Natural Variants of the Cellular Slime Mold Acrasis rosea

SYNOPSIS. Twenty different isolates of the cellular slime mold Acrasis rosea, obtained from diverse sources and geographic regions, were studied to determine similarities and differences in their development and structure in culture and their sensitivity or resistance to selected chemicals incorporated into the culture media. Six different classes of fruiting were defined based on the size, distribution, and type of sorocarps formed on the yeast, Rhodotorula, streaked on agar. In the course of these studies a significant mutant, NC-18V (variant), developed spontaneously from the wild type, normal parent strain NC-18N. The mutant differed considerably from all other Acrasis isolates, appeared several times in purified parental cultures, and represents the first laboratory derived variant of A. rosea to be described. Purified strains of the variant (V) and normal (N) cultures were obtained by single-spore isolation. Normal and variant amebae were mixed in ratios of 10:1 and 100:1 (N:V) and spore and stalk cells were selected from different sorocarps in various regions of the culture plate for analysis. The results of these selection experiments clearly indicate that the individual variant amebae have increased migratory ability and that they develop smaller, morphologically different, and more numerous sorocarps that form at distances further from the food source than NC-18N. Some isolates of Acrasis no longer were able to fruit and were classified as “non-fruiters” and a few other isolates formed only a few, small sorocarps on rare occasions. These isolates were mixed together in various combinations of 2 and 3 to screen for cell interaction, but no synergism contributing to fruiting was found. Although fruiting of many A. rosea isolates was inhibited by exposure to continuous light or constant darkness, some “escape”fruiting was noted in certain isolates even when small inocula were used. Single spore isolates of these escape fruiters still fruited in continuous light or dark, but fruiting was always greatly enhanced by a routine 12 hr light : 12 hr dark incubation cycle. It was shown by biochemical studies that actidione, crystal violet, malachite green, ethyl violet, and 5-fluorodeoxyuridine selectively killed some isolates and permitted a classification of isolates as either sensitive or resistant. In a further study of cell interaction between 2 different sets of Acrasis isolates with contrasting biochemical and morphologic markers the formation of neotypes or recombinants could not be demonstrated. The results of this study clearly indicate the existence of significant variation in A. rosea and the potential for application of these differences to developmental studies.     

LENGTH OF THE LIGHT-DARK CYCLE AND PLANT GROWTH

Tukey , H. B., Jr ., and H. J. Ketellapper . (California Inst. Tech., Pasadena.) Length of the light-dark cycle and plant growth. Amer. Jour. Bot. 50(2): 110–115. Illus. 1963.—It has been shown that the length of the light-dark cycle which causes maximal growth of tomato, pea, peanut, and soybean plants is close to 24 hr for cycles consisting of equal periods of light and darkness. The exact optimum for tomato plants was determined by temperature; the optimal cycle length was 20 hr at 30 C and 27–30 hr at 14 C. Such an interaction between temperature and cycle length was not found in pea plants, because peas were less sensitive to cycle length than peanuts, tomatoes, and soybeans and did not respond to changes in cycle length of 2–3 hr. The response to cycle length was not influenced by the conditions in which the seedlings had been raised prior to the treatment. Seedlings raised in a 16-hr light, 8-hr dark regime responded in the same manner as those raised in continuous light. The response to cycle lengths of 18, 24, 36, and 48 hr was not changed qualitatively by the temperature during the growth determination. Small changes in cycle length had no characteristic effects on the rates of photosynthesis, respiration or stem elongation. Stem elongation showed a rapid and initial increase in rate when the light was turned off. It was concluded that plants possess an endogenous time-measuring device with a period of 24 hr. For maximal growth to occur the external periodicity must be synchronized with the endogenous period of the plant. Efforts to obtain direct evidence for this hypothesis were not successful since no overt rhythms could be found in tomato plants.     

LIGHT-MEDIATED INHIBITION OF IN VITRO DEVELOPMENT OF RUDIMENTARY EMBRYOS OF ILEX OPACA

The mature seeds of Ilex opaca Ait. contain rudimentary heart-shaped embryos. When excised embryos of cv. Farage were grown in vitro with a 16-hr photoperiod, only 20 % reached germination size after 13-day incubation, while 75% of the embryos reached the same stage when incubated in darkness. This light inhibitory effect increased with the length of daily light exposure as the daily photoperiod reached 4 hr. Nearly 50% growth reduction resulted as the cultures were preincubated in light continuously for 2 days before a 10-day dark incubation. After 4 days of light incubation the inhibitory effect could no longer be reversed by the subsequent dark incubation. Once the heart-shaped embryos started to grow in darkness they become progressively insensitive to subsequent light inhibition. After a 6-day initial dark incubation the embryos become immune from the inhibitory effect of light. This light inhibitory effect on in vitro embryo growth was universal in all 11 tested cultivars.     

LEAF INITIATION CORRELATES WITH TIME OF MAXIMAL SENSITIVITY OF THE SDP XANTHIUM (ASTERACEAE) TO DARK INTERRUPTION

The hypothesis was tested that the well-known maximal sensitivity to a light break at or near the middle of the dark period of short-day plant Xanthium is correlated with a specific stage of leaf initiation. Samples were collected at various hours before and during noninductive 6-hr dark periods. Lengths of leaf primordia were calculated from serial transverse sections. The reproducible results confirmed that leaf initiation occurred at or near middark under the 18:6 hr light: dark growing conditions. The author suggests the working hypothesis that for a light break to be effective in nullifying the effect of a “long” night in photoperiodically sensitive plants, the light must react with a specific early stage of leaf initiation.     

THE HETEROTROPHIC CAPABILITIES OF CYCLOTELLA MENEGHINIANA1

Cyclotella meneghiniana grew heterotrophically in darkness when glucose in concentrations from 5 mg/liter to 10 g/liter was provided. The other compounds tested did not support growth. However, in continuous light (300 ft-c) growth wax not enhanced if glucose wax provided. Under diurnal conditions of light (300 ft-c) approximately 12–14 hr of darkness were required to observe the enhancement effects of glucose. Uptake studies with labeled glucose indicated that uptake is not dependent on glucose, but that it occurs only at low light intensities. Cells required 12–14 hr of darkness to develop the uptake system.     

THE DISTRIBUTION OF PHOTOSYNTHATE IN ASCOPHYLLUM NODOSUM AS IT RELATES TO EPIPHYTIC POLYSIPHONIA LANOSA12

The brown alga Ascophyllum nodosum is not a major source of organic carbon for its epiphytic red alga Polysiphonia lanosa. Plants pulse-labeled for 24–25 hr with NaH¹⁴CO₃ were examined for exudation and translocation. The maximum amount of radioactive carbon compounds lost from A. nodosum during this experimental period was less than 0.3% of the total ¹⁴C fixed by the alga, and of this amount, only 5% could, have moved through the frond. The remaining fraction of the ¹⁴C lost from the thallus was released into the water. The total exudate from A. nodosum was collected for 1 week in a series of flasks of filtered seawater changed at 12-hr intervals corresponding with the beginning of the light and dark periods, respectively. During 7 days at 15 C only 1.5% of the total ¹⁴C originally fixed had been released as radioactive organic carbon, whereas at 5 C, 0.6% of the total ¹⁴C fixed was found in the medium. No significant difference in the rate of exudation of organic ¹⁴C was observed in light or darkness. After fractionation of the exudate it was found that only 10% of the radioactivity in these exudates was composed of organic acids or amino acids. P. lanosa, on the other hand, is perfectly capable of fixing its own carbon. The photosynthetic rates measured by H¹⁴CO₃ uptake confirm the observations of Bidwell: 3.96 mg CO₂/g/hr (0.09 m mole/g/hr).     

RNA metabolism in apices of Pharbitis nil daring floral induction

RNA metabolism was studied in apices of Pharbitis nil duringand after floral induction. In continuous light ³H-uridine accumulatedin RNA at a constant rate over an 18 hr period. In darkness,however, the rate of accumulation of label into RNA was constantuntil the 10th hour at which time a rapid burst of accumulationoccurred, peaking at the 14th hour of darkness and followedby a net loss of label. The RNA involved in this burst is probablymRNA due to its size and poly(A) content. This phenomenon doesnot seem to be associated with floral induction, since the siteof perception is the apex, and it also occurs under conditionswhere floral initiation is inhibited by a brief light interruptionof the dark period. Immediately after floral induction by a16-hr dark period the rate of RNA synthesis was suppressed about14%. This suppression lasts for about 12 hr and was followedby a twofold increase in the rate of RNA synthesis, comparedto non-induced apices, at 64 hr after the beginning of the inductivedark period. These post-induction changes were found to occurin all RNA fractions. ¹Present address: Department of Radiation Biology and Biophysics,University of Rochester School of Medicine and Dentistry, Rochester,N.Y. 14642, U.S.A. (Received March 15, 1976; )     

PHOTOCONTROL OF THE ORIENTATION OF CELL DIVISION IN ADIANTUM. I. EFFECTS OF THE DARK AND RED PERIODS IN THE APICAL CELL OF GAMETOPHYTES

When protonemata of Adiantum capillus-veneris L. which had been grown filamentously under continuous red light were transferred to continuous white light, the apical cell divided transversely twice, but the 3rd division was longitudinal. An intervening period of darkness lasting from 0 to 90 hr either between the 1st and the 2nd cell division or between the 2nd and the 3rd one did not affect the number of protonemata in which the 3rd cell division was longitudinal. The insertion of red light instead of darkness greatly decreased the percentage of 1st longitudinal divisions occurring at the 3rd division, and increased the number of transverse divisions. Fifty percent reduction of induction of 1st longitudinal division was caused by ca. 50 hr exposure to red light between 1st and 2nd division and by ca. 20 hr between 2nd and 3rd division, and total loss was induced by an exposure of ca. 100 hr or longer to red light in the former and by ca. 40 hr longer in the latter. Thus, by using an appropriate intervening dark period or exposure to red light, the orientation and timing of cell division could be controlled in apical cell of the fern protonemata.     

Alarm reaction in bleak (Alburnus alburnus (L.), Cyprinidae) in response to chemical stimuli from injured conspecifics

The response of bleak (Alburnus alburnus (L.)) to alarm substance (from skin extract of conspecifics) was quantified, using a video camera, in laboratory experiments across two light and one dark periods (18 hrs). In the light alarm substance induced hiding in refuges (vegetation) and formation of aggregations. There was no such reaction during darkness or during a second light period.     

STUDIES ON THE ECOLOGICAL AND PHYSIOLOGICAL SIGNIFICANCE OF AMPHICARPY IN GYMNARRHENA MICRANTHA (COMPOSITAE)

The 2 types of fruit (aerial and subterranean) borne by the dwarf desert annual Gymnarrhena micrantha were compared with regard to their responses to factors affecting their formation, dispersal, germination and seedling mortality. The 2 types of fruit differed markedly in several respects. In comparison with the subterranean fruits, the aerial ones are much smaller and more numerous, but the formation of the inflorescence in which they develop is more dependent on a favorable supply of soil moisture. The aerial fruits are dispersed by wind, after becoming detached by a complex series of hygroscopic movements which involve several organs and tissues, while the subterranean fruits never leave the dead parent plant, germinating right through its tissues. Germination of the subterranean fruits starts after a shorter incubation period and is less temperature-dependent in both light and dark. Light stimulated germination of both types of fruit, increasing their germination rates and final percentages, but not affecting the duration of the incubation period. In the subterranean fruits, the rate of germination was equally stimulated by light over the entire temperature range, with a well-defined optimum at 15 C in both light and dark. In the aerial fruits, the same optimum was found only in the light, rates in darkness increasing with decreasing temperatures. In the aerial fruits, alternations of light and dark were more favorable to germination than either continuous light or dark, the full effect being obtained with a single 8-hr or 16-hr light period, provided it was preceded by 16 or 8 hr of darkness, respectively. Similar reactions to combinations of light and dark were not observed in the subterranean fruits. Seedlings developing from the subterranean fruits were much larger, but grew at a relatively much slower rate than those from aerial fruits. The former were distinctly more tolerant of unfavorable soil-moisture regimes, such as low moisture supply and drought. It was concluded that the 2 types of fruit serve 2 distinct functions in the biology of the plant. The aerial fruits are adapted to the function of increasing the distribution of the species within suitable habitats, while the subterranean fruits are adapted to increasing the probability of the survival of the species.     

EFFECT OF BLUE AND YELLOW LIGHT DURING THE LATER DEVELOPMENTAL STAGES OF SPHAEROBOLUS

When fruiting cultures of Sphaerobolus are transferred from continuous light to darkness the discharge of global masses continues for 1 day but then stops for the next few days. Experiments are reported in which this darkness is interrupted after 24 hr by brief (0.5-2 hr) treatment with light of different wavelengths and of equated low intensity (ca. 100 lux). Interruption by blue (ca. 448 mμ) or by green (ca. 500 mμ) light has no effect, but treatment with yellow (ca. 585 mμ) or red (ca. 650-700 mμ) leads to substantial discharge 24 hr later. If, however, the yellow treatment is followed immediately with blue there is little or no discharge; but if the order of this treatment is reversed, a high level of discharge results. This is somewhat greater than that resulting from treatment with yellow light alone. If, following a yellow treatment there is an interval of several hours before a blue treatment, the blue has less effect in negating the action of the yellow light. It is shown that, although in the final light-sensitive stages in development of the sporophore before it opens, yellow and red light are stimulatory but blue and green are not; in the phototropic response of the mature sporophores blue light is effective and yellow is not.     

Daily changes in concentrations of prolactin in serum of prepubertal bulls exposed to short- or long-day photoperiods

Early temporal changes in concentrations of prolactin (PRL) in serum after a sudden change in photoperiod and daily responsiveness to PRL-releasing and inhibiting factors were investigated in prepubertal Holstein bull calves exposed to different photoperiods. In calves switched from 8-hr light: 16-hr dark to 16-hr light:8-hr dark, there was no observable change in the daily pattern of serum concentrations of PRL after 1, 2, or 4 days. On the other hand, in animals switched from 16-hr light:8-hr dark to 8-hr light:16-hr dark, there was a consistent increase in serum PRL from 33.4 ng/ml on Day 0 to maximum values of 57.3, 62.7, and 78.9 ng/ml between 14 and 18 hr after onset of light on Days 1, 2, and 4, respectively. Thus, absence of light allowed expression of a daily rhythm in serum concentrations of PRL that persisted for at least 4 days after the photoperiod switch. There were no differences in L-dopa inhibition of PRL release in animals exposed to 16-hr light:8-hr dark at 3 or 15 hr after onset of light. However, thyrotropin-releasing hormone-induced release of PRL was greater 3 hr after onset of light (11 hr after onset of dark) compared with release at 9, 15, and 21 hr after onset of light in animals exposed to 16-hr light:8-hr dark, but not in bulls exposed to 8-hr light:16-hr dark. The results provide evidence that the cue for the putative photosensitive period of PRL secretion in cattle may be more closely associated with onset of dark, not onset of light.     

SOME FACTORS AFFECTING THE GERMINATION OF SEED OF THE SAGUARO CACTUS (CARNEGIEA GIGANTEA)

Alcorn , Stanley M. (U. S. Dept. of Agric., Tucson, Ariz.), and Edwin B. Kurtz , Jr . Some factors affecting the germination of seed of the saguaro cactus (Carnegiea gigantea). Amer. Jour. Bot. 46(7): 526–529. 1959.—Germination of saguaro cactus seeds is stimulated by red light (approx. 6550 A) or daylight and far-red light (approx. 7350 A) counteracts this effect. About 0.1% germinate in continuous darkness. A single exposure to red light was most effective when the seeds were imbibed 24 hr., but maximum germination resulted from multiple exposures to red light during a 72-hr. imbibition period. The optimum temperature for germination was 25°C.; no germination occurred at 15°C. and only slight germination at 35°C. Imbibition of light-treated seeds in 0.05 to 0.2% KNO₃ increased germination. Germination of seeds in either light or dark was increased by imbibing the seeds in 500 to 1000 p.p.m. gibberellic acid.     

A STUDY OF LIGHT INTENSITY,PERIODICITY, AND WAVELENGTH ON ZOOSPORE PRODUCTION BY PROTOSIPHON BOTRYOIDES KLEBS12

When mature Protosiphon cells were placed in darkness, zoospore production was more extensive and was completed in a shorter time at a temperature of 27 C than at 22 or 15 C. Cool-white fluorescent (Sylvania) light inhibited the process measurably at a radiation intensity of 0.6±10³ ergsjcm²-sec; inhibition was 96% complete at 14±10³ ergs/cm²-sec. For mature cells previously grown under repeated 12-12 hr light-dark cycles, a dark period of approximately 2 hr at 22 C allowed cell division to proceed to a stage such that reillumination did not inhibit continued development of zoospores. Monochromatic light from 402 to approximately -494 nm, as compared to darkness, inhibited zoospore formation; maximal inhibition was at 432-461 nm. In contrast, monochromatic light from 522 to 726 nm stimulated zoospore formation relative to darkness. Synchronous zoospore production was obtained using the following regimes: (A) 12 hr cool-white alternated with 12 hr yellow, (B) 12 hr cool-white alternated with 12 hr blue. Under regime A synchronous zoospore release (following synchronous production) occurred near the end of the yellow irradiation period, while under regime B it occurred near the end of the cool-white irradiation period. The significance of this in terms of photoprocesses and possible photoreceptors is discussed.     

THE DEPENDENCE OF FLOWERING IN SEVERAL LONG-DAY PLANTS ON THE SPECTRAL COMPOSITION OF LIGHT EXTENDING THE PHOTOPERIOD

The results of experiments in which the length, time, and spectral composition of photoperiod extensions and light breaks were varied are presented. The plants used included Hyoscyamus niger L. (annual henbane); Beta vulgaris L. (annual sugar beet); Hordeum vulgare L. (barley); Anethum graveolens L. (dill); Lolium temulentum L. (darnel); and Petunia hybrida Vilm. (petunia). Brief light breaks in the middle of each night failed to cause flower induction. Extended breaks and 8-hr extensions of the photoperiod were effective, particularly those with light from BCJ, rubyred, or incandescent lamps. For all lamp types and species, 8-hr extensions prior to each daylight period were more effective than those given at the end of each day. Four-hour light breaks were most effective when given in the middle of each night. The flowering caused by 4-hr breaks with BCJ light from 8 pm to 12 pm was suppressed when the BCJ light was preceded by 4 hr of fluorescent light. When light from BCJ or fluorescent lamps was interpolated for 2 hr at various times during 8-hr extensions with light from the other type of lamp, BCJ light stimulated flowering the most, and fluorescent light inhibited it the most, when interpolated at the end of the daylight period. These results are discussed, and a model of how phytochrome participates in the flowering of long-day plants is presented.     

PHOTOPERIODIC ADAPTATIONS IN EUPATORIUM RUGOSUM

Racial differences based on flowering response to several photoperiods were detectable in two widely separated populations of white snakeroot, Eupatorium rugosum Houtt. The most favorable photoperiod for advanced flowering in Georgia stocks was 12 hr, for those from North Dakota, 14 hr. The difference in latitude between these populations was approximately 12° and represents a mean difference of 75 days in the frost-free season. Under noninductive photoperiod a 1-hr interruption of white light in the middle of 15 hr of darkness stimulated floral initiation in North Dakota plants, whereas the same application at the beginning or at the end of the dark period failed to produce flower buds. The effect of red light (660 mμ) for 10 min given in the middle of the long night was similar to white light on the northern strain, and was negated by far-red (730 mμ). Georgia stocks initiated flowering under 15 hr of darkness but were retarded by white light applied in the middle of the period, thus differing in basic response from North Dakota plants. Red light, in contrast to effects observed in North Dakota plants, retarded initiation of flower buds. This effect was offset by far-red light. When compared with other studies on long-day and short-day species our results suggest that photoperiodic adaptations related to latitudinal distribution occur in white snakeroot. The North Dakota strain showed correspondence to long-day types while short-day tendencies were exhibited by Georgia plants.     

FACTORS AFFECTING DARK SURVIVAL OF THE BROWN TIDE ALGA AUREOCOCCUS ANOPHAGEFFERENS (PELAGOPHYCEAE)1

Aureococcus anophagefferens Hargraves et Sieburth is a pelagophyte responsible for the harmful brown tides in New York, New Jersey, and Rhode Island, USA. Recent reports of blooms in new areas, Maryland, USA, and Saldanha Bay, South Africa, suggest that the alga may be expanding its range, possibly through anthropogenic transport. Experiments tested the ability of A. anophagefferens to survive dark conditions, such as those that might be encountered during transport in ballast tanks or recreational boats. Laboratory cultures were stored in complete darkness for various lengths of time under different conditions. After returning cultures to optimal light and growth conditions, we recorded the time until growth resumed. Cultured A. anophagefferens was able to survive for at least 30 days in the dark. Temperature played a major role in dark survival, because cultures stored at 6° C and 12° C recovered faster than those stored at 18° C or 24° C. Growth phase at the time of storage had a minor effect on recovery, with exponential phase cultures resuming growth more quickly than stationary phase cells. Although the alga is known to have heterotrophic capabilities, the addition of low levels (1–3 μM) of organic nutrients did not appear to increase dark survival. Salinities within normal estuarine and oceanic ranges also did not affect survival. The ability of A. anophagefferens to survive dark periods could allow it to be transported by anthropogenic means to new regions, and temperature and length of storage appear to be key factors determining cell viability during prolonged darkness.     

Schistosoma mansoni and Schistosoma haematobium: Emergence of schistosome cercariae from snails with darkness and illumination

Biomphalaria glabrata and Bulinus globosus were infected with Schistosoma mansoni and Schistosoma haematobium, respectively, and the effect of different illumination conditions at 25 C on cercarial output was observed for 4 days. In both species, a dark period of 10–14 hr on Day 2 of the observation period resulted in an emergence pattern on Day 3 similar to the regular pattern recorded for Day 1. Total cercarial output on Day 3 was within 30% of the control (Day 1) output. A dark period of between 0 and 8 hr resulted in suppression of cercarial emergence and in abolishment of the regular hourly emergence pattern on Day 3. A dark period of 16–20 hr resulted in an emergence pattern with two peaks, the first occurred at Hour 1, and the other at Hour 5 of the subsequent light period. Interjection of a 1-hr dark period during the light period of Day 3, following short (2–8 hr) exposure to dark on the preceding day, produced an increase in cercarial shedding of S. mansoni immediately after restitution of the light conditions. On the other hand, in S. haematobium, cercarial output was stimulated during the interposed dark period itself.     

PHOTO-INHIBITION OF SPORULATION IN ALTERNARIA SOLANI

Lukens, R. J. (Connecticut Agric. Expt. Sta., New Haven.) Photo-inhibition of sporulation in Alternaria solani. Amer. Jour. Bot. 50(7): 720–724. Illus. 1963.—Day-old conidiophores from starved cultures of Alternaria solani require a 12-hr dark period to produce conidia. If the cultures are illuminated during the dark period, conidial production is inhibited. The action spectrum of light inhibiting conidial formation contains 2 maxima, a sharp one at 450 mμ and a broad one extending from 375 to 425 mμ. The entire action spectrum corresponds approximately to the absorption spectra of riboflavin-5-phosphate mononucleotide (FMN) and of 6-carotene. FMN nullifies the effect of light in inhibiting sporulation, but b-carotene does not. Flavins appear to be essential for conidial formation and are photo-inactivated. It is likely that flavins are photo-receptors through which light inhibits conidial formation in A. solani.     

QUANTITATIVE STUDIES OF THE VEGETATIVE SHOOT APEX OF EQUISETUM SCIRPOIDES

Equisetum scirpoides Michx., propagated from a single clone, was grown in a controlled growth chamber at 24 ± 1 C under a photoperiod of 16 hr light/8 hr darkness. The apical cell of aerial vegetative shoots gives rise to derivatives (merophytes) in a helical sequence. Each newly formed merophyte divides anticlinally to form two superposed cells that are parallel to a lateral face of the apical cell. Radial longitudinal divisions then take place in the two superposed cells. Shoot tips were fixed every 2 hr for 24 hr to determine the mitotic index of the apical cell, six subjacent cells, and the remaining cells above the level of leaf initiation. Average mitotic indices for the 24-hr period were 3.9%, 3.9%, and 7.0%, respectively. The results indicate that the apical cell is quite active mitotically; there was no clear evidence of endopolyploidy in cells of the shoot apex, young leaves or in the developing cortex, based upon cytophotometric measurements of DNA content.