Nectar: plant interface for complex interaction with biotic environment

Angiosperms’ nectar, fl oral and extrafl oral, is a valuable energetic alimentary resource for a large variety of animals from insects to small mammals, birds, marsupials and reptiles. It frequently mediates mutualistic relationships between the two partners. In recent years it was clearly demonstrated that this relationships actually often involves other partners: nectar dwelling micro-organisms. Yeasts and bacteria may alter considerably the nectar composition and can be the causal agents of some plant diseases. Nectar has biochemical defences to inhibit micro-organism proliferation, i.e., a heterogeneous arsenal of proteins with anti-fungal and anti-microbial activity that has just been discovered in the last years. Nonetheless yeasts are almost ubiquitous in nectar and their direct and indirect interactions with nectar foragers are almost unknown as well as the consequences for plant reproduction. A recent advance in nectar biology was the recognition of some secondary compounds, especially alkaloids and non-protein amino acids, in modulating the foraging behaviour of nectar feeders through several effects on insect neurophysiology. All these studies demonstrate that nectar has a wider range of more complex interactions than previously thought.