Effect of ínductive photoperiod and gibberellin treatment on peroxidase enzyme system in relation to floral induction inImpatiens balsamina L

Gibberellins A₃ and A₁₃ cause floral induction inImpatiens balsamina, a qualitative short day plant, under non-inductive 24-h photoperiods (continuous illumination). However, the influence of the two inductive factors,i.e. gibberellins and short days (8-h photoperiods) on the peroxidase enzyme system is different. The total peroxidase activity decreases under both inductive and non-inductive photoperiods, with or without gibberellin treatment. The electrophoretic pattern of isoperoxidases changes only in response to gibberellin treatment. Under 24-h photoperiods, treatment with gibberellins A₃ and A₁₃ causes the appearance in the stem of three additional isoenzymes of peroxidase (Rm 0.50, 0.71 and 0.76). These bands do not appear in the leaves, which are non-essential for gibberellin-caused floral induction in this plant. Under 8-h photoperiods also, gibberellins induce the appearance of new isoenzyme bandsi.e. two in the stem (Rm 0.50 and 0.76) and one in the leaves (Rm 0.05). These may be correlated with the synergistic increase in the number of floral buds in these plants in response to simultaneous exposure to two inductive factors.     

TEMPERATURE,PHOTOPERIOD AND LIGHT INTERACTIONS ON GROWTH AND FERTILITY OF GLOSSOPHORA KUNTHII (PHAEOPHYTA,DICTYOTALES) FROM CENTRAL CHILE1

Excised ligulae of Glossophora kunthii from central Chile were cultured of temperatures of 5–25° C, photoperiods of 16:8 and 8:16 h LD cycles, with photon irradiances of 10 and 50 μmol · m^?2· s^?1. Growth of the ligulae, number of fertile ligulae and number of tetrasporangia forming on the ligulae were assessed. Ligulae tolerated temperatures between 10 and 23°C. Temperature interacted with daylength and photon dose, determining quantitative responses in the growth and fertility of ligulae. Growth was least at 8:16 h LD and was not affected significantly by temperature. It was greatest at 16:8 h LD, 50 μmol · m^?2· s^?1 and increased with temperature up to 20°C. Percentage of fertile ligulae and number of tetrasporangia increased with temperature at the 8:16 h LD cycle, reaching a maximum at 20°C. Fertility was low at 16:8 h LD, except at 20° C (and low photon dose) suggesting that reproduction at 20° C is independent of daylength in this species. Ligulae grew larger at the long-day photoperiods and the proportions of fertile ligulae were higher at the short-day photoperiods, irrespective of the total photon dose received. These results suggest that some aspects of growth and fertility are controlled by photoperiod.     

Formal properties of the circadian system underlying photoperiodic time-measurement in Japanese quail

Summary The photosensitive phase for the photoperiodic response of Japanese quail was delineated with 3 h main photoperiods and 0.25 h night breaks in cycles (T) of 24 and 27 h. UnderT24 there was one peak of induction of testicular growth and luteinizing hormone release, while underT27 there were two, the first of which had a phase angle which was about 1.5 h more positive than that of the peak inT24. In contrast, the phase angle of locomotor activity underT27 was 3–4 h more positive than underT24. During entrainment to 1 h photoperiods in cycles between 19.1 and 25.7 h in length the rate of testicular growth (k) remained close to zero even though the subjective night of the activity rhythm was illuminated in some treatments. The ratek also remained close to zero when quail were exposed to 3 h photoperiods in cycles between 21 and 36 h in length, and underT30 the critical daylength for photoperiodic induction was only 1.5 h shorter than that underT24. The results suggest that asT is altered the changes in the phase angle of the photoinducible phase are smaller than those of the rhythm of locomotor activity, indicating the involvement of oscillators with different entrainment properties. This hypothesis is neither supported nor excluded by consideration of the internal coincidence model.     

Vulva formation in Pristionchus pacificus relies on continuous gonadal induction

One of the best known features of vulva development in Caenorhabditis elegans is the induction of vulval precursor cells by the gonadal anchor cell. Induction is crucial for the initiation of pattern formation within the C. elegans vulva equivalence group, and it is therefore surprising to find that this aspect of vulva formation, in particular, varies greatly among nematodes. In some species which form vulvae in the posterior body region, no gonadal signal is necessary for vulva induction. In other nematodes, such as Panagrolaimus, Oscheius, and Rhabditella, vulva formation depends on two temporally distinct gonadal inductions which specify the different cell fates. Here we report our analysis of vulva induction in Pristionchus pacificus, a specieswhich has recently been used as a genetic system to analyze the evolution of vulva development. Cell ablation studies in P. pacificus show that another mode of vulva induction exists. P. pacificus vulva formation depends on a continuous gonadal induction that starts several hours after hatching and continues until the birth of the anchor cell, some 20 h later. Mutations defective in gonadal induction result in the absence of vulva differentiation, suggesting that only one signaling system is involved in the gonadal-epidermal interaction. This new mode adds further to the great variety of gonadal inductions among nematode species. Received: 25 February 1999 / Accepted: 20 April 1999     

Flower development in the passion fruit Passiflora edulis requires a photoperiod‐induced systemic graft‐transmissible signal

Different organisms use gradual seasonal changes in photoperiod to correctly time diverse developmental processes, such as transition to flowering in plants. Florigen is a systemic signal formed in leaves exposed to specific environmental cues, mainly photoperiodic, and capable of triggering flower induction in several species. Here we show that in Passiflora edulis, a perennial climbing vine, flower initiation occurs throughout the year; however, without long photoperiods, flower primordia show arrested growth and differentiation at an early stage. Our results support the existence of a positive, systemic, graft‐transmissible signal, produced in mature leaves under LDs, that is required for normal flower development beyond sepal formation. Our results also suggest that Gibberellin acts to inhibit flower development. We provide evidence for genetic variation in the response to short photoperiods. A genotype capable of forming developed flowers under short photoperiods produces a positive graft transmissible signal allowing normal flower development under short days in a cultivar which normally aborts flower development under these conditions. We believe these findings contribute towards discovering the chemical nature of this interesting mobile signal involved in flower development.     

Effect of Genotype and Explant Age on Callus Induction and Subsequent Plant Regeneration from Root-derived Callus of Indica Rice Genotypes

An attempt has been taken to establish an efficient plant regeneration system in vitro from 3, 5, 7 and 9-days-old root segments of four Indica (Bangladeshi) rice genotypes. Genotypic effects were observed in callus induction and subsequent plant regeneration. Moreover, the stage of development of the root explants also played a significant role in callus formation and subsequent plant regeneration. Younger explants were more efficient in both callus induction and plant regeneration. Plants regenerated in vitro were successfully established in soil and produced fertile seeds.     

Synergy between the light-induced acute response and the circadian cycle: a new mechanism for the synchronization of the Phaseolus vulgaris clock to light

PvLHY and Lhcb expression has been studied in primary bean leaves after exposure of etiolated leaves to two or three white light-pulses and under different photoperiods. Under the tested photoperiods, the steady-state mRNA levels exhibit diurnal oscillations with zenith in the morning between ZT21 and 4 for PvLHY and between ZT4 and 6 for Lhcb. Nadir is in the evening between ZT12 and 18 for PvLHY and ZT18 and 24 for Lhcb. Light-pulses to etiolated seedlings induce a differentiated acute response that is reciprocally correlated with the amplitude of the following circadian cycle. In addition, the clock modulates the duration of the acute response (descending part of the curve included), which according to the phase of the rhythm at light application extends from 7 to 18 h. This constitutes the response dynamics of the Phaseolus clock to light. Similarly, the waveform of PvLHY and Lhcb expression during the day of different photoperiods resembles in induction capability (accomplishment of peak after lights-on) and duration (from lights-on phase to trough) the phase-dependent progression of acute response in etiolated seedlings. Consequently, the peak of Lhcb (all tested photoperiods) and PvLHY (in LD 18:6) attained in the photophase corresponds to the acute response peak, while the peak of PvLHY during the scotophase (in LD 12:12 and 6:18) corresponds to the circadian peak. Thus, the effect of the response dynamics in the photoperiod determines the coincidence of the peak with the photo- or scotophase, respectively. This represents a new model mechanism for the adaptation of the Phaseolus clock to light.     

FIELD AND CULTURE STUDIES OF A POPULATION OF ENDARACHNE BINGHAMIAE (PHAEOPHYTA) FROM SOUTHERN CALIFORNIA1

Abundances of the erect, blade phase of Endarachne binghamiae J. Ag. (Scytosiphonales, Phaeophyta) varied seasonally at a southern California rocky intertidal site. Blade cover and density were much greater in the fall through early spring; blades were mostly absent from quadrats during the summer. Blade abundances were negatively correlated with both seasonal variations in seawater temperature and photoperiod. Laboratory culture studies failed to provide evidence for sexual reproduction. The life history appears to be of the “direct” type with plurangia-produced zooids germinating into crustose disks. Most disks developed erect blade clusters under spring/fall (17° C) and winter (13° C) temperatures over the range of natural photoperiods employed (14:10, 12:12, 10:14 h LD). In contrast, cultures held under the summer temperature (21° C) produced almost entirely crustose growths regardless of photoperiod. Similar results were obtained for cultures grown at 100 and 200 μE · m^?2· s^?1. E. binghamiae blades were fertile throughout the year and produced viable zooids indicating that reproductive seasonality did not influence the seasonal pattern of blade abundance. Culture and field studies suggest that the initiation of new erect blade clusters from crustose disks is confined to the cooler months of the year (winter and spring). The summer reduction or absence of E. binghamiae blades appears to be due to increased mortality rates and temperature constraints on the development of new erect bladed thalli. Hypothetical causes of mortality are desiccation stress, sand burial, increased grazing activity and a genetically-based short life span.     

Diapause‐inducing signals prolong nymphal development in the two‐spotted spider mite Tetranychus urticae

Female two‐spotted spider mite Tetranychus urticae are grown under different photoperiods and the photoperiodic regulation of diapause is examined. The photoperiodic response curve for diapause induction was of the long day–short day type, with critical day lengths (CDLs) of 2 and 12.5 h; diapause was induced between these CDLs. The preimaginal period is significantly longer in diapausing females than in non‐diapausing females; moreover, a significant positive correlation is detected between diapause incidence and deutonymphal period. Diapause incidence is high when long‐night photoperiods are applied against a background of continuous darkness in the stages including the deutonymph; this stage appears to be the most sensitive to photoperiod. These observations suggest that diapause‐inducing conditions inhibit nymphal development, particularly in the deutonymphal stage when photoperiodic time measurement for determination of reproduction or diapause is carried out.     

Development in the red alga,Griffithsia pacifica: Control by internal and external factors

Summary Development in the red alga Griffithsia pacifica is affected by both external and internal factors. Under 16:8 photoperiods, both cell division and cell elongation show a diurnal rhythm. The rhythm of division persists for at least 7 cycles in continuous light, and can be reset; this indicates that the timing of cell division is controlled by an endogenous rhythm. Both cell division and elongation require light, but the rate of division of apical cells and the rate of cell elongation are both relatively insensitive to either light intensity or photoperiod. In contrast. division in nodal cells, which leads to branch formation, is strongly promoted by high light intensity or long photoperiods. By manipulating the conditions of illumination, one can obtain Griffithsia plants varying from unbranched to highly branched.     

Are cuttings suitable for assessing maturity type in potato (Solanum tuberosum)?

Two experiments were carried out to evaluate the potential of single‐node cuttings of potato (Solanum tuberosum) as a tool to assess genotypic differences in maturity type. Plants were exposed to different photoperiodic treatments (different photoperiods, different numbers of photoperiodic cycles), and cuttings were taken at different plant ages. Cuttings from early (and to a lesser extent also late) maturing varieties exposed to short photoperiods showed strong induction to tuberise, irrespective of plant age; the induction increased with an increase in the number of short photoperiodic cycles. The response of cuttings taken from early‐maturing varieties exposed to long photoperiods depended on plant age: cuttings showed stronger induction when mother plants were older; cuttings from late‐maturing varieties hardly tuberised after exposure to long photoperiods. The tuberisation of the cuttings did not depend on the length of the long photoperiod (18 or 24 h) or on the number of cycles of a photoperiod of 18 h. Tuberisation on cuttings did not properly reflect the tuber formation on the mother plants, although within varieties, significant correlations between tuberisation on cuttings and tuber yield per plant 9 weeks after planting were found with different numbers of photoperiodic cycles of 12 h. Our experiments show that the cutting technique cannot be used on older plants to assess the maturity type of potato varieties, as there are interactions between photoperiod, genotype, plant age and number of photoperiodic cycles, in the reflection of the degree of induction to tuberise on single‐node cuttings.     

Sexual difference in the photoperiodic induction of pupal diapause in the flesh fly Sarcophaga similis

The flesh fly Sarcophaga similis enters pupal diapause in response to short days, but averts diapause under long days. This species shows a sexual difference in the photoperiodic induction of diapause, with females having shorter critical daylength than males. Here, we proposed two hypotheses to explain this sexual difference. First, we proposed a sexual difference in the qualitative evaluation of photoperiods. This hypothesis assumes under the external coincidence model that although the photoinducible phase of both sexes locates at late scotophase, in males, it locates at a slightly earlier phase. However, the results of night interruption experiments clearly ruled out this hypothesis. Because we verified that S. similis evaluated photoperiods quantitatively, we next proposed a sexual difference in the quantitative evaluation of photoperiods. This hypothesis incorporates concepts of a hypothetical substance accumulation that shows a diapause‐inducing effect and an internal threshold that serves as a reference to determine the diapause/nondiapause developmental program. In long‐day exposure experiments and night interruption experiments, females consistently showed a lower incidence of diapause than males. Thus, the present study data satisfactorily meet the second hypothesis, that is a sexual difference in the quantitative evaluation of photoperiods exists in S. similis.     

Seasonality of Mobbing Intensity in the Pinyon Jay

In the wild, pinyon jays (Gymnorhinus cyanocephalus) mob owls at all times of year, but our observations of wild birds suggested that the mobbing response was strongest during the breeding season. To test this, we placed four groups of five wild caught adult pinyon jays in environmental chambers during late autumn when their testes were regressed. These birds received photoperiods of 12, 12, 13 and 14 h for 30 days prior to being exposed singly to a live great horned owl (Bubo virginianus). Three groups of five birds were maintained under natural photoperiods in outdoor aviaries and were tested with the owl in Aug., Sep. and Nov. Birds on long artificial photoperiods mobbed more strongly than birds exposed to shorter photoperiods. The jays under natural photoperiods showed the opposite response: those tested in November mobbed significantly more strongly than birds tested in August. Jays with the weakest mobbing responses were molting, and those with the strongest responses seemed to be closest to reproductive readiness. There was no correlation between gonad size and mobbing intensity, but our results suggest a strong relationship between reproductive readiness and mobbing intensity in pinyon jays.     

亚轮生奇异蕨(Adoketophyton subverticillatum)在贵州都匀泥盆系蟒山群的发现及其意义

Adoketophyton subverticillatum (Li et Cai) Li et Edwards (亚轮生奇异蕨)是云南早泥盆世坡松冲植物群中颇具代表性的、研究较为详细的一种植物, 目前对其整体形态特征和解剖结构都有较深入的认识。本文通过系列针修法, 将采自贵州都匀包阳剖面蟒山群下段的一块植物化石新材料归入A. subverticillatum。基于目前对 Adoketophyton时空分布的认识, 认为该属可作为早泥盆世植物群的代表分子, 并据此推断蟒山群下段的时代应为早泥盆世。Adoketophyton subverticillatum在都匀的发现, 表明贵州都匀蟒山群中的植物与云南坡松冲植物群在属、种一级上存在扩散与交流现象。Adoketophyton以及其他相关植物的研究表明, 在高大气CO₂浓度的早泥盆世, 叶性结构如孢子叶、苞片、枝叶复合体等已广泛分布于华南板块。     

Factors governing the induction of diapause in Ephestia elutella and Plodia interpunctella (Lepidoptera)

Diapause in fully grown larvae of Ephestia elutella and Plodia inferpunctella was induced by low temperature and short photoperiods. Light intensities below 1 lx affected the induction of diapause in both species. At 20 and 25d?C, the critical photo-period for E.elutella was c. 14 h, and for P.interpunctella c. 13 h. The sensitive phase in both species occurred at about the time of the fourth larval moult. In E.elutella about seven short photoperiods were required for larvae to enter diapause. In P.interpunctella high population density during larval development increased the proportion of larvae entering diapause. The conditions inducing diapause in laboratory stocks, and in stocks collected from the field, were different. Laboratory stocks of both species did not enter diapause at 25d?C and required short photoperiods for diapause at 20d?C. Some larvae of the field stock of E.elutella entered diapause in constant darkness at 30d?C, the number being increased at low R.H., and almost all did in short photoperiods at 25°C. At 20T, most larvae of this stock entered diapause regardless of photoperiod, and at 15°C all did. In P.interpunctella up to one-third of larvae of the field stock entered diapause in short photoperiods at 25d?C, and all did if transferred to short photoperiods at 20d?C. In unheated premises, falling temperatures normally induce diapause in E.elutella each autumn, photoperiod only being important if temperatures are high. In P.interpunctella, photoperiod is a more important factor because it can override the effect of falling temperature to a greater extent than in E.elutella. In both species, however, different field populations may respond in different ways.     

Predation risk affects diapause induction in the spider mite Tetranychus urticae

Whenever diapause induction triggers movement into another microhabitat or the development of protective morphological structures, this may also alter predation risk. If the risk of being eaten is lower in the diapause phase, then there may be selection favouring diapause induction in response to predators or their cues. In this article, we studied the effect of the predatory mite Typhlodromus pyri on diapause induction in the spider mite Tetranychus urticae. We used a Greek strain because under long-night photoperiods and low temperature only part of the population enters diapause, thereby leaving room for the impact of another factor. In spider mite groups under predation, the percentage diapause induction increased whenever night-lengths were such that diapause was induced (13–16 h of night). Given this diapause induction in response to predation risk, the question arises whether entering diapause helps spider mites to escape from predation and contribute more offspring to the spring generation next year.     

Patterns of comb row development in young and adult stages of the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus

The development of comb rows in larval and adult Mnemiopsis leidyi and adult Pleurobrachia pileus is compared to regeneration of comb plates in these ctenophores. Late gastrula embryos and recently hatched cydippid larvae of Mnemiopsis have five comb plates in subsagittal rows and six comb plates in subtentacular rows. Subsagittal rows develop a new (sixth) comb plate and both types of rows add plates at similar rates until larvae reach the transition to the lobate form at ～5 mm size. New plate formation then accelerates in subsagittal rows that later extend on the growing oral lobes to become twice the length of subtentacular rows. Interplate ciliated grooves (ICGs) develop in an aboral‐oral direction along comb rows, but ICG formation itself proceeds from oral to aboral between plates. New comb plates in Mnemiopsis larvae are added at both aboral and oral ends of rows. At aboral ends, new plates arise as during regeneration: local widening of a ciliated groove followed by formation of a short split plate that grows longer and wider and joins into a common plate. At oral ends, new plates arise as a single tuft of cilia before an ICG appears. Adult Mnemiopsis continue to make new plates at both ends of rows. The frequency of new aboral plate formation varies in the eight rows of an animal and seems unrelated to body size. In Pleurobrachia that lack ICGs, new comb plates at aboral ends arise between the first and second plates as a single small nonsplit plate, located either on the row midline or off‐axis toward the subtentacular plane. As the new (now second) plate grows larger, its distance from the first and third plates increases. Size of the new second plate varies within the eight rows of the same animal, indicating asynchronous formation of plates as in Mnemiopsis. New oral plates arise as in Mnemiopsis. The different modes of comb plate formation in Mnemiopsis versus Pleurobrachia are accounted for by differences in mesogleal firmness and mechanisms of ciliary coordination. In both cases, the body of a growing ctenophore is supplied with additional comb plates centripetally from opposite ends of the comb rows. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.