Developmental and Structural Section
Zhang, Xiaohui , Sawhney, Vipen , Davis, Arthur .
Multiple ontogenetic pathways lead to phloem development at the floral-nectary epidermis of disc florets of Echinacea purpurea (Asteraceae).
Each centrally-located disc floret on the capitulum of purple coneflower (Echinacea purpurea) possesses an annular nectary surrounding the style base, atop the inferior ovary. Studies of ten developmental stages ranging from very young buds to mature buds to florets beyond the fourth day of anthesis, have been investigated using light and fluorescence microscopy, plus scanning- and transmission-electron microscopy. Results confirm that phloem traces supply the nectariferous tissue in this species, without any xylem. Moreover, sieve tube elements (STEs) and companion cells (CCs) may be found just below or very rarely, actually within, the epidermis. Different ontogenetic pathways of phloem development at the epidermis vary in their frequency and complexity. These pathways have been described according to variations observed in the occurrence of anticlinal or periclinal cell divisions of STE-CC precursor cell(s), which eventually lead to mature STE and CCs that can also vary in their relative positions to one other. Floral nectaries exhibiting these novel pathways of phloem development at the epidermis serve as useful systems for investigations into in situ phloem ontogeny, and the factors governing phloem initiation and maturation in the complete absence of xylem.
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1 - Shaanxi Normal University, College of Life Sciences, Xi'an, 710062, China
2 - UNIVERSITY OF SASKATCHEWAN, Department Of Biology, 112 SCIENCE BLDG, SASKATOON, SK, S7N 5E2, Canada
3 - UNIVERSITY OF SASKATCHEWAN, Department Of Biology, 112 SCIENCE PLACE, SASKATOON, SK, S7N 5E2, Canada
sieve tube elements.
Presentation Type: Oral Paper:Papers for Sections
Location: Union D/Hyatt
Date: Monday, July 9th, 2012
Time: 1:45 PM