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Developmental and Structural Section

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

Tobacco floral nectaries: II. Roles of plastids in nectar production and nectary protection.

At stage 2 (S2) of flower development, the nectary is a well-differentiated gland comprised solely of parenchyma and bounded by a single epidermis. Vascular bundles occur interior to the nectary tissue near gynoecium locules, never traversing it. During S2 and S4, young parenchyma amyloplasts divide to increase their number per cell. Each amyloplast contains a few starch grains and some electron-dense lamellae. Between S4 and S9, amyloplasts become larger and fill with multiple starch grains so each cell appears engorged with starch. Change in nectary color, from lime green to yellow-orange between S2 and S9, is attributed to further synthesis and conversion of carotenoids associated with the plastids. A major transition associated with plastids occurs between S9 and S12. As starch is degraded, it leaves space for electron-dense spherical bodies to form in the stroma. Early on, these spherical bodies display small acicular crystals protruding from them. As more starch is degraded, these spherical bodies increase in number, as do acicular crystals. We believe the crystals are composed of beta-carotene. We call these plastids amylochromoplasts because they simultaneously contain both starch and beta-carotene. By S12 most, but not all, plastids are devoid of starch and they are called chromoplasts which contain many, large electron-dense spherical bodies and large beta-carotene crystals. This extraordinary conversion of starch to sugars and the buildup of beta-carotene serve to provide copious amounts of attractive nectar, and a protective barrier for the developing gynoecium. Both biochemical and molecular data indicate that this is a unique process.


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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:
plastids.

Presentation Type: Oral Paper
Session: 16-2
Location: 400/Hilton
Date: Monday, August 15th, 2005
Time: 1:45 PM
Abstract ID:186


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