Flower Volatile Overview

Introduction & Chemical Diversity

Floral volatile organic compounds (VOCs) represent a vast and diverse chemical landscape, crucial for plant ecology. Over 1700 compounds have been identified (Ref: Knudsen et al., 2006). Systematic reviews highlight recurring patterns:

Most Frequently Detected Individual Floral VOCs

Percentage of surveyed plant species (N=305) in which each specific VOC was detected. Data from Farré-Armengol et al. (2020), Fig 1A[2].

Most Common Dominant (>25%) Individual Floral VOCs

Percentage of surveyed plant species (N=305) where the specified VOC constituted >25% of the total floral scent blend. Data from Farré-Armengol et al. (2020), Fig 1B[2].

Biosynthesis Pathways

Most floral VOCs originate from these core pathways:

Terpenoids: Via MEP (plastid; monoterpenes, C10) and MVA (cytosol; sesquiterpenes, C15) pathways.[3]
Benzenoids/Phenylpropanoids: From L-Phenylalanine (Shikimate pathway), yielding C6C1, C6C2, and C6C3 structures.[3]
Fatty Acid Derivatives: Primarily C6 "Green Leaf Volatiles" from C18 fatty acids via the LOX pathway.[3]
Others: Including Nitrogen- and Sulphur-containing compounds.[2][3]

Pathway Overview Diagram

Simplified schematic of major floral volatile biosynthesis routes. Hover over nodes for structures.

Regulation of Floral Scent Emission

Scent production and emission are tightly controlled processes:

Temporal Regulation: Emission often follows circadian rhythms synchronized with pollinator activity (e.g., LHY controls timing)[1], and changes across developmental stages.[3]
Spatial Regulation: Specific organs often produce distinct VOCs.[3]
Transcriptional Control: Key transcription factors (e.g., ODO1, EOBII in Petunia) orchestrate pathway gene expression.[1][3]

Examples of Regulatory Mechanisms

Specific examples illustrating the regulation of floral scent emission.

Regulatory Aspect	Specific Example	Organism / Context	Function / Timing	Reference
Circadian Clock Gene	LHY (homologs)	Petunia hybrida, Nicotiana attenuata	Represses scent pathway genes (e.g., ODO1) in the morning, determines timing of nocturnal emission.	[1]
Rhythmic Gene Expression	PAL, BSMT1/2, EGS, IGS, ADT, CM1 etc.	Petunia hybrida	mRNA levels oscillate diurnally, contributing to rhythmic emission.	[1]
Transcription Factor (Activator)	ODO1 (R2R3-MYB)	Petunia hybrida	Master positive regulator of multiple benzenoid pathway genes.	[1]
Transcription Factor (Activator Cascade)	EOBII -> EOBI (R2R3-MYBs)	Petunia hybrida	Sequential activation leading to scent production.	[1]
Transcription Factor (Repressor)	PhMYB4 (R2R3-MYB)	Petunia hybrida	Specifically represses C4H (eugenol/isoeugenol path).	[3]
Developmental Regulation	Methyl Benzoate Emission	Antirrhinum majus	Peaks at anthesis; involves enzyme activity & substrate availability.	[3]

Ecological Functions & Environmental Factors

Floral scent plays vital roles in mediating interactions and responding to the environment:

Ecological Functions: Primarily attracting pollinators, but also defending against antagonists and contributing to reproductive isolation.[2][3]
Biotic Factors: Pollinator type is a major selective pressure, leading to correlations summarized below (Pollination Syndromes Table).[2]
Abiotic Factors: Climate significantly influences scent profiles (Climate Correlations Table). Pollutants like ozone can degrade scent signals.[2]
Phylogeny: Scent traits show moderate phylogenetic conservation but also frequent convergent evolution.[2]

Floral Scent Characteristics & Pollination Syndromes

Summary of significant correlations from Farré-Armengol et al. (2020)[2].

Pollinator Group	Key Scent Trait Correlations	Common Associated VOCs/Notes
Wind	Lower richness, Higher FAD %	GLVs (defense).
Birds	Lower total VOC richness	Often scentless.
Bats	Higher S-compound richness/ %	Dimethyl Disulfide/Trisulfide.
Lepidoptera	Higher total/Benzenoid/N-compound richness	Linalool, Benzyl Acetate, Indole.
Beetles	Higher N-compound richness	Variable (fruity, spicy, aminoid).
Flies	Higher N-compound richness	Amines, S-compounds (mimics), Benzaldehyde.
Bees	Generalists	Linalool, β-Ocimene, etc. common.

Climate Correlations with Floral Scent Composition

Summary of significant phylogenetic correlations from Farré-Armengol et al. (2020)[2].

Scent Trait	Climatic Variable	Correlation	Interpretation
Sesquiterpene Richness/Emission	Mean Annual Temp	Positive (+)	High temp favors less volatile VOCs.
Monoterpene Relative %	Precipitation / Temp	Negative (-)	More prevalent in drier/warmer conditions.
FAD Richness/Relative %	Precipitation	Positive (+)	More common in wetter areas.
FAD Richness/Relative %	Aridity Index	Negative (-)	Less common in arid areas.
N-Compound Emission	Precipitation	Negative (-)	Reduced emission in wetter climates.
S-Compound Richness/Relative %	Precipitation	Negative (-)	Less prevalent in very wet regions.
Gaussen Aridity Index: Lower values indicate higher aridity.

Key References

[1] Fenske, M. P., & Imaizumi, T. (2016). Circadian Rhythms in Floral Scent Emission. Frontiers in Plant Science, 7, 462. [DOI]
[2] Farré-Armengol, G., Fernández-Martínez, M., Filella, I., Junker, R. R., & Peñuelas, J. (2020). Deciphering the Biotic and Climatic Factors That Influence Floral Scents: A Systematic Review of Floral Volatile Emissions. Frontiers in Plant Science, 11, 1154. [DOI]
[3] Muhlemann, J. K., Klempien, A., & Dudareva, N. (2014). Floral volatiles: from biosynthesis to function. Plant, Cell & Environment, 37(8), 1936-1949. [DOI]

Flower Volatile Compounds