Many plants produce a rich floral nectar to entice animals to their flowers. This attraction of bats, birds, or insects benefits the plants by increasing cross-pollination between different individuals and by improving seed production. The nectar in flowers is produced by a specialized floral organ termed the nectary gland. The nectaries of ornamental tobacco are simple in structure and of extremely large size. Further, ornamental tobacco produces hundreds of flowers per plant, so isolation of nectary tissues for gene cloning and biochemical analyses is greatly facilitated. Thus, ornamental tobacco is the ideal system to study nectary development and function. Understanding the mechanisms of nectary function in tobacco will facilitate interpretation of nectary function in other plant species that are more difficult to study because of small nectary size and multiplicity of nectary types. This project will utilize ornamental tobacco to understand the regulation of nectar production, which is a critical element of flower function and angiosperm biology.
While it is clear that nectar is rich in sugars, the metabolic source of the sugars in nectar remains unknown. This project hypothesizes that starch deposited in the nectary gland during development is degraded at floral maturity to produce sugars that flow into nectar. The first goal of the project is to identify specific structural changes in nectary starch that occur during the transition from developing to secreting nectaries. This will provide insight into the biochemical processes required for nectary starch formation and usage. The second goal is to quantify the flow of transported sugars both into starch and directly into nectar. This will determine whether starch is the sole source of nectar sugars. Third, this project will identify starch metabolic genes that are expressed at various stages in the nectary gland and will finally identify proteins that are actively involved in starch biosynthesis and catabolism in nectaries. Identification of these proteins and their genes will provide potential targets for manipulation to improve pollinator attraction. Together, the results of this project will permit full evaluation of the role that starch plays in nectar secretion, and provide insight into the regulatory mechanisms that underlie starch deposition and catabolism during nectary development.
Because nectar sugars are one of the most important factors that attract insect pollinators to flowers and because increased pollinator visitation results in greater pollination and higher seed yields, understanding the production of sugars in nectar will provide new targets for genetic manipulation to increase the agricultural yield of many fruits, nuts, berries, vegetables, forages, fiber and oilseed crops as well as flowers. Such increases in food, fiber, and floral production will be required in the coming decades as the world's population approaches 10 billion. Furthermore, these studies will determine how nectary starch metabolism is co-regulated with flower development to allow optimum timing and flux of carbohydrate into nectar, a process of enormous adaptive significance to many flowering plant species.
