Photomorphogenesis – Definition, Meaning, Stages, Importance, Facts

Definition Of Photomorphogenesis

Photomorphogenesis is the growth and development of plants in response to light signals. It is a very paramount process in plant biology that controls the most imperative functions undertaken by plants, including seed germination, stem elongation, or epicotyl elongation, expansion of the leaf, and flowering.

Light as a cardinal factor in the environment sets these processes into interrogation through light-driven alteration of growth patterns and physiological responses using photoreceptors like phytochromes. Conclusions: The mechanism of photomorphogenesis is the means to finding out how plants can best develop and survive under varying light intensities. This is the secret regarding how farming practices and crop yield can be optimised.

Phytochrome-Mediated Photomorphogenesis

The details are given below:

Structure and Function of Phytochromes

There exists a chromophore and a polypeptide moiety in each phytochrome protein. This light binding to the chromophore results in the formation of a holo-protein that may be thought of as a single pigment-absorbing colour. Phytochrome's perception of red and far-red light greatly controls plant development, including seed germination.

Phytochrome Activation and Deactivation

There exist two forms of phytochromes: one inactive, Pr, and the other representing the active state, Pfr. They are induced by red light as a result of the conversion of Pr to its active form, Pfr, and turned off by far-red light in which the Pfr is reverted to Pr. It is due to phytochromes that plants can respond to any fluctuations in light exposure.

Role of Phytochromes in Seed Germination

Phytochromes are implicated in the induction of seed germination. The Pfr form senses red light as an indicator of a favourable condition for growth. Pfr initiates the expression of genes that result in breaking the dormancy of seeds and allows seed germination.

Phytochrome Regulation of Gene Expression

On activation, phytochromes in the Pfr form enter the nucleus. They regulate gene transcription by interacting with transcription factors. Another such example of regulation is the transition from seedling growth to flowering.

Cryptochrome-Mediated Photomorphogenesis

The details are given below:

Structure and Function of Cryptochromes

Cryptochromes are part of a class of photoreceptors that contain a flavin chromophore, which may be activated through blue light; hence, this forms a significant controller in the processes for the plant's circadian rhythm, photoperiodism, and other growth processes.

Mechanisms of Cryptochrome Activation

Blue light activates cryptochromes by causing conformational changes in them to physically interact with other proteins which are controlling gene expression. This allows the plant to coordinate its internal clock with the prevailing illumination in the environment.

Influence of Cryptochromes on Circadian Rhythms and Photoperiodism

The cryptochromes appear to play a role in the active circadian rhythm maintenance by controlling the clock genes' expression. Further, they take part in photoperiodism by enhancing the ability of a plant to measure day length; this is to correctly time flowering and other seasonal responses.

Phototropin-Mediated Photomorphogenesis

The details are given below:

Structure and Function of Phototropins

In addition to this, the LOV domain-containing phototropins are photoreceptors for blue light and mediate several light-dependent physiological responses, including phototropism, chloroplast movement, and stomatal opening.

Role of Phototropin in Phototropism

This is because the cell elongation in the shaded part of the plant stem enhances, making it lean towards the light. Differential tissue growth in plants leads them to bend towards light for optimising light capture by leaves, due to the stimulated phototropins as a result of sensing blue light.

Phototropins and Stomatal Opening

Phototropins are the principal cause of stomata opening by blue light. They activate the proton pumps, increasing the turgor pressure of the guard cells, thus opening the stomata. This facilitates gaseous exchange and transpiration.

Photoreceptors

The components are:

Phytochrome

Phytochromes are red and far-red light photoreceptors, changing activity on active/inactive form change, and in response to light, regulate seed germination, stem elongation, and flowering promotion.

Cryptochrome

Cryptochromes are blue-light photoreceptors controlling gene expression in the processes of circadian rhythms and photoperiodism that aim to entrain the endogenous rhythm of the plant to the environment.

Phototropins

Phototropins are photoreceptors that perceive blue light controlling phototropism, chloroplast movement, and opening of the stomata. They help the plant, through these mechanisms, achieve optimum light exposure and gas exchange for photosynthetic efficiency.

UVR8

UVR8 is a UV-B receptor that gives plants the ability to respond to ultraviolet light. It controls UV-B-induced photomorphogenic and stress responses, thus safeguarding them from UV-B damage by the activation of protective pathways.