How Blue, Green and Red Light Affects Plant Growth

Written by Eva Reet Singh

And reviewed by Saisha Sikka

https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.619987/full

Image made for representation, and is not an actual diagram/representation of what happened in the research

This research paper aims to investigate the effects of varying intensities of blue, green, and red light on photosynthesis in lettuce. 

Most people believed that red and blue light were the most important for photosynthesis, while green light didn’t matter much because leaves don’t tend to absorb it as strongly. But new research

on lettuce plants shows that this isn’t the case. The use of different light colours and the growth of the plant itself are primarily determined by the intensity of the light. Here is why:

A study was conducted where scientists tested lettuce leaves under red, blue, and green light, both separately and in mixtures, while varying the brightness. They measured how much carbon dioxide the leaves absorbed, how efficiently the plants used the light that hit them, and how well the internal processes, like the electron transport chain[a process in which high-energy is passed through a series of protein complexes embedded in a membrane] and how well the biological catalyst - Rubisco - worked.

The experiment concluded that at low light levels, red light gave the best results for photosynthesis because leaves absorb it very well. Green light performed the worst under dim light, since most of it passed through the leaf without being absorbed. But at high light levels, it was different. The green light was working as well as the red light and better than the blue. This is because green light can travel deeper into the leaf, reaching cells that red or blue light doesn't when the surface is already saturated. Inside the leaf, the electron transport system worked efficiently with both red and green light at high intensities, while Rubisco activity stayed about the same, no matter the colour. This is because Rubisco activity doesn't depend on the colour of light; instead, it reacts to temperature, the level of carbon dioxide, and the amount of enzyme present and functioning.

These findings show that green light is far from wasted by the plants. In a highly bright environment, it plays a vital role in sustaining photosynthesis deep within the leaf, instead of simply touching the surface. This is useful for indoor farming and greenhouses that rely on artificial lights. Instead of using only red and blue LEDs, adding green light could help plants grow more successfully.

To summarise, the study reveals that the effect of light on plants depends not only on its colour, but also on the intensity of the colour too. Red is most effective in low light, but green catches up and becomes equally important when the light is intense. Blue is valuable too, but not always the most efficient on its own. By understanding how plants respond to different kinds of light, we can design better ways to grow crops and also be able to understand how plants have adapted to use the full range of sunlight in nature, using each colour in differing ways to ensure that even in conditions where the light may change, they can still efficiently capture what they need to grow and survive.