Abstract Detail

Development and Structure

St. Clair, Mallory K. [1], Smith, Annika [2], Castillo, Raiza [1], John, Grace [1], Soltis, Douglas E. [1], Soltis, Pamela [2].

Cellular dynamics of nectar spur elongation in three species of Chilean nasturtiums (Tropaeolum sect. Chilensia).

Pollinator-mediated selection has driven much of the morphological evolution of flowers, and floral nectar spurs have evolved repeatedly in both monocots and eudicots. The repeated evolution of floral nectar spurs raises questions at the intersection of plant evolution, ecology, and development. Tropaeolaceae, a family of herbaceous vines native to Central and South America comprising the single genus, Tropaeolum, has floral nectar spurs that expand late in floral development and have significant interspecific variation in length (1mm-7cm). However, from a cellular perspective, it is unclear how spur length varies between species—is this variation due to more cellular divisions, cell expansion, or a combination of both? Additionally, Tropaeolum spurs are unusual, as they develop from the floral receptacle, in contrast to nectar spurs from most other clades, which develop from petals. The cellular dynamics of petal-derived spurs have been examined in several clades (e.g., Aquilegia, Linaria, Dactylorrhiza), with various combinations of cell elongation versus division observed. We hypothesized that the receptacle-derived spurs of Tropaeolum would vary in length primarily due to increased cell divisions, and that cell elongation alone would be unlikely to account for spur length variation, as it does in some petal spurs. Our goal was to determine whether nectar spur elongation, and thus variation in spur length, occur primarily through cell division, cell expansion (anisotropy), or a combination of these two mechanisms in three species of Chilean nasturtiums (Tropaeolum sect. Chilensia): T. azureum, T. brachyceras, and T. tricolor. These three species are an ideal study system because, while they are closely related, sympatric in parts of their ranges in central Chile, and have similar phenologies, they also have variability in floral morphology that is associated with different pollination syndromes. To determine the cellular basis for Tropaeolum nectar spur length variability, we analyzed spur length, the number of epidermal cells along the length of the spur, and cell size using whole mount slides of flowers collected and fixed in the field.

1 - University of Florida, Gainesville, FL, 32611, USA
2 - University Of Florida, Florida Museum Of Natural History, PO Box 117800, Gainesville, FL, 32611, United States
3 - University Of Florida, Florida Museum Of Natural History, PO Box 117800, Gainesville, FL, 32611, United States

Keywords:
nectar spur development
Tropaeolum
anisotropy
cell division.

Presentation Type: Poster
Session: P1, Development and Structure Posters
Location: Virtual/Virtual
Date: Monday, July 19th, 2021
Time: 5:00 PM(EDT)
Number: P1DS014
Abstract ID:914
Candidate for Awards:Developmental and Structural Section best poster