The Effect Of Different Colour Filters On Leaves And Plant Growth

Factors that affect photosynthesis

Question:

Write an essay on "The Effect of Different Colour Filters on Leaves and Plant Growth". 

Photosynthesis is the basis of life on earth’s surface and how different light colours influence it is a matter of importance. This experiment is concerned with the effects of different light on the rate of photosynthesis and its effect on leaf & plant growth. Leaves of a healthy plant were exposed to different coloured light and kept for seven days. The result showed different effects of diverse light colours on the process of photosynthesis. After white light, blue and red lights are efficient for conducting adequate photosynthesis. Yellow and green lights are least suitable for this process.

Autotrophs such as green plants capture free energy from environment through photosynthesis and chemosynthesis. The process of photosynthesis occurs in a series of enzyme-mediated pathways that uses sunlight and carbon-di-oxide to produce glucose (Zelitch 2012). Photosynthesis can be represented as a chemical equation:

6CO₂ + 6H₂O ------> C₆H₁₂O₆ + 6O₂

^{Sunlight energy}

There are five main factors that affect the rate of photosynthesis: light intensity, the colour of light, temperature, carbon di-oxide level and water. In this experiment the effects of different colour wavelengths were investigated. In nature plants often face fluctuations of light intensity and spectral quality which is essential to drive the processes of photosynthesis. Plants have many adaptations to cope with these light fluctuations (Hart 2012).

Photosynthesis takes place in two stages known as the light reaction and dark reaction. The light harvesting antenna complex of photosystem II (LHCII) accumulates the maximum light energy. These complexes were found to play a central regulatory role by remarkably leading the magnitude of energy delivered to the reaction centres (Gutu et al. 2013). As light energy/photons reaches chlorophyll molecules, the light harvesting complex absorbs that energy by exciting electrons. These electrons move along an electron transport chain, eventually transferring their energy form of ATP and NADPH. ATP and NADPH act as highly charged energy carriers ready to provide energy to continue photosynthesis in the dark reactions. By utilising the energy of the ATP and NADPH, as well as some other special molecules including CO₂ and H₂O, carbohydrate (glucose) is formed as the final product (Blankenship 2013).

The rate of photosynthesis always occurs more efficiently under white light.  Red and blue light also have good photosynthetic rate (Lin et al. 2013). The process of photosynthesis gradually drops under yellow and green light respectively. While certain wavelengths are absorbed by the plants others are reflected. The main photosynthetic pigments chlorophyll a and chlorophyll b absorb all colours in visible light spectrum but green and that’s why plants appear green. Sun gives off most of its energy as green wavelengths and it might seem inefficient that plants don’t use the green spectrum. This is a protection strategy of plants. Chlorophyll-a, chlorophyll-b and other pigments easily destroyed by excessive light energy. When these pigments break down, they stop absorbing light and also DNA become damaged. So plants have adapted these absorption spectrums to maintain their needs by using least abundant light waves. In general, light absorbed in the blue region is used for plant development and light absorbed in the red and far red regions are used for flowering or orienting (Hart 2012).

Process of photosynthesis

Other accessory pigments like carotenoids also absorb light.  Red and blue have the greatest impact on plant growth. Green light is least effective. Absorption in the spectral region between 500 nm to 600 nm is very low because green light is reflected by the plants. Blue light is primarily responsible for vegetative leaf growth. Red light combined with blue light encourages flowering (Hart 2012 and Abidi et al. 2013).

This topic was a very interesting way to know the systems of photosynthesis and the effects of different colour wavelengths on photosynthesis and plant growth. Different colour lights have different effects on this anabolic process. Knowing the factors affecting the most important metabolic process on earth is a vital understanding because green plants are termed producers because they yield their own food via photosynthesis. Humans and animals are consumers and all the food they ingest originates directly or indirectly from these plants.

As discussed in the review of literature, exposing a plant in white light will result in fastest rate photosynthesis, followed by blue or red. The change in leaf colour and leaf health after seven days under different lights will show the effects of different light. To measure the rate of photosynthesis, counting oxygen produced during the reaction is required by arranging special set-ups.

1. Healthy and living green plants
2. Containers and fertile potting soil
3. Colour (blue, red, yellow, green, black and transparent) sheets
4. Scissor
5. Tapes
6. Ruler
7. Camera
8. Water
9. Sufficient sunny area to keep the plants

Plants were potted in containers filled with good quality soil. Then placed in an open space under adequate sunlight.

The filters were prepared by cutting the coloured sheets. They were cut according to the leaf sizes.

Leaves were then covered with different coloured filters. Each colour had five replicas. Filters were secured properly so they do not fall away.

Transparent filters were used as control sets.  

The plants were rotated daily basis and water was given twice a day. These processes were continued for seven days.

The plants were observed every day for maintaining the plant’s health.

After seven days the filters were removed and results noted.

The results were collected after seven days and tabulated below:

Filer colour	Rate of photosynthesis
Blue	Comparatively high
Red	Moderate
Yellow	Much less
Green	Lesser  in amount
Black	No photosynthesis
Transparent (control)	Highest

The leaf under blue filter after seven days.

The leaf under red filter after seven days.

The leaf under yellow filter after seven days.

The leaf under green filter after seven days.

The leaf under black filter after seven days.

The leaf under transparent filter (control set) after seven days.

A graph was assumed from the result for showing overall the effects of various light colours in photosynthesis:

This experiment was performed to determine the effects of different colour wavelength on photosynthesis and plant growth. The results found in this experiment shows diverse effects of different wavelengths on photosynthesis. The best result as found in case of the control set prepared by transparent sheet. The control leaf was very bright green and healthy. A better result was observed in case of blue lights. The leaf was fairly green and healthy. A moderate result was occurred under red filters. The leaf appeared moderate green in colour.  Very reduced result noted for both yellow and green setup. The leaf of yellow setup appeared pale green in colour. Leaf of the green setup became yellowish in colour after seven days. These pale colouration of the leaves indicates significant reduction of photosynthetic process. Almost no photosynthesis occurred under the black filters because of light deficiency. Leaf was shrivelled and brownish and broke when the filters were removed.

Impact of light on photosynthesis

As described in the review of literature the rate of photosynthesis is always take place more efficiently under white light. That is why the leaf of the control set was green and healthy. After white light, blue light has highest photosynthetic rate. The leaf under blue filter was in a better health and green condition. Red light is also a good element of photosynthesis and the leaf appeared moderately green after seven days under red filter. The rate of photosynthesis steadily drops under yellow and green light. The leaf of yellow setup appeared pale green in colour because photosynthesis was very less and some yellow light was absorbed by the xanthophyll pigments. The leaf under green filter was yellowish due to lack of chlorophyll a & chlorophyll b and photosynthesis rate was almost null. The leaf under black set was on a verge of dying due to lack of sunlight and considerable inhibition of photosynthesis.

The major photosynthetic pigments chlorophyll a and chlorophyll b absorb all colours in visible light spectrum but green wavelength. Thus, green light is least effective. Other accessory pigments like carotenoids and xanthophyll absorb light waves of orange and yellow (Kastner et al. 2012). 

Thus, from this experiment and as stated by other authors it can be concluded that the rate of photosynthesis always takes place more efficiently under white light. If elements of white light is separated, blue and red lights are quite good for photosynthesis (Ruban 2014).

Knowing these facts about light colours and their effects on photosynthesis can be useful in agriculture. The blue spectrum empowers phototropin and cryptochrome to facilitate many plant responses such as movement of the chloroplast, phototropic curvature, inhibition of growth elongation, stomatal opening and seedling growth regulation. The blue wavelengths boost vegetative growth through strong root growth and intense photosynthesis (Hart 2012). Thus, blue lights are often used as a supplementary light source for seedlings and undeveloped plants during their vegetative stage of the growth cycle. Blue lights provide a more tailored spectrum according to the plants being cultivated.  (Lin et al. 2013 and Xu 2016).

Red light affects photochromic reversibility and is the most vital event for photosynthesis, flowering and fruiting regulation. The red wavelength encourages the growth of stem, flowering and fruit and chlorophyll production. Tomato plants showed the most growth in the vegetative phase under red (670 nm) light.  In the germination phase, irradiation of 680nm encouraged the highest growth frequency (Suyanto et al. 2012 and Xu 2016).

The blue and red lights are sometimes called the grow lights. Outdoor environments usually mimicked with various colours and spectral range from the grow light (Abidi et al. 2013). Depending on the type of crops being cultivated, the stage of cultivation (e.g. the germination, vegetative phase, the flowering and fruiting phase), the required photoperiod, definite arrays of spectrum and time periods are necessary for a particular plant. These light spectrums are used for horticulture, plant propagation and food production on an industrial level (Xu 2016). These lights are also important for photomorphogenesis (light-mediated development) where plant growth patterns respond to the light spectrum. The rate of photosynthesis is dependent upon photosynthetically active radiation (PAR) which defines the spectral range of radiation from 400 nm to 700 nm that photosynthetic organisms are able to use during the course of photosynthesis (Lin et al. 2013). Agricultural & plant product industries can increase their productivity by manipulating PAR and combining essential light waves for better plant yield.  

References

Abidi, F., Girault, T., Douillet, O., Guillemain, G., Sintes, G., Laffaire, M., Ahmed, H.B., Smiti, S., Huché-Thélier, L. and Leduc, N., 2013. Blue light effects on rose photosynthesis and photomorphogenesis. Plant Biology, 15(1), pp.67-74.

Blankenship, R.E., 2013. Molecular mechanisms of photosynthesis. John Wiley & Sons.

Gutu, A., Nesbit, A.D., Alverson, A.J., Palmer, J.D. and Kehoe, D.M., 2013. Unique role for translation initiation factor 3 in the light color regulation of photosynthetic gene expression. Proceedings of the National Academy of Sciences, 110(40), pp.16253-16258.

Hart, J.W., 2012. Light and plant growth (Vol. 1). Springer Science & Business Media.

Kastner, A., Jones, M., Mefford, A. and Richardson, T., 2014. Chlorophyll and Accessory Pigment Absorption of CO2 under Various Wavelengths of Light. Journal of Introductory Biology Investigations, 1(3).

Lin, K.H., Huang, M.Y., Huang, W.D., Hsu, M.H., Yang, Z.W. and Yang, C.M., 2013. The effects of red, blue, and white light-emitting diodes on the growth, development, and edible quality of hydroponically grown lettuce (Lactuca sativa L. var. capitata). Scientia Horticulturae, 150, pp.86-91.

Ruban, A.V., 2014. Evolution under the sun: optimizing light harvesting in photosynthesis. Journal of experimental botany, p.eru400.

Suyanto, H., Rupiasih, N.N. and Handayani, D., 2012. Influence of Light Wavelengths on Growth of Tomato. Bumi Lestari, 12(2).

Xu, Y., 2016, May. Seven dimensions of light in regulating plant growth. In VIII International Symposium on Light in Horticulture 1134 (pp. 445-452).

Zelitch, I. ed., 2012. Photosynthesis, photorespiration, and plant productivity. Elsevier.