Floral Initiation and Vascular Development in Lateral Buds of Kalanchoe Raymond Kessler1 and Stan P

HORTSCIENCE 27(2):144-146. 1992. Floral Initiation and Vascular Development in Lateral Buds of Kalanchoe Raymond Kessler1 and Stan P. Myers2 Department of Horticulture, Mississippi State University, Mississippi State, MS 39762 Additional index words . photoperiod, Kalanchoe blossfeldiana Fig. 1. Lateral spice form the third node of ‘Gelbe Melody’ after 21. short days. Abstract.Early development of lateral buds is demonstrated as one of the evocation events in Kalanchoes (Kalanchoe blossfeldiana Poelln.). Lateral buds of ‘Cactus Candy’, ‘Gelbe Melody’, and ‘Jupiter’ that were»5»5 mm long or less showed no signs of a change to the reproductive state after 21 short days. However, larger lateral buds for ‘Jupiter’ did show floral initiation while those of ‘Cactus Candy’ and ‘Gelbe Melody’ did not. Studies of the vascular arrangement indicate the presence of four dorsal and four ventral bundles connecting leaves to the stem. Vascular connections to lateral buds arise from vascular cambium but do not appear to connect to any of the bundles that supply leaves. Morphological events occurring in the shoot same orthostichery, indicating the role of a tip of K. blossfeldian a during floral initiation flowering inhibitor (Harder et al., 1949). and development have previously been de- Schawbe (1985) has presented convincing scribed for several cultivars (Fredericq, 1960; evidence for the involvement of a flowering Roodenburg, 1939; Stein and Stein, 1960). inhibitor. Fig. 2. Lateral spice form the third node of ‘Ju- Coincident with this process, active devel- For commercial forcing, flowering lateral piter’ after 21 short days. opment of previously formed lateral buds just shoots are often equal to if not more impor- below the apex is resumed. Depending on tant than the terminal inflorescence in terms the number of short days received by plants, of overall flower counts. However, the ex- many of these lateral buds will initiate flower tent of lateral shoot development varies con- buds and contribute to the overall floral can- siderably between cultivars. Securing an opy (Roodenburg, 1939). understanding of factors that control flow- The uppermost set of maturing leaves is ering of lateral buds would prove beneficial the most sensitive in the perception of pho- in determining how cultivars vary in this re- toperiod by kalanchoes (Runger, 1968). In- spect. An important first step is to determine duction of the terminal apex appears to the anatomy at the leaf axil and whether the precede that of lateral branches even when a extent of vascular development is associated single induced leaf subtends an axillary shoot. with lateral bud development and initiation. Work on translocation of the flowering stim- The purpose of this study was to determine ulus has concentrated on movement of the the arrangement of vascular tissues to leaves hypothetical succulence-inducing factor and lateral buds in kalanchoe and its involve- ‘Metaplasin’ (Harder and Gummer, 1944) or ment in floral initiation of lateral buds. a photomorphogenic stimulus (Stein and Stein, Sixty-three cuttings each of ‘Cactus Candy’, Fig. 3. Cross section of a kalanchoe stem about 1960) that appears to move to the apex in ‘Gelbe Melody’, and ‘Jupiter’ were taken from one-half the distance between the fourth and fifth nodes; P, phloem; X, xylem; D4, dorsal the same orthostichery above a single in- stock plants, directly stuck in 9 × 10-cm bundles to leaves at the fourth node; D3, dorsal duced leaf, but with some lateral spread. The (height x width) pots containing medium [1 bundles to leaves at the third node; V1-V2, ven- same pathway may be involved in the move- sphagnum peat : 1 soil : 1 perlite (by vol- tral bundles supplying opposite leaf pairs at the ment of the flowering stimulus. Harder and ume)], and placed under intermittent mist for fourth and third nodes. Witsch (1940) proposed that the floral stim- 2 weeks. The stock plants and cuttings were ulus is transmitted along vascular strands to maintained under long days using 50 the apex and a functional phloem is neces- µmol·m–2·s–1 incandescent lighting from 10 sary. However, when a leaf under long days PM to 2 AM. After propagation, each plant was interposed between an induced leaf and was treated with 0.8 g slow-release fertilizer the apical meristem, flowering was delayed (14N-6.2P-11.6K, Osmocote, Sierra and the inhibitory effect was restricted to the Chemical, Milpitas, Calif.) and 0.4 g aldi- carb (Temik; Union Carbide, Research Tri- Received for publication 3 June 1991. Accepted angle Park, N.C.). Plants were then placed for publication 20 Sept. 1991. This paper is a por- in growth rooms with a 9-h photoperiod at a tion of a thesis submitted by R.K. in parital ful- constant 21C. Illumination was provided by fillment of MS degree requirements. The cost of fluorescent (40 W, 120 V) and incandescent publishing this paper was defrayed in part by the lamps with a light intensity of 660 payment of page charges. Under postal regula- µmol·m–2·s–1 on the perimeter and 876 tions, this paper therefore must be hereby marked –2 –1 advertisemen t solely to indicate this fact. µmol·m ·s at the center. Plants were 1 Present address: Dept. of Horticulture, Iowa State watered when the soil appeared dry. Fig. 4. Cross section of the stem about one-fourth University, Ames, IA 50011. For 21 days after the beginning of short of the way below node 4. D, dorsal bundle to 2 Present address: Agronomy Dept., 605 Bradfield days, three plants of each cultivar were re- a leaf at the fourth node; V, ventral bundles to Hall, Cornell University, Ithaca, NY 14853. moved and tissue samples taken of the up- a leaf at the fourth node. 144 HORTSCIENCE, VOL. 27(2), FEBRUARY 1992 Fig. 5. A cross section just below the fourth node. D, dorsal bundle to a leaf at the fourth node; LB, vascular bundles to the lateral bud at the fourth node. permost three nodes just below the apex. The first node was in the most acropetal position and possessed leaves recently unfolded from the apex while the third had leaves that were essentially fully expanded. Node sections were Fig. 6. Proposed three-dimensional arrangement Fig. 7. Proposed three-dimensional arrangement excised »5 mm above and below the node of dorsal bundles in the kalanchoe stem. D1, of ventral bundles in the kalanchoe stem. V1- line and leaves were removed with 3 to 5 dorsal bundles supplying leaves in one ortho- V2, ventral bundles supplying the same leaf in mm of petiole remaining. Each section was stichery; D2, dorsal bundles supplying leaves one orthostichery but the proximal half of op- then cut in half vertically, perpendicular to in the orthostichery above. posite leaves in the orthostichery above. the node line. Also, samples of node and internode regions were taken from vegetative stock plants for a study of the vascular ar- cultivars as long as buds were <5 mm long. bundle pair will supply opposite leaves at the rangement. Samples were cut 5 mm above A typical vegetative lateral bud for ‘Gelbe third node. As the fourth node is approached the fourth node and 5 mm below the fifth Melody’ after 21 short days is shown in Fig. acropetally, leaf traces begin to diverge from node to assure sampling a region with fully 1. Absence of floral expression was found bundles D and V below the node (Fig. 4). developed vascular tissue but small enough even though all the buds for ‘Jupiter’ and The larger central trace (D) will connect the to be managed microscopically. Leaves were buds at the third node for ‘Gelbe Melody’ dorsal bundle of the leaf while the two out- removed with 3 to 5 mm of petiole remaining had differentiated procambial strands. A few side traces (V) will connect the ventral bun- on the stem. samples taken 19, 20, and 21 days after the dles. Figure 5 shows a section just below the All tissues were preserved with a killing beginning of short days were larger than 5 junction of petiole and stem. The dorsal bun- and fixing solution [18 ethanol : 1 glacial mm, had differentiated procambial strands, dle to the leaf (D) is evident while an out- acetic acid : 1 formalin (by volume)]. A bu- and possessed expanding leaves. None of growth from the vascular cambium (LB) that tyl alcohol series was used for dehydration these buds for ‘Cactus Candy’ or ‘Gelbe will connect to the lateral bud has begun. (Jensen, 1962), followed by embedding with Melody’ showed signs of a change to the We propose a schematic arrangement of paraffin (melting point 56.4C), sectioned to floral state. However, larger buds for ‘Ju- vascular strands in the opposite and decus- 10-µm-thick ribbons and mounting on glass piter’ at nodes 3, 2, and 3 after 19, 20, and sate orthostichery common to kalanchoe (Figs. slides using Haupt’s adhesive (Johansen, 21 short days, respectively, did show a change 6 and 7). There were four dorsal bundles; 1940). Staining of slides was accomplished to the floral state (Fig. 2). Flower initiation, bundle pairs D1 supply leaves in one or- using a safranin/fast-green system. therefore, does not seem to be correlated with thostichery while bundle pairs D2 supply Sections of lateral buds for all three cul- vascular development to lateral buds. How- leaves in the orthostichery above (Fig. 6). tivars exhibited an overall increase in size ever, we could not determine when these Four ventral bundles supplied leaves at a node, and degree of organelle differentiation bas- procambial strands became functional in two bundles per leaf (Fig. 7). One bundle ipetal from the apex; ‘Jupiter’ exhibited the translocation.

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