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Developmental and Structural Section

Horner, Harry T. [2], Healy, Rosaria [2], Thornburg, Robert W. [3], Palmer, Reid G. [1].

Developmental and histochemical differences between floral nectaries of tobacco (Nicotiana LxS8) and soybean (Glycine max L.).

Floral nectaries of ornamental tobacco and soybean were studied microscopically from their initiation to beyond their active secretory stage. The tobacco nectary forms a circular, peripheral mound in the basal wall of the gynoecium. The soybean nectary forms a discoid mound between the base of the gynoecium and staminal ring. Both differ greatly in their time of development and their manner of secretion. The tobacco nectary develops over several days and remains active for sometime post-anthesis. It is not innervated by any vasculature, and its special parenchyma becomes engorged with starch prior to secretion. During this time, the nectary color changes from green to orange as carotenoids accumulate. In contrast, soybean nectaries initiate, secrete, and degenerate over a one- to two-day period. Phloem fingers innervate the soybean nectary, and its special parenchyma contains relatively little starch accumulation prior to secretion. Histochemical localization of RNA in special parenchyma of both nectaries shows intense staining early in development, indicating highly metabolic cells. In both nectaries protein accumulation increases, and in the tobacco nectary starch engorges the special parenchyma prior to secretion. At the time of secretion these cells remain intact. During soybean nectary secretion the special parenchyma cells display apoptosis. Tobacco nectary cells remain intact for sometime after secretion before they eventually degenerate. Both nectaries secrete nectar through special epidermal stomates. In tobacco, the stomates occur in two vertical zones opposite each other, whereas in soybean they mainly occur on the nectary ridge and the side toward the gynoecium. A number of tobacco genes have been identified as being expressed during the life of its nectary. Some of them have a reasonably high level of homology in soybean. In situ hybridization is being used to determine spatial and temporal patterns of expression of these genes in the nectaries of both taxa.

1 - Iowa State University, USDA ARS CICGR and Agronomy, Ames, Iowa, 50011, USA
2 - Iowa State University, Genetics, Development and Cell Biology, Ames, Iowa, 50011, USA
3 - Iowa State University, Biochemistry, Biophysics and Molecular Biology, Ames, Iowa, 50011, USA


Presentation Type: Paper
Session: 52-1
Location: Alpine A (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 1:00 PM
Abstract ID:193

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