino acids and in the rate of conversion of glucose into free amino acids.     

INTRACELLULAR AND EXTRACELLULAR AMINO ACID POOLS OF THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) GROWN ON UNENRICHED SEAWATER IN HIGH-CELL-DENSITY DIALYSIS CULTURE1

The consumption of inorganic macronutrients (NO₃^?+ NO₂^?, NH₄⁺, and PO₄^?3) and the composition of intra- and extracellular dissolved free amino acid pools (IDFAA and EDFAA, respectively) were determined in continuous-reservoir batch dialysis cultures of the marine diatom Phaeodactylum tricornutum Bohlin maintained on unenriched natural seawater as a growth medium. Nutrient diffusion (Nd), which equals the nutrient uptake of the culture, increased with the cell density and the age of the culture. A concentration of 6.77 × 10⁷ cells · mL^?1 was obtained in stationary phase, which coincided with the NO₃^?+ NO₂^? diffusion limit (Nd_max) of the dialysis apparatus. The Nd_max for NH₄⁺ occurred much earlier, at the end of exponential growth, whereas Nd_max for PO₄^?3 was not attained during the growth cycle of the culture, even in early stationary phase. A significant depletion (77%) of the IDFAA pool during exponential phase was followed by a reestablishment–to approximately 60% of the initial level–of internal pools during linear and stationary growth phases. This recovery occurred during the illuminated portion of the photoperiod (12:12 h LD) and involved principally the amino acids GLN, GLU, β-GLU, and ASN. The recovery of GLN and ASN levels was particularly significant, because the intracellular concentrations of these amino acids were higher at the end of the growth cycle than before. The EDFAA pool was generally dominated by the amino acids SER and GLY+THR; however, during active growth, ORN and LYS often constituted an important fraction. The EDFAA concentration increased until linear growth phase was reached, during which a higher concentration of total free amino acids was attained in darkness than under illumination. The EDFAA component diminished afterward, and in stationary phase this fraction returned to concentrations equivalent to those observed at the beginning of the growth cycle. The variations in EDFAA concentrations were expressed by a pronounced decrease in the cellular excretion of amino acids with increasing cell density. These cellular responses of Phaeodactylum tricornutum in dense culture, specifically the regulation of amino acid excretion and intracellular pool size, may affect the N-conversion coefficient (Y_N). Consequently, by prolonging the linear phase of growth and reducing the concentration of autoinhibitory metabolites by diffusion, a markedly enhanced final cell density can be achieved in cultures grown on natural unenriched seawater.     

THE EFFECTS OF HORMONES UPON THE DEVELOPMENT OF EXCISED FLORAL BUDS OF AQUILEGIA

Young excised floral buds of Aquilegia were grown on defined medium containing kinetin, indoleacetic acid (IAA), or gibberellic acid (GA₃). Only when 10⁻⁶ or 10⁻⁷ m kinetin was added to the basal medium was there a significant increase in the number of initiated whorls of primordia. Buds on the basal medium or on medium with IAA or GA₃ failed to initiate carpels. On medium with 10⁻⁶ or 10⁻⁷ m kinetin, buds successfully initiated a normal whorl of five carpels. A high level of inorganic nitrogen was also required for the initiation of carpels. With 10⁻⁵ m kinetin, individual buds initiated from 6–18 carpels. Staminodial primordia of these buds were replaced with carpels, or the floral apex enlarged to accommodate a single whorl of many carpels. Kinetin did not support the further differentiation of the floral organs. Sepals, petals, and carpels did differentiate on medium with GA₃, but stamens aborted. However, on medium with GA₃ and kinetin, stamen primordia differentiated into short filaments and anthers. Further unknown growth factors appear to be required for the complete differentiation of floral primordia into mature organs.     

DAYLENGTH AND LIGHT RESPONSES IN GROWTH AND FERTILITY OF GLOSSOPHORA KUNTHII (PHAEOPHYTA,DICTYOTALES) FROM PACIFIC SOUTH AMERICA1

Excised ligulae of Glossophora kunthii (C. Ag.) J. Ag. were cultured in photoperiods of 4–24 h and photon fluence rates of 10–75 μmol.m^?2.s^?1. Daylength interacted with irradiance on the growth of the ligulae. Maximal growth of primary ligulae occurred in long-day regimens with high irradiances suggesting an effect of irradiance on photosynthesis and growth. In contrast, growth of secondary ligulae was greatest in short-day regimes. Differences were significant at the highest irradiance tested. Differentiation of tetrasporangia on the ligulae is a short-day photoperiodic response. Daylengths of 8.5 h or less induced a sharp increase in numbers of fertile ligulae and tetrasporangia attaining maturity. Interruptions of the dark period decreased the development of tetrasporangia; the number of interruptions had a cumulative inhibitory effect. Differentiation of reproductive structures was influenced by interactions of photoperiod and irradiance. Maximum numbers of tetrasporangia were formed at short-day regimes and low irradiances; differentiation was completely inhibited at long-day conditions and high irradiance.     

感光性的遗传背景对水稻短光诱导雄性不育特性表达的影响研究

通过对双亲及Ｆ１的感光性分析和Ｆ２群体单株的感光性及短光不育特性分析表明,强感光性对弱感光性表现为显性;具短光不育特性的单株其感光性均表现为中度以上感光（短日出穗促进率〉１５％）。对宜ＤＩＳ与宜Ｄ２Ｓ的光敏性、感光性分析和不育基因的等位性测定表明,两者感光性与光敏性符合正相关的结论,它们的不育主基因是等位的。可以认为,对短光低温不育水稻,短光不育基因需要在感光性基因存在时才能得到表达,同一不育基因     

TRANSPORT OF LYSINE FROM CEREBROSPINAL FLUID OF THE CAT

—The clearance from cerebrospinal fluid of l-[¹⁴C]lysine and l-[³H]arginine was measured during ventriculo-cisternal perfusions of anaesthetized cats. Increasing in the perfusate the concentration of unlabelled l-lysine produced a gradual reduction in clearance of the labelled amino acids without altering the uptake of l-[¹⁴C]lysine by the choroid plexus. Net transport of l-lysine out of cerebrospinal fluid occurred by saturable and non-saturable components. The saturable component satisfied Michaelis-Menton kinetics, while the behaviour of the non-saturable component was consistent with diffusion. A V_max of 0·017 μmol/min and an affinity constant (k_t) of 0·83 mm were estimated. The clearance of l-lysine was unaffected by the addition to the perfusate of high concentrations of selected neutral amino acids, but was stimulated by the presence of l-cystine. Conversely, a high concentration of l-lysine did not affect the clearance of glycine or cycloleucine. The dibasic amino acids appear to be removed from cerebrospinal fluid by a relatively specific, mediated transport system which may serve to regulate their concentrations in the cerebrospinal fluid.     

A circadian clock measures photoperiodic time in the male lizard Anolis carolinensis

Summary Photoperiod plays an important role in controlling the annual reproductive cycle of the male lizard Anolis carolinensis. The nature of photoperiodic time measurement in Anolis was investigated by exposing anoles to 3 different kinds of lighting paradigms (resonance, T cycles, and night breaks) to determine if photoperiodic time measurement involves the circadian system. Both the reproductive response and the patterns of entrainment of the activity rhythm were assessed. The results show that the circadian system is involved in photoperiodic time measurement in this species and that a discrete photoinducible phase resides in the latter half of the animals' subjective night. Significantly, the ability of the circadian system to execute photoperiodic time measurement is crucially dependent on the length of the photoperiod. Resonance, T cycle and night break cycles utilizing a photoperiod 10–11 h in duration reveal circadian involvement whereas these same cycles utilizing 6 or 8 h photoperiods do not.Abbreviation CRPP circadian rhythm of photoperiodic sensitivity     

BIOCHEMTCAL CHANGES IN THE BRAIN OF EXPERIMENTAL ANIMALS IN RESPONSE TO ELEVATED PLASMA HOMOCYSTINE AND METHIONINE

The effects of high plasma concentrations of homocystine and methionine on the free amino acids of brain have been examined. Incorporation of the label from [³⁵S]methionine into the free amino acid pools of rabbit brain was enhanced in response to high plasma homocystine or high plasma homocystine and mcthionine. Under comparable conditions a marked decrease in the incorporation of the label from [¹⁴C]glycine into the free pool was observed. The corresponding incorporation of ³⁵S and ¹⁴C into brain proteins parallelled the results obtained with incorporation into the free pools of amino acids. Amino acid analyses of the free amino acid pools of rabbit brain revealed a general decrease in the concentration of amino acids in response to high plasma homocystine or high plasma homocystine and methionine. Inhibition of protein synthesis which occurs under the above experimental conditions is a general phenomenon. myelin and other brain fractions being equally affected. The decrease in concentration of brain amino acids also results in a diminution in concentration of the neurotransmitters GABA, dopamine and noradrenaline. The possible relationship of the observed changes to homocystinuria is discussed.     

Induction of reproductive diapause via perception of photoperiod through the compound eyes in the adult blow fly, Protophormia terraenovae

Covering and surgical removal of the compound eyes were performed to localize photoreceptors for photoperiodic responses in the blow fly Protophormia terraenovae (Diptera, Calliphoridae). Adult females showed a long-day photoperiodic response to control reproductive diapause. When the compound eyes were bilaterally covered with silver paint, diapause incidence increased under diapause-preventing conditions, i.e., a long-day photoperiod and constant light, as though flies were kept under constant darkness. Neither silver painting on a medial region of the head capsule nor control painting in which both compound eyes were painted in a clear solvent caused significant effects on diapause incidence. Unilateral painting of the compound eye caused an increment of diapause incidence under constant light but no effects under a long-day photoperiod. When the compound eyes were bilaterally removed, all the flies developed their ovaries both under a long-day and a short-day photoperiod. Unilateral removal of the compound eye also caused ovarian development under a short-day photoperiod, whereas removal of one antennal lobe or all ocelli caused no effects on diapause incidence. Since P. terraenovae completely lost responsiveness to photoperiod after blinding of the compound eyes, it is likely that this fly perceives photoperiod through its compound eyes. Accepted: 18 February 1997     

Responses to stepwise photoperiodic changes for the larval diapause of the Indian meal moth Plodia interpunctella

Abstract The Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae) diapauses as a last‐instar (fifth) larva. At 30 °C, no larvae enter diapause under any photoperiodic conditions; at 25 °C, the photoperiodic response curve is a long‐day type with a critical length of approximately 13 h light; at 20 °C, diapause is induced moderately even under long days (> 13 h). Cumulative effects of short days or long days on diapause induction are determined by alternate, stepwise and gradually changing regimes of photoperiod at 25 °C. When the larvae are repeatedly exposed to LD 16 : 8 h and LD 12 : 12 h photoperiods every other day, the incidence of diapause is 37%. When the larvae are placed under an LD 16 : 8 h photoperiod for 2 days and then under an LD 12 : 12 h photoperiod for 1 day, it is 38 %. Exposure to an LD 16 : 8 h photoperiod for 1 day and then to an LD 12 : 12 h photoperiod for 2 days induces only 15% diapause. This may indicate that the photoperiodic information is not accumulated in a simple fashion despite the generally accepted hypothesis (i.e. photoperiodic counter). Larvae exposed to an LD 16 : 8 h photoperiod for 5 days after oviposition express a very high incidence of diapause even under short days between an LD 2 : 22 h and LD 12 : 12 h photoperiod. After 10 days exposure to an LD 16 : 8 h photoperiod, however, the short day does not induce diapause strongly. On the other hand, an LD 12 : 12 h photoperiod in the early larval life is highly effective in the induction of diapause. A gradual increase or decrease of photoperiod (2 min day^?1) shows that the direction of photoperiodic change does not affect the diapause determination.     

EVOLUTION OF TRADE-OFFS BETWEEN SEXUAL AND ASEXUAL PHASES AND THE ROLE OF REPRODUCTIVE PLASTICITY IN THE GENETIC ARCHITECTURE OF APHID LIFE HISTORIES

Life‐history theory postulates that evolution is constrained by trade‐offs (i.e., negative genetic correlations) among traits that contribute to fitness. However, in organisms with complex life cycles, trade‐offs may drastically differ between phases, putatively leading to different evolutionary trajectories. Here, we tested this possibility by examining changes in life‐history traits in an aphid species that alternates asexual and sexual reproduction in its life cycle. The quantitative genetics of reproductive and dispersal traits was studied in 23 lineages (genotypes) of the bird cherry‐oat aphid Rhopalosiphum padi, during both the sexual and asexual phases, which were induced experimentally under specific environmental conditions. We found large and significant heritabilities (broad‐sense) for all traits and several negative genetic correlations between traits (trade‐offs), which are related to reproduction (i.e., numbers of the various sexual or asexual morphs) or dispersal (i.e., numbers of winged or wingless morphs). These results suggest that R. padi exhibits lineage specialization both in reproductive and dispersal strategies. In addition, we found important differences in the structure of genetic variance–covariance matrices ( G ) between phases. These differences were due to two large, negative genetic correlations detected during the asexual phase only: (1) between fecundity and age at maturity and (2) between the production of wingless and winged parthenogenetic females. We propose that this differential expression in genetic architecture results from a reallocation scheme during the asexual phase, when sexual morphs are not produced. We also found significant G × E interaction and nonsignificant genetic correlations across phases, indicating that genotypes could respond independently to selection in each phase. Our results reveal a rather unique situation in which the same population and even the same genotypes express different genetic (co)variation under different environmental conditions, driven by optimal resource allocation criteria.     

THE INFLUENCE OF GROWTH SUBSTANCES ON THE INDUCTION OF APOGAMY IN PTERIDIUM GAMETOPHYTES

Experiments employing sequences of three media demonstrated the effect of growth substances on the induction of apogamy. The most effective sequence was 4% sucrose 1–14 days, 4% sucrose plus growth substance 15–28 days, and 0.1% sucrose 29–56 days. In this sequence concentrations of NAA, IAA, and GA promoted apogamous shoot formation. A higher NAA concentration than optimal for shoot formation stimulated apogamous root formation in all medium sequences. Kinetin was without effect or inhibitory to apogamy. Combination of kinetin/GA or GA/NAA concentrations did not increase the apogamous response. One combination of the kinetin/NAA concentrations had a synergistic effect on the apogamous shoot formation. Additions of GA to the synergistic kinetin/NAA combination had an antagonistic effect on the apogamous response.     

Adaptive significance of the recurrent photoperiodic response in a spring‐breeding carabid beetle,Carabus yaconinus

Seasonal changes in the photoperiodic sensitivity for reproduction in adults of a spring‐breeding carabid beetle, Carabus yaconinus (Coleoptera: Carabidae), were examined by transferring adults from outdoor to photoperiodic conditions in various seasons. Newly‐emerged adults transferred to the laboratory in September to December showed a long‐day photoperiodic response, but lost photoperiodic sensitivity gradually during winter. In late April, overwintered adults were not sensitive to the photoperiod, with females continuing to have mature eggs under both long‐day and short‐day conditions. In contrast, in late June and late July, the adults were sensitive to the photoperiod, with only those kept under short‐day conditions re‐entering reproductive diapause. This recovery of photoperiodic sensitivity appears to play a definitive role in maintenance of diapause in autumn for adults that have reproduced. The adults collected in late April regained photoperiodic sensitivity in two months even after being kept under unchanged conditions. Therefore, no environmental cue is required for recovery of photoperiodic sensitivity, which apparently recovers with the lapse of time. Our results suggest that the recurrent photoperiodic response is required in long‐living adults of C. yaconinus to regulate the timing of reproduction, and also indicate a difference in photoperiodic sensitivity in summer between overwintered and newly‐emerged adults.     

EFFECTS OF TETRODOTOXIN, CALCIUM AND MAGNESIUM ON THE RELEASE OF AMINO ACIDS FROM SLICES OF GUINEA-PIG CEREBRAL CORTEX

Abstract— Tetrodotoxin, Ca²⁺-deprivation and high-Mg²⁺ were used in an effort to identify the portion of the evoked release of endogenous amino acids, labelled via metabolism of [¹⁴C]-glucose, and several exogenous labelled amino acids, that came from nerve terminals when slices of guinea pig cerebral cortex were superfused with glucose-free solutions and stimulated electrically. With some exceptions, spontaneous release of labelled amino acids was decreased by 2 μm -tetrodotoxin but increased in Ca²⁺-free medium and in solutions containing an extra 24 mm -MgCl₂. Tetrodotoxin suppressed 85–90% of the stimulated release of almost all labelled amino acids, but had a smaller effect on the release of endogenous ¹⁴C-labelled threonine-serine-glutamine (unseparated). In Ca²⁺-free solution, the stimulated release of endogenous ¹⁴C-labelled glutamate, aspartate and GABA was suppressed by 80–90%, but that of endogenous ¹⁴C-labelled threonine-serine-glutamine was unaffected as was most of the release of the other labelled amino acids. In medium containing an extra 24mM-MgCl₂, the stimulated release of endogenous ¹⁴C-labelled glutamate, aspartate and GABA was suppressed by 75-85%, that of exogenous labelled aspartate and GABA by 50–65%, but the release of the other labelled amino acids was unaffected. The control stimulated releases of endogenous ¹⁴C-labelled glutamate, aspartate and GABA were much larger than those of other labelled amino acids but were reduced by tetrodotoxin, Ca²⁺-deprivation and high-Mg²⁺ to a level similar to that of the control stimulated releases of the other labelled amino acids. These results suggest that almost all of the stimulated release of endogenous ¹⁴C-labelled glutamate, aspartate and GABA came from nerve terminals while those of the other labelled amino acids came from other tissue elements. In addition, they are in accord with a transmitter role for glutamate, aspartate and GABA in cerebral cortex.