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Why does light make plants "awaken"? Unveiling the mystery of photomorphogenesis!
With the in-depth study of plant behavior, scientists have found that light is not only a source of energy, but also a key factor affecting plant development. Photomorphogenesis is the process by which plants develop in response to different wavelengths of light, whereby the growth pattern and morphology of the plant change depending on the spectrum of light it receives. This process is very different from photosynthesis, which is an energy conversion process. This article will explore how plants regulate their responses to light, as well as the scientific principles and historical background of this process.
Photomorphogenesis is key to plant growth and can only occur under specific wavelengths of light.
Key stages of plant development
Seed germination
Light has a profound effect on plant development, with the most dramatic effects occurring when a seedling first breaks through the soil. Usually, the shoot appears after the radicle first emerges from the seed and becomes established. As the buds grow, exposure to light will result in secondary root growth and branching. The coordinated growth of roots and shoots occurs due to the mediation of hormones.
Seedling Development
In conditions lacking light, plants develop a pattern of growth called "etiolation." This pattern allows the seedlings to become elongated, making it easier for them to break through the soil. When seedlings are exposed to light, there is a rapid switch to photomorphogenesis and clear developmental differences emerge. We can distinguish these two states as follows:
- Characteristics of yellowing: obvious apical hook, no leaf growth, no green pigment, rapid stem elongation, etc.
- Characteristics of de-chlorosis: expansion of apical hook, promotion of leaf growth, production of green pigment, inhibition of stem elongation, etc.
Photoperiodism
Some plants rely on light signals to decide when to switch from vegetative growth to the flowering stage. This type of photomorphogenesis is called photoperiodism and involves the use of red photoreceptors (phytochromes) to detect day length. Plants only begin to flower once they reach a "critical day length," which coordinates flowering with the changing seasons. For example, long-day plants require long periods of light, while short-day plants require shorter periods of light before they can bloom.
Plant growth is affected by the length and color of light, which is the core of the photoperiod phenomenon.
The role of photoreceptors in photomorphogenesis
Plants' responses to blue, red, and infrared light rely on several different photoreceptor systems. Photoreceptors for red and infrared light are called phytochromes, and there are at least five known species. Blue light receptors are often called cryptochromes, and these receptors play an important role in plant growth and flowering.
Influence of red light/far-infrared light
Plants use phytochromes to detect and respond to red and far-red wavelengths of light. Phytochrome is a signaling protein that promotes photomorphogenesis in response to red and far-red light. According to the different action wavelengths, photosensitive pigment can be divided into Pr form that absorbs red light and Pfr form that absorbs far-red light, Pfr is the activated form.
The impact of blue light
Plants contain a variety of blue light photoreceptors, among which cryptochrome is the first blue light receptor to be isolated and characterized, and is mainly responsible for the plant's response to blue light. These cryptochromes regulate seedling growth, leaf expansion, circadian rhythms and flowering time.
The effects of ultraviolet light
Plant responses to UV light are equally important, with the UV resistance gene 8 (UVR8) being shown to be a UVB photoreceptor that triggers photomorphogenic responses. These responses are essential for initiating processes such as seedling elongation, leaf expansion, and biosynthesis.
The ability of plants to respond to light is evolutionarily crucial as they must adapt to changing environmental conditions.
Studying the complexity of photomorphogenesis not only helps us understand the growth mechanisms of plants, but may also influence agricultural techniques and environmental management strategies in the future. As science and technology continue to advance, our knowledge of how plants sense and respond to light is also growing. Can this knowledge unlock more secrets of plant growth for us?
