Floral Bud Formation Research Articles

Isoperoxidases in Epidermal Layers of Tobacco and Changes during Organ Formation in vitro

AbstractThe content and pattern of soluble isoperoxidases were determined in epidermal explants taken from different internodes of tobacco plants in the vegetative and floral states. There were qualitative and quantitative differences in the isoperoxidases, with a decrease in content and fewer bands being observed acropetally, i.e., in going from the base of the stem towards the apex. Epidermal explants from floral branches were grown in in vitro culture, with various media moditications, to form de novo floral or vegetative buds, roots or callus. Changes in soluble isoperoxidases were followed electrophoretically in relation to these varying morphogenetic pathways. In each of them, the number of bands increased on both the anodic and cathodic sides with time in culture. Compared to each other these four morphogenetic programmes were different in their peroxidase zymograms, mainly through varying kinetics in the development of activity of the isoenzymes. The changes observed during root and vegetative bud formation agree with previously published data, and the changes during floral bud formation agree with those observed in vivo.

In Vitro Formation and Development of Floral Buds on Tobacco Stem Explants

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(-7)m) but did not affect floral development. When supplied with high 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.

Flowering response of &lt;italic&gt;Lemna perpusilla&lt;/italic&gt; 6746 to a single dark period

Lemna perpusilla 6746 is induced to flower by a single long dark period, but the floral buds once formed disappear after several days under 5000 lux/25°C. Such regression of floral buds is prevented by lowering the light intensity or temperature, but if the light intensity and/or temperature are lowered beyond critical levels, new floral buds form. If the cultures are subjected to 100 lux/20°C, neither regression nor new formation of floral buds occurs. Under such conditions, the number of floral fronds reaches maximum about 6 days after the inductive dark period and reamins unchanged for at least 10 days, while the percentage of floral fronds rapidly decreases thereafter, owing to the dilution by newly developed vegetative fronds. When the cultures are subjected to various lengths of a single dark period (25°C) followed by 100 lux/20°C, flowering responses represented by the number of floral fronds per flask show rhythmic fluctuation with a cycle length of about 24 hr. Similar rhythmic response is observed when a brief light interruption is given at different times during a single long dark period.

Regulation of organogenesis in small explants of superficial tissue of Nicotiana tabacum L.

Small explants composed of 3-6 layers of epidermal and subepidermal cells excised from floral branches of Nicotiana tabacum are capable of de novo organogenesis. Continuous mitoses without organogenesis, or mitoses followed by the formation of floral buds, vegetative buds or roots can be obtained by varying the auxin-cytokinin-sucrose ratio in the medium. The physiological stage of the floral branches, and light and darkness had also an influence on the de novo organogenesis. Best floral-bud formation was obtained when explants were taken from plants in which the terminal bud was in the green-fruit stage, and were cultured on a medium with indole-3-acetic acid and kinetin both at 10(-6) M and with 3% sucrose, in the light. For differentiation of vegetative buds, the optimal auxin/cytokinin ratio was one tenth of that for floral-bud formation, while the sucrose concentration was the same. Optimal conditions for root formation were: explants from plants in which the terminal bud carried a mature fruit; 10(-7) M kinetin, 10(-5) M indole-3-butyric acid, and 1% sucrose in the medium; and culture in darkness. The optimal medium for callus formation contained 5×10(-6)M 2,4-dichlorophenoxyacetic acid, 10(-7) M kinetin and 3% sucrose.

Flower Formation in Excised Tobacco Stem Segments; II. Reversible Removal of IAA Inhibition by RNA Base Analogues

The RNA base analogues, 2-thiouracil, 6-azauracil and 8-azaguanine incorporated singly into the medium, increased the number of floral buds in excised stem segments of Nicotiana tabacum variety Wisconsin No. 38 cultured in vitro. Combined treatments with 2 and 3 base analogues were even more effective. The effects were prevented by the corresponding natural counterparts, uracil, uridine, and guanosine respectively. These nucleic acid constituents added to cultures without base analogues did not affect the number of floral buds formed. In stem segments from the lower internodes treatments with the analogues effected a transition from vegetative to floral bud formation, thus in a sense removing the floral gradient as defined by Chouard and Aghion.The inhibition of flower bud formation ordinarily achieved even with low concentrations of indole-3-acetic acid (IAA) was counteracted by low concentrations of 2-thiouracil, 6-azauracil and 8-azaguanine. Reversal to vegetative bud formation was not achieved even with high IAA concentrations in the presence of the base analogues.Stem segments excised from young, vegetative tobacco plants never formed floral buds in vitro. Thus, the inhibiting effect of IAA and the promoting effect of base analogues seem to be on the expression and not on the induction of flowering. The regulatory action of the IAA and base analogues in flower bud formation is tentatively ascribed to their differential effects on RNA synthesis.

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

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.