Floral initiation in sorghum hastened by gibberellic acid and far-red light

Combinations of far-red light (FR) (4 min) and gibberellic acid (GA₃), given at the beginning of a daily 12-h dark period in a growth room, were used to study floral induction in four maturity genotypes of the milo group of sorghum (Sorghum bicolor (L.) Moench). The 12-h dark period without GA₃ application or FR induced flowering in only the early genotype; FR hastened initiation in the early genotype, while GA₃ hastened floral initiation in the two intermidiate-flowering genotypes. GA₃ and FR together had a strong synergistic effect, hastening floral initiation by 30 to more than 80 d in the early and intermediate genotypes. Red light (R) did not hasten flowering; FR preceded by R gave the same effect as FR alone. GA₃ promoted stem elongation equally whether floral initiation occurred or not; thus, its effect on stem elongation was independent of floral initiation. The capacity of GA₃ to induce flowering in sorghum, a short-day plant, seems to be enhanced by phytochrome being in the P_R form at the beginning of the night when GA₃ was applied.Abbreviations FR far-red light - GA(s) gibberellin(s) - GA₃ gibberellic acid - R red light     

In vitro flowering of Boronia megastigma Nees. and the effect of 6-benzylaminopurine

Successful flower bud initiation and development was achieved on Boronia megastigma in vitro. The effect of cytokinin on flowering was investigated in environmental conditions that promote flowering as well as under conditions that stimulate vegetative growth (nonfloral promotory conditions). Flower initiation and differentiation was enhanced by cytokinin; however, many flower buds reverted when the media contained high levels of cytokinin. Anthesis occurred only on media that had no cytokinin added and under floral promotory conditions.     

Effects of Ring D-Modified Gibberellins on Gibberellin Levels and Development in Selected Sorghum bicolor Maturity Genotypes

Plants of early flowering mutant and wild type genotypes of Sorghum bicolor were treated with ring D-modified gibberellins (GAs), and the effects on endogenous GA levels were determined. The growth and timing of floral initiation in 58M plants grown under 18-h days (which significantly delays floral initiation in this short day plant) following treatment with these compounds, relative to GA₃ and GA₅ treatments, were also investigated. Application of the endo-isomer of C16,17-dihydro-GA₅ (endo-DiHGA₅), the exo-isomer of C16,17-dihydro-GA₅ (exo-DiHGA₅), and C16α,17-dichloromethanodihydro-GA₅ (DMDGA₅) altered GA levels in both genotypes. Each ring D-modified GA significantly inhibited shoot growth while significantly decreasing levels of GA₁ and increasing levels of its immediate precursor, GA₂₀. Gibberellin A₈ levels also decreased. Tillering was not affected by any treatment. For the early flowering genotype 58M, grown under noninductive long days, both dihydro-GA₅ isomers promoted floral initiation while shoot growth was strongly inhibited, and floral development was strongly advanced beyond floral stage 4. Gibberellin A₃ and GA₅, applied under the same conditions, promoted shoot growth slightly and gave ``floral-like' apical meristems that did not develop past floral stage 1. These results suggest that the reduced shoot growth of sorghum, which follows application of those ring D-modified GAs, is due to their inhibiting the 3β hydroxylation of GA₂₀ to GA₁, thereby reducing the GA₁ content. That floral initiation was hastened and floral development promoted in genotype 58M by application of both isomers of DiHGA₅ are in contrast to the effects of other GA biosynthesis inhibitors, which act earlier in the GA biosynthesis pathway, but are consistent with results seen for long day grasses. This suggests that endo-DiHGA₅ and exo-DiHGA₅ may be acting directly in promoting floral initiation and subsequent floral apex development of this short day plant under long day conditions. Received October 3, 1996; accepted January 22, 1997     

Photoperiodic Responses of Brassica campestris cv. Ceres

The photoperiodic responses of Brassica campestris L. cv. Ceres were investigated to determine the suitability of this plant for further studies on the spectral require ments for floral initiation. This is a long-day plant, sensitive to one inductive photocycle on the fourth day from germination. The flowering response increased with the length and intensity of a single period of supplementary light used to extend an 8-hour daylength and was greatest at 25°C. Application of nitrates retarded floral initiation by about two days under short day conditions, but did not affect the re sponse to one long day. Gibberellic acid induced earlier floral initiation under short day conditions. The photoperiodic response was little affected by omitting the main light period immediately before or after the supplementary light, as long as the intensity of supplementary light was greater than 5000 lux. Short interruptions (5–10 minutes) of a single 16-hour dark period with high energy red or far-red radiation did not promote flowering. When given continuously during a single 16-hour dark period, far-red radiation was more effective in flower promotion than an equal energy of red.     

Fruit set in a deceptive orchid: The effect of flowering phenology,display size,and local floral abundance

We investigated the effect of flowering time, display size, and local floral density on fruit set in Tolumnia variegata, a pollination-limited orchid that offers no reward to its pollinator(s). During 1990, natural variation in flowering time, display size, and fruit set were monitored in 508 plants at one locality in Puerto Rico. The following season, orchid floral abundance per host tree (Randia aculeata) was manipulated to investigate its effect on fruit set. Four floral abundance treatments were established (700, 500, 300, and 100), each replicated four times. Flowering time was the most important trait affecting fruit set. The proportion of plants setting at least one fruit was significantly high early and late in the season, but low during the flowering peak. Thus, strong disruptive selection differential on flowering phenology was found. Display size had little effect on fruit set. A weak, but significant disruptive selection differential on display size was found. Orchid floral abundance per host tree had a significant effect on fruit set. Early in the season, T. variegata flowers with intermediate number of conspecific flowers exhibited a greater probability of setting fruit than those in host trees with fewer or more flowers. Our results show that flowering phenology may be evolutionarily unstable, possibly a consequence of the deception pollination system. Furthermore, a deception strategy would be relatively unsuccessful in populations where plants are found in either very dense or sparse patches.     

Species‐specific responses to combined water stress and increasing temperatures in two bee‐pollinated congeners (Echium,Boraginaceae)

1. Water stress and increasing temperatures are two main constraints faced by plants in the context of climate change. These constraints affect plant physiology and morphology, including phenology, floral traits, and nectar rewards, thus altering plant–pollinator interactions.
2. We compared the abiotic stress responses of two bee‐pollinated Boraginaceae species, Echium plantagineum, an annual, and Echium vulgare, a biennial. Plants were grown for 5 weeks during their flowering period under two watering regimes (well‐watered and water‐stressed) and three temperature regimes (21, 24, 27°C).
3. We measured physiological traits linked to photosynthesis (chlorophyll content, stomatal conductance, and water use efficiency), and vegetative (leaf number and growth rate) and floral (e.g., flower number, phenology, floral morphology, and nectar production) traits.
4. The physiological and morphological traits of both species were affected by the water and temperature stresses, although the effects were greater for the annual species. Both stresses negatively affected floral traits, accelerating flower phenology, decreasing flower size, and, for the annual species, decreasing nectar rewards. In both species, the number of flowers was reduced by 22%–45% under water stress, limiting the total amount of floral rewards.
5. Under water stress and increasing temperatures, which mimic the effects of climate change, floral traits and resources of bee‐pollinated species are affected and can lead to disruptions of pollination and reproductive success.

     

Influence of Water Stress on Flowering and Seed Production of Macroptilium atropurpureum cv. Siratro

Macroptilium atropurpureum cv. Siratro was grown in large soilbeds with a constant water table below, developing a dawn leafwatêr potential of --0.25 MPa. Water stresses equivalentto -0.7 or -1.0 MPa were developed over 14 d, causing reducedstem and bud elongation, leaf expansion, and bud differentiationand survival. Apex size, the proportion of buds which were floralor vegetative, the early phases of floral initiation, and seedformation on advanced inflorescences were little affected duringthe water deficit period. Upon rewatering previously stressed plants showed increasesrelative to control plants in the rates of shoot appearance,leaf expansion and new node appearance. The ratio of buds becomingfloral was independent of watering treatment, and the enhancedrate of floral bud production in the previously-stressed treatmentswas due to higher rates of total bud differentiation which persistedfor up to six weeks after rewatering. Survival of floral budswas reduced by previous stress, but number of flowers per inflorescence,pod setting, seed number per pod and 100-seed weight were independentof treatment. Seed production was controlled by inflorescencedensity. Rate of seed production was independent of treatmentduring water deficit and four weeks subsequently, and was thenenhanced by 46 and 54 per cent relative to the control in the–0.7 and –1.0 MPa treatments respectively. Macroptilium atropurpureum, Siratro, floral initiation, flowering, seed production, water stress, bud development     

Effect of Gibberellic Acid and Phosfon on the Critical Dark Period Reqnirement for Flowering of Impatiens balsamina cv. Rose

The critical dark period requirement for flowering of Impatiens balsamina L. cv. Rose, an obligate short day plant, is about 8.5 hours. While GA₃ completely substituted for the dark period requirement, Phosfon prolonged it to 9.5 hours. GA₃ hastened and Phosfon delayed the initiation of floral buds under all photoperiods. Floral buds opened into flowers only during 8 and 14 hour photoperiods in control and Phosfon-treated plants but during all photoperiods in GA₃-treated ones. The delay in floral bud initiation and flowering was correlated with shifting up of the node bearing the first floral bud and flower respectively. While GA₃ increased the numher of floral buds and flowers in all photoperiods except 8-hour, Phosfon increased their number in the 14-hour photoperiod only. The number of flowering plants decreased with increasing photoperiod regardless of GA₃ and Phosfon application. The effect of Phosfon was completely or partially overcome, depending upon the photoperiod, by simultaneous application of GA₃.     

A Developmental Pattern of Flowering in Colored <Emphasis Type="Italic">Zantedeschia</Emphasis> spp.: Effects of Bud Position and Gibberellin

The restricted flowering of colored cultivars ofZantedeschia is a consequence of developmental constraints imposed by apical dominance of the primary bud on secondary buds in the tuber, and by the sympodial growth of individual shoots. GA₃ enhances flowering inZantedeschia by increasing the number of flowering shoots per tuber and inflorescences per shoot. The effects of gibberellin on the pattern of flowering and on the developmental fate of differentiated inflorescences along the tuber axis and individual shoot axes were studied in GA₃ and Uniconazole-treated tubers. Inflorescence primordia and fully developed (emerged) floral stems produced during tuber storage and the plant growth period were recorded. Days to flowering, percent of flowering shoots and floral stem length decreased basipetally along the shoot and tuber axes. GA₃ prolonged the flowering period and increased both the number of flowering shoots per tuber and the differentiated inflorescences per shoot. Activated buds were GA₃ responsive regardless of meristem size or age. Uniconazole did not inhibit inflorescence differentiation but inhibited floral stem elongation. The results suggest that GA₃ has a dual action in the flowering process: induction of inflorescence differentiation and promotion of floral stem elongation. The flowering pattern could be a result of a gradient in the distribution of endogenous factors involved in inflorescence differentialtion (possibly GAs) and in floral stem growth. This gradient along the tuber and shoot axes is probably controlled by apical dominance of the primary bud. Online publication: 7 April 2005     

Polyamine, ethylene and other physico-chemical parameters in tomato (Lycopersicon esculentum) fruits as affected by salinity

Tomato plants ( Lycopersicon esculentum Mill. cv. Daniela) were grown in perlite bags under greenhouse conditions to study the effect of different salinity levels (20, 40 and 60 m M NaCl) on fruit fresh weight, firmness, color, ethylene production, total 1-aminocyclopropane-1-carboxylic acid (ACC) and polyamine levels. Saline treatments were applied at different times: at the beginning of the plant growth period, and at the developmental stages of flowering of the first cluster and fruit growth of first cluster. Salinity, in general, increased fruit firmness, the intensity of red color, total ACC and ethylene production, while decreasing the final fruit weight. Polyamine levels (spermidine and putrescine) were also increased with salinity, especially when it was applied at the fruit growth of first cluster stage. The relationship between fruit firmness and elevated polyamine content as a result of saline stress is discussed.     

Flowering dynamics in Arum italicum (Araceae): relative role of inflorescence traits, flowering synchrony, and pollination context on fruit initiation

We studied the relative role of inflorescence traits, flowering synchrony, and pollination context for infructescence and fruit initiation in two Spanish populations of Arum italicum, a species in which inflorescences are the pollination unit. In this species, a specialized inflorescence organ, the appendix, is important for pollinator attraction. However, the short floral longevity and the production of mostly one inflorescence per plant make its pollination potentially dependent on strong flowering synchrony and on external factors not controlled by the plant (the pollination context). The flowering period in both sites lasted >3 mo. Day-to-day variation in simultaneous antheses was high, and 11-50% of antheses occurred on days during which no pollen donor was present. Inflorescence traits, flowering synchrony, and between-plant distance all influenced infructescence and fruit initiation, but their relative importance differed between sites. In one large population, infructescence initiation was positively related to inflorescence traits; in a smaller population infructescence initiation increased with the number of donor inflorescences. In both sites, percentage of fruits initiated per infructescence was dependent on a combination of inflorescence traits, flowering synchrony, and between-plant distance. Plants producing 2-4 inflorescences had higher probability of infructescence initiation and overlapped their antheses with more plants than single-inflorescence ones.     

Aggregated flowering phenologies among three sympatric legumes – The degree of non-randomness and the effect of overlap on fruit set

The flowering phenologies of three sympatric legumes, Dillwynia hispida Lindley, D. uncinata (Turcz.)J.Black and Pultenaea densifolia F.Muell. (Fabaceae), were measured over a three-year period in a semi-arid ecosystem. Each species produced a single flowering episode per year which lasted about 15 weeks and which overlapped considerably with those of the remaining two species. A comparison of the actual flowering schedules over two years with those generated from Monte Carlo simulations showed that the flowering schedules of the three species were significantly clumped. Fruit-to-flower ratios on D. hispida plants were calculated over two flowering periods and these values were correlated with conspecific and heterospecific flower abundances to determine whether the extent of overlap in flowering schedules was associated with elevated or depressed levels of fruit set. Partial correlations between heterospecific floral densities and fruit-to-flower ratios were usually positive, indicating a possible selective advantage favouring these convergent flowering schedules.     

Reproductive biology of Alpinia blepharocalyx (Zingiberaceae): another example of flexistyly

The floral biology and breeding system of Alpinia blepharocalyx were studied in Yunnan province, southwest China. Our results indicate that populations of A. blepharocalyx have two floral morphs, which differ in flowering behaviour: the cataflexistylous morph in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes curved under the anther at afternoon, and the anaflexistylous morph in which the receptive stigma is curved under the indehiscent anther first and moves into a reflexed superior position above the anther as it begins to shed pollen in the afternoon; the flowering period of both floral morphs is 12 hours; the stylar movements in the two floral morphs are synchronous, and they have similar traits to those found in other Alpinia species previously reported. Also, on average, cataflexistylous flowers are larger than anaflexistylous flowers, especially the labellum and corolla tube length; moreover, the P/O ratio of the two floral morphs is significantly different: the cataflexistylous morph has more pollen grains and fewer ovules than the anaflexistylous morph; the evolutionary significance of this comparison is discussed. Cataflexistylous flowers were observed to produce a lower concentration of nectar than that of anaflexistylous flowers before 11:00 a.m., but they then have higher nectar concentration; cataflexistylous flowers always have more nectar than anaflexistylous flowers. Flowers of A. blepharocalyx were visited by fewer insects at a lower frequency, including honey bees (Apis cerana cerana) and two species of carpenter bees (Xylocopa spp.). No significant differences were found in the fruit set among the hand-pollination treatments regardless of selfing (geitonogamy and autogamy) or crossing (intermorph and intramorph); but all hand-pollination treatments exhibited much higher fruit set than the controls; meanwhile, no fruit set occurred in the unpollinated bagged plants. Pollen tube growth was examined using fluorescence microscopy following self, intramorph, and intermorph hand pollinations at different times of the day; the pollen tubes of both floral morphs have the same growth rate and the capability to reach the ovary. Both the results of pollen tube growth and fruit sets under different pollination conditions show that A. blepharocalyx is self-compatible and dependent upon insects for pollination. The distinctive flexistyly mechanism of A. blepharocalyx is likely a floral mechanism that promotes effective intermorph pollen transfer.     

THE EFFECT OF ENVIRONMENTAL PARAMETERS ON THE GERMINATION,GROWTH, AND DEVELOPMENT OF SUAEDA DEPRESSA (PURSH) WATS

A study was made to determine the effect of environmental parameters on the germination, growth, and development of Suaeda depressa (Pursh) Wats. Germination tests showed that seeds germinated in solutions containing up to 4 % NaCl with no toxic effects indicated after treatment with distilled water. The rate of germination and the percentage germination decreased with increased salinity. The effect of environmental parameters on growth was measured by shoot height, side shoot development, leaf length, and dry weight. Growth was greatest in 1 % NaCl solutions with adequate available nitrogen. With increased salinity and low available nitrogen levels plant growth decreased. A 10-hr photoperiod stimulated immediate floral induction. Although flowering and completion of the life cycle occurred in solutions containing up to 4 % NaCl, increased salinity decreased the rate of floral induction and the dry weight of flowers and fruit produced. This study indicates that environmental parameters such as salinity, available nitrogen, and photoperiod can create a variety of growth forms, causing taxonomic confusion.     

Action du CCC et du B 995 sur la mise à fleur d'une plante bisannuelle,l'Œnothera biennis

Summary Oenothera biennis L. is a typical biennial plant with an absolute cold requirement for subsequent floral initiation under long-day conditions. Flowering of vernalized Oe. biennis is associated with transition from a rosette habit to the formation of a long flower-bearing stem. Vernalization in Oe. biennis consists of two consecutive stages: (1) preparation for flowering; (2) preparation of stem elongation. At the end of the second stage, the level of endogenous gibberellin-like substances is sufficient to allow the stem elongation which is requisite for subsequent floral development.Applications of (2-chloroethyl)trimethylammonium chloride (CCC) via the roots, when made after the cold treatment, have no effect on internodal elongation and subsequent flowering of vernalized Oe. biennis. Relatively small amounts of CCC applied onto the apical bud of the rosette promote stem growth. However, 750 g of CCC act as a growth inhibitor and delay the beginning of stem elongation but this retardant has no effect on the number of flower buds.In contrast, N-dimethylaminosuccinamic acid (B 995), when applied after a cold treatment, delays the beginning of stem growth, this delay increasing with greater amounts of applied B 995. However, with relatively small amounts of B 995, the rate of later stem growth increases rapidly so that treated plants flower at the same time as controls.If gibberellic acid (GA₃) is applied on the apical bud just at the same time as B 995, it reverses the effects of the growth retardant, even when the amount of B 995, applied by itself, is sufficient to inhibit entirely stem elongation and flowering.B 995 is particularly effective if the preceding cold treatment was just sufficient for effective vernalization. If the cold treatment was extended beyond this time, a greater amount of retardant was required to obtain the same degree of stem growth inhibition.B 995 probably acts by interference with the metabolism of endogenous gibberellin-like substances. The delay of floral initiation in vernalized Oe. biennis by B 995 is a consequence of the retarded internode elongation; if this retardation exceeds a certain limit, the plant is devernalized and exhibits a cold requirement identical with the original one.     

Preliminary characterization of floral response of <Emphasis Type="Italic">Xerophyta humilis</Emphasis> to desiccation,vernalisation, photoperiod and light intensity

Xerophyta humilis is a monocotyledonous resurrection plant found in arid and semi-arid summer rainfall areas of Southern Africa, which undergoes desiccation to survive periods of extreme drought. In order for X. humilis to thrive in their natural habitat, correct timing of the floral transition, coincident with wet periods of sufficient duration, is essential. In this study, the environmental cues involved in the regulation of the floral transition in X. humilis were analysed. No single parameter tested was sufficient to induce flowering, but it was found that flowering was promoted by a combination of a cool period experienced while plants were hydrated, followed by transfer to long-day photoperiods of relatively high light intensity. Plants retained competence to flower if desiccated during exposure to cold, but no flowering occurred if dried prior to this exposure. These data suggest that exposure to cold temperature facilitates vernalisation and subsequent exposure to high light and long days are inductive for floral initiation in X. humilis.     

Control of floral transition in the bioenergy crop switchgrass

Switchgrass (Panicum virgatum L.), a perennial warm season bunchgrass native to North America, has been a target in the U.S. as a renewable bioenergy crop because of its ability to produce moderate to high biomass yield on marginal soils. Delaying flowering can increase vegetative biomass production by allowing prolonged growth before switching to the reproductive phase. Despite the identification of flowering time as a biomass trait in switchgrass, the molecular regulatory factors involved in controlling floral transition are poorly understood. Here we identified PvFT1, PvAPL1‐3 and PvSL1, 2 as key flowering regulators required from floral transition initiation to development of floral organs. PvFT1 expression in leaves is developmentally regulated peaking at the time of floral transition, and diurnally regulated with peak at approximately 2 h into the dark period. Ectopic expression of PvFT1 in Arabidopsis, Brachypodium and switchgrass led to extremely early flowering, and activation of FT downstream target genes, confirming that it is a strong activator of flowering in switchgrass. Ectopic expression of PvAPL1‐3 and PvSL1, 2 in Arabidopsis also activated early flowering with distinct floral organ phenotypes. Our results suggest that switchgrass has conserved flowering pathway regulators similar to Arabidopsis and rice.     

The presentation of treatment responses from block experiments after analysis of variance of transformed data

In pearl millet, severe water deficit during the period of panicle development delays flowering. The flowering response of both main shoot and tillers to water stress during panicle development was investigated using four hybrids. Panicle initiation of all tillers occurred in the three early genotypes despite water stress. In the late genotype, however, panicle initiation of tillers occurred only after the release of stress. The delay in flowering due to water stress was more pronounced in the tillers than in the main shoot. However, the proportion of tillers producing an inflorescence was increased by water stress. Grain yield losses on the main shoot by water stress were compensated by an increase in tiller grain yields. Delay in flowering and buffering by tillers provide an important adaptive mechanism to overcome a period of drought stress prior to flowering.     

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.