Nectary structure and function in relation to angiosperm reproductive success: Developmental and evolutionary perspectives

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Nectaries are plant glands that secrete nectar, a solution rich in carbohydrates but also containing other solutes at lower concentrations. Despite being small and cryptic, nectaries are extremely important ecologically for fostering beneficial interactions between plants and organisms in their environment, both in Canada and internationally. Floral nectaries typically reside in strategic locations leading to the visitor's contact of anthers (pollen-producing organs) and stigmas (pollen-receiving sites, where pollination occurs). Thus, mutualistic relationships occur when flower-visiting animals such as bees and other insects gather nectar as an important food source from floral nectaries, leading eventually to seed and fruit set. Major parts of our daily diets can be attributed directly to pollination by insects, and hence to nectaries. Some flower bases even possess spurs, tubular extensions that conceal nectar available only to animals with sufficient tongue length to attain it. And for an extremely beneficial species, the honey bee (Apis mellifera), nectar is the precursor of a highly valued commodity in Canada and worldwide - honey.***The study of nectaries requires microscopy. Each nectary typically has three structural components: an epidermis (a layer of covering cells), several subepidermal layers of glandular cells, plus a vascular supply (plumbing). We shall investigate these three components by searching for mechanisms of cellular growth and development leading to new knowledge about nectary form and function, in an evolutionary context. We shall study I) nectar-yielding floral spurs which are unique by the formation of a bifurcation (like the letter Y) at their tip. Interestingly, hummingbirds and certain insects have bifurcated tongues. Using light, confocal, and scanning-electron microscopy, we shall magnify the cells of spurs throughout their development, to determine how these Y-branched spurs develop. Also, use of a dental impression material applied at regular intervals to the same, living spur will even allow us to trace individual files of epidermal cells as they divide and elongate; II) the sugar-conducting form of plant plumbing called phloem will be examined in a variety of floral nectaries in which we have already discovered differences in companion cells, special cells that unload arriving sugar to be secreted externally as nectar. Also, we shall survey floral nectaries of a very large family, the Asteraceae, to expand our discovery of phloem that forms in the epidermis, a unique occurrence in plants; and III) strange sterile flowers called "agamous type" mutants from several species which form nectaries - sometimes still functional - amidst their petals and sepals. We shall compare nectary structure and nectar production in these mutant and normal plants, to learn more about the origin of floral nectaries still present when pollination cannot even occur.**