Photomorphogenesis

Photomorphogenesis is the growth and development process in plants that is regulated by light. It involves a series of physiological and biochemical changes that are triggered by different light wavelengths, intensities, and directions. The process is crucial for plant survival as it influences various aspects such as germination, flowering, chlorophyll synthesis, and circadian rhythms.

Overview

Photomorphogenesis is a complex process that involves the interaction of several photoreceptor proteins, including phytochromes, cryptochromes, and phototropins. These photoreceptors absorb specific light wavelengths and initiate signal transduction pathways that lead to changes in gene expression and ultimately, plant development.

Photoreceptors

Phytochromes

Phytochromes are a class of photoreceptors that absorb red and far-red light. They exist in two interchangeable forms: Pr (red-absorbing) and Pfr (far-red absorbing). The conversion between these two forms allows plants to sense day length, shade avoidance, and seed germination.

Cryptochromes

Cryptochromes absorb blue and ultraviolet-A light. They play a significant role in controlling circadian rhythms, seedling development, and flowering time.

Phototropins

Phototropins are blue-light receptors that regulate phototropism, chloroplast movement, and stomatal opening. They help plants optimize light capture and reduce water loss.

Light-regulated processes

Germination

Light signals, particularly red and far-red light, regulate seed germination in many plant species. This process is primarily controlled by phytochromes.

Flowering

The timing of flowering is crucial for plant reproductive success. Photoperiod, the relative lengths of day and night, is a key environmental cue that plants use to determine the optimal time for flowering. Both phytochromes and cryptochromes are involved in photoperiod perception.

Chlorophyll synthesis

Light is essential for chlorophyll synthesis, a process that enables plants to convert light energy into chemical energy through photosynthesis. Cryptochromes and phytochromes regulate the expression of genes involved in chlorophyll biosynthesis.

See also

• Phototropism
• Photoperiodism
• Circadian rhythms in plants
• Photosynthesis