Rachis vascularization and leaflet venation in developing leaves of Fraxinus pennsylvanica

Dickson

1986

Physiologia Plantarum

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Long‐distance transport in plants requires precise knowledge of vascular pathways, and these pathways differ among species. This study examines the 14C translocation pathways in honeylocust (Gleditsia triacanthos L.) and green ash (Fraxinus pennsylvanica Marsh.), species with compound leaves, and compares them with those of cottonwood (Populus deltoides Bartr. ex Marsh.), a species with simple leaves. The stem vasculature of honeylocust conforms to a 2/5 helical phyllotaxy and that of green ash to a decussate phyllotaxy. The plastochron is relatively long in both species – 2.5+ days in honeylocust and 4.5+ days in green ash. Consequently, the transition from upward to downward translocation from mature source leaves is abrupt and occurs close to the apex. Export of 14C from localized treatment positions within a leaf was found to vary both quantitatively and spatially. To determine export patterns, 14CO2 was administered to either individual leaflets of once‐pinnate or pinnae of bipinnate leaves of honeylocust, and to either individual veins of simple or leaflets of compound leaves of green ash. Transections of either the petiole or rachis base were then examined for 14C by micro‐autoradiography. In all cases, as treatment positions advanced acropetally in the leaves, the bundles translocating 14C were situated more dorsally in the basal petiole and rachis vasculatures. 14C was confined to the right side of the vasculature when structures on the right side of a leaf were treated. Compound leaves of both species mature acropetally. Thus, mature basal pinnae of honeylocust and basal leaflets of green ash translocate acropetally to younger leaf parts that are still rapidly expanding. All translocation pathways, both in the stem and leaf, conformed with vascular organization previously determined by anatomical analyses.

mentioning

confidence: 52%

Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

“…2G). The extreme dorsal bundles of the semicircular arc were unlabeled when pinna 4 was treated because these bundles serve the terminal appendage (Larson 1984a).…”

Section: Export Pathways Within Mature Leavesmentioning

confidence: 99%

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¹⁴C Translocation pathways in honeylocust and green ash: Woody plants with complex leaf forms

Dickson

1986

Physiologia Plantarum

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Vascularization of a Multilacunar Species: Polyscias Quilfoylei (Araliaceae) I. The Stem

1986

American J of Botany

The odd‐pinnate leaves of Polyscias quilfoylei have a sheathing leaf base that completely encircles the stem. At each node, many traces depart the vascular cylinder and traverse an obliquely upward course through the leaf base before aggregating in the rachis. Lateral traces diverge from parent traces in the stem vasculature at variable times relative to the leaf they serve, from variable positions in the vascular cylinder and from parent traces of variable ages. The stem vasculature is formed by the coalescing of leaf traces from as many as five leaves. All bundles departing the vascular cylinder at a node to serve a leaf are true leaf traces originating independently in the stem. Leaf traces develop acropetally from their positions of origin on parent traces. Primordial leaves are first served by the median trace and later by lateral traces. Many traces were recognized in the internodes subtending embryonic leaves, but they could not be related either to a specific leaf or to a specific position within a leaf. Because these traces had not yet achieved contact with a primordial leaf site, they were assumed to be in the process of developing acropetally at the time of sampling. Observations suggest that the multiple traces in this species might perform a similar function of integrating the vascular cylinder that subsidiary bundles perform in certain uni‐ and trilacunar species.

Vascularization of a Multilacunar Species: Polyscias Quilfoylei (Araliaceae) Ii. The Leaf Base and Rachis

1986

American J of Botany

Multiple leaf traces depart the stem vasculature at a node to form the rachis vasculature of the odd‐pinnate leaf of Polyscias quilfoylei. The median (M) trace departs the vascular cylinder directly, but the converging lateral traces follow acropetal, oblique pathways through the en‐sheathing leaf base. The leaf traces are partitioned into sub‐bundles within the leaf base, and some sub‐bundles merge with others to form composite bundles. Most mergers in the leaf base occur among sub‐bundles of adaxial and lateral traces; cross‐overs of bundles from opposite sides of the M‐trace are infrequent. The rachis vasculature distal to the leaf base is similar in structure and appearance to that of the stem. Vascularization of the leaflet pair at each rachis node involves partitioning and reaggregating of the trace sub‐bundles. However, these processes are more extreme and bundle cross‐overs are more frequent at rachis nodes than at the leaf base. At the more distal rachis nodes, lateral traces situated nearer the M‐trace contribute to leaflet vascularization. The M‐trace contributes sparingly to vascularization of lateral leaflets; it forms that part of the midvein that extends to the extreme lamina tip of the terminal leaflet.