In vitro formation and development of floral buds on tobacco stem explants: effects of kinetin and other factors

Stem segments were excised from plants of Wisconsin 38 tobacco (Nicotiana tabacum L.) in three regions differing in their distance below the inflorescence. They were cultured in vitro in 8- or 16-hr days. After 8 weeks, floral and vegetative buds were counted, and extent of floral development was assessed. Kinetin at 10(-5)m inhibited formation and development of floral buds regardless of indoleacetic acid concentration. Supplied at this concentration with adequate auxin, kinetin stimulated vegetative bud formation and may have caused floral bud abortion. Indoleacetic acid (>/= 10(-6)m) inhibited vegetative and floral bud formation when supplied with low kinetin concentration (/= 10(-6)m), it inhibited floral bud formation and stimulated vegetative bud formation. More floral buds were formed in 16-hr days than in 8-hr days. Few formed on explants other than those derived from the region nearest the inflorescence regardless of other treatment.     

Flower formation in vitro in a quantitative short-day tobacco: interrelation between photoperiod and infructescence development

The flowering response of thin layers excised from branch internodes of Nicotiana tabacum cv. Maryland Catterton (quantitative short-day plant for induction) was studied under three photoperiodic treatments. The explants were excised from inflorescences bearing flowers only, flowers and green fruits, or from infructescences with green fruits only. The aim of the study was to investigate the post-inductive photoperiodic effects on in vitro flower bud formation in a quantitative short-day tobacco and the relation with infructescence development. Short days quantitatively enhanced the flower bud regeneration capacities of explants in all stages of development, both as number of explants induced to produce flowers and as mean number of flowers per explant. There was no significant difference in flower bud formation on explants of the first two stages, which produced much more flowers than those of the third stage. Observations in planta showed that, during the 20 days separating the second stage from the first stage, there was no significant difference in the number of floral buds and flowers present on the inflorescence; however, the branch internodes lengthened, as did the floral buds and flowers. During the 10 days leading to the third stage, the number of capsules did not change significantly, but a high rate of floral abscission occurred. The present results show that in Nicotiana tabacum cv. Maryland Catterton short day quantitatively controls not only the inductive step of the flowering process, but also affects the capacity to regenerate flower buds during the late post-inductive phases. The responsiveness to the photoperiodic signal decreases only when the plant exhibits only fruits.     

The effect of photoperiod on flower formation in vitro in a quantitative short-day cultivar of Nicotiana tabacum

Superficial cell layers of a quantitative short-day tobacco plant ( Nicotiana tabacum L. cv. White Burley) were excised from different parts of the inflorescence (i.e. pedicels, branch internodes, rachises), and cultured in continuous darkness, continuous light or 8 h light/16 h dark daily. The flowering response in vitro of the different types of explants was investigated with respect to the effect of light on the post-evocation phases of the flowering process and explant commitment. Treatment effect was qualitatively and quantitatively influenced by explant origin. Three morphogenic features were observed: flower neoformation, caulogenesis and rhizogenesis (the latter on rachis explants only). Under all treatments, the highest flowering potential was shown by pedicels, while the highest vegetative potential was shown by rachises. Branch internodes showed an intermediate response, but with a tendency towards caulogenesis, which probably reflects their phylogenetic origin. Thus, opposite gradients of the neoformation of flowering and vegetative buds on explants were observed under all treatments. Pedicels formed new single flowers rather than inflorescences, while rachises regenerated mainly inflorescences. In darkness, flowering was limited mostly to pedicels. Vegetative bud formation was higher than floral bud regeneration in all types of explant. Continuous light enhanced the flowering response mostly in pedicel and branch internode explants. Short days enhanced flower bud formation in vitro on all types of explant. Results with respect to microsporogenesis, flower and inflorescence anomalies observed under darkness also seem to support the existence of a quantitative photoperiodic control on floral neoformation in vitro in this plant. These results suggest that in Nicotiana tabacum cv. White Burley in vivo floral induction, initiation and development are governed by the same photoperiodic requirements.     

Effect of ABA on the in Vitro Induction of Floral Buds of Dendrobium candidu Wall.ex Lindl.

An in vitro flowering system of Dendrobium candidurn Wall. ex Lindl., a wild species of orchid, was established. Callus was induced from seeds and protocorms formed on MS agar medium supplemented with 0.3 mg/L NAA under diffused light. Floral buds were induced when protocorms were cultured on MS agar medium supplemented with 2 mg/L 6-BA and 0.5 mg/L NAA, the frequency of floral bud induction being 27.0%. When protocorms were precultured on MS medium supplemented with 0. 5 mg/L ABA for 15 days and then transfered onto MS medium supplemented with 2 mg/L 6-BA, the frequency of floral bud induction increased greatly reach 84.0 % during a period of 5 months. Meanwhile the number of branches and floral buds also increased and in some instances inflorescence appeared. Never the less, no floral bud was formed if protocorms continued to be cultured on the ABA-containing MS medium.     

石斛离体培养中ABA对诱导花芽形成的影响

由兰科植物铁皮石斛（Ｄｅｎｄｒｏｂｉｕｍ ｃａｎｄｉｄｕｍ Ｗａｌｌ．ｅｘ Ｌｉｎｄｌ．）种子诱导形成的愈伤组织,在光照下置于ＭＳ附加０．３ ｍ ｇ／ＬＮＡＡ 的培养基上繁殖,可以形成原球茎。将原球茎转入ＭＳ含２ ｍ ｇ／Ｌ ６－ＢＡ 和０．５ ｍ ｇ／ＬＮＡＡ 的培养基上,花芽形成频率为２７．０％ 。原球茎先在０．５ ｍ ｇ／ＬＡＢＡ的培养基上预培养１５ ｄ,再转入含２ ｍ ｇ／Ｌ６－ＢＡ 的ＭＳ培养基上培养,花芽形成频率明显提高,可达８４．４％ ,而且每株植株花的数目增加;但是在仅有ＡＢＡ 的ＭＳ培养基上培养的原球茎再生的植株未见花芽形成     

Floral gradient in flowering tobacco in relation to free amino acids

By employing TCLs (thin cell layers) culture, the floral gradient in flowering tobacco of different developmental stages was confirmed. The TCLs from early flowering tobacco regenerated more floral buds than those from the tobacco plants in full blooming or fruiting stages. Analysis of free amino acid levels revealed the acropetal gradient of Pro in flowering tobacco stem. L-Pro. L-Trp. D,L-Met and L-Arg were respectively added into the culture medium for testing their influence on floral bud formation from tobacco pedicel segments. Only L-Trp evidently enhanced the floral bud neoformation.     

Responsiveness to abscisic acid of embryos of dormant oat (Avena sativa) seeds. Involvement of ABA-inducible proteins

An in vitro bioassay system for floral bud formation has been established using Nicotiana tabacum L. cv. MC, explants excised from floral stalks cultured on modified Murashige-Skoog medium containing excess auxin and antiauxin. Three auxins. indolyl-3-acetic acid (IAA), 4-chloroindolyl-3-acetic acid and 5,6-dichloroindolyl-3-acetic acid, were tested for floral bud-forming activity; IAA was most efficient. Three antiauxins. 5,7-dichlorindolyl-3-isobutyric acid (5,7-Cl₂-HBA), p -chlorophenoxyiso butyric acid and 2,3,5-triiodobenzoic acid, were tested for the ability to reverse the inhibition of floral bud formation caused by excess IAA. Only 5,7-Cl₂-HBA was very effective. Leaf exudates from short day- and long day-treated tobacco plants were added to the bioassay system which contained 1 µ M 6-benzylaminopurine, 5 µ M IAA and 5 µ M 5, 7-Cl₂-HBA, Interestingly, only the leaf exudate from short day-treated plants stimulated floral bud formation. Moreover, the buds produced grew into large. well-developed ones with shapes similar to those of the natural floral buds of intact tobacco plants.     

穗花牡荆花芽分化过程中形态和生理指标变化

以穗花牡荆为研究材料,通过探究其花芽分化进程和生理特性,为花期调控技术提供成花机理。采用物候期观察和石蜡切片相结合的方法并测定花芽分化过程中相关生理指标,研究花发育过程中的形态和生理变化。结果表明,穗花牡荆花芽分化为一年多次分化型,其进程可划分为七个时期：未分化期、总轴花序原基分化期、初级分轴花序原基分化期、次级分轴花序原基分化期、小花原基分化期、花器官分化前期和花器官分化后期。同一植株不同位置花芽及同一花序中不同单花分化的进程不同,第一季花期后各阶段的花芽分化形态常存在重叠。花芽分化过程中不同时期叶片和花芽的可溶性糖和可溶性蛋白质含量均有上升下降的变化,总体上叶片中营养物质含量高于花芽保证营养供应。花芽分化过程中,IAA、ABA、CTK和GA3整体水平上先升后降有利于花芽分化进行。研究认为,花芽中大量的可溶性糖和蛋白质积累及较高的碳氮比,有利于穗花牡荆花芽形态分化顺利完成。低水平的GA3/ABA和IAA/CTK有利于花序的形成,ABA/CTK和ABA/IAA比值升高促进小花原基和小花萼片原基的分化, GA3/CTK、GA3/ABA和GA3/IAA比值升高促进花瓣原基、雄雌蕊原基发育。     

Chemical Factors Controlling Floral Bud Formation of Torenia Stem Segments Cultured in Vitro II. Effects of Growth Regulators

Correlative effects between growth regulators added to a mediumand different physiological states of explants on adventitiousbud formation and flowering were investigated using Toreniastem segments cultured in vitro. Indoleacetic acid stimulatedfloral bud formation and its development in explants taken fromreproductive plants. These stimulative effects were clearlyseen in explants taken from plants in which flower abscissionwas taking place, but insignificant when explants were preparedfrom younger materials. Abscisic acid acted in a reverse wayto auxin, greatly promoting floral bud initiation and floweringof originally vegetative explnts. Zeatin at a concentrationof 1 mg/liter inhibited floral bud formation, and at a low concentrationsit was generally ineffective. However, floral bud formationand flowering of explants taken either from basal parts of stemsor from 18- to 20-week-old plants were promoted by zeatin treatment.The action of gibberellic acid seemed rather indirect: at aconcentration of 0.01 mg/liter, it generally stimulated floralbud formation but at a concentration of 1 mg/liter, it was ofteninhibitory. (Received January 17, 1981; Accepted February 21, 1981)     

Clonal variation in floral stage timing in the common dandelion Taraxacum officinale (Asteraceae)

We investigated the hypothesis that dandelion clones (Taraxacum officinale Weber, sensu lato; Asteraceae) differ in their floral stage timing characteristics under a constant set of environmental conditions. To test this hypothesis, plants representing nine different dandelion clones (identified by DNA fingerprinting) were grown in groups of five (N = 45) in a growth chamber for a period of 8 mo, with chamber settings similar to environmental conditions at peak dandelion flowering time for their population sites. Five flowering phenology parameters were monitored daily for a total of 301 buds developing during this time: (1) time to bud; (2) time to full opening and inflorescence maturation (i.e., first anthesis); (3) time to re-closure of an inflorescence; (4) time to fruit (full re-opening of the inflorescence); and (5) total flowering time. Scape length at the appearance of a fully expanded infructescence was also measured for each individual. Significant differences in mean time to inflorescence, mean time to re-closure, mean time to fruit, and mean total flowering time were revealed among some dandelion clones (Kruskal-Wallis, P ≤ 0.0005). No differences in mean number of inflorescence buds per plant (P = 0.2217), mean time to bud (P = 0.2396), or mean scape length (P = 0.3688) were detected among the nine clones. These results suggest that differences in floral stage timing may in part involve varying genotypic environmental response characteristics and that these differences may have potential fitness effects. Further research is needed to determine if such clonal differences are observed under a broader range of uniform environmental conditions.