Light and Plants
Plants derive their energy through a process called photosynthesis. This is a chemical reaction that converts carbon dioxide into sugars using light energy. Plants are most receptive to light waves that range from 400 to 700 nanometers in length, which the human eye also perceives as visible light. Within that range, plants most readily absorb blue and red light, and reflect green light, which is why they appear to us as green in color.
Blue light encourages foliar, or leaf, growth in plants. Phototropins and cryptochromes are both proteins in plant cells that best capture the energy of blue light. Cryptochromes regulate several plant functions, including germination and growth, by transferring protons from light to various chemical receptors which trigger hormonal and enzymatic growth processes. These are still under intense study by scientists.
Phototropins play a role in chloroplastic movement, and stomata opening in leaves. Chloroplasts are cell organelles that optimize photosynthesis by their position and arrangements in leaves. Phototrophins also trigger a hormone called auxin which pump protons out of cells on the side of the plant farthest from the light, dropping pH. Enzymes called expansins react to the acid by breaking bonds in the cell structure, causing those cells to swell. As a result, the shaded side of the stem elongates, so the whole plant bends toward the light. This process is known as phototropism.
Red light, in combination with blue light, facilitates bloom and fruiting. Phytochromes are the red-light specific proteins in plant cells. When they absorb red light wavelengths, they change in structure, initiating a chemical response which trigger gene activation to initiate flowering and fruit growth.
It has also been found that many small seeds with low food reserves, like lettuce, need the action of phytochromes, and therefore red light, to germinate properly.