Advances in metabolism and regulation of floral scent.

Floral scent is a complex mixture of low molecular weight volatile compounds, which gives the flower its unique fragrance. Plant scent is mainly composed of terpenoids, benzenoids/phenylpropanoids, fatty acid derivatives, and compounds containing nitrogen or sulfur. These volatile compounds act as attractants to pollinators that provide the plant with reproductive benefit. While in plant cells, these compounds could be toxic to those organisms that ingest the plant. Scent substances from the air in the vicinity of the flower are sampled, providing a more realistic image of the volatile profile. Most of the floral scent compounds are emitted from petal epidermal cells or highly specialized secretory structures such as scent glands. The composition of floral scents is changing during the flower lifespan in relation to flower stage and pollination status, endogenous rhythms, environmental conditions. Most floral scent compounds are produced by only a few major biochemical pathways, such as isoprenoid, phenylpropanoid/benzenoid and fatty acid pathways. Traditional biochemical method, homology cloning technology, and genomics approach have been used to clone genes involved in floral scent production. Recent progress in the molecular biology of floral scents offers tools for modification of fragrance in flowering plants, including introducing new genes, regulating the expression of endogenous genes or transcription factors. But many difficulties remain to be overcome.