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Developmental and Structural Section

Horner, Harry T. [1], Healy, Rosaria [1], Thornburg, Robert W. [2].

Tobacco floral nectaries: I. Nectar secretion involves massive nectary starch degradation and beta-carotene synthesis.

The circular tobacco floral nectary is embedded in the base of the gynoecium wall, and appears lime green early in development (S2). As the gynoecium begins to mature (S4-S6), it changes to yellow (S6-S9), and then orange at anthesis (S12). Between S2 and S9 stages, the special nectary tissue shows increasing levels of starch, and by S9 this tissue is engorged with starch. Vibratome cross and longitudinal sections of the gynoecium and nectary, cut at 30 micrometers, depict these changes when viewed between crossed polarizers. Between S9 and S12 the completely starch-engorged nectary undergoes a dramatic transition from starch filled to beta-carotene filled, beginning at the innermost part of the nectary and progressing toward the nectary epidermis. This concomitant conversion is intimately associated with the plastids. Nectar production is directly related to starch degradation to mono- and disaccharides, and a host of other compounds, including proteins that are produced by the nectary cells. One protein identified as Nec 1 is involved in hydrogen peroxide formation that provides the nectar with oxidizing, antimicrobial protection. We believe that the development of the antioxidant beta-carotene in the nectary may serve to protect it from the oxidative environment surrounding it. These results suggest that the floral nectary is a very dynamic and biologically transitional system in which metabolically active plastids are a key organelle. Some of the pertinent biochemical activities accorded to this short period of dramatic nectary development will be discussed.


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1 - Iowa State University, Department Genetics, Development & Cell Biology, Bessey Microscopy Facility, 3A Bessey Hall, Ames, Iowa, 50011-1020, USA
2 - Iowa State University, Biochemistry, Biophysics and Molecular Biology, Ames, Iowa, 50011, USA

Keywords:
beta-carotene, floral nectary, starch, tobacco.

Presentation Type: Oral Paper
Session: 16-1
Location: 400/Hilton
Date: Monday, August 15th, 2005
Time: 1:30 PM
Abstract ID:183


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