Overexpression of the cucumber LEAFY homolog CFL and hormone treatments alter flower development in gloxinia (Sinningia speciosa)

Leafy (LFY) and LFY-like genes control the initiation of floral meristems and regulate MADS-box genes in higher plants. The Cucumber-FLO-LFY (CFL) gene, a LFY homolog in Cucumis sativus L. is expressed in the primordia, floral primordia, and each whirl of floral organs during the early stage of flower development. In this study, functions of CFL in flower development were investigated by overexpressing the CFL gene in gloxinia (Sinningia speciosa). Our results show that constitutive CFL overexpression significantly promote early flowering without gibberellin (GA(3)) supplement, suggesting that CFL can serve functionally as a LFY homolog in gloxinia. Moreover, GA(3) and abscisic acid (ABA) treatments could modulate the expression of MADS-box genes in opposite directions. GA(3) resembles the overexpression of CFL in the expression of MADS-box genes and the regeneration of floral buds, but ABA inhibits the expression of MADS-box genes and flower development. These results suggest that CFL and downstream MADS-box genes involved in flower development are regulated by GA(3) and ABA.     

[14C]-Assimilate partitioning in photoperiodically induced seedlings of Pharbitis nil. The effect of benzyladenine

Partitioning of [¹⁴C]-labeled assimilates was studied in relation to photoperiodic floral induction and evocation in one-week-old Pharbitis nil Choisy cv. 'Violet' seedlings. In plants kept under 16 h photoperiods, one 15 h night induced 100% axillary flowering whereas a 24 h night induced both terminal and axillary flowering. A 15 min night break of red light given 8 h after the beginning of the dark period inhibited flowering. Total [¹⁴C]-assimilate distribution among major sinks (plumules + epicotyl and roots + hypocotyl) from a single source cotyledon was unchanged by one inductive night; however, import of [¹⁴C]-assimilates into shoot apices was increased in induced plants compared to vegegative controls. This increase was several-fold in plants subjected to a 24 h night. N⁶-Benzyladenine (BA) application to cotyledons or plumules under non-saturating night lengths increased the number of floral buds per plant without affecting the position of the first floral bud (i.e. the speed of induction). The same treatment caused increased label accumulation in induced apices, while it only slightly affected non-induced ones. The mode of action of BA on flowering through growth stimulation and resulting assimilate mobilization is discussed.     

Wheat SOC1 functions independently of WAP1/VRN1, an integrator of vernalization and photoperiod flowering promotion pathways

Heading time in bread wheat ( Triticum aestivum L.) is determined by three characters – vernalization requirement, photoperiodic sensitivity and narrow-sense earliness (earliness per se) – which are involved in the phase transition from vegetative to reproductive growth. The wheat APETALA1 ( AP1 )-like MADS-box gene, wheat AP1 ( WAP1 , identical with VRN1 ), has been identified as an integrator of vernalization and photoperiod flowering promotion pathways. A MADS-box gene, SUPPRESSOR OF OVEREXPRESSION OF CO 1 ( SOC1 ) is an integrator of flowering pathways in Arabidopsis . In this study, we isolated a wheat ortholog of SOC1 , wheat SOC1 ( WSOC1 ), and investigated its relationship to WAP1 in the flowering pathway. WSOC1 is expressed in young spikes but preferentially expressed in leaves. Expression starts before the phase transition and is maintained during the reproductive growth phase. Overexpression of WSOC1 in transgenic Arabidopsis plants caused early flowering under short-day conditions, suggesting that WSOC1 functions as a flowering activator in Arabidopsis . WSOC1 expression is affected neither by vernalization nor photoperiod, whereas it is induced by gibberellin at the seedling stage. Furthermore, WSOC1 is expressed in transgenic wheat plants in which WAP1 expression is cosuppressed. These findings indicate that WSOC1 acts in a pathway different from the WAP1 -related vernalization and photoperiod pathways.     

Ethylene and ABA interactions in the regulation of flower induction in Pharbitis nil

Hormones are included in the essential elements that control the induction of flowering. Ethylene is thought to be a strong inhibitor of flowering in short day plants (SDPs), whereas the involvement of abscisic acid (ABA) in the regulation of flowering of plants is not well understood. The dual role of ABA in the photoperiodic flower induction of the SDP Pharbitis nil and the interaction between ABA and ethylene were examined in the present experiments. Application of ABA on the cotyledons during the inductive 16-h-long night inhibited flowering. However, ABA application on the cotyledons or the shoot apices during the subinductive 12-h-long night resulted in slight stimulation of flowering. Application of ABA also resulted in enhanced ethylene production. Whereas nordihydroguaiaretic acid (NDGA) - an ABA biosynthesis inhibitor - applied on the cotyledons of 5-d-old seedlings during the inductive night inhibited both the formation of axillary and of terminal flower buds, application of 2-aminoethoxyvinylglycine (AVG) and 2,5-norbornadiene (NBD) - inhibitors of ethylene action - reversed the inhibitory effect of ABA on flowering. ABA levels in the cotyledons of seedlings exposed to a 16-h-long inductive night markedly increased. Such an effect was not observed when the inductive night was interrupted with a 15-min-long red light pulse or when seedlings were treated at the same time with gaseous ethylene during the dark period. Lower levels of ABA were observed in seedlings treated with NDGA during the inductive night. These results may suggest that ABA plays an important role in the photoperiodic induction of flowering in P. nil seedlings, and that the inhibitory effect of ethylene on P. nil flowering inhibition may depend on its influence on the ABA level. A reversal of the inhibitory effect of ethylene on flower induction through a simultaneous treatment of induced seedlings with both ethylene and ABA strongly supports this hypothesis.     

Two lily SEPALLATA-like genes cause different effects on floral formation and floral transition in Arabidopsis

Two AGL2-like MADS-box genes, Lily MADS Box Gene (LMADS) 3 and LMADS4, with extensive homology of LMADS3 to the Arabidopsis SEPALLATA3 were characterized from the lily (Lilium longiflorum). Both LMADS3 and LMADS4 mRNA were detected in the inflorescence meristem, in floral buds of different developmental stages, and in all four whorls of the flower organ. LMADS4 mRNA is also expressed in vegetative leaf and in the inflorescence stem where LMADS3 expression is absent. Transgenic Arabidopsis, which ectopically expresses LMADS3, showed novel phenotypes by significantly reducing plant size, flowering extremely early, and loss of floral determinacy. By contrast, 35S::LMADS4 transgenic plants were morphologically indistinguishable from wild-type plants. The early-flowering phenotype in 35S::LMADS3 transgenic Arabidopsis plants was correlated with the up-regulation of flowering time genes FT, SUPPRESSOR OF OVEREXPRESSION OF CO 1, LUMINIDEPENDENS, and flower meristem identity genes LEAFY and APETALA1. This result was further supported by the ability of 35S::LMADS3 to rescue the late-flowering phenotype in gigantea-1 (gi-1), constans-3 (co-3), and luminidependens-1 but not for ft-1 or fwa-1 mutants. The activation of these flowering time genes is, however, indirect because their expression was unaffected in plants transformed with LMADS3 fused with rat glucocorticoid receptor in the presence of both dexamethasone and cycloheximide.     

钙在植物花发育过程中的作用

对于园林观赏植物,开花是一个非常重要的发育阶段,它直接影响花卉的品质。近年来,植物花发育的分子生物学研究进展迅速,并取得了一些突破性成果。钙作为第二信使在植物信号转导中起着非常重要的作用,大量研究显示,钙有可能参与开花控制。本文总结了钙信号与植物花发育这一领域的最新研究进展,包括以下几个方面的内容：钙在植物成花诱导(包括光周期诱导和低温诱导)中的作用;花芽分化时期钙在植物叶芽和花芽中的动态分布及组织培养条件下不同钙浓度对花芽分化的影响;钙与花衰老的关系。     

钙在植物花发育过程中的作用

对于园林观赏植物,开花是一个非常重要的发育阶段,它直接影响花卉的品质。近年 来,植物花发育的分子生物学研究进展迅速,并取得了一些突破性成果。钙作为第二信使在植物信号转导中起着非常重要的作用,大量研究显示,钙有可能参与开花控制。本文总结了钙信号与植物花发育这一领域的最新研究进展,包括以下几个方面的内容：钙在植物成花诱 导（包括光周期诱导和低温诱导）中的作用;花芽分化时期钙在植物叶芽和花芽中的动态分布及组织培养条件下不同钙浓度对花芽分化的影响;钙与花衰老的关系。      

Changes in the content of endogenous auxins in apical buds ofchenopodium rubrum L. Induced with respect to the endogenous rhythm in capacity to flower

The content of endogenous auxins was examined in apical buds ofChenopodium rubrum plants induced by a photoperiodic cycle of 16h darkness and 8h light followed by a dark period of various duration so as to correspond with either maximal or minimal flowering response in the endogenous rhythm in capacity to flower initiated by the photoperiodic treatment. Apical buds of potentially generative plants contained less auxins than apical buds of plants which remained in the vegetative state. Apical buds from plants treated with kinetin (1. 10^-3 M) and therefore remaining in the vegetative state showed an auxin level comparable to that of untreated plants exhibiting minimal flowering response irrespective of the duration of the second dark period. Plants cultivated on a sucrose solution (0.6 M) during the second dark period became generative even at the normal minimum of flowering. The auxin content of the apical buds was low, similarly as in untreated plants induced for a period leading to maximal flowering response. On the other hand, apical buds from plants grown on sucrose solution during a dark period leading to the manifestation of maximal flowering response showed a relatively high auxin content comparable to that found in untreated plants which had obtained a more extended induction by three photoperiodic cycles. The results are discussed with respect to the possible role of endogenous auxins in the regulation of the changes in growth correlations occurring in the shoot apex during photoperiodic induction and in the expression of the competence to flower.     

Flowering response of Ipomoea batatas scions grafted onto Pharbitis nil stocks

Young seedlings of Ipomoea batatas (L.) Lam. cv. Big One did not form floral buds, but were induced to flower when grafted onto Pharbitis nil Chois. cv. Violet with its cotyledons exposed to a 16 h dark period (SD). Four SD were required to induce flowering in I. batatas scions when the grafted plants were first grown under an 8 h dark period (LD) for 18 days and then exposed to SD. Transmission of the flowering stimulus across the graft union required 4 days. It was also slow in the graft combination of P. nil and P. nil , but increased greatly when the graft union was established more completely. These results suggest that the flowering stimulus of P. nil may move symplastically and its life may be between 4 and 6 days. Although the leaves of I. batatas inhibited flowering, the flowering response of P. nil grafted onto I. batatas suggested that the involvement of a transmissible flowering-inhibitor was unlikely.     

Possible role of jasmonic acid in the regulation of floral induction, evocation and floral differentiation in Lemna minor L.

Jasmonic acid (JA) is implicated in a wide variety of developmental and physiological processes in plants. Here, we studied the effects of JA and the combination of JA and ethylenediamine-dio-hydroxyphenyl-acetic acid (EDDHA) on flowering in Lemna minor in axenical cultures. JA (0.475-47.5 nmol l(-1)) enhanced floral induction in L. minor under long-day (LD) conditions. Under the same conditions, at a concentration of 237.5 nmol l(-1), JA inhibited floral induction, and at a concentration of 475 nmol l(-1) it prevented floral induction. Under LD conditions with LD preculture, a combination of EDDHA (20,500 nmol l(-1)) and JA (47.5 nmol l(-1)) had a synergistic effect on the promotion of floral induction. Floral induction was enhanced to the greatest extent in experiments with LD precultures. Microscopic examination of microphotographs of histological sections showed that JA and, to an even greater extent, JA+EDDHA at optimal concentrations promote apical floral induction (evocation). Furthermore, JA, and to an even greater extent JA in combination with EDDHA in an optimal concentration, also promote flower differentiation, especially the development of stamens, as is evident from the microphotographs. The experimental results show that JA promotes floral induction in other species of Lemnaceae from various groups according to their photoperiodic response. The results support our hypothesis that, in addition to previously ascribed functions, JA may regulate floral induction, evocation and floral differentiation. Our hypothesis is supported also by the results obtained by quantitative determination of endogenous JA levels in L. minor at three growth stages. The levels of endogenous JA decreased from 389 ng JA g(-1) (fresh weight) of L. minor during the vegetative stage to 217 ng JA g(-1) during the evocation stage, and to 37.5 ng JA g(-1) during the flowering stage, which proves that JA is used for flowering.     

Regulation of flowering plants of different biotypes

The patterns of control of flowering are analyzed in plants of different biotypes. The photoperiodic reaction of flowering taken as an example, the whole net of control is considered: from the environmental stimulus through its physiological transformation in the leaf in the corresponding hormonal impulse which, in turn, controls the realization of genetic programme and formation of generative organs in the stem buds. The photoperiodically neutral plants taken as an example, the patterns of age control of flowering are considered. In plants of different photoperiodic groups the synthesis of complementary components of florigen was shown to proceed either autonomously under the photoperiodic effect or under the inducing effect of definite photoperiods. The autonomous and inducible mechanisms of biosynthesis of the flowering hormones have a common base, the genetic system to which the environment sends its stimuli through the hormonal interactions. The interaction of hormonal and genetic developmental factors is considered, the evocation of flowering in the stem buds taken as an example.     

Photoperiodic Regulation of Flowering in Cowpeas (Vigna unguiculata (L.) Walp.)

To test the proposition that photoperiodic controls synchronizethe flowering of cowpeas, Vigna unguiculata (L.) Walp. [V. sinensis(L.) Savi], the day-length requirements for floral initiationand for flowering were investigated in several short-day accessions.No evidence was found of different critical photoperiods atdifferent stages of development, but exposure to only 2–4short days was required for floral initiation compared withabout 20 for development to open flowers. Pod setting was increasedafter exposure to even one short day more than the number requiredfor flower opening. Floral buds at higher nodes appeared to require fewer shortdays for development to flowering than buds at the lower nodes,and displayed faster rates of development. Inflorescence budsdid not resume development if they were exposed to 15 or morelong days following inflorescence initiation. Thus, any tendencytowards synchronous flowering in cowpeas is not due to the criticalday-length for flower development being shorter than that forflower initiation, but could be the result of cumulative photoperiodicinduction of plants and the more rapid development of later-formedflowers. Vigna unguiculata (L.) Walp., cowpeas, flower initiation, flower development, fruit set, photoperiodism     

A tobacco calcium/calmodulin-binding protein kinase functions as a negative regulator of flowering

A tobacco calcium/calmodulin-binding protein kinase (NtCBK1) was isolated and identified. The predicted NtCBK1 protein has 599 amino acids, an N-terminal kinase domain, and shares high homology with other calmodulin (CaM)-related kinases. Whereas NtCBK1 phosphorylates itself and substrates such as histone IIIS and syntide-2 in the absence of CaM, its kinase activity can be stimulated by tobacco CaMs. However, unlike another tobacco protein kinase designated NtCBK2, NtCBK1 was not differentially regulated by the different CaM isoforms tested. The CaM-binding domain of NtCBK1 was located between amino acids 436 and 455, and this domain was shown to be necessary for CaM modulation of kinase activity. RNA in situ hybridization showed that NtCBK1 was highly regulated in the transition to flowering. Whereas NtCBK1 mRNA was accumulated in the shoot apical meristem during vegetative growth, its expression was dramatically decreased in the shoot apical meristem after floral determination, and in young flower primordia. The expression of NtCBK1 was up-regulated to high levels in floral organ primordia. Fluctuations in NtCBK1 expression were verified by analysis of tobacco plants expressing green fluorescent protein under the control of the NtCBK1 promoter, suggesting a role of NtCBK1 in the transition to flowering. This conclusion was confirmed by overexpressing NtCBK1 in transgenic tobacco plants, where maintenance of high levels of NtCBK1 in the shoot apical meristem delayed the switch to flowering and extended the vegetative phase of growth. Further work indicated that overexpression of NtCBK1 in transgenic tobacco did not affect the expression of NFL, a tobacco homologue of the LFY gene that controls meristem initiation and floral structure in tobacco. In addition, the promotion of tobacco flowering time by DNA demethylation cannot be blocked by the overexpression of NtCBK1.     

Inhibitory Effect of Methyl Jasmonate on Flowering and Elongation Growth in Pharbitis nil

The effect of methyl jasmonate (JA-Me) on the floral bud formation and elongation growth in the short-day plant Pharbitis nil was investigated. The placing of 4-day-old seedlings of P. nil in a solution of JA-Me for a period of 24 h before an inductive (16 h or 14 h of darkness) night led to a dramatic reduction in the number of flower buds formed by the plant. Plants treated with JA-Me also totally lost their capacity to form a generative terminal bud. JA-Me applied after photoinduction does not inhibit flowering. Gibberellic acid (GA3) partly reverses the inhibitory effect of JA-Me. Plants treated simultaneously with JA-Me and GA3 formed about 3 flower buds more than plants treated with JA-Me only. JA-Me at a concentration of 10-7 M stimulates slightly, but at higher concentrations it inhibits root growth and shoot growth. A distinct lack of correlation between the effect of JA-Me on inhibition of flowering and shoot and root growth was noted. This indicates the independent action of JA-Me in controlling both processes.