β-Ocimene, a Key Floral and Foliar Volatile Involved in Multiple Interactions between Plants and Other Organisms

Abstract

β-Ocimene is a very common plant volatile released in important amounts from the leaves and flowers of many plant species. This acyclic monoterpene can play several biological functions in plants, by potentially affecting floral visitors and also by mediating defensive responses to herbivory. The ubiquity and high relative abundance of β-ocimene in the floral scents of species from most plant families and from different pollination syndromes (ranging from generalism to specialism) strongly suggest that this terpenoid may play an important role in the attraction of pollinators to flowers. We compiled abundant evidence from published studies that supports β-ocimene as a generalist attractant of a wide spectrum of pollinators. We found no studies testing behavioural responses of pollinators to β-ocimene, that could directly demonstrate or deny the function of β-ocimene in pollinator attraction; but several case studies support that the emissions of β-ocimene in flowers of different species follow marked temporal and spatial patterns of emission, which are typical from floral volatile organic compound (VOC) emissions that are involved in pollinator attraction. Furthermore, important β-ocimene emissions are induced from vegetative plant tissues after herbivory in many species, which have relevant functions in the establishment of tritrophic interactions. We thus conclude that β-ocimene is a key plant volatile with multiple relevant functions in plants, depending on the organ and the time of emission. Experimental behavioural studies on pure β-ocimene conducted with pollinating insects will be necessary to prove the assumptions made here.

Keywords: (E)-β-ocimene; dominant VOCs; floral scent; trans-β-ocimene.

Figure 1

Chemical structure of the two β-ocimene stereoisomers, cis- and trans-β-ocimene (also referred to as (Z)- and (E)-β-ocimene, respectively).

Figure 2

Occurrence and abundance of β-ocimene in floral scents. Bar charts showing (a) the percentage of plant species with the most common floral volatiles; (b) the percentage of plant species where the most abundant floral volatiles represent more than 25% of the total floral scent; and (c) the percentage of plant species where the most abundant floral volatiles represent more than 50% of the total floral scent.

Figure 3

Ancestral phylogenetic reconstruction of floral emissions of trans-β-ocimene. One thousand trees were simulated with a mapped discrete character with states “Emitter” and “Non-emitter”. Trees had an average of 231.716 changes between states. The changes were: 117.436 Emitter→Non-emitter and 114.28 Non-emitter→Emitter. Mean times spent in each state were: 50.47% Emitter and 49.53% Non-emitter.