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     

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     

Genetic Regulation of Development in Sorghum bicolor: III. Asynchrony of Thermoperiods with Photoperiods Promotes Floral Initiation

Asynchronous thermo- and photoperiods were observed to hasten floral differentiation (initiation) in the short day plant Sorghum bicolor (L.) Moench. Shifting the 12 hour thermoperiod forward 0.5 or 2.5 hours hastened floral initiation compared to controls with synchronous thermo-and photoperiods. Delaying the day-night temperature change until 2.5 hours after either the dark-light or light-dark transition also hastened floral initiation. Inasmuch as sorghum milo-type maturity genotypes containing the genes designated Ma₁Ma₂ (class I) were most responsive to asynchrony of the thermo- and photoperiods while those containing ma₃^R (class III) were not responsive, the maturity genes appear to control the plant's response to both photoperiod and temperature. Gibberellic acid promoted the effect of thermo- and photoperiod asynchrony on floral initiation. The results suggest that in sorghum both temperature and photoperiod may act as phase setting signals in what has previously been termed photoperiodism.     

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.     

Effect of Gibberellin Biosynthesis Inhibitors on Native Gibberellin Content, Growth and Floral Initiation in Sorghum bicolor

CCC, uniconazol, ancymidol, prohexadione-calcium (BX-112), and CGA 163′935, which represent three groups of gibberellin (GA) biosynthesis inhibitors, were applied as a soil drench to Sorghum bicolor cultivars 58M (phyB-1, phytochrome B-deficient mutant) and 90M (phyB-2, equivalent phenotypically to wild type, PHYB, except for small differences in flowering dates). The inhibitors that block steps before GA₁₂ (CCC, uniconazol, and ancymidol) lowered the concentrations of all endogenous early-C13α-hydroxylation pathway GAs found in sorghum: GA₁₂, GA₅₃, GA₄₄, GA₁₉, GA₂₀, GA₁, and GA₈. In contrast, the inhibitors that block the conversion of GA₂₀→ GA₁, (CGA 163′935 and BX-112) drastically reduced GA₁ and GA₈ levels, but they either did not change or caused accumulation of intermediates from GA₁₂ to GA₂₀. Combinations of pre-GA₁₂ inhibitors and GA₃ plus GA₁ strongly reduced GAs other than GA₁ and GA₃. Each of these compounds inhibited shoot growth in both cultivars and delayed floral initiation in 90M. Floral initiation of 58M was also delayed by CCC, uniconazol, and ancymidol but not by CGA 163`935 and BX-112. This separation of shoot elongation from floral initiation in sorghum is novel. Both inhibition of shoot growth and delayed floral initiation were almost completely relieved by a mixture of GA₃ and GA₁ in both 58M and 90M. This observation, plus the much lower levels of endogenous GA₃ than of GA₁ observed in these experiments, implies that GA₁ is the major endogenous GA active in shoot elongation. CGA 163′935 and BX-112 also failed to promote tillering in 58M, whereas inhibitors active before GA₁₂ did so. The possibility that the GA₂₀→ GA₁ inhibitors fail to block flowering and promote tillering in 58M because biosynthetic intermediates between GA₁₂ and GA₂₀ accumulate and/or because 58M is altered in GA metabolism in this same region of the biosynthetic pathway is discussed. Received April 7, 1998; accepted July 31, 1998     

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.     

Floral induction by gibberellic acid in Impatiens balsamina,a qualitative short-day plant

Summary In the qualitative short-day plant Impatiens balsamina, gibberellic acid (GA₃) not only promoted the formation of floral buds in response to suboptimal photoinductive conditions and reduced the number of SD cycles that are required for their development into flowers, but also caused initiation of floral buds under non-inductive photoperiods. In plants treated with repeated applications of GA₃, the floral buds developed into flowers irrespective of whether the apex was left intact or was removed. In those that received a single application of GA₃ the floral buds developed into flowers only in decapitated plants.     

Induction of flowering ofImpatiens balsamina treated with gibberellic acid and resorcinol

Under strictly non-inductive photoperiods (24-h photoperiods) floral buds were initiated on plants receiving 25 treatments with Reso (resorcinol) or 8 treatments with GA₃ (gibberellic acid) or GA₃ + Reso, while water treated control plants did not flower at all. Although a single treatment of plants with GA₃ or GA₃ + Reso is not adequate to cause induction under LD conditions, its effect is added to the sub-threshold induction caused by one SD (short day: 8-h photoperiod) cycle. The initiation of floral buds was hastened with an increasing number of SD cycles accompanying respective number of treatments, the effect of GA₃ alone or together with Reso being more pronounced than that of Reso alone. GA₃ increased the number of floral buds more than Reso, the number being the highest in plants receiving the respective number of treatments with the combination GA₃ + Reso under both inductive as well as non-inductive photoperiods. Deceased.     

Effect of Gibberellic Acid, 2,3,5-Triiodobenzoic Acid and Indole Acetic Acid on Growth and Development of Impatiens balsamina during Different Photoperiods

This paper deals with the effect of 100 mg/1 each of GA₃ TIBA and IAA singly and in combination with each other on stem elongation, development of lateral branches and floral bud initiation in Impatiens balsamina plants exposed to 8-, 16- and 24-h photoperiods. GA₃ enhances stem elongation, the enhancing effect decreasing with IAA as well as with TIBA during 8-h but increasing during 16- and 24-h photoperiods. It decreases the number of lateral branches, the decrease being greatest during 16-, less during 8- and the least during 24-h photoperiods. The time taken for floral buds to initiate with and length of branches during 16-h photoperiods. During 8-h photoperiods, IAA delays the initiation of floral buds, while GA₃ hastens it when used together with TIBA or IAA or both. GA₃ increases the number of floral buds on the main axis but decreases it on lateral branches, while TIBA decreases the number on the main axis but increases it on lateral branches. IAA reduces the number of floral buds on the main axis only when used alone, but on both the main axis as well as on lateral branches when used together with GA₃ and TIBA. Floral buds were not produced on lateral branches when plants were treated with GA₃, TIBA and IAA all together. GA₃ and TIBA induced floral buds even under non-inductive photoperiods, the number of buds and reproductive nodes being less in TIBA- than in GA₃-treated plants during 24-h photoperiods. The time taken for floral buds to initiate with GA₃ and TIBA during noninductive photoperiods is much longer than that during 8-h inductive photoperiods with or without GA₃ or TIBA application. IAA completely inhibits the GA₃- and TIBA-caused induction during 24-h, but only delays it and reduces the number of reproductive nodes and floral buds during 16-h photoperiods.     

Endogenous Gibberellins and Shoot Growth and Development in Brassica napus

Greenhouse-grown oilseed rape (Brassica napus, annual Canola variety `Westar') plants were harvested at six dates from the vegetative phase until the early pod (silique)-fill/late flowering stage. Endogenous gibberellin (GA)-like substances were extracted from stems, purified, and chromatographed on silica gel partition columns prior to bioassay in serial dilution using the `Tan-ginbozu' dwarf rice microdrop assay. The concentrations of total endogenous GA-like substances were low during vegetative stages (1 nanogram GA₃ equivalents/gram dry weight), and rose 300-fold by the time of floral initiation. After floral initiation the concentration of GA-like substances fell, then rose again during bolting to maximal levels during the early pod-fill stage (940 nanograms per gram dry weight). The qualitative profiles of GA-like substances varied across harvests, with higher proportions of a GA₁-like substance at the early pod-fill stage. In a second study stems were similarly harvested at eight dates and the concentrations of endogenous GA₁, the principal bioactive native GA of oilseed rape, were determined by gas chromatography-selected ion monitoring using [17,17-²H]GA₁ as a quantitative internal standard. The concentration of GA₁ increased at about the time of floral initiation and then subsequently fell, thus confirming the pattern noted above for total GA-like substances. The exogenous application of paclobutrazol (PP333), a persistent triazole plant growth regulator (PGR) which blocks GA biosynthesis, or another triazole, triapenthenol (RSW0411), prevented flowering as well as bolting; plants remained at the vegetative rosette stage. These results imply a causal role for endogenous GA, in the control of bolting, which normally precedes anthesis. Further, the rise in the concentration of total endogenous GA-like substances, including GA₁, which was associated with floral initiation, and the prevention of visable floral development by the triazole PGRs, also indicates a role for endogenous GAs in the regulation of flowering in B. napus.     

Elevation in the Sucrose Content of the Shoot Apical Meristem of Sinapis alba at Floral Evocation

Nanogram tissue samples from apical meristems of Sinapis alba were assayed for sucrose, total soluble hexosyl equivalents ( glucose and fructose plus hexoses from sucrose hydrolysis), and total soluble glucosyl equivalents ( glucose plus glucose from sucrose hydrolysis). On dry weight basis, sucrose concentration increased by more than 50% within 10 hours after the start of either a long photoperiod or a short photoperiod displaced by 10 hours in the 24-hour cycle (`displaced short day'). (These treatments induce flower initiation) Glucose and fructose concentrations were close to zero in vegetative meristems and remained low compared to sucrose in meristems of induced plants. Within a single meristem, the peripheral and the central zones had similar concentrations of sucrose. Our results indicate that an early physiological event in floral transition is the accumulation of sucrose in the meristem.     

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     

Floral development in bolting garlic

Garlic (Allium sativum L.) is a completely sterile plant, propagated only vegetatively. The aim of this research was to study the sequence of morphological processes occurring during floral initiation and development of a number of bolting garlic accessions from the Allium gene bank in Israel by using SEM. The garlic inflorescence is an umbel-like flower arrangement, the branches (flower clusters) of which arise from a common meristem. The numerous flowers have a distinct morphology typical of the genus Allium. Flower-stalk elongation precedes the swelling of the apical meristem and its subdivision into several centers of floral development. Within clusters, floral primordia develop unevenly. Differentiation of topsets begins after floral differentiation on the peripheral part of the apical surface, and their size, number and rate of development vary among genotypes. At least four morphological types differing in flower/topset ratio were distinguished among the 12 clones studied in this investigation. For further studies of flowering physiology and fertility restoration, only clones which can differentiate the greatest proportion of normal flowers and the least of topsets in the apical meristem should be selected. Received: 28 June 2000 / Revision accepted: 6 November 2000     

C类花器官特征基因AGAMOUS(AG)调控植物花分生组织维持与终止研究进展

花分生组织的维持与终止在植物花器官发生和世代交替起着至关重要的作用。成功的花分生组织决定能够确保植物正常的生殖发育和生命周期进程。诸多研究表明AGAMOUS(AG)基因作为花器官分化和开花决定的主效调节因子,能够协调花发育过程中多种细胞命运决定。然而,关于AG参与调控植物世代交替及花分生组织维持与终止的分子调控机制尚不清晰。综述了近年来AG基因参与调控植物花分生组织维持与终止的研究进展及现状,以期为深入研究植物花器官分化过程中干细胞的维持和终止,以及干细胞活动与其他发育过程之间的分子调控过程提供参考。     

Histomorphological changes in shoot apices of <Emphasis Type="Italic">Lactuca sativa</Emphasis> treated with gibberellic acid

Lettuce plants were treated with gibberellic acid (GA₃) and uniconazole (UZ; a gibberellin synthesis inhibitor) to investigate the influence of GA₃ on cell division frequency in the shoot apical meristem (SAM) during stem elongation and flower initiation in lettuce (Lactuca sativa) grown in a greenhouse. GA₃ (0.1 mM) was sprayed on the surface of outer leaves and uniconazole solution (0.86 mM) was applied to the soil. GA₃ increased cell division frequency in the peripheral zone and the rib meristem of shoot apices, and this was associated with the stimulation of stem elongation. UZ treatment decreased cell division frequency in the peripheral zone, rib meristem and subapical pith, and this was associated with restricted stem elongation. Treatment with UZ and GA₃ together induced minor stem elongation. Flower induction occurred 3 d earlier in the GA₃ and UZ+GA₃ treatments than in the control, while the UZ treatment delayed flower initiation for more than 9 d relative to the control.     

Studies on the Transmission of Floral Effects of Photoperiod and Gibberellin from One Branch to the Other inImpatiens balsamina

In two branched plants ofImpatiens balsamina with intact apex and leaves floral buds are induced only in the branch which is either exposed to 8-h (inductive) photoperiods or receives GA₃ treatment if maintained under 24-h (non-inductive) photoperiods. GA₃ induces floral buds on the treated branch even if the leaves on that branch are removed, showing that while leaves are essential for photoperception, these are not neoessary for GA₃ to cause induction. The effect of the inductive photoperiods or GA₃ treatments to a branch is not transmitted to the other branch which is treated with water and is maintained under non-inductive photoperiods even when the latter is defoliated but is transmitted if the apioal or both the apical and axillary buds on the branch receiving inductive photoperiods or GA₃ treatment are excised. It, therefore, appears that the existence of strong sinks in the form of axillary and apical buds on the treated branch prevents the transmission of photoperiodic as well as GA₃ effects to the other branch in this plant.