Photoperiodism, the clock of production

Photoperiodism, the clock of production

Did you know that different plants require different durations of light for growth and development? This phenomenon is called photoperiodism. Let us talk about it today.

Earth is in a perpetual state of rotation which results in the diurnal effect, day and night. The tilted axis that Earth rotates upon produces the seasons. Our ever-rotating 'marble of life' requires all living things to perceive and adapt to their environment.

Sunrise or sunset, summer or winter?

Flowering and blooming periods have implications for seed and fruit production. Flowering plants are responsible for fruit production, therefore, the timing of fruit production has implications for many. Most plants choose to flower in spring or summer and bloom in the daytime. This is due to the abundance of pollinators and favorable weather.

However, there are some flowering plants that are real night owls. Did you know that some flowers only bloom at night? Species such as the moonflower, casa blanca lily, nicotiana, evening primrose are night-bloomers. Over a period of time, flowering plants have evolved along with their respective pollinators. While some are evolved for butterflies and sunshine, others have evolved to make use of nocturnal moths' services.

Some plants may seem delicate in appearance, but are incredibly hardy in nature. Many flowering species choose to flower in the harsh conditions of winter. Winter Jasmine, hellebores, and winter aconite are some examples of flowering plants that have evolved to bloom in the low light and frigid conditions of winter.

What is photoperiodism?

Photoperiodism is the response of a plant to seasonal changes in day length. The effects of day length on flowering plants were first published in 1920, by Garner and Allard. They described two types of plants: long-day and short-day plants. Long-day plants would flower with greater periods of light, often over 12 hours. While short-day plants would only flower under a certain limit of light exposure, with the threshold being around 8 to 10 hours.

However, photoperiodism does not only affect flowering. It also affects other plant processes which are important in agriculture. Bud dormancy, a state of physiology when most processes are suspended is affected by light. This state allows plants to survive adverse conditions. Bulb and tuber initiation are also impacted by light. These processes store sugars in certain areas of the plant. Common examples of bulbs include onions and garlic. Common examples of tubers include potatoes and dahlia.

How do these ‘blind’ plants see the light?

Leaves perceive the light. One might say that the leaves are the eyes of plants. These plant organs do a fantastic job at perceiving light and can identify its quality, quantity, and direction. There are certain chemical pathways present in the leaves. These pathways are known as photoreceptors and detect the differences in the wavelengths of light. This results in the plant being able to recognize different colors of light.

Simply put, the rates of photosynthesis keep track of the light environment. These rates are monitored by the levels of sugar production over time. Then several other processes react to the rates of sugar production to produce a response to the light environment.

What makes light perception so important?

Plants perceive water availability and temperature in their environment as well. Why is then light perception so important? It is because light helps the plant to make the best decisions with respect to its physiology during the diurnal (day and night) transitions. This increases the fitness of a plant thereby improving its ability to produce viable seeds and have good growth. Plants also reserve the evenings for their cellular respiration process. Consequently, the additional energy released at night allows the plant to grow and mature. Flowers will often undergo maturation in the evenings due to the extra available energy.

When did light perception evolve?

The evolution of light perception happened in two phases. The first phase took place in the Cyanobacteria, the first organism to produce oxygen as a byproduct. These organisms developed time-sensing mechanisms. The second phase was because of green algae. They provided the toolkit that eventually evolved into the ability of modern plants for perceiving light. Photoperiod sensing helps develop stress tolerance in plants and algae.

Light also controls gene expression. There are many genes in plants, however, they don’t express themselves at once or in the same way. Certain genes express under certain conditions. Much like how some people can get dark tanned skin and others simply turn red with sunburn. Light controls 90% of gene expression in some microalgae and around 50% in modern terrestrial plants. The physiology of a plant is driven by gene expression and appearance is determined by its physiology. Therefore, the light received often dictates the appearance.

What is breakfast without cereal?

Light has a major impact on the levels of agricultural output. Certain crops require long day lengths to produce high yields. Whereas others may require a certain ratio of day-and-night hours.

When it comes to our bowls of cereal, light equals quantity. Most grains have higher yields when lots of light coincides with the grain-filling period. Grain filling is the storing of carbohydrates in the kernels or seeds. Years of plant breeding have produced many varieties. They can deal with different stresses and light environments. However, grains around the world are still being planted during a period where grain filling can coincide with long daylight hours.

Lights, camera, plant tissue culture!

Plant tissue culture (PTC) also takes light quality and quantity into account. Light is one of the important microenvironmental factors that control plant growth, development, metabolism, and even chlorophyll content in plant cells/tissues. To learn more about microenvironmental factors in PTC, have a look at our article on "4 conditions for microenvironment in plant tissue culture".

According to scientists, germination of somatic embryos shows improvement when supplemented with red LED light. This is an example of how light quality affects PTC.

Light natural or artificial, has an effect on plants in nature and laboratories.

Feeling blue?

If you are wondering does light affect me too? The answer is, yes! Blue light has relaxing qualities and white light can be used as a treatment for depression. There are many other color-mood combinations. So next time you are feeling down put on some lights and do some mood-photosynthesizing. We are not so vastly different from plants.

We hope this article will be useful for many of you to understand the concept of photoperiodism in plant science. For more articles like this, keep checking our space!

By Christos Tripodis | 26 October 2021

References

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