Photocontrol of the orientation of cell division inAdiantum

The rate of transition from one- to two-dimensional growth of fernAdiantum gametophytes under white light depends on the age of gametophyte cultured under red light. When gametophytes were cultured for longer period under red light, the rate of transition decreased and the number of abnormal gametophytes increased. Although the first step of the transition was the first longitudinal cell division following the two transverse ones (Wada and Furuya, 1970), the time-lapse-video study revealed that the apical cell of protonemata became flattened in the plane perpendicular to the incident ray of white light before the first longitudinal cell division. Analytical study of growing part of the apical cell with grains of activated charcoal as markers revealed that the apical cell flattening occurred evenly throughout the equatorial circumference of the cell even in the shaded side of the protonemata as well as in the side irradiated with white light.     

红光下培养方式对雨生红球藻细胞增殖及其活力的影响

研究重点针对雨生红球藻绿色游动细胞的增殖培养阶段,分析了在利于细胞增殖的红光条件下,几种培养方式的调整对增殖过程和细胞活力的影响。结果显示:（1）在红光下,增殖平台期维持时间长,细胞活力稳定,细胞中性脂无累积,但进入平台期前,细胞中性脂有规律波动,进入平台期后相对稳定;通过更新率为20%的半连续培养,细胞数产出较批次培养提高57%;半连续培养中细胞呈现胁迫调节的时间较批次培养晚。随着培养时间增加,半连续培养下细胞营养盐吸收能力降低。（2）初始接种密度与细胞增殖速率及细胞光合活力呈负相关:初始密度低的细胞增殖速率较高,细胞光合作用活力高。（3）在培养过程中添加CO2时,最大密度均有提高,达6.0105 cells/mL,较无添加组提高54%;细胞分裂速率均有提高,但红光下较白光下增殖速率高（分别为0.223/d和0.198/d）;添加CO2降低培养液pH,利于维持适宜增殖的pH环境。叶绿素荧光参数以及细胞粒径在红光和白光下有显著差异:红光下,Fv/Fm显著高于白光下;红光下补充CO2显著减小细胞粒径,而白光下粒径无显著变化。研究结果显示,在红光下,采用间断式半连续培养补充CO2培养绿色游动细胞,有利于提升细胞活力与产出。     

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.     

PHOTOCONTROL OF THE ORIENTATION OF CELL DIVISION IN ADIANTUM. III. EFFECTS OF METABOLIC INHIBITORS

5-Fluorouracil, 8-azaguanine and ethionine were tested on the orientation of cell division to see whether the two-dimensional development of the fern Adiantum gametophytes was due to newly synthesized protein(s). Using the system in which the orientation of cell division was controlled experimentally by sequential treatment with red light, white light and darkness and by the direction of irradiation, all the inhibitors decreased the rates of cell elongation and cell division of the gametophytes, but did not specifically affect the two-dimensional differentiation at all.     

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.     

INFLUENCE OF THE TONIC EFFECT OF GRAVITATION AND AUXIN ON CELL ELONGATION AND POLARITY IN ROOTS

The influence of a longitudinal (tonic) gravitational force and of auxin on the pattern of growth and cell polarity has been studied on intact roots of wheat seedlings. A klinostat technique was used for controlling gravitation. Growth in length was evaluated as cell division activity, rate of cell elongation (μ/h) and duration of elongation (h). Exogenous auxin (1-NAA) increases the rate of cell elongation in all concentrations tested (10⁻⁸ — 3 × 10⁻⁷m ) and shortens the time of elongation with increasing concentration. It promotes rate of cell elongation in roots as it does in shoots. It also accentuates the polar insertion of root hairs and their growth. The tonic effect of gravitation resembles that of an increase in auxin both in light and darkness. The results are discussed in relation to plagiotropic growth of roots, root growth promotions by auxin, and the difference between root and shoot growth.     

CELL DIVISION AND CELL ELONGATION IN LEAF DEVELOPMENT OF XANTHIUM PENSYLVANICUM

Maksymowych, Roman. (Villanova U., Villanova, Pa.) Cell division and cell elongation in leaf development of Xanthium pensylvanicum. Amer. Jour. Bot. 50(9) : 891–901. Illus. 1963.—Cell division in different parts of the lamina and cell enlargement of the upper epidermis and palisade mesophyll were studied in vertical and horizontal planes during the entire period of growth. The leaf plastochron index (L.P.I.) was used for designation of developmental stages of the leaf. From cell-length data and measurements of cell area the absolute rates of elongation (dX/dpl) and relative rates of elongation (dlnX/dpl) were calculated. The increase in number of cells in the early plastochrons is exponential and cell division stops at about L.P.I. 3.0. Divisions cease first at the tip and last in the basal lobes of the leaf, indicating a basipetal trend of this process. Cells are elongating while division is in progress, though this elongation proceeds at low rates and for a limited time. Palisade cells elongate in the vertical plane at higher rates and at least 1 plastochron sooner than the upper epidermis. The latter cells, however, expand in area with higher absolute and relative rates, and about 2 plastochrons in advance of the palisade mesophyll. The rates are not constant during the whole period of development but are represented by the bell-shaped curves with maximal peaks around L.P.I. 3.0 for the middle portion of the lamina. The increase in volume of the 2 types of cells stops around L.P.I. 5.0, or shortly after. In addition to unequal durations of cellular enlargement, both tissues expand at differential rates, which for the upper epidermis is high in the horizontal plane but low in the vertical plane, while the opposite is true for the palisade mesophyll. It is suggested that palisades and spongy mesophyll are separated and intercellular spaces formed during the course of development because of the greater rate of expansion in area of the upper epidermis.     

Growth and cell cycle of Ulva compressa (Ulvophyceae) under LED illumination

The cell‐cycle progression of Ulva compressa is diurnally gated at the G₁ phase in accordance with light–dark cycles. The present study was designed to examine the spectral sensitivity of the G₁ gating system. When blue, red, and green light‐emitting diodes (LEDs) were used for illumination either alone or in combination, the cells divided under all illumination conditions, suggesting that all colors of light were able to open the G₁ gate. Although blue light was most effective to open the G₁ gate, red light alone or green light alone was also able to open the G₁ gate even at irradiance levels lower than the light compensation point of each color. Occurrence of a period of no cell division in the course of a day suggested that the G₁ gating system normally functioned as under ordinary illumination by cool‐white fluorescent lamps. The rise of the proportion of blue light to green light resulted in increased growth rate. On the other hand, the growth rates did not vary regardless of the proportion of blue light to red light. These results indicate that the difference in growth rate due to light color resulted from the difference in photosynthetic efficiency of the colors of light. However, the growth rates significantly decreased under conditions without blue light. This result suggests that blue light mediates cell elongation and because the spectral sensitivity of the cell elongation regulating system was different from that of the G₁ gating system, distinct photoreceptors are likely to mediate the two systems.     

REGIONS OF CELL DIVISION AND ELONGATION DURING STEM GROWTH OF XANTHIUM

Regions of cell division and cell elongation were established during stem growth of Xanthium pensylvanicum (cocklebur). From percent mitosis it was determined that the region of cell division in a Xanthium stem of Plastochron Index (PI) 13.89 was 20 mm long, starting from the stem apex and proceeding in a basipetal direction. Measurements of cortical cell lengths demonstrated that mature cell length in the stem of the same plant was reached at about 55 mm distance from the stem apex. Between 20 and 55 mm distance from the apex, shoot growth occurred by cell elongation alone. The maximum rate of change in cell length (dC/dX) was at about 15 mm distance from the stem apex. The length of the apical growth region was a function of the age of the plants. The older the plant, the longer its apical region of elongation. Growth of Xanthium stems was due primarily to elongation of internodes; the nodal regions did not seem to elongate.     

CELL DIVISION STUDIES OF THE SHOOT APEX OF DATURA STRAMONIUM DURING TRANSITION TO FLOWERING

Seedlings of Datura stramonium L., although not photoperiodically sensitive, are useful for floral transition studies when raised in a growth chamber at a constant temperature of 25 C with a photoperiod of 8 hr of light (1,600-2,000 ft-c) and 16 hr of darkness. A terminal flower is formed after the seventh or eighth leaf primordium is produced. A constant rate of leaf initiation up to the time of flowering enables specific apical stages to be obtained and studied. Changes in the mitotic index, substantiated with calculated rates of cell division (measured by the accumulation of metaphases following treatment with colchicine) were studied in shoot apical zones during transition to flowering. Fluctuations in the mitotic index of each zone in the vegetative and transition apex with respect to apical stage as well as time of day were not statistically significant. The mitotic index of the summit zone of the vegetative apex was significantly lower than in the other zones whose mitotic indices were not significantly different from one another. During floral transition the mitotic index of the summit zone as well as the central zone (just below the summit zone) significantly increased while no significant changes were detected in the flank zones. It was shown that the mitotic index could be considered representative of the rates of cell division in Datura.     

INTERACTIONS OF LIGHT/DARK CYCLES AND NITROGEN PULSES ON THE TIMING OF CELL DIVISION IN THE NITROGEN-LIMITED MARINE DIATOM CYLINDROTHECA FUSIFORMIS (BACILLARIOPHYCEAE)1

Cell division in most eukaryotic algae grown on alternating periods of light and dark (LD) is synchronized or phased so that cell division occurs only during a restricted portion of the LD cycle. However, the phase angle of the cell division gate, the time of division relative to the beginning of the light period, is known to be affected by growth conditions such as nutrient status and temperature. In this study, it is shown that the phase angle of cell division in a diatom, Cylindrotheca fusiformis Reimann and Lewin, is affected by the N-limited growth rate; cell division occurred later in the dark period (12:12 h LD cycle) when the growth rate was infradian (D = 0.42 d^?1) than when it was ultradian (D = 1.0 d^?1). Nitrogen-pulses did not affect the phase angle of the division gate, but could shift the time of peak cell division activity within the division gate. The effects, if any, of N-pulses were dependent upon the growth rate and the time of day that the pulses were administered. These responses indicate that the timing of cell division in this diatom is not determined solely by the zeitgeber from the LD cycle, but rather that a LD cycle control mechanism and a N-mediated control mechanism are both involved and are somewhat interdependent. In addition, an increase in protein was observed immediately after administering a N-pulse to C. fusiformis in the ultradian growth mode indicating that the accumulation of protein can be uncoupled from the cell division cycle.     

THE TRANSITION FROM FILAMENTOUS TO TWO-DIMENSIONAL GROWTH IN FERN GAMETOPHYTES. I. THE REQUIREMENT FOR PROTEIN SYNTHESIS IN GAMETOPHYTES OF PTERIDIUM AQUILINUM

Two-dimensional (2-D) development of gametophytes of Pteridium aquilinum was estimated by the percentage of plants with at least one cell wall at an oblique angle, relative to the long axis. Inhibition of cell division per se was assayed by counting the cell number per filamentous (1-D) gametophyte. Specific concentrations of 8-azaguanine, 5-fluorouracil, p-fluorophenylalanine, actinomycin D, streptomycin, and cycloheximide were found to selectively inhibit 2-D development. A reduction in the percentage of 2-D gametophytes was accompanied by a reduction in the relative protein content (protein per dry weight). A comparable association was found only during the initial stages of 2-D development; after 5 days the relative protein content decreased as the percentage of 2-D gametophytes increased. Different intensities of white light resulted in a 10-fold difference in the percentage of 2-D plants with no alteration of the relative protein content. These results demonstrate that no strict relationship between 2-D development and relative protein content occurred in these gametophytes.     

Effects of Colchicine and Light on Cell Form in Fern Gametophytes. Implications for a Mechanism of Light-induced Cell Elongation

Spores of the fern, Onoclea sensihilis L., suffer a disruption of normal development when they are cultured on media containing colchicine. Cell division is inhibited, and the spores develop into giant spherical cells under continuous white fluorescent light. In darkness only slight cell expansion occurs. Spherical cell expansion in the light requires continuous irradiation. Photosynthesis does not seem to be involved, since variations in light intensity do not affect the final cell diameter; the addition of sucrose to the medium does not permit cell expansion in darkness; and the inhibitor DCMU does not block the light-induced cell expansion. Continuous irradiation of colchicine-treated spores with blue, red or far-red light produces different patterns of cell expansion. Blue light permits spherical growth, similar to that found under white light, whereas red and far-red light promote the reestablishment of polarized filamentous growth. Although ethylene is unable to induce polarized cell expansion in colchicine-treated spores in darkness or white and blue light, it enhances filamentous growth which already is established by red or far-red irradiation. Both red and far-red light increase the elongation of normal filaments (untreated with colchicine) above that of dark-grown plants, but under all 3 conditions the rates of volume growth are identical. Light, however, does cause a decrease in the cell diameters of irradiated filaments. These data are used to construct an hypothesis to explain the promotion of cell elongation in fern protonemata by red and far-red light. The model proposes light-mediated changes in microtubular orientation and cell wall structure which lead to restriction of lateral cell expansion and enhanced elongation growth.     

LIGHT-DEPENDENT INHIBITION OF CELL DIVISION AND RHIZOID ELONGATION IN GEMMAE OF THE FERN,VITTARIA GRAMINIFOLIA

Gametophytes of the shoe-string fern Vittaria graminifolia produce linear, six-celled propagules called gemmae. The terminal cells of each gemma elongate into primary rhizoids in culture, and the inner body cells divide asymmetrically to produce prothallial or rhizoid initials. The initiation of both asymmetric cell division and rhizoid elongation is delayed by light intensities greater than 2 w/m². The maximal rates of cell division and rhizoid elongation are unaltered. A 24-hr pulse of high light intensity delays cell division and rhizoid elongation to the same extent, whenever applied during the first 3 d of culture. The model we propose for cell division hypothesizes the existence of a preparatory phase of finite duration prior to mitosis that is sensitive to light intensity. If a cell is irradiated by light intensities greater than 2 w/m² while in the preparatory phase, its entrance into mitosis is delayed. A similar model is proposed for the initiation of rhizoid elongation. Despite the fact that both cell division and rhizoid elongation are dependent on photosynthesis, direct measurements of CO₂-uptake rates show that the inhibitory effects of high light intensities are not due to an inhibition of photosynthesis.     

THE ROLE OF LIGHT IN HISTOGENESIS AND DIFFERENTIATION IN THE SHOOT OF PISUM SATIVUM. III. THE INTERNODE

Thomson, Betty F., and Pauline Monz Miller. (Connecticut Coll., New London.) The role of light in histogenesis and differentiation in the shoot of Pisum sativum. III. The internode. Amer. Jour. Bot. 50(3): 219–227. Illus. 1963.—Seedlings of Pisum sativum were grown under constant conditions and exposed daily to red or white fluorescent light or kept in total darkness. Counts and measurements of internodal cells in both transverse and longitudinal directions show that light does not alter the sequence or pattern of tissue differentiation, including the sequence of xylem maturation within the vascular bundle. Light does accelerate the rate of a constant course of differentiation. Light advances the time of division and enlargement of cortex, xylem, phloem, and pith cells in the longitudinal direction but reduces both the final number and the final length attained in all cases. It is concluded that light accelerates all phases of shoot growth and differentiation and that cell division and elongation in the later phases of internodal growth are reduced by light because of accelerated cell maturation.     

GROWTH REGULATION BY ETHYLENE IN FERN GAMETOPHYTES. II. INHIBITION OF CELL DIVISION

Ethylene, a natural product of sensitive fern (Onoclea sensibilis L.) gametophytes, has been demonstrated to inhibit cell division in light-grown prothallia. When plants were grown on Knop's solution plus 1 % sucrose under 300 ft-c or more of white light, all ethylene concentrations from 1–1000 μl/liter reduced the rate of increase of cell number by about one-half. The over-all rate of increase of cell number was regulated by various environmental and chemical factors, but regardless of the rate established in control cultures, ethylene treatment of 1–1000 μl/liter produced a relative 50 % depression of cell number. Ethylene was specific for inhibition of cell division and was not a general inhibitor of growth. The ethylene inhibition did not result from a reduction of photosynthesis or energy supply. Further demonstration of ethylene as the active gaseous component resulted when cultures were grown in small enclosed containers with an ethylene absorbent, mercuric perchlorate, and consequently the cell number of gametophytes was restored to the level of unenclosed controls.     

EFFECTS OF PHOTOCYCLES AND PERIODIC AMMONIUM SUPPLY ON THREE MARINE PHYTOPLANKTON SPECIES. I. CELL DIVISION PATTERNS1

Cell division patterns in Thalassiosira weissflogii (Grun.), Hymenomonas carterae (Braarud and Fagerl), and Amphidinium carteri (Hulburl) grown in cyclostat culture were analyzed as functions of the periodic supply of light and the limiting nutrient (ammonium) and of combinations of these two factors. In all three species, division patterns were phased by light/dark cycles in N–limited as well as N–replte conditions, and also to ammonium pulses in N–limited growth in continuous light. Both the degree and timing of the cell cycle phasing varied among species. When both stimuli were present, the influence of the photocycle overrode the N–pulse stimulus in H. carterae and A. carteri. while in T. weissflogii, division was always phased by the timing of the N–pulse regardless of the phase angle between the photocycle and the pulse.     

THE TRANSITION FROM FILAMENTOUS TO TWO-DIMENSIONAL GROWTH IN FERN GAMETOPHYTES. IV. INITIAL EVENTS

Time-lapse photomicrography and autoradiography were used to study the initial events leading to the first cell division following transfer from red to white light. The first responses to white light, an apical swelling and a reduced rate of elongation, were often observed within the first 1–2 hr after the transfer; these two changes were not always initiated at the same time. Only the dome region of the cell participated in the elongation in red, as demonstrated by the displacement of anion exchange resin markers. The dome region as well as the region proximal to the dome was associated with the apical swelling, including regions formed in red. The average duration of the G1, S, G2, and M phases was found to be approximately 4, 3, 3.5, and 1 hr, respectively.     

ROLE OF ASYMMETRIC CELL DIVISION IN PTERIDOPHYTE DIFFERENTIATION. II. EFFECT OF CA2+ ON ASYMMETRIC CELL DIVISION,RHIZOID ELONGATION,AND ANTHERIDIUM DIFFERENTIATION IN VITTARIA GEMMAE

Gametophytes of Vittaria graminifolia reproduce vegetatively by means of gemmae. Each gemma consists of a linear array of six cells: four body cells and a knob-shaped terminal cell at each end. When gemmae are shed from the gametophyte onto Knop's mineral medium, the two terminal cells do not divide, but elongate to form primary rhizoids. The body cells undergo asymmetric cell division, and the smaller daughter cells differentiate into either secondary rhizoids or prothalli. When gibberellic acid is included in the medium, antheridia are formed as a result of asymmetric cell division instead of vegetative structures. We studied the effect of Ca²⁺ on asymmetric cell division, rhizoid elongation, and antheridium formation in gemmae cultured on Knop's mineral medium and variations of Knop's medium. Ca²⁺ inhibited the onset of cell division and rhizoid elongation, but was required for differentiation of antheridia. Treatments which lowered the Ca²⁺ content of gemmae (EGTA and dilute HCl extraction, culture on verapamil-containing and Ca²⁺-deficient medium) caused an early onset of cell division and rhizoid elongation. The stimulation of growth was most pronounced when gemmae were deprived of Ca²⁺ during the first 24 hr of culture. The proportion of cell divisions which differentiated into antheridia in response to GA was greatly reduced when the Ca²⁺ status of gemmae was lowered with verapamil and Ca²⁺-EGTA buffers.     

Photoregulation of asymmetric cell division followed by rhizoid development in the fern Ceratopteris prothalli

Strap-shaped prothalli of CERATOPTERIS: richardii grown in the dark have an apical meristem, a subapical elongation zone and a basal growth cessation zone [Murata et al. (1997) Plant Cell Physiol. 38: 201]. When the dark-grown prothalli were irradiated with continuous white light, marginal cells of the elongation zone divided asymmetrically, and the resulting smaller cells developed into rhizoids. The asymmetric division was also induced by brief irradiation of red light. The effect of red light was cancelled by subsequent irradiation of far-red light, indicating that the asymmetric division was regulated by phytochrome. Since the response to red light was not observed at 10(1) J m(-2) and saturated at 10(2) J m(-2) and the response is photoreversible by far-red light, the photoresponse was classified as a low-fluence response of phytochrome. Although the asymmetric division was induced by brief irradiation of red light, continuous irradiation of white, blue or red light was necessary to induce rhizoid growth. These results indicate that asymmetric division and subsequent cell growth are independently regulated by light in CERATOPTERIS: prothalli.