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.
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.competition | phenotypic plasticity | thigmomorphogenesis | canopy development P lant growth in dense vegetations is dominated by a fierce battle over resources. In competition for light, small size inequalities can have major effects on light capture and thus competitive power (1-3). Therefore, it is essential for plants in dense stands to timely respond to neighbor detection cues and adjust growth to that of their competitors. Reduction of the red (R):far-red (FR) ratio, signaled through phytochromes and caused by horizontal FR reflection from neighboring plants, is seen as the earliest above-ground detection signal of neighbors. The R:FR is decreased even before true shading occurs through overlap of leaves, and induces shade-avoidance responses such as upward leaf movement (hyponasty) and stem elongation that secure light capture during subsequent plant competition (reviewed in refs. 4-6). Accordingly, low R:FR can induce shade-avoidance responses in plants grown without neighbors (7,8), and plants blinded to FR-enrichment in a dense canopy fail to respond to neighbors at an early stage of competition (9). Although some additional above-ground neighbor detection signals are known, e.g., blue light depletion (10, 11) and volatile ethylene accumulation (11), none of these acts as early as a decrease in the reflected R:FR.The paradigm of decreased R:FR as the earliest neighbor-detection signal in competition for light has been a breakthrough in mechanistic plant competition research. Interestingly, this paradigm is based on research on stem-forming forbs and trees (12-14), but has not been studied in plants that lack an appreciable height growth before competition in the vegetative life stage, e.g., rosette species such as Arabidopsis thaliana and many other species. Here we study early neighbor detection in dense stands of Arabidopsis. Hyponasty appears to be the earliest shade-avoidance response and occurs exclusively in leaves that touch neighboring leaf tips, before a physiologi...
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.
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.
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