Red:far-red light conditions affect the emission of volatile organic compounds from barley (Hordeum vulgare), leading to altered biomass allocation in neighbouring plants

Since the publication of this paper it has become apparent that an error was made in the scale of the vertical axis in Fig. 6I. This has no impact at all on any of the conclusions in the paper since the differences between the treatments remain as published. The authors apologise for this error and a corrected version is reproduced below.

Red:far-red light conditions affect the emission of volatile organic compounds from barley (Hordeum vulgare), leading to altered biomass allocation in neighbouring plants

BACKGROUND AND AIMS

Volatile organic compounds (VOCs) play various roles in plant-plant interactions, and constitutively produced VOCs might act as a cue to sense neighbouring plants. Previous studies have shown that VOCs emitted from the barley (Hordeum vulgare) cultivar 'Alva' cause changes in biomass allocation in plants of the cultivar 'Kara'. Other studies have shown that shading and the low red:far-red (R:FR) conditions that prevail at high plant densities can reduce the quantity and alter the composition of the VOCs emitted by Arabidopsis thaliana, but whether this affects plant-plant signalling remains unknown. This study therefore examines the effects of far-red light enrichment on VOC emissions and plant-plant signalling between 'Alva' and 'Kara'.

METHODS

The proximity of neighbouring plants was mimicked by supplemental far-red light treatment of VOC emitter plants of barley grown in growth chambers. Volatiles emitted by 'Alva' under control and far-red light-enriched conditions were analysed using gas chromatography-mass spectrometry (GC-MS). 'Kara' plants were exposed to the VOC blend emitted by the 'Alva' plants that were subjected to either of the light treatments. Dry matter partitioning, leaf area, stem and total root length were determined for 'Kara' plants exposed to 'Alva' VOCs, and also for 'Alva' plants exposed to either control or far-red-enriched light treatments.

KEY RESULTS

Total VOC emissions by 'Alva' were reduced under low R:FR conditions compared with control light conditions, although individual volatile compounds were found to be either suppressed, induced or not affected by R:FR. The altered composition of the VOC blend emitted by 'Alva' plants exposed to low R:FR was found to affect carbon allocation in receiver plants of 'Kara'.

CONCLUSIONS

The results indicate that changes in R:FR light conditions influence the emissions of VOCs in barley, and that these altered emissions affect VOC-mediated plant-plant interactions.

Canopy light cues affect emission of constitutive and methyl jasmonate-induced volatile organic compounds in Arabidopsis thaliana

The effects of plant competition for light on the emission of plant volatile organic compounds (VOCs) were studied by investigating how different light qualities that occur in dense vegetation affect the emission of constitutive and methyl-jasmonate-induced VOCs. Arabidopsis thaliana Columbia (Col-0) plants and Pieris brassicae caterpillars were used as a biological system to study the effects of light quality manipulations on VOC emissions and attraction of herbivores. VOCs were analysed using gas chromatography-mass spectrometry and the effects of light quality, notably the red : far red light ratio (R : FR), on expression of genes associated with VOC production were studied using reverse transcriptase-quantitative PCR. The emissions of both constitutive and methyl-jasmonate-induced green leaf volatiles and terpenoids were partially suppressed under low R : FR and severe shading conditions. Accordingly, the VOC-based preference of neonates of the specialist lepidopteran herbivore P. brassicae was significantly affected by the R : FR ratio. We conclude that VOC-mediated interactions among plants and between plants and organisms at higher trophic levels probably depend on light alterations caused by nearby vegetation. Studies on plant-plant and plant-insect interactions through VOCs should take into account the light quality within dense stands when extrapolating to natural and agricultural field conditions.

Plant neighbor detection through touching leaf tips precedes phytochrome signals

Plants in dense vegetation compete for resources, including light, and optimize their growth based on neighbor detection cues. The best studied of such behaviors is the shade-avoidance syndrome that positions leaves in optimally lit zones of a vegetation. Although proximate vegetation is known to be sensed through a reduced ratio between red and far-red light, we show here through computational modeling and manipulative experiments that leaves of the rosette species Arabidopsis thaliana first need to move upward to generate sufficient light reflection potential for subsequent occurrence and perception of a reduced red to far-red ratio. This early hyponastic leaf growth response is not induced by known neighbor detection cues under both climate chamber and natural sunlight conditions, and we identify a unique way for plants to detect future competitors through touching of leaf tips. This signal occurs before light signals and appears to be the earliest means of above-ground plant-plant signaling in horizontally growing rosette plants.

Biogenic volatile organic compounds and plant competition

One of the most important factors to shape plant communities is competition between plants, which impacts on the availability of environmental factors such as light, nutrients and water. In response to these environmental parameters, plants adjust the emission of many different biogenic volatile organic compounds (BVOCs). BVOCs can also elicit responses in neighbouring plants, thus constituting a platform for plant-plant interactions. Here, we review the relationship between BVOC emissions and competition among neighbouring plants. Recent progress indicates that BVOCs can act both as allelochemicals and as neighbour detection signals. It is suggested that BVOCs provide information about neighbouring competitors, such as their identity or growth rate, that classic neighbour detection signals cannot provide.