Light quality, volatile emissions and plant–plant interactions

Volatile organic compounds (VOCs) play various roles in plant–plant interactions, and constitutively produced VOCs might act as a cue to sense neighbouring plants. Plants adjust to environmental changes using a variety of cues derived from proximate vegetation. Above-ground information transfer through neighbour-induced changes in light quality and the responses initiated by these cues are well described. The dominant above-ground light signal appears to be a reduced red:far-red light ratio (R:FR), caused by reflection of far-red and absorption of red light by leaves of neighbouring vegetation. In addition to changes in light quality, volatile organic compounds (VOCs) emitted by neighbouring plants might also serve as cues for surrounding plants. VOCs are particularly well studied in the context of plant–herbivore interactions. On herbivore-induced plant damage, the emission of many VOCs increases. These herbivore-induced VOCs serve in various systems as attractants for predators and parasitoids of the herbivores. Interestingly, herbivore-induced VOCs have also been shown to induce resistance in proximate neighbours, indicating that VOCs can serve as chemical cues between plants. For example, in cabbage (Brassica oleracea), exposure to VOCs from herbivore-infested conspecifics primes direct and indirect defence responses in intact plants. Volatile information transfer is not restricted to intraspecific interactions. For example, VOCs produced by clipped sagebrush (Artemisia tridentate) can induce resistance to herbivory in wild tobacco (Nicotiana attenuata).

A recent paper in Annals of Botany.mimics the proximity of neighbouring plants using a supplemental far-red light treatment on plants of a variety of barley (Hordeum vulgare) and finds that total VOC emissions are reduced under low red to far-red light conditions. The blend of compounds emitted is also altered, and when plants of a different barley variety are exposed to this blend of VOCs their pattern of carbon allocation is affected. Changes in red to far-red light conditions influence the emissions of VOCs in barley, and these altered emissions affect VOC-mediated plant–plant interactions.

Kegge, W., Ninkovic, V., Glinwood, R., Welschen, R.A., Voesenek, L.A., and Pierik, R. (2015) Red: far-red light conditions affect the emission of volatile organic compounds from barley (Hordeum vulgare), leading to altered biomass allocation in neighbouring plants. Annals of Botany, 115(6), 961-970.
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’.
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. 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’. 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.