Transition from absolute to quantitative short-day control in Nicotiana tabacum cv. Maryland Mammoth

The response in vitro of thin cell layers, excised from different stem regions of Nicotiana tabacum cv. Maryland Mammoth plants at various developmental stages, was studied under different photoperiodic treatments. The aim was to determine at which stage of plant development, and in which region of the stem, the absolute short-day requirement, indispensable for the induction of the flowering process in this genotype, becomes quantitative and whether it remains short-day. The explants were cultured on a medium suitable for flower neoformation, and were exposed for 30 days to the following treatments: continuous darkness, 8 h light/16 h dark per day, 16 h light/8 h dark per day, and continuous light. The first flowers on explants were observed from plants that were still in the vegetative state, but whose apex showed an accelerated production of axillary vegetative buds, as observed histologically. These explants were excised from the first 10 internodes below the first node with a leaf ≥ 5 cm in length (apical site), and produced flowers only under short-day treatment. When the apical dome initiated the organization of the terminal flower, the apical site explants developed flowers under both short-day and long-day treatments. At the same stage, explants from the 15th to the 20th internode below the first leaf ≥ 5 cm in length also formed flowers, but only under short-day. When the plant showed a complete inflorescence, flowers were also present on explants from the most basal stem internodes and from the inflorescence branches. At this stage, flower neoformation occurred under all treatments; however, under short-day the number of explants showing flowers not associated with vegetative buds on the same sample greatly exceeded that observed under other treatments, as did the mean number of flowers per explant (except the basal regions). In conclusion, in the post-inductive phases of the flowering process, the photoperiodic requirement of this genotype is always short-day. The superficial tissues of the stem require either absolute or quantitative short-day treatment, depending on their position on the stem and the stage of evolution of the flowering process in the terminal apex.     

STUDIES ON THE FLORAL HISTOGENESIS AND PHYSIOLOGY OF PERILLA. III. EFFECTS OF INDOLEACETIC ACID ON THE FLOWERING OF APICAL BUDS AND EXPLANTS IN CULTURE

Raghavan , V. (Princeton U., Princeton, N. J.) Studies on the floral histogenesis and physiology of Perilla. III. Effects of indoleacetic acid on the flowering of apical buds and explants in culture. Amer. Jour. Bot. 48(10): 870–876. Illus. 1961.—The responses of apical buds and explants of a short-day plant, Perilla frutescens (L.) Britt. var. 'Tall Late,' when grown in vitro in White's medium supplemented with indoleacetic acid (IAA) and subjected to short-days (SD) or long-days (LD), are described. Additions of varying concentrations of IAA to the medium inhibited the flowering of the photoinduced apical buds in 2 ways. There was a progressive delay in the appearance of the first signs at the apex and a gradual transition from the more flower-like structures in lower concentrations of IAA (0.1 mg/liter) to sterile cones in higher doses. The sterile cones had florets with well-developed calyx and corolla lobes, but lacked the sporogenous tissues. When subjected to LD, visible signs were observed only in buds grown in 0.1 and 1.0 mg/liter IAA, the pronounced effect of the auxin being in the step-wise inhibition in the formation of the non-sporogenous tissues of the differentiating florets. Flowering of the explants with the 1st pair of unfolded leaves was also inhibited by IAA in either SD or LD, but the 1st signs appeared relatively faster than in apical buds. When photoinduced, explants with the 1st and 2nd pairs of unfolded leaves flowered in all concentrations of IAA tried (up to 100 mg/liter) while those kept in LD remained entirely vegetative.     

THE CULTURE OF APICAL BUDS OF XANTHIUM AND THEIR USE AS A BIOASSAY FOR FLOWERING ACTIVITY OF ECDYSTERONE

Conditions were developed for the sterile culture of shoot tips of Xanthium pensylvanicum Wallr. for use as a bioassay for flower-controlling chemicals. By using a modified Murashige-Skoog medium (minus the auxin but including kinetin) and light intensity much higher than usual for plant tissue cultures, fast growth and development of the shoot tips was achieved. Under short-day conditions (8 hr day: 16 hr night), the cultures from vegetative shoots flowered and fruited; under noninductive conditions (using a 2 hr light-break in the middle of the dark period), the shoot tips continued vegetative development. Both intact plants and cultured tips could be photoinduced in the first days after germination. Ecdysterone, a potent insect moulting hormone, was tested in the bioassay system. It was without either qualitative or quantitative effect on flowering or vegetative development on either cultured shoot tips or intact plants irrespective of whether they were under inductive or noninductive photoperiodic conditions.     

STUDIES ON THE FLORAL HISTOGENESIS AND PHYSIOLOGY OF PERILLA. II. FLORAL INDUCTION IN CULTURED APICAL BUDS OF P. FRUTESCENS

Raghavan , V., and W. P. Jacobs . (Princeton U., Princeton, N. J.) Studies on the floral histogenesis and physiology of Perilla. II. Floral induction in cultured apical buds of P. frutescens. Amer. Jour. Bot. 48(9): 751–760. Illus. 1961.—The morphological and histological changes induced in apical buds and explants of P. frutescens (L.) Britt. var. ‘Tall Late’ in short days and long days when cultured in White's medium have been followed. When photoinduced in culture, apical buds showed visible signs of changes in 30.9 days, and produced normal flowers in 81.6 days. Apical buds in LD showed similar transformations at the apices, but with continued LD treatment, they elongated to form sterile structures, superficially resembling Selaginella cones. The normal flowers formed in culture were similar to those formed on the intact plant, while the individual florets of the LD-cone differentiated only the non-sporogenous tissues in them. A less pronounced sequence of changes resulted when apical buds stripped of their older pairs of apical leaves were LD- or SD-treated. When explants with the 1st pair of unfolded leaves or with the 1st and 2nd pairs of unfolded leaves were photoinduced in vitro, the responses were relatively fast. However, explants with the 1st and 2nd pairs of unfolded leaves in LD remained entirely vegetative. When unfolded leaves were implanted in the same medium separated from the buds and both were photoinduced or given LD, the buds formed the typical 1st signs, but did not differentiate into normal flowers. This inhibition of flowering resulted in the formation of sterile cones, consisting of florets with non-sporogenous tissues only. The results have suggested the possibility of the sterile cone-like structures being an intermediate stage in the flowering of Perilla. The role of a possible inhibitor produced by mature leaves of SD plants in LD is discussed.     

Interaction du photopériodisme et des effets de la zéatine, du saccharose et de ľeau dans la floraison du Chenopodium polyspermum

Interaction of photoperiodism and zeatin, sucrose and water effects on the flowering of Chenopodium polyspermum Root removal in Chenopodium polyspermum, a quatitative short-day plant, enhances flowering under non-inductive conditions. Presence of roots may be mimicked by zeatin applications on buds. Induction of flowering by short days may be counteracted by applications of zeatin, and appearance of flowers depends on the balance between number of inductive short days and zeatin quantity applied. Sucrose added in the culture medium or applied on buds acts as zeatin. Applications of water on buds may also delay flowering. These results show the plurifactorial regulation of the floral development of this plant. The relations between the non-specificity of the induction and the specificity of the morphogenetic response are discussed.     

CnFL,a FLORICAULA/LEAFY homolog in Chrysanthemum nankingense is dramatically upregulated in induced shoot apical meristems

A FLORICOULA/LEAFY (FLO/LFY) homolog CnFL gene was isolated from the flower bud of a short-day Chrysanthemum nankingense plant during the flowering induction period. The sequence of CnFL contained a 1236 bp open reading frame that encoded a putative protein of 412 amino acids, which shared 68.67% homology with FLO and 60.23% homology with LFY. The spatial expression patterns of CnFL were analyzed using quantitative real-time PCR in different tissues and the apical meristem during short-day flowering induction. The results indicated that CnFL was highly expressed in the flower buds while its expression was also detected in the stems, young leaves, and vegetative apical meristem. During the period of flowering induction, CnFL expression increased remarkably and reached its highest levels after 15 days of induction. The expression of CnFL in the apical shoot after short-day flowering induction indicates that CnFL regulation is controlled primarily by photoperiodicity.     

Auslösung der Blütenbildung bei der Langtagpflanze Hyoscyamus niger im Kurztag durch 2-Thiouracil

Summary Aqueous solutions of 2-thiouracil (TU) were applied selectively either to the growing point or to the leaves of the long-day plant Hyoscyamus niger in order to determine whether this antimetabolite has an effect on the synthesis of the floral stimulus in the leaves. Applications to the growing point were made by means of a small glass tube covering the shoot apex; application to the leaves was performed by vacuum infiltration. In all experiments all leaves except the three youngest fully expanded leaves and the 8–10 youngest primordia were removed before application. Plants were recorded as having initiated flowers when flower primordia were visible under a dissection microscope 5 weeks after the experiment.TU was inhibitory to photoperiodic induction by long-days of 16 hours when applied to the growing point during the second 8 hours of the daily photoperiod. A concentration of 5·10^-3 M of TU fully suppressed flowering without significant inhibition of leaf primordia increment; however, leaves developing from treated primordia had reduced leaf blades. These results are in agreement with findings already published by other investigators.However, when the leaves were infiltrated by TU, the antimetabolite did not inhibit photoperiodic induction but on the contrary initiated flowering even under short-day conditions. This effect was investigated in more detail by repeated daily infiltrations of TU-solutions in concentrations of 10^-5–10^-2 M during the second part of an 8 hour photoperiod up to 5 following days. Even after one single infiltration of a 10^-4 M solution 18% of the treated plants were flowering; the percentage of flowering plants increased with increasing concentrations of TU and number of days of application up to approximately 80%. In no case was a flower initiation of 100% obtained. Leaves developing from primordia after infiltration of the leaves with TU have reduced and deformed leaf blades, indicating that TU is transported to the shoot apex to some extent.Some possible explanations of this inductive effect of TU were tested experimentally. Oxygen uptake of the leaves was not decreased and the respiratory quotient was not affected by TU. Photoperiodic induction is not stimulated by low concentrations of TU when applied to the growing point. Infiltration of the leaves by solutions of 2,4-dinitrophenol (10^-4 M) and sodium azide (10^-3 M) had no inductive effect under short-day conditions; a single complete defoliation (except for the 8–10 youngest primordia) is also not inductive. Under short-day conditions additional leaves remaining on the plant that were not infiltrated by TU decreased the percentage of flowering plants but did not fully suppress flower initiation.From these results it is concluded that TU does not act by inhibition of particular metabolic processes concerned in flower initiation or by inhibition of the synthesis of an inhibitor. We suggest that application of TU may lead to synthesis of a floral stimulus in the leaves under short-day conditions also.     

PRECONDITIONING OF GERMINATION IN LETTUCE AT TIME OF FRUIT RIPENING

Koller , D. (The Hebrew U., Jerusalem. ² ) Preconditioning of germination in lettuce at time of fruit ripening. Amer. Jour. Bot. 49(8): 841–844. 1962.—The effects of controlled environments during maturation on subsequent germination response of the seed were investigated with the light-sensitive lettuce ‘Grand Rapids.‘ The plants matured under a variety of temperature/photoperiod combinations, after completing vegetative growth and flower initiation under identical conditions. Good seed set was obtained only at night temperatures between 17 and 23 C, under short-day (8-hr) conditions. Seed germination was tested at 20, 23 and 26 C, in continuous dark and after a light-break, respectively. The conditions under which the seed had ripened brought about quantitative changes in the germination response. The stimulating effects of a light-break on germination at high temperatures did not change, but maturation under high temperatures or in continuous light increased the high-temperature tolerance of seed germination both in continuous dark and after a short light-break.     

Flowering response of day-neutral and short-day cultivars of Nicotiana tabacum L. interactions among roots,genotype, leaf ontogenic position and growth conditions

The interaction between roots and leaves as a function of the capacity of differently positioned leaves to induce flowering of four cultivars of Nicotiana tabacum L. was assessed under long-and short-day growth conditions with three types of manipulations: 1) repeated rooting of the shoot tip, 2) removal of apical leaves, and 3) removal of basal leaves. Repeated rooting of the shoot tip increased the number of nodes produced by all cultivars; however, a substantial extension of vegetative growth was only caused by rerooting in conditions where apical leaves exhibited little or no inductive capacity. The simplest and most consistent interpretation of these data is that floral initiation in tobacco results from an interaction of inputs from the leaves and the roots and that the root influence can be overridden by a strong leaf signal.     

Some physiological responses to d,l abscisin (dormin)

Summary The responses to synthetic d,l abscisin have been studied in a variety of tests. When fed in aqueous solution continuously to leaves of seedlings growing under long day conditions, d,l abscisin caused the cessation of extension growth and the formation of typical resting-buds in Betula pubescens, Acer pseudoplatanus and Ribes nigrum. Abscisin also inhibited the growth of non-dormant buds of potato when applied to the whole tubers, but was much less effective when applied to isolated tuber plugs.Abscisin accelerates the senescence of leaf discs of a wide variety of species, but is less effective when sprayed on to attached leaves, except at relatively high concentrations (50–100 ppm).Abscisin inhibited flower induction in the long day species, Lolium temulentum and Spinacia oleracea, when applied to the leaves during a period of exposure to 15-long-day cycles. Abscisin promoted flowering in the short-day plants Pharbitis nil, Ribes nigrum and strawberry when applied under long day conditions, but it did not induce flowering in certain other typical short day plants. Tuberization in Solanum andigena and two cultivars of S. tuberosum was promoted by abscisin when applied to the leaves of plants growing under long-day conditions.     

Initiation of Flowering and Changes in Endogenous Inhibitors and Promoters in Olive Buds as a Result of Chilling

Olive trees require a period of chilling temperatures, either diurnally fluctuating, or at a constant—but definite—level before inflorescences develop. In this study, bud and leaf samples were taken at weekly intervals during this critical period from trees receiving temperatures favorable for flowering and from trees under temperature conditions known to prevent flowering. Extracts were obtained from these samples, separated by paper chromatography and the different growth-active materials were bioassayed by the mung bean rooting test for the presence of promoters and inhibitors. Extracts from buds on trees under conditions unfavorable for flowering generally consisted only of promoters. Extracts from buds on trees placed under conditions favorable for flowering showed a definite and consistent pattern for the presence of rooting inhibitors and promoters. Within one or two weeks after being placed under such conditions a strong inhibitor band appeared from R_f 0.50 to 0.70. This persisted for 6 to 7 weeks, gradually decreasing in intensity, followed by promoters at these bands. During this period all other bands, at different R_f values, showed strong promoters. Extracts from leaves on shoots under temperature regimes favorable for flowering showed a pattern like the buds in the appearance and disappearance of inhibitors and at the same R_f values but with about one week lag in time. Bud extracts from defoliated shoots on trees under temperature conditions known to result in inflorescence production failed to show the characteristic inhibitor pattern associated with flowering. Such defoliated shoots do not form inflorescences.     

Effects of Photoperiod on the Apparent Viscosity of Leaf Cytoplasm in Kalanchoe blossfeldiana: 2. Some Long- and Short-term Effects of Daylength and Spectral Composition of Light

The effects of a range of daylength treatments upon the apparentviscosity of the mesophyll cytoplasm were tested in Kalanchoeand some other daylength-sensitive species by means of a centrifugationtechnique. In Kalanchoe, apparent viscosity increases with increasingshort-day induction, the rise being rapid initially but fallingoff subsequently in the same way as the flowering response.Since the response to light-break treatment is equivalent tolong-day conditions, the effect is truly photoperiodic. Theshort-day increase appears to be only partially reversible uponreturn to long-days. Single leaves may be treated and the effect is not translocatedto the opposite member of a leaf pair. The immediate response to change from light to dark and viceversa is oscillatory; e.g. in the dark an initial fall is succeededby a steep rise and then a more gradual fall in apparent viscosity. Light-breaks with red light are equivalent to white light, andthose with far-red light to darkness. No reversal of red effectsby far-red light has yet been demonstrated. In other species tested, apparent viscosity was significantlyhigher under short-day in Chrysanthemum and Michaelmas Daisy,and under continuous light in Epilobium, i.e. in the daylengthswhich induce flowering. The results are discussed in relationto the present theories of photoperiodism.     

CHARACTERIZATION OF STARCH GRAINS IN THE NONARTICULATED LATICIFER OF EUPHORBIA PULCHERRIMA (POINSETTIA)

Starch grain morphology in laticifer amyloplasts of Euphorbia pulcherrima Willd. (poinsettia) was examined for evidence of starch metabolism in vegetative and flowering plants. Laticifer starch grains in vegetative plants were rod shaped with lengths ranging from 3 to 60 μm. Average grain size was significantly larger in stems than leaves, and in older than younger tissues. Starch grain length frequency was unimodal and approximated a normal probability distribution in stems, but was skewed positively toward smaller grains in leaves. Frequency distributions were shifted toward larger grains in older tissues. Under short-day photoperiod (flowering) conditions, round starch grains formed in latex of stems, and the average length of rod-shaped grains decreased in latex of stems and leaves. Round grains did not occur in laticifers of leaves or bracts. Round starch grains often occurred in aggregates of two or more subunits. Changes in size and shape of latex starch grains indicate that amyloplasts in fully differentiated laticifers metabolize starch. Identification of metabolically active amyloplasts in differentiated laticifers suggests that the function of these organelles may involve starch mobilization under certain physiological conditions.     

Expression of <Emphasis Type="Italic">FLOWERING LOCUS T</Emphasis> from <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> induces precocious flowering in soybean irrespective of maturity group and stem growth habit

The flowering integrator gene FLOWERING LOCUS T (FT) in Arabidopsis thaliana is conserved between diverse plant species and is thought to be the flowering signal ‘‘florigen’’, a universal long-distance mobile signal. In soybean, two FT homologs having a function to induce flowering in Arabidopsis have been identified. In this study, we showed that the expression of FT from Arabidopsis by the Apple latent spherical virus (ALSV) vector promoted precocious flowering and terminated vegetative growth in a wide range of genotypes of soybean, without using a short-day treatment. Four determinate and two indeterminate cultivars, infected with ALSV expressing FT (FT-ALSV), set flower buds on shoot apices and terminated vegetative growth at the fourth- to seventh-node stages under long-day conditions. In contrast, non-infected, healthy plants did not set flower buds on shoot apices at the same stage under the same conditions. After flowering, soybean cultivars infected with FT-ALSV, belonging to different maturity groups and stem growth habits, matured and produced seeds. The results suggest that the basic flowering pathway controlled by FT in A. thaliana might also be conserved in soybean. A system for precocious flowering and shortening of generation time using FT-ALSV would be a useful and novel technology for efficient soybean breeding.     

Phénolamides et induction florale de Cichorium intybus dans différentes conditions de culture en serre ou in vitro

Phenolamides and floral induction of Cichorium intybus in different conditions of culture in glass-room or in vitro. Three complexes between phenols and amines (phenolamides) have been found in Cichorium intybus L., a plant with an absolute requirement of vernalisation followed by long days for flowering. Upon hydrolysis, these complexes (A, B and C) liberate aromatic amines whose exact identification is in progress, but which are closely related to dopamine, tyramine and serotonin, respectively. In a first series of experiments, phenolamides were studied in the buds of plants grown in the greenhouse under varying conditions. Only buds from plants which flower in long days contained large amounts of these compounds. Much smaller amounts were found in buds at the end of vernalisation (at 2–4°C) before long-day treatment as well as in buds kept in the vegetative state after vernalisation by being grown in short days (8 h light) or in total darkness. In a second series of experiments, phenolamides were studied in bud-forming calli induced in vitro on explants of tuberised root. After sixteen days of culture in continuous light, large quantities of phenolamide were found in the buds and calli of the upper part of the explant, while the lower part which never produces buds contained much less. Buds formed under continuous light produce inflorescences in approximately one month. Various other culture conditions make it possible to maintain the explants in the vegetative state. This can be obtained by short-day conditions, or otherwise under continuous illumination by decreasing the sugar or increasing the NAA levels in the medium. After 13 days of culture, the phenolamide levels were much lower under all of these conditions, than under conditions favourable to floral induction. Compound C is absent or present in trace amounts in vegetative buds. The significance of the differences observed between floral and vegetative buds is supported by the sensitivity of the analytical techniques used. The accumulation of phenolamides in tissues of Cichorium intybus appears to be closely linked to floral induction. Under continuous light it begins very early in young buds and even in the calli that bear these buds.     

Effects of 6-benzylamino-purine and 1-naphthaleneacetic acid on the epiphyllous bud formation in Bryophyllum

Summary The effects of the kinin 6-benzylamino-purine and of 1-naphthaleneacetic acid (NAA) on the epiphyllous bud formation in Bryophyllum were studied under controlled environment.In B. daigremontianum which requires long days for epiphyllous budding, buds were formed under continuous short days after application of the kinin. Similarly, such a treatment caused budding in attached non-aging leaves of B. calycinum which normally form buds only after detachment from the plant. This stimulatory effect of the kinin was strictly bound to the treated leaves (or leaf parts), which also showed an increased growth compared with the opposite non-treated leaves. Root formation in the developing buds was inhibited by the kinin.In both species NAA inhibited the epiphyllous budding under inductive conditions. A similar inhibitory effect was exerted by terminal and axillary buds.The results are discussed in the light of other investigations in this and related fields. It is concluded that epiphyllous bud formation is under the control of a correlative inhibition similar to apical dominance. It is further concluded that even though day-length controls both flowering and epiphyllous budding in B. daigremontianum the two processes must be affected through different biochemical systems.     

The maryland mammoth allele and rooting both perturb the fate of florally determined apices in Nicotiana tabacum.

The stability of the florally determined state in terminal and axillary buds of two tobacco cultivars was studied. We used Hicks and Hicks Maryland Mammoth, near-isogenic cultivars of Nicotiana tabacum differing at the recessive maryland mammoth locus which confers short-day behavior. The experimental design consisted of growing plants in short-day conditions and subjecting them to three bioassays in long-day conditions: in vitro culture of apices consisting of meristems and three to four leaf primordia; rooting of buds consisting of meristems and 8 to 12 leaves, leaf primordia, and internodes; and release from apical dominance of axillary buds in situ. Cultured terminal and axillary apices expressed floral determination, indicating that meristems can be florally determined. Two lines of evidence indicate that rooting destabilizes an already acquired florally determined state: cultured apices from both axillary and terminal buds produced fewer nodes after excision than homologous buds which were rooted; and a lower percentage of rooted axillary buds from Hicks Maryland Mammoth plants expressed floral determination than did homologous axillary buds grown out in situ in noninductive conditions. Rooted buds from the two genotypes expressed floral determination at different frequencies, but produced abnormal inflorescences at similar frequencies, indicating that roots and the maryland mammoth allele influence common as well as unique processes associated with floral determination.     

EXPERIMENTAL CONTROL OF FLOWERING IN LEMNA. II. SOME EFFECTS OF MEDIUM COMPOSITION,CHELATING AGENTS AND HIGH TEMPERATURES ON FLOWERING IN L. PERPUSILLA 6746

Hillman , William S. (Yale U., New Haven, Conn.) Experimental control of flowering in Lemna. II. Some effects of medium composition, chelating agents and high temperatures on flowering in L. perpusilla 6746. Amer. Jour. Bot. 46(7): 489–495. Illus. 1959.—-L. perpusilla 6746 flowers as a short-day plant on Hutner's medium (containing ethylenediaminetetraacetic acid [EDTA]) at constant temperatures from 25 to 30°C., but eventually flowers also in old cultures under 16 or 24 hr. of light. This old-culture flowering is more pronounced in dilute medium. Flowering is rapid under both long and short days at constant temperatures from 25 to 28°C. in media not containing EDTA; the addition of 10^-5 M EDTA or of similar or higher concentrations of numerous other chelating agents suppresses flowering under long days but not under short (8 hr. light). This effect does not depend on promotion or inhibition of vegetative growth. At 29 to 30°C., a short-day requirement is manifested even in media permitting flowering under long days at the lower temperatures. Temperatures above 31°C. completely inhibit flowering under all conditions. Brief periods of high temperature given to plants under short-day conditions inhibit flowering when given during the dark period but not during the light period. The implications of these observations for the further study of flowering are discussed.