Control of cell division in a green alga, Ankistrodesmus gracilis

The proliferation pattern of Ankistrodesmus gracilis, a speciesof Chlorococcales, is described. Under standard conditions,various proliferation patterns; di-, tri-, tetra-, or multichotomicalcell division were observed. Light-dark diurnal rhythms, LD12 : 12 and 14 : 10 induced growth patterns which formed two-to several-ten-celled colonies, whereas the rhythms LD 16 :8 to 20 : 4 induced only the formation of two-celled colonies.These inductions were observed at a cell density of 4.0?10⁶cells/ml. Dichotomical cell division occured at a cell densityof more than 1.5?10⁷ cells/ml. No influence of self-shadingon the pattern of colony formation was detected. (Received May 30, 1974; )     

Influence of photoperiod on low temperature acclimation for cold-hardiness in Drosophila auraria

ABSTRACT. Imagines of Drosophila auraria Peng, a reproductive diapause species, developed cold-hardiness at low temperatures to a greater extent when exposed to a diapause-inducing photoperiod (LD10:14 h) than when exposed to a diapause-preventing photoperiod (LD 16:8h). Imagines kept at 18°C, which was the temperature at which they were reared to eclosion, did not survive a test exposure to -5°C for 8 days regardless of age or photoperiod. When transferred to 10 or 5°C, either from eclosion or from 8 days after eclosion, the survival rate, on testing, rose with time since transfer and rose faster and higher with a photoperiod of LD 10:14h than with LD16:8h. Flies transferred to 15°C only showed improved ability to survive the test if they were kept in LD 10:14h. When cultured at 18°C to the age of 8 days after eclosion, diapause was terminated in about 30% of females even at LD 10:14h. In these post-diapause females the ability to develop cold-hardiness at lower temperatures was somewhat less than in the diapausing females, but apparently greater than in the non-diapause females. These results suggest that the physiological mechanism which promotes cold-hardiness under a diapause-inducing photoperiod is not directly linked to the process causing reproductive diapause.
In Sapporo, flies from a natural population became tolerant to cold in October when they entered diapause and daily mean temperature fell below 15°C and the light/dark cycle fell below LD 12:12h.     

Photoperiodic induction of diapause in the spider mite Tetranychus urticae: qualitative or quantitative time measurement?

Abstract. Insects and mites may measure photoperiods eitfier by classifying them as long or short relative to a critical value (qualitative time measurement) or by using the absolute value (quantitative time measurement). The spider mite Tetranychus urticae is thought to use a qualitative mechanism of time measurement. In this paper we present the results of experiments with an inbred line of the spider mite (to keep genetic variation in photoperiodic responses small), to test whether quantitative aspects also play a role. Differences in diapause incidence in different long-night photoperiods at different temperatures may be an indication of quantitative responses to photoperiod. The effect of temperature on the photoperiodic response curve was studied at 16^oC, 19^oC and 22^oC. The response curves appeared to be similar at 16^oC and 19^oC, with a critical nightlength between 10 and 11 h. At 22^oC, diapause induction was less than 100% in all long-night regimens and die critical nightlength had shifted to 12 h. Maximum diapause induction (93%) occurred in a light-dark cycle with a 16 h dark phase (LD 8:16 h). Diapause induction was lowest in long-night photoperiods with dark phases of 20 h and longer. The number of light-dark cycles needed for 50% diapause induction at 19^oC varied. between 12.1 and 14.7 for LD 6:18 h, between 10.9 and 12.5 for LD 8:16 h, between 10.6 and 11.6 for LD 10:14 h, and between 10.1 and 10.7 for LD 12:12 h. Independent of die light-dark regimen, diapause induction took place in some individuals after receiving 8 cycles and virtually all individuals entered diapause after 16 cycles. No effect was found of the photoperiodic treatment during prediapause development (LD 6:18 h, LD 8:16 h, LD 10:14 h, LD 12:12 h) on diapause duration. The average diapause duration at LD 10:14 h and 19^oC was 61 days over all four treatments. We explained the results by hypothesising that nightlengths are assessed qualitatively and mat the photoperiodic clock operates more accurately near the critical nightlength.     

CELL DIVISION PERIODICITY IN 13 SPECIES OF MARINE PHYTOPLANKTON ON A LIGHT: DARK CYCLE1

The division rates of 26 clonal cultures representing 13 species of planktonic marine algae (6 diatoms, 2 flagellated chrysophytes, 2 coccolithophores, 1 cryptomonad flagellate, I dinoflagellate, 1 green alga) were determined every 2 h for 48 h during exponential growth on a 14:10 LD cycle in nutrient-replete batch culture. Cyclic oscillations in the division rate were detectable in 22 of these clones. Of 14 diatom clones examined, four displayed nearly constant division rates throughout the LD cycle and ten showed strong periodicity favoring division during the light periods. In contrast, all other algae (12 clones) exhibited division rate maxima during periods of darkness, and clearly detectable decreases in cell number for time intervals of 4–8 h during periods of illumination. Intraspecific differences in division periodicity were found among eight clones of the diatom Thalassiosira pseudonana (Hustedt) Hasle & Heimdal and six clones of the coccolithophore Emiliania huxleyi (Lohm.) Hay & Mohler.     

Growth and Antithraquinone Biosynthesis by Galium mollugo L. Cells in Batch and Chemostat Culture

The kinetics of growth, nutrient uptake, and anthraquinone biosynthesisby suspension cultures of Galium mollugo L. cells were examinedin batch and continuous (chemostat) culture. In batch culture,although the initial growth rate was constant (minimum doublingtime = 35 h) characteristic changes in cell composition wereobserved during the growth cycle particularly cell dry weight(between 3.9 and 9.2 g/10⁹ cells), cell anthraquinone (22–80mg/10⁹ cells), and cell protein (0.7–1.6 g/10⁹ cells).Using a chemostat steady state growth was established at twodifferent specific growth rates with mean doubling times of40 h and 25 h. Phosphate was established as the growth-limitingnutrient in chemostat culture at a concentration of 11 µgP ml^–1. In steady state growth at a doubling time of 40h the cell composition remained constant although this was differentfrom any cells grown in batch culture. The cell anthraquinonelevel in steady state growth was between 7 and 30 times lowerthan in batch culture. This result raises the question of therelative importance of growth rate and the growth-limiting nutrientin determining accumulation of secondary products by culturedplant cells.     

DNA Levels in Dividing and Developing Plastids in Expanding Primary Leaves of Avena sativa

The amounts of plastid DNA in the primary leaves of 4-d-oldlight- and dark-grown seedlings of Avena sativa were measuredby microspectrofluorometry using the DNA-fluorochrome DAPI (4',6-diamidino-2-phenylindole). In the light-grown primary leaves (40–45 mm long) therewas a marked increase in DNA level per plastid from 10.2 to18.5 ? 10^–15 g between 2.0 mm and 10 mm from the leafbase, resulting from the rate of plastid DNA synthesis beinghigher than the rate of plastid division. Beyond 30 mm the plastidDNA level was reduced to 14 ? 10^–15g due to chloroplastdivision rates being higher than the rate of plastid DNA synthesis,while from 20 mm plastid DNA levels were constant at 2.2 ? 10^–12g per cell, which corresponds to 16000 plastome copies per cell. Observations of dark-grown leaves establish that, in Avena,light is not necessary for plastid division and the dark-grownleaf cells accumulate higher amounts of plastid DNA than light-grownleaf cells. Plastid nucleoids showed a change of distribution after completionof plastid DNA synthesis in light-grown leaves. A change inthe distribution of plastid nucleoids was also observed duringthe greening of etioplasts of dark-grown leaves while plastidDNA level remained constant. Such changes in plastid nucleoiddistribution appear to be independent of plastid DNA synthesisand correlate with the formation of grana stacks. Key words: Avena sativa, microspectrofluorometry, plastid DNA     

Photoperiodic and temperature effects on the intensity of larval diapause in Sesamia nonagrioides

Abstract. The intensity of larval diapause in Sesamia nonagrioides Lef (Lepidoptera: Noctuidae) was investigated under laboratory conditions. Newly hatched larvae were exposed to different stationary photoperiods (from LD 7 : 17 h to LD 14 : 10 h), at a constant temperature of 25 °C. Diapause incidence was higher when larvae were exposed to daylengths shorter than the critical value (LD 12 : 12 h), whereas the within‐treatment variation in the larval period appeared to be significantly correlated with the photoperiod applied. The incidences of diapause and the duration of larval development were also measured after exposing larvae to short photoperiods (LD 8 : 16 h, LD 10 : 14 h or LD 12 : 12 h) in combination with various temperatures (20, 22.5 or 25 °C). Although an increase in the incidence of diapause appeared with the lowering of the temperature, no statistical differences were observed in the time needed for pupation within the photoperiodic treatments at the temperatures of 20 and 22.5 °C. Furthermore, when diapausing larvae were transferred to the long photoperiod of LD 16 : 8 h, they immediately proceeded to pupation, regardless of the photoperiod or the temperature to which they had been previously exposed, indicating that there were no differences in the intensity of diapause. Photoperiodic changes from LD 10 : 14 h to LD 12 : 12 h or to LD 14 : 10 h at different larval ages reduced the intensity of diapause with (a) early age of transfer and (b) increase of daylength. By contrast, when larvae were transferred from the long photoperiod of LD 14 : 10 h to shorter, such as LD 10 : 14 h or LD 12 : 12 h, a small increase in the intensity of diapause with the shortening of the daylength was apparent. These results support the hypothesis that insects may compare the duration of the photoperiod and could classify them as either longer or shorter in relation to the critical value.     

Induction of Cell Division Synchrony and Variation of Cytokinin Contents through the Cell Cycle in Tobacco Cultured Cells

Cell division synchrony was induced in tobacco {Nicotiana tabacum)cultured cells by several treatments. Very high synchrony throughouttwo cell cycles was induced by aphidicolin treatment (inhibitorof DNA polymerase , 10 µg/ml) and by treatment with lowtemperature (4°C) and hydroxyurea (50 µg/ml). Themitotic index reached its maximum (52% and 40% in aphidicolinand hydroxyurea treatments, respectively) at 11 h after removalof the added chemical. During the treatments, the cells werearrested in the G₁/S phase of the cell cycle. In the aphidicolin-inducedsystem, incorporation of ¹⁴C-thymidine confirmed that DNA synthesiswas started immediately after removal of the chemical. The aphidicolin-induced synchronous cells were used to studythe contents of butanol-soluble cytokinins during the cell cycle.Cytokinin contents increased conspicuously at the G₂/M boundary. ¹Present address: Department of Biology, Otsuma Women's University,Chiyodaku, Tokyo 102, Japan. (Received May 14, 1985; Accepted November 8, 1985)     

Inductive and Inhibitory Effects of Light on Cell Division in Chattonella antiqua

The cell division of a red tide flagellate, Chattonella antiqua,was synchronously induced under light and dark regimes of 10L14D(a light period, L, for 10 h followed by a dark period, D, for14 h), 12L12D and l4L10D. In all regimes cell number began toincrease ca. 14 h after the onset of L and almost doubled duringone LD cycle. When the light-off timing of the last L was changedor the whole L was shifted, cells that had been synchronizedunder 12L12D invariably began to divide ca. 14 h after the onsetof L. This shows that the timing of cell division was determinedby the time of the onset of L. When cells were continuously exposed to light after a cell division,the subsequent cell division was inhibited. This effect waslimited to cells that had been synchronized under short-dayconditions. Thus it can be concluded that light has both inductive and inhibitoryeffects on cell division in this alga, the latter effect dependingupon the previously given light and dark regimes. (Received December 21, 1984; Accepted February 28, 1985)     

The S phase is discrete and is controlled by the circadian clock in the marine dinoflagellate Gonyaulax polyedra

Cloned cultures of the dinoflagellate Gonyaulax polyedra grown in a 12-h light-12-h dark cycle (LD 12:12) were synchronized to the beginning of G₁ by a two sequential filtration technique. After the second filtration, with the cultures growing in LD 12:12, not many cells had divided after 1 day, but approximately half underwent cell division after 2 days. Flow cytometric measurements of the cells revealed that there is one unique S phase starting about 12 h prior to cell division and lasting for less than 4 h. A majority of cells in cultures synchronized in the same way but maintained in continuous light (LL) after filtration also divided synchronously after 2 days. Just as for the cultures in LD 12:12, those in LL have a similar discrete DNA synthesis phase prior to division. It is concluded that the circadian control of cell division acts before the S phase, giving rise to a discontinuous DNA synthesis phased by the circadian clock.     

Summer diapause and nymphal growth in a subtropical cockroach: response to changing photoperiod

Abstract.  The effects of photoperiod on nymphal growth and adult reproduction were investigated in a small cockroach, Margattea satsumana, living on the subtropical, Hachijo island (33°N), Japan. Nymphal development is slow under constant photoperiods at 25 °C. The shortest mean duration of nymphal development (176 days) is observed at LD 14 : 10 h, followed by LD 12 : 12 h (221 days) and LD 16 : 8 h (309 days). Nymphal development is further prolonged when the nymphs are transferred from LD 12 : 12 to LD 16 : 8 h at 90 days after hatching. However, rapid and synchronized development is observed when nymphs were transferred in the opposite direction. A decreased change in photoperiod from LD 14 : 10 to LD 12 : 12 h also reduces the duration of nymphal development, and this cannot be explained by the results obtained at constant photoperiods. Similarly, nymphs reared at LD 16 : 8 h during the first 60 days mature more rapidly when transferred to LD 12 : 12 h than when transferred to LD 14 : 10 h. The developmental suppression induced by long days may represent a form of summer diapause that is terminated rapidly by short days. Based on these observations and field-census data, it is suggested that this cockroach has a univoltine life cycle overwintering as nondiapause adults, and that this life cycle is stabilized by the response to changing photoperiod.     

Inhibition of Cell Division and DNA Synthesis by Gibberellin in Isolated Zinnia Mesophyll Cells

A culture system of isolated mesophyll cells of Zinnia eleganswas used to examine the action of gibberellic acid (GA) on celldivision. Isolated Zinnia mesophyll cells cultured in a mediumcontaining auxin and cytokinin reinitiated cell division ina partly synchronized manner. When mesophyll cells isolatedfrom 21-day-old seedlings were used, GA added to the culturemedium at concentrations of 1 x 10^–6 M or higher suppressedthe initial rise in the number of divided cells. Tracer experimentswith [³H]-dThd revealed that GA treatment inhibited the incorporationof [³H]-dThd into DNA in the nucleus without inhibiting theuptake of [³H]-dThd into the cells, indicating that GA inhibitedDNA synthesis. GA applied at 48 h inhibited the incorporationof [³H]-dThd into DNA during the following 24 h, but GA appliedat 72 h did not inhibit the incorporation during the subsequent24 h. This suggests that GA affects the process of reinitiationof DNA synthesis, but does not affect DNA synthesis once cellshave become proliferative. (Received January 14, 1986; Accepted March 31, 1986)     

The Nuclear Endoreduplication Cycle in Metaxylem Cells of Primary Roots of Zea mays L.

The nuclear DNA content of metaxylem cells in roots of Zea mayscv. Golden Bantam reaches 16C or 32C by successive rounds ofDNA endoreduplication. Each phase of endoreduplication (endo-S)is separated by a non-DNA synthetic phase (endo-G). These phasesseem to occur in zones at fixed distances from the root tip.The duration of the phases in two of the endoreduplication cycles(4C–8C, 8C–16C) has been estimated in two ways.The first makes use of the rate of movement of cells throughthe positions along the root where the different phases of thecycle are occurring, the second uses labelling with methyl-[³H]thymidineand autoradiography. Both methods indicate that the endo-S phaseswhich cause the nuclear DNA content to rise from 4C to 8C andfrom 8C to 16C last 8–10 h, and that the intervening endo-Gphase lasts 8–12 h. DNA endoreduplication keeps pace withthe increase of nuclear volume; cell volume increases at a morerapid rate, however. Comparison of the endoreduplication cyclein the metaxylem with the mitotic cycle in the adjoining filesof parenchyma cells shows that the mitotic cells complete theircycle more slowly. DNA synthesis, endoreduplication cycle, mitotic cycle, root apex, Zea mays     

Photoperiod modifies daily maps of light and dark sensitivity for N-acetyltransferase activity in pineal glands of 3-week oldGallus domesticus

Summary N-acetyltransferase (NAT) activity in pineal glands exhibits a circadian rhythm with peak activity occurring in the dark-time. We previously showed that inGallus domesticus chicks pretreated with LD12:12, NAT activity was increased by dark exposure (peak dark sensitivity occurred during the expected dark-time) or decreased by light at night (peak light sensitivity occurred early in the night during the time of dark sensitivity). In this study we mapped dark sensitivity vs time (for NAT activity increase in response to 2 h dark pulses), and light sensitivity vs time (for NAT activity decrease in response to 10 min or 30 min light pulses) over a cycle for 3-week old chicks,Gallus domesticus, pretreated with long (LD16:8) or short photoperiod (LD8:16). Sensitivity to light was increased in the second 8 h after L/D by LD8:16. Sensitivity to dark was increased in the first 8 h after L/D by LD16:8.Abbreviations LD16:8 a light-dark cycle consisting of 16 h of light alternating with 8 h of dark - LD8:16 a light-dark cycle consisting of 8 h of light alternating with 16 h of dark - DD constant dark - LL constant light - L/D lights-off - D/L lights-on - NAT pineal serotonin N-acetyltransferase - NAT activity is given in nmoles/pineal gland/h - chick used here to denote a young bird of either sex of the speciesGallus domesticus from hatching to three weeks of age     

Photoperiodic control of diapause in Pseudopidorus fasciata (Lepidoptera: Zygaenidae) based on a qualitative time measurement

In the zygaenid moth, Pseudopidorus fasciata, both larval diapause induction and termination are under photoperiodic control. In this study, we investigated whether photoperiodic time measurement (with a 24-h light-dark cycle) in this moth is qualitative or quantitative. Photoperiodic response curves, at 22, 25, and 28 degrees C indicated that the incidence of diapause depended on whether the scotophases exceeded the critical night length (CNL) or not. All scotophases longer than the CNL-induced diapause; all scotophases shorter than the CNL-inhibited diapause. The CNL was 10.5h at 25 and 28 degrees C, and 10h at 22 degrees C. By transferring from various short photoperiods (LD 8:16, LD 9:15, LD 10:14, LD 11:13, LD 12:12, and LD 13:11) to a long photoperiod (LD 16:8) at different times, the number of light-dark cycles required for 50% diapause induction at 25 degrees C was 7.14 at LD 8:16, 7.2 at LD 9:15, 7.19 at LD 10:14, 7.16 at LD 11:13, and 7.13 at LD 12:12, without showing a significant difference between the treatments. Only at LD 13:11 (near the CNL), the number of light-dark cycles was significantly increased to 7.64. The intensity of diapause induced under different short photoperiods (LD 8:16, LD 9:15, LD 10:14, LD 11:13, and LD 12:12) at 25 degrees C was not significantly different with an average diapause duration of 36 days. The duration of diapause induced under LD 13:11 was significantly reduced to 32 days. All results indicate that the night-lengths are measured as either "long" or "short" compared with some critical value and suggest that photoperiodic time measurement for diapause induction in this moth is based on a qualitative principle.     

Daily rhythms of nuclear protein fractions in rat liver

Abstract

Daily changes of a number of nuclear functions of rat liver were analysed in rats kept in a light‐dark (LD 12 : 12) cycle and constant temperature. Measurements of the DNA content of rat liver with diphenylamin revealed a mean value of about 3 mg/g liver freshweight without showing significant daily rhy thmicity. When related to mg DNA, no significant rhythmicity could be observed in the total protein content and only a slight rhythmicity in the nuclear protein content. Injection of cycloheximide(2mg/100gbody weight) 10 h before killing the animals resulted in an about 10–20% decrease of the protein content of the tissue as well as of the nucleus and probably in a loss of cell water. Nuclear proteins were separated into nuclear sap proteins, chromatin proteins and restproteins, the first 2 fractions of which were further fractionated by means of polyacrylamide SDS electrophoresis. Considerable differences in the protein content of some of the bands were observed: some bands appeared only at a certain time of day (at 6 h), other bands showed a high amplitude rhythmicity with a maximum at 18 h, whereas other bands— as for example the histone containing bands— varied only slightly during 24 h.     

Effects of Photophase and Altitude on Oviposition Rhythm of the Himalayan Strains of Drosophila Ananassae

The effects of varying photophase and altitude of origin on the phase angle difference (Ψ) of the circadian rhythm of oviposition during entrainment to light‐dark (LD) cycles and the aftereffects of such photophases on the period of the free‐running rhythm (τ) in constant darkness (DD) were evaluated in two Himalayan strains of Drosophila ananassae, the high‐altitude (HA) strain from Badrinath (5,123 m above sea level=ASL) and the low‐altitude (LA) strain from Firozpur (179 m ASL). The Ψ (i.e., the hours from lights‐on of the LD cycle to oviposition median) of both strains was determined in LD cycles in which the photophase at 100 lux varied from 6 to 18 h/24 h. The HA strain was entrained by all LD cycles except the one with 6 h photophase in which it was weakly rhythmic, but the LA strain was entrained by only three LD cycles with photophases of 10, 12, and 14 h, but photophases of 6, 8, 16, and 18 h rendered it arrhythmic. Lights‐off transition of LD cycles was the phase‐determining signal for both strains as oviposition medians of the HA strain occurred～6 h prior to lights‐off, while those of the LA strain occurred～1 h after lights‐off. The Ψ of the HA strain increased from～2 h in 8 h photophase to～11 h in 18 h photophase, while that of the LA strain increased from～11 h in 10 h photophase to～15 h in 14 h photophase. The aftereffects of photophase of the prior entraining LD cycles on τ in DD were determined by transferring flies from LD cycles to DD. The τ of the HA strain increased from～19 to～25 h when transferred to DD from LD 8:16 and LD 18:6 cycles, respectively, whereas the τ of the LA strain increased from～26 to～28 h when transferred to DD from LD 10:14 and LD 14:10 cycles, respectively. Thus, these results demonstrate that the photophases of entraining LD cycles and the altitude of origin affected several parameters of entrainment and the period of the free‐running rhythm of these strains.     

The combined effect of photoperiod and temperature on the calling behaviour of the true army worm, Pseudaletia unipuncta

ABSTRACT. Pseudaletia unipuncta (Haw.) (Lepidoptera: Noctuidae) virgin females, maintained at either 10 or 25d?C under LD 12:12 or 16:8 h, started calling at different ages. For a given photoperiod, calling was initiated 11 days later at 10d?C than at 25d?C, while for a given temperature, calling at LD 12:12 h was 3–4 days later than at LD 16:8 h. At 10d?C 50.8% of females did not call within 35 days at LD 12:12 h compared with 30.8% at LD 16:8 h. Calling started earlier in the scotophase at 10d?C than at 25d?C and at LD 16:8 h than at LD 12:12 h. Under all treatments calling generally advanced on successive nights. The time elapsed between the mean onset time of calling and the mid-scotophase was relatively constant under both photoperiod conditions at 25d?C, but at 10d?C was more variable. The mean time spent calling increased significantly with calling age but did not differ significantly between the four experimental conditions tested. Older (15 days) females transferred from 10d?C, LD 16:8 h to 25d?C at either LD 163 or 12:12 h, required less time to initiate calling than younger (5 days) ones. Those transferred from 10d?C, LD 12:12 h took the same time, regardless of their age at the time of the transfer. Females experiencing either a decrease or increase in daylength as well as a temperature increase, required respectively more or less time to initiate calling, compared with individuals that only experienced an increase in temperature. If temperature was the only parameter changed females that initiated calling soon after the transfer immediately adjusted their calling periodicity to prevailing conditions. When both temperature and photoperiod were altered, it took several days before calling periodicity adjusted to the new regime. The ecological implications of temperature and photoperiodic conditions on the possible autumn migration of P. unipuncta are discussed.     

Cell Cycle Changes in the Shoot Apex of Silene coeli-rosa During the Second and Third Days of Floral Induction

The cell cycle in Silene coeli-rosa shoot apices was measuredto test whether or not early components of the floral stimulus,produced during the 2nd and 3rd long days (LD) of an inductiveLD treatment, resulted in an increase in the duration of G₂phase in constant 20–24 h cell cycles. Plants were grownat 20°C in short days (SD) of 8 h light and 16 h darknessfor 28 d (day 0). Starting on day 0, plants were given SD or3 LD each comprising an identical 8 h day and 16 h photo-extension,or 3 dark-interrupted (d.i.) non-inductive LD, interrupted at1700 h of each day with 1 h of darkness. The cell cycle (percentagelabelled mitoses method) and changes in cell number were determinedin the shoot apical meristem. During days 1–2 of the SDtreatment, the cell cycle and mean cell generation time (MCGT)was 18 and 32 h, respectively, giving a growth fraction of 56%.During days 2–3, the cell cycle and MCGT shortened to15 and 23 h, respectively (growth fraction = 65%). During days1–2 of the LD and d.i. LD treatments, cell cycles andMCGTs were 9–10 and 27–29 h, respectively, resultingin smaller growth fractions (about 33%). Thus, shortened cellcycles and altered growth fractions occurred regardless of whetheror not the treatment was inductive. The LD treatment resultedin a marked shortening of G₁ and, to a lesser extent, S-phase,whilst G₂ remained constant. These changes were consistent withincreases in the proportion of cells in G₂ during the photoextensionof each LD which were suppressed during the comparable periodsof the d.i. LD treatment. The latter treatment resulted in eachphase occupying virtually identical proportions of the cellcycle as in the SD treatment. Thus, the unique cell cycle responsesto the initial part of the inductive LD treatment were increasesin the proportion of cells in G₂ coupled with G₁ and G₂ beingof similar duration. Cell cycle, mean cell generation time, shoot apex, Silene coeli-rosa     

Short- and Long-day Responses in the Pre-adult Developmental Duration of Two Species of Camponotus Ants

We assessed the effect of different day/night lengths on the pre-adult developmental time of two species of Camponotus ants that normally develop in dark underground nests. We assayed larval (egg-to-pupal formation), pupal (pupal formation-to-adult emergence), and pre-adult (egg-to-adult emergence) durations in these ants under three different light/dark (LD) cycles of 12:12?h, 10:14?h, and 14:10?h. We observed that the pre-adult development time of ants under these day lengths was significantly different. Although both species developed fastest under 12:12?h LD, when asymmetric LD cycles were compared, night-active species (Camponotus compressus) developed faster under short days (10:14?h) and day-active species (C. paria) developed faster under long days (14:10?h). This day/night-length-mediated difference in pre-adult developmental duration was mostly due to modulation of larval duration; however, in day-active species it was also via altered pupal duration. These results thus indicate that the two species of Camponotus ants respond differently to short and long days, suggesting that seasonal timers regulate pre-adult development time in tropical ant species living in dark underground nests. (Author correspondence: vsharma@jncasr.ac.in/vksharmas/gmail.com)