2013 Volume 8 Issue 1 Pages 32-40
Plants use light as both a primary energy source and a signal for morphogenesis. Plant growth and morphogenesis are strongly affected by light intensity, photoperiod, and quality. Light quality studies have shown, for example, that plants receiving low levels of red light, in shaded locations (e.g., under dense plant canopies), exhibit rapid stem elongation and flowering. Photoreceptors-complexes of proteins and pigments in plant cells-act as “antennae” to absorb particular light spectra and generate signals to change gene expression through signal transduction systems in plant cells. By modifying gene expression, light signals control not only plant growth, but also flowering time, fruit color, or the functional chemical content of crops. Artificial light sources have now achieved long life, good energy efficiency, and increased luminance. Today, we can use various types of artificial lamps (e.g., fluorescent, metal halide, or hig-pressure sodium) to suit the lighting aims in horticultural crop production, but light-emitting diodes (LEDs) are now the most advanced artificial light sources available. Their energy efficiency is projected to overcome that of fluorescent lamps within 5 years. In addition, because LEDs can radiate narrow spectra, specific lights can be used to control specific plant growth responses, such as plant shape or flowering time, without the need for chemical growth regulators. We can also use new photo-selective filters to modify sunlight and thus control plant growth and insect and disease activity. These new light technologies are still expensive, but expected cost reductions will make the technologies available for protected horticultural production.
