Mechanisms and consequences of neighbour detection in Arabidopsis thaliana

The global human population is rising rapidly every year, which in turn increases the demands for food production. For that reason, crop production must be intensified. Intensification of agriculture requires crop plants to grow in high densities, creating a very competitive environment especially for light. This competition becomes more intense in the presence of weeds. Light quality is changed inside the dense canopy due to the absorption of Red (R) and Blue (B) light for photosynthesis and the reflection of Far-red (FR) light from neighbour plants. A reduced R:FR ratio triggers the Shade Avoidance Syndrome (SAS); a suite of responses that enhance individual plant fitness in dense stands by allocating carbon to petiole or stem elongation and upward movement of the leaf, thus ensuring light capture. This goes at the expense of carbon allocation to leaf blades and to harvestable organs such as seeds or roots. These characteristics in combination with competition with weeds cause serious reductions of crop yield. To combat these yield reductions, sustainable ways to suppress weeds and to minimize the allocation of resources towards SAS in the unwanted organs should be developed. In this thesis, I tried to study the basic principles needed to achieve this by studying two different scenarios. The first one was to change the planting patterns in dense stands. While the second to modify the shade avoidance responses in dense stands from the very early stage up to a fully shade avoiding developed canopy. Finally, I also investigated molecular mechanisms of shade avoidance regulation to generate knowledge for future modifications of SAS components.