Análisis e interpretación de resultados de las encuestas a los jefes

Acropetal dissection of bud clusters on the elongated cluster stem revealed a hierarchical arrangement (Figure 5.19) which resembled that observed in Experiment Two with non-GA3 treated plants (Section 5.4.3.1). The elongated cluster stem

however, made it visually easier to identify the relationship between buds in the cluster when treated with GA3. While the earliest initiated buds were present individually on

the cluster stem, smaller crown buds were present towards the apex as a single unit covered in scales (Figure 5.19A-C). As each bud scale was removed on this unit, two buds were visible (Figure 5.19C, D & E). One was a separate and well-developed crown bud, and the second comprised a bud containing more buds and scale leaves. It was concluded therefore that the apical meristem of the cluster was located within the latter complex.

The comparative maturity and order of arrangement of crown buds within a cluster was determined by the location of scale leaves and buds on the elongated stem, i.e. the buds at the proximal end were considered most mature. Buds were arranged in a spiral pattern along the stem axis of the cluster (first bud initial which developed adventitiously), with a single bud developing at each node at an approximate 90º angle of phyllotaxy (Figure 5.19F). Floral shoots of gentians present an opposite leaf arrangement at a node, and an opposite decussate phyllotaxy (Bell and Bryan, 2008), hence at each node, two axillary buds each of similar level of development were located (Figure 5.2). In contrast, only one axillary bud at a node was stimulated to differentiate during the development of crown buds in a cluster (Figure 5.19). Hence arrangement of two equally sized axillary buds at a node was not observed in sequential sections

(Figure 5.11, Figure 5.16 & Figure 5.17). These individual buds developed sequentially as a spiral from the proximal to distal end of the cluster stem (Figure 5.19). Each bud was positioned at an approximate 90º angle to the preceding bud. This progressive development of buds from the apex of the cluster stem, resulted in the presence of buds of different sizes and stages at any single point in time. Hence gentian plants possess two different types of phyllotaxy; one within the bud cluster and the other on floral shoots. Such variation in phyllotaxy was also noted in other plants (Bell and Bryan, 2008), e.g. Wollemia nobilis (Tomlinson and Murch, 2009) and Populus deltoides (Larson, 1975), and in some species such differences denotes a change from vegetative to reproductive phases (Poethig, 1990; Poethig, 2003). In contrast to changes in phyllotaxis within the same shoot observed in these species however, the phyllotactic arrangements within clusters and floral shoots appear to be predetermined in gentians. On the other hand, the abortion of the axillary meristem can occur even when bud primordia are at the very early stages of their formation (Bell and Bryan, 2008). If this occurred within the bud cluster, the phyllotaxy would be the same as that in the floral shoot. This latter scenario is however is considered unlikely, as the bud cluster appears consistent in developing one bud per node. While this angle of investigation was inconclusive, and was not an objective of the current study, the reason for differences in phyllotaxis within the crown bud cluster and floral shoot will be of interest for study further.

control GA A B D C I H G F E

Figure 5.18 Plants of ‘03/04-114’ following treatment application of either, (A) control or (B) foliar GA3, after seven months. (C) control and treated plants after 10 months (7/12/09). (D) Compact bud clusters (red circle) in control treated plant. (E-I) Elongated stem with separated bud cluster, (E & F) at the distal end (red circle and white arrows), (F & G) with scale leaves (white arrows) and, (H & I) buds/shoots arising at the distal end (white arrows).

Figure 5.19 Progressive dissection of a bud cluster on an elongated stem of ‘03/04- 114’ following foliar application of GA3; (A) non-dissected with most distal- positioned crown bud/shoot (1) emerging, (B) crown buds 2-4 revealed, (C-E) crown buds 4-6 revealed. (F) Diagrammatic illustration of arrangement of buds within the cluster (cross-sectional view); earliest formed axillary bud (1) to the last (5). More buds, including the apical bud of the stem cluster, were present within crown bud 5.

A D C B X X X X vr p c c

Figure 5.20 Transverse section of (A & B) floral shoot and (C & D) storage root of ‘Diva’ at increasing magnification; (A) section at the base of the shoot illustrating vascular ring, (B) magnified image illustrating lignified cells, (C) full section of the storage root indicating xylem vessels in the centre, and magnified in (D). Orange and red fluorescence indicates the xylem vessels. c - cortex, p -pith, vr - vascular ring, x – xylem.

A E D C B F G cb X X X vr X p 250 μm 250 μm 250 μm 250 μm 250 μm

Figure 5.21 Transverse sections of the elongated cluster stem following treatment with GA3 and control ‘Diva’; (A) proximal end of the elongated stem with the centre magnified in (B) to illustrate the vascular ring similar to stem, indicating position of further magnification presented in (C), indicating xylem vessels. (D) Distal end of the elongated stem indicating position of magnified image presented within (E), indicating the arrangement of xylem vessels and, (F) possible initiation of a bud. (G) Arrangement of xylem vessels at base of the cluster in control treatment. Orange and red fluorescence indicates the xylem vessels. cb - crown bud, p - pith, vr - vascular ring, x – xylem.

Transition zone = vertical rhizome

Apical bud =adventitious bud

Crown buds= axillary buds (Opposite decussate phyl- lotaxy with the opposite bud missing)

Floral shoot emerging from a crown bud

(axillary buds in opposite decus- sate phyllotaxy) 90º Cluster stem Remaining's of last years shoot Crown bud clusters Arrangement of Crown bud clusters on the transi- tion zone

Arrangement of buds with- in a single cluster follow- ing elongation of the clus- ter stem

Figure 5.22 Schematic diagram illustrating the arrangement of crown bud clusters on the transition zone, and hierarchical arrangement of buds within the cluster, as apparent following elongation of the compressed cluster stem (i.e. when GA treated).