PHOTOPERIOD INDUCED CHANGE IN PHYLLOTAXIS IN XANTHIUM

Photoperiodic floral induction in Xanthium, achieved by subjecting the plants to two long nights, is accompanied by a transient change of the phyllotaxis from the (2, 3) contact parastichy pattern of vegetative plants, to a (3, 5) pattern during the transition. To specify the phyllotaxis, two parameters were estimated from transverse sections of apical buds of control and treated plants: the divergence angle, α, and the plastochron ratio, a. The plastochron ratio decreased progressively during transition from the vegetative to the reproductive state of growth, from a = 1.48 initially to a = 1.15 six days after the beginning of induction. The divergence angle was not altered during the transition. This change in phyllotaxis is interpreted as a change in the relative positioning of leaf primordia on the transitional apex. This transient change appears to be identical with the previously described long-term change of the phyllotaxis of Xanthium brought about by treatment of plants with gibberellic acid.     

Development of the shoot apex ofChenopodium rubrum L. after photoperiodic induction in the cotyledon stage

Development of the shoot apex up to floral differentiation was investigated in the short-day plantChenopodium rubrum. The changes occurring in the apex from energence until full opening of the cotyledons (Figs 1–4), development during photoperiodic induction (Figs. 5–8), as well as the resulting floral differentiation (Figs. 9–10) are described. It was aimed at excluding the influence of plastochron changes on the interpretation of ontogeny of the shoot apex. For that reason two planes of longitudinal sections and two plastochron stages were compared. In young plants zonation does not become fully evident prior to floral differentiation. The anatomical structure of the shoot apex does not change substantially during the first two inductive cycles which proved to be obligatory under the given experimental conditions. The changes occurring during two further inductive cycles correspond to the total activation of the meristems as manifested by the growth and branching of the apex preceeding floral differentiation proper.     

CHANGE IN EPILOBIUM PHYLLOTAXY DURING REPRODUCTIVE TRANSITION

The ontogeny of Epilobium hirsutum grown under natural summer photoperiod in a glasshouse was divided into vegetative, early transitional, transitional, and floral stages. Bijugate phyllotaxy, common to both the vegetative and early transitional stages, is transformed into spiral phyllotaxy during the transitional stage by an initial change in the divergence angle of a single primordium inserted at a unique level on the shoot. Leaf primordia subsequently are inserted in a spiral arrangement in the indeterminate floral shoot apex. The early transitional shoot apical meristem is about 1.5 times the volume of the vegetative meristem but expands at about two-thirds the relative plastochron rate of volume increment of the vegetative meristem. There are progressive decreases in the plastochron and relative plastochron rates of radial and vertical shoot growth through ontogeny. Relative chronological rates of shoot growth, however, are not altered during ontogeny. Spiral transformation results from changes in the relative points of insertion of leaf primordia on the shoot meristem. These changes are accompanied by an increased rate of primordia initiation on a more circular shoot meristem. The change in phyllotaxy during ontogeny is similar to that which was artificially induced by chemical modification of auxin concentration gradients in the shoot apex, with the additional feature that there is an initial increase in the volume of the shoot meristem prior to the natural spiral transformation. Size of the shoot apical meristem, however, appears to have little influence on Epilobium phyllotaxy; but the geometric shape of the meristem is well correlated with bijugate to spiral transformations. This suggests that geometric parameters of the shoot meristem should be considered in theoretical models of phyllotaxy.     

FLORAL INDUCTION DOES NOT ALTER THE GROWTH PARAMETERS OF FUCHSIA

Floral induction by night interruption of Fuchsia hybrida cv. Lord Byron, a quantitative long-day plant with decussate phyllotaxis and an indeterminate flowering habit, altered neither the rate of leaf initiation nor the rate of leaf expansion; nor did flower initiation and development change the vegetative growth of the plants. This was diagnosed using plastochron duration and plastochron ratio measurements before, during, and after a 10-day induction period. A comparison between indeterminate and determinate flowering is made using these two parameters.     

RNA synthesis in the cells of the apical meristem of Sinapis alba during transition from the vegetative to the reproductive condition

Summary Vegetative plants of Sinapis alba, a long-day species, were induced to flower by exposure to a single 20-hr long day. RNA synthesis in the apical meristem of vegetative (control) and induced plants was investigated by using ³H-uridine and autoradiography of sections.Light-microscope autoradiographs showed a sharp increase in total RNA synthesis per cell in induced meristems. This increase occurred as early as 18 hr after the start of the long day, i.e. at the presumed time of the arrival of the floral stimulus at the meristem. At the same time, electron-microscope autoradiographs showed that there were changes in the pattern of RNA synthesis in the meristematic cells. The ratio of the number of grains in the nucleus to that in the cytoplasm slightly decreased and the ratio of the number of grains in the chromatin to that in the nucleolus greatly increased.Experiments with 2-thiouracil (2-TU), a pyrimidine analogue which was shown to inhibit RNA synthesis in Sinapis, indicated that this compound was most inhibitory to floral induction between the 12th and the 20th hour after the start of the long day, i.e. at the same time as important quantitative and qualitative changes in RNA synthesis were detected in induced meristems by autoradiographic methods. It was thus assumed that 2-TU inhibits floral induction via its effect on these (or on one of these) changes.     

蓝堇草属(毛茛科)花形态发生的扫描电子显微镜观察

花的发生和发育过程研究可以发现早期进化的轨迹,为系统发育的研究提供重要线索。蓝堇草属(Leptopyrum)为毛茛科唐松草亚科一单种属,仅包含蓝堇草一种,其花的发生和发育过程仍为空白。为了深入理解唐松草亚科乃至毛茛科花发育多样性和演化规律,该文运用扫描电子显微镜(SEM)观察了蓝堇草各轮花器官的形态发生和发育过程。结果表明:该属植物所有的萼片、花瓣、雄蕊和雌蕊均为螺旋状发生,花器官排列式样也为螺旋状; 5枚萼片原基宽阔,5枚花瓣原基圆球形、位于萼片原基的间隔,且在后期表现为延迟发育现象,雄蕊原基较小、为圆球形; 花瓣原基和雄蕊原基连续发生,无明显的时空间隔,但与萼片原基有时空间隔; 心皮原基为马蹄形对折,柱头组织由单细胞乳突组成; 胚珠倒生、具单珠被。该属花器官螺旋状排列、胚珠具单珠被在唐松草亚科中是独有的性状,花发育形态学证据支持了该属的特殊性。     

COMPARATIVE FLOWER DEVELOPMENT IN THE CLEISTOGAMOUS SPECIES VIOLA ODORATA. I. A GROWTH RATE STUDY

In Viola odorata, chasmogamous (CH) or open flowers and small, short-petioled leaves are produced under 11 hr or less of daylight, cleistogamous (CL) or closed flowers and large, long-petioled leaves under 14 hr or more of daylight, and intermediate floral and leaf forms under transitional photoperiods. CL flowers are approximately four times smaller than CH flowers and differ morphologically in repressed growth of the anterior petal spur and staminal nectaries, and recurving of the style which remains enclosed within the cone formed by anther appendages. Both CH and CL shoot systems conform to a (2 + 3) phyllotaxis with minor differences in leaf divergence angles and phyllotactic indices. The larger CL leaf grows significantly faster than the CH leaf, and an increased rate of leaf initiation occurs in the CL apex represented by a plastochron of 3.4 days compared to 4.3 days in the CH apex. The plastochron index was used to indirectly age young floral primordia nondestructively until prophase of meiosis I within the anthers. This event occurs 8 days earlier in the CL than the CH flower. Time from meiosis until flower maturity, determined by direct observation, is about 14 days for the CL flower, versus 21 days for the CH flower.     

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.     

PHOTOPERIODIC ADAPTATION IN DESERT POPULATIONS OF XANTHIUM STRUMARIUM

Reproductive adaptation to photoperiod is diverse among desert populations of Xanthium. Chihuahuan Desert populations require dark periods of 9.5–10.5 hr for reproduction, and Sonoran Desert populations require 9–10.5 hr. Many Chihuahuan populations from western Texas two weeks from sowing need only 10 cycles of 11-hr nights to produce 100% flowering, but Sonoran populations from western Mexico four weeks from sowing need 18 cycles or more. Some Sonoran plants produce buds only at a cooler temperature program, 24–15 C, but Chihuahuan plants produce them more readily under the warmer program, 30–24 C. Chihuahuan plants that were germinated under 11-hr nights and four different temperature programs were induced to flower in each condition. Differences in photoperiod and ripeness-to-flower (maturity) responses were also demonstrated under natural day lengths in central Texas. Although desert populations occurring at approximately the same latitude in either the Chihuahuan or Sonoran Desert are exposed to similar day lengths, each population may be adapted to different photoperiod cues that maximize its utilization of the local growing conditions.     

LEAF INITIATION RATES AND VOLUME GROWTH RATES IN THE SHOOT APEX OF CHRYSANTHEMUM

The leaf initiation rate and apical volume growth rate of lateral shoots of Chrysanthemum morifolium ‘Improved Albatross III’ were determined for plants growing under controlled environment conditions. After removal of the terminal bud, the top two lateral buds produced leaves at a rate of 1.4 to 1.6 leaves/day for the first 9 or 10 days. At about the 10th day there appeared to be an abrupt shift to a lower initiation rate of 0.7 to 0.8 leaves/day. Defoliation by periodic removal of leaves larger than 1 cm caused a statistically significant increase in initiation rate, but not to as high a rate as that of the first 10 days of bud growth. Volume growth rates of the apical region were determined from transverse sections of five apices, according to the method of Richards (1951). The apical region was found to have a radial expansion rate of 0.1623/plastochron and a vertical expansion rate of 0.0494/plastochron. The volume growth rate was calculated to be 0.3740/plastochron and the volume doubling time to be 1.85 plastochrons or 56 to 63 hr.     

Effects of culture conditions on development in continuous light of floral buds in Lemna perpusilla 6746

Effects of temperature on the subsequent development in continuouslight of floral buds formed after a single short-day cycle inLemna perpusilla 6746, a short-day plant, were studied usingfronds selected in relation to the order of emergence. The floralbuds developed to stage 1 regardless of the temperature duringthe following CL. The rate of development, however, was slowerat lower temperature. The minimum number of days in CL neededfor the abortion of once formed floral buds increased with adecrease in temperature, accompanied by an increase in the frondplastochron. Furthermore, when the frond plastochron was alteredby manipulation of the environmental conditions, i.e., lightintensity or medium strength, the minimum number of days inCL required for the abortion of the floral buds also changed.These results suggest that the development pattern of floralbuds in this plant is highly correlated with the frond plastochron. (Received September 20, 1977; )     

EFFECTS OF LEAF EXCISION ON FLOWERING OF XANTHIUM APICAL BUDS IN CULTURE UNDER INDUCTIVE AND NONINDUCTIVE PHOTOPERIODS

Apical buds of Xanthium were grown in aseptic culture under short-day cycles known to induce flowering in the intact plants or under “light-break” conditions known to prevent flowering. The total light provided in each 24-hr cycle was the same under the two photoperiods. Various numbers of leaves were excised from the apical buds. Excision of leaves did not change the response to photoperiod: even with all leaves excised the apical buds cultured under short-day conditions reached the same average floral stage as the control buds, and those under light-break conditions all remained vegetative. Fresh weight was not significantly changed by the excisions, either. However, excision of the young leaves resulted in an increase in the number of new leaves developed by the apical bud during the two-week culture period.     

Effect of Gibberellic Acid and Monophenols on Flowering of lmpatiens balsamina in Relation to the Number of Inductive and Non-inductive Photoperiodic Cycles

A single treatment of plants with GA₃ (gibberellic acid) is not adequate to cause induction under LD (long day: 24-h photo-period) condition, but its effect is added to the sub-threshold induction caused by one SD (short day: 8-h photoperiod) cycle. Floral bud initiation is hastened, and the number of floral buds and flowers per flowering plant increases in plants receiving a single treatment with the combination GA₃+ SA (salicylic acid) accompanying a single SD cycle. However, the increase on 10 replicate basis is more marked in plants receiving three treatments with the combination GA₃+β-N (β-naphthol) and five treatments with the combination GA₃+ SA accompanying six and 10 SD cycles, respectively. The number of floral buds and flowers decreases with an increase hi the number of SD cycles, but it is higher in plants treated with GA₃, SA or GA₃+β-N than in the water-treated controls. — Under long days, treatment of plants with the combinations GA₃+ SA or GA₃+β-N accelerates the initiation as well as increases the number of floral buds. While a minimum of five treatments with GA₃ or of 25 with SA or β-N alone is needed for floral bud initiation under a 24-h photoperiod, three treatments are adequate to induce floral buds with the combination GA₃+ SA or GA₃+β-N under continuous illumination. Ten or more treatments with these combinations under a 24-h photoperiod produce more flowers than the same treatments under an 8-h photoperiod.     

In vitro pollen embryogenesis in Nicotiana tabacum L. and its relation to pollen sterility,sex balance,and floral induction of the pollen donor plants

Pollen sterility, sex balance, and floral induction of the pollen donor plants were tested for a possible relation to embryogenesis from in vitro cultured tobacco pollen (Nicotiana tabacum L. var. Badischer Burley). The pollen grains destined to become embryos in culture (P-grains) were sterile for the donor plants as judged by their staining reaction with acetocarmine and fluorescin-diacetate, and by an in vitro germination test. They were produced in high frequency in flowers which exhibited a shift in sex balance towards femaleness. Sex balance could be measured by the relative length of pistil to stamens. High P-grain frequency, high pollen sterility, and a shift in sex balance towards femaleness could be induced by raising the donor plants under short days and/or low temperature (18–15° C) as compared to long days at 24° C. Short days and/or low temperature also reinforced floral induction, revealing that the tobacco variety Badischer Burley is a quantitative short day and low temperature plant and that the variety follows the rule that conditions of strong floral induction shift sex balance towards femaleness. At 12° C and short days, contabescent flowers were formed with completely sterile anthers containing a few and mostly collapsed P-grains. Based on these results, it is now possible to predict conditions by which haploids via pollen embryogenesis might be produced in high frequency from low-yielding and recalcitrant species.Abbreviations DPF dead pollen grain frequency - LD24 long days at 24° C - PD pollen dimorphism - P:S ratio of pistil to stamen length - SD15 short days at 15° C     

STRUCTURAL CHANGES IN POPULUS DELTOIDES TERMINAL BUDS AND IN THE VASCULAR TRANSITION ZONE OF THE STEMS DURING DORMANCY INDUCTION

Morphological and anatomical changes in shoots of vigorously growing cottonwood plants (Populus deltoides Bartr.) were studied during dormancy induction in 8-hr short days (SD) and in control plants grown in 18-hr long days (LD). Pronounced structural changes occurred in terminal buds after 4 wk and full dormancy was achieved in 7 wk of SD. Leaf expansion ceased after 5 wk of SD as foliage leaves matured to the terminal bud base at leaf plastochron index 0 (LPI 0). Within the bud, total leaf length (lamina + petiole) decreased and stipule length increased progressively each week; thus, the ratio total leaf length/stipule length decreased rapidly, especially at the position of incipient bud-scale leaves LPI - 1 and LPI - 2. These bud-scale leaves were fully developed by wk 6 and were derived from enlarged stipules and aborted laminae. The full complement of primordia within the bud at the start of SD eventually matured as foliage leaves and the first bud-scale leaf (LPI - 1) was initiated immediately following transfer to SD. Acropetal advance of the primary-secondary vascular transition zone (TZ) was associated with leaf maturation. However, it did not advance throughout the entire vascular cylinder as in LD, but only in those leaf traces serving mature leaves beneath the terminal bud. In both LD and SD treatments the same linear relationship was maintained between LPI of the TZ and LPI of the most recently matured leaf; both parameters simultaneously increased in LD and decreased in SD. Thus, the relationship between leaf maturation and advance of the TZ was maintained irrespective of environment.     

Floral initiation in Rudbeckia hirta (Asteraceae) under limited inductive photoperiodic treatments

Two experiments were conducted to examine the response of Rudbeckia hirta to limited inductive photoperiodic treatments. The first examined the effects on plants grown to an thesis of the second axillary inflorescence, and the second examined the early histological events within the meristem. Plants of Rudbeckia hirta were grown to maturity under short days (SD). At maturity, half the plants were placed in long days (LD). In the first experiment, the plants remained under LD for 0, 8, 16, 24, or 32 days before being returned to SD with an additional group remaining under LD as a control. In the second experiment, the plants remained under LD for 0, 4, 8, 12, 16, 20, 24, or 28 days before being returned to SD. Meristems were sampled 0, 4, 8, or 12 days after return to SD and histologically examined. Four groups of plants receiving 32, 36, 40, or 44 LD were used as a continuous LD control. When grown to anthesis, plant height and branch number increased as the number of inductive cycles increased. Plants receiving 24 or more LD reached anthesis earlier than plants receiving fewer LD. Histological examination of plants receiving only 4 LD showed they never progressed beyond early floral initiation. After 12 LD, the meristems continued to develop even when returned to SD, indicating that enough of the floral stimulus had reached the meristem to initiate flowering. Once involucral bract primordia initiated, floral development continued whether in LD or SD conditions.     

A MORPHOMETRY STUDY OF THE ULTRASTRUCTURE OF ECHINOCEREUS ENGELMANNII (CACTACEAE). II. THE MATURE,ZONATE SHOOT APICAL MERISTEM

The shoot apical meristems of adult Echinocereus engelmannii plants are zonate and have a tunica, central mother cells, a peripheral zone, and a pith-rib meristem. An ultrastructural, stereological study showed that each zone has its own distinct ultrastructure, but that the differences between the zones are quite small, both on a protoplasmic basis and on a cytoplasmic basis. Furthermore, the ultrastructure present in the adult apices differed only slightly from that which had been found in seedling apices, demonstrating a long-term stability of structure. The standard deviations found in the sample were small, indicating little variability from one plant to the next and suggesting that there are little or no cyclic changes during the plastochron or a 24-hr photoperiod. The ultrastructures found in the shoot apical meristems differed significantly and markedly from mature tissues of the same plants.     

Puzzle box,a tobacco line with flowers that mix floral and inflorescence characteristics

We characterized the development of a tobacco morphological mutant, puzzle box, previously obtained by selection for resistance to an inhibitor of an enzyme in the polyamine biosynthetic pathway. Puzzle box plants are shorter than wild type with smaller leaves and an irregular leaf plastochron. The diameter and shape of the puzzle box shoot apex are similar to wild type. In puzzle box plants, the terminal flower develops but not the cymose inflorescence. This flower has a variable phenotype with more than five sepals, five petals, and five stamens. The organs in the fourth whorl are produced by carpellike primordia and contain tissue biochemically similar to wild type transmitting tissue. These organs form a cylinder within which additional floral organs are produced. Some cultures of puzzle box buds and excised cylinders produce additional floral organs. The inflorescence and floral programs may be expressed together in puzzle box.