About nectar and nectaries

NECTAR. Many flowering plants attract potential pollinators by offering a reward of floral nectar. The primary solutes found in most nectars are varying ratios of sucrose, glucose and fructose, which can range from as little a 8% (w/w) in some species to as high as 80% in others. This abundance of simple sugars has resulted in the general perception that nectar consists of little more than sugar-water; however, numerous studies indicate that it is actually a complex mixture of components. Additional compounds found in a variety of nectars include other sugars, all 20 standard amino acids, phenolics, alkaloids, flavonoids, terpenes, vitamins, organic acids, oils, free fatty acids, metal ions and proteins.

NECTARIES. An organ known as the floral nectary is responsible for producing the complex mixture of compounds found in nectar. Nectaries can occur in different areas of flowers, and often take on diverse forms in different species, even to the point of being used for taxonomic purposes. Nectaries undergo remarkable morphological and metabolic changes during the course of floral development. For example, it is known that pre-secretory nectaries in a number of species accumulate large amounts of starch, which is followed by a rapid degradation of amyloplast granules just prior to anthesis and nectar secretion. These sugars presumably serve as a source of nectar carbohydrate.

WHY STUDY NECTAR? Nearly 75% of all worldwide crops are dependent on animals to achieve efficient pollination. In addition, U.S. pollinator-dependent crops have been estimated to have an annual value of up to $15 billion. Many crop species are largely self-incompatible (not self-fertile) and almost entirely on animal pollinators to achieve full fecundity; poor pollinator visitation has been reported to reduce yields of certain species by up to 50%. Remarkably, the molecular events involved in the development of floral nectaries, as well as the synthesis and secretion of nectar, are poorly understood. Indeed, no genes have been shown to directly affect the de novo production or quality of floral nectar. Understanding the genetic and molecular mechanisms behind nectar production may allow targeted studies to improve overall pollination efficiency in mulitple crop species, as well as having the potential for greatly impacting apiculture.

For a more in-depth description of our understanding of nectar production in the Brassicaceae, we suggest the following review articles and video:

Kram BW, Carter CJ (2009) Arabidopsis thaliana as a model for functional nectary analysis. Sexual Plant Reproduction 22: 235-246

Bender et al (2012) Functional genomics of nectar production in the Brassicaceae. FLORA 207: 491-496