Photomorphogenesis

Plants make use of light in a variety of ways that go far beyond their ability to photosynthesise low-molecular-weight sugars using only CO₂ , light, and water, as demonstrated in the video below. Photomorphogenesis in plants can be defined as the growth and development of plants as a result of the presence or absence of light. It enables plants to make the most of their available light and space.

Photoperiodism is the ability of a plant to detect the passage of time by utilising light. Plants are able to identify the time of day and year by sensing and utilising different wavelengths of solar radiation. Phototropism is a directional reaction in plants that permits them to grow in the direction of, or even away from, the sun.

The ability of plants to detect light in their environment is critical for their survival and competitiveness; it is also critical for their reproduction. Plants respond to light in a variety of ways, each mediated by a distinct photoreceptor. They are made up of a protein that is covalently bound to a light-absorbing pigment known as a chromophore to function as photoreceptors. The two proteins are referred to as a chromoprotein when they are together.

Photomorphogenesis

Photomorphogenesis is the term used to describe any change in the structure and function of an organism as a result of variations in light intensity. It is a common aspect of development in fungi, protists, and bacteria, and it is found in plants as well.

There are two critical steps in the process of photomorphogenesis:

• Pattern specification is the process by which cells and tissues acquire the ability to respond to light at various stages of their development.
• The pattern realisation phase, during which the photoresponse takes place.
• The following are the two methods in which the plant responds to light signals:
• Photoresponse mediated by phytochrome oxidase
• Photoresponse mediated by cryptochrome in the presence of blue light

Photoreceptors

Photomorphogenesis is a process that is controlled by photoreceptors.

When a seed that has been growing in full darkness is exposed to light, the photoreceptors in the seed are stimulated, resulting in the seed becoming active. This is due to the fact that the seeds are exposed to electromagnetic radiation, particularly at wavelengths in the red or far-red range. By using receptors to send signals into the nucleus, a signal transduction pathway is established, which stimulates the genes responsible for growth and development.

The following types of photoreceptors are found in plants:

• Phytochrome
• Cryptochrome
• Phototropin
• UVR8

Phytochrome

A phytochrome is a protein that has formed a covalent connection with a chromophore. The phytochrome receptors are responsible for detecting the wavelengths of red to far-red light.

A plant possesses numerous phytochromes, which can work independently of one another at times and be dependent on one another at other times, either at the same time or at various points in the development of the plant’s organs.

The phytochrome proteins’ reactions are defined by their reversibility in the red and far-red spectrums. Phytochrome is a pigment that is involved in photomorphogenesis, such as leaf expansion and stem lengthening.

Cryptochrome

Cryptochrome is a pigment that can detect green, UVA, and blue light.

It is a flavin protein that contains two chromophores, one for blue light and the other for green light.

Flavin is a chromophore that is employed in several applications. Cryptochrome is responsible for the regulation of leaf growth, stem elongation, and the circadian rhythms of plants.

They can be found in both plants and animals, and they play a role in the regulation of their circadian rhythms.

They are also capable of sensing magnetic fields in a variety of species.

Phototropins

These are blue-light receptors that regulate all of the reactions in plants that are aimed at increasing their photosynthetic efficiency through photosynthesis. Phototropism, stomatal opening in reaction to light, and chloroplast mobility in response to changes in light intensity are all controlled by these hormones.

UVR8

It is an ultraviolet-B detecting protein that can be found in a variety of sources including plants. In the ultraviolet spectrum between 280 and 315 nm, it can detect stress and activate the plant’s response to it.

Importance of Photomorphogenesis 

• Plant growth and development are impacted by a variety of environmental conditions, one of which is light. Light, on the other hand, induces a variety of responses in the plant body that are not related to photosynthesis. These responses have a significant impact on the course of plant growth as well as the ultimate look of the plant. They are morphogenic responses induced by light.
• For example, many plants’ seeds do not germinate unless they are exposed to light during their development. The fact that seeds germinate in light demonstrates that seedlings require light to flourish. Photomorphogenic activities, such as those that occur in seedlings and leaves of adult plants, are also advantageous to the plant.
• When it comes to older plants, photomorphogenesis reactions are equally significant. Many of these responses, such as the formation of reproductive structures or the formation of dormant buds that can withstand a cold winter (i.e., the phenomena of photoperiodism and vernalisation), are in response to the relative lengths of day and night.

Conclusion

Photomorphogenesis is a type of developmental biology in which light-mediated development occurs, with plant growth patterns responding to the spectrum of light. This is an entirely different process than photosynthesis, which is a process in which light is used as an energy source. Photographic receptors called phytochromes, cryptochromes, and phototropins are photochromic sensory receptors that limit the photomorphogenic impact of light to the ultraviolet (UV) A and ultraviolet (UV) B, blue, and red regions of the electromagnetic spectrum, respectively.

The photomorphogenesis of plants is frequently investigated by growing the plants under carefully controlled frequency-controlled light sources. Photomorphogenesis occurs at least three times during the course of a plant’s development: during seed germination, during seedling development, and during the transition from the vegetative to the blooming stage (photoperiodism).