Light quality regulates apical and primary radial growth of Arabidopsis thaliana and Solanum lycopersicum

Abstract

For a horticultural crop such as tomato (Solanum lycopersicum), the initial growth phase of young plants can take place in multi-layer systems to reduce space. Here LEDs form the ideal lighting system, as they decouple light intensity from heating and can thus be placed in close proximity to the plants. Moreover, the spectral quality control of LEDs may be utilized to steer the plants towards a desired compact and sturdy phenotype. To achieve this, we must understand how light quality affects plant elongation and stem thickness during early plant development. Therefore, we assessed apical and radial growth of tomato and Arabidopsis thaliana (Arabidopsis) plants grown in white, red, or blue LED conditions. Our analysis revealed that in both species the red LED condition increased cell elongation in hypocotyls and stems, whereas the blue LED condition decreased cell elongation, compared to the white light condition. In seedlings, hypocotyls were thinner in the red LED condition, and thicker in the blue LED condition, compared to white light. However, in flowering plants, Arabidopsis showed sensitivity of primary radial growth to light quality, while tomato plants appeared indifferent. Finally, analysis of Arabidopsis photoreceptor mutants suggested that cryptochromes and type II phytochromes are the main regulators of light-mediated apical and primary radial growth. To summarize, LEDs can be used to regulate both apical and primary radial plant growth, but the resulting phenotypes may be plant age- or species-specific.