What is the Difference Between Photoperiodism and Phototropism

The main difference between photoperiodism and phototropism is that photoperiodism is the response of plants to the lengths of dark and light periods in a day, whereas phototropism is the growth of plants in response to light.

Photoperiodism and phototropism are two responses in plants to the light. Generally, plant hormones govern both processes. Furthermore, photoperiodism is not a directional movement, while phototropism is a directional movement. 

Key Areas Covered 

1. What is Photoperiodism
     – Definition, Features, Importance
2. What is Phototropism
     – Definition, Features, Importance
3. What are the Similarities Between Photoperiodism and Phototropism
      – Outline of Common Features
4. What is the Difference Between Photoperiodism and Phototropism
      – Comparison of Key Differences

Key Terms 

Auxin, Negative Phototropism, Photoperiods, Photoperiodism, Phototropism, Positive Phototropism, Response to Light

What is Photoperiodism 

Photoperiodism is the physiological response of plants to the length of the day or night. Generally, the light or dark periods are known as photoperiods. Moreover, these photoperiods are responsible for the conversion of vegetative buds into flower buds in plants. Photoreceptor proteins such as phytochromes or cryptochromes in leaves play a critical role in sensing the lengths of the night lengths. Furthermore, based on the developing response, there are three types of plants: short-day plants, long-day plants, and day-neutral plants. 

Figure 1: Photoperiodism

Short-day Plants 

Basically, short-day plants induce flowering when the lengths of the night exceed their critical photoperiod. But, the moonlight or lightning is not sufficient to interrupt the length of the night. Moreover, some examples of short-day plants are rice, marijuana, kenaf, cotton, green gram, etc. In the Northern hemisphere, these plants bloom during summer or fall.  

Long-Day Plants 

Long-day plants induce flowering when the length of the night is less than their critical photoperiod. In the Northern hemisphere, these plants bloom during late spring or early summer. Some examples of long-day plants are oats, carnation, henbane, barley, wheat, pea, etc. 

Day-Neutral Plants 

Day-neutral plants do not induce flowering based on the photoperiod. However, flowering occurs after attaining a certain overall developmental stage or age, or in response to alternative environmental stimuli, such as vernalization. Some examples of day-neutral plants are roses, tomatoes, cucumbers, etc.

What is Phototropism 

Phototropism is the growth of a part of a plant in response to the direction of the light. Generally, the hormone responsible for the growth is auxin. Basically, it is responsible for regulating the elongation of the newly differentiated cells at the tips of both stem and root. Moreover, based on the direction of the elongation in response to light, there are two types of phototropism. They are positive and negative phototropism. 

Positive Phototropism 

Positive phototropism occurs in the apex of the stem. Generally, it is responsible for the growth of the stem apex towards the light. However, when the plant receives directional sunlight, auxin in the apical meristem tends to gather in the shaded side, resulting in the higher elongation of cells in the shaded side compared to the bedazzling side. It, in turn, bends the tip of the stem towards the light source.

Figure 2: Positive Phototropism

Negative Phototropism  

The apex of the root shows negative phototropism as it grows away from the light source. Normally, this is due to the concentration of auxin at the bottom side of the root, elongating cells in the apex into the soil.  

Similarities Between Photoperiodism and Phototropism 

• Photoperiodism and phototropism are two types of responses in plants to the light. 
• Hormones govern both processes. 
• Photoreceptors are responsible for accepting the light as the stimuli. 
• They also occur in animals. 

Difference Between Photoperiodism and Phototropism 

Definition 

Photoperiodism refers to the growth, development and other responses of plants and animals based on the length of day and night, while phototropism refers to the movement of a plant or animal towards or away from light. Hence, this is the main difference between photoperiodism and phototropism.

Significance 

Moreover, photoperiodism is responsible for the induction of flowering in response to the duration of light in a day while phototropism is the curvature growth in the parts of plants towards or away from the light. 

Directionality 

Another difference between photoperiodism and phototropism is that photoperiodism does not respond to the direction of light while phototropism responds to the direction of light. 

Perception of the Stimuli 

Leaves perceive the stimuli in photoperiodism while apical meristem perceives the stimuli in phototropism. 

Photoreceptors 

Phytochromes and cryptochromes act as photoreceptors in photoperiodism while carotenoids act as photoreceptors in phototropism. 

Hormone 

Florigen is the hormone which mediates photoperiodism while auxin is the hormone which mediates phototropism. 

Effect 

Photoperiodism converts a vegetative bud into a floral bud while phototropism results in the differential growth in the elongation zone. Thus, this is also an important difference between photoperiodism and phototropism.

Types 

Short-day, long-day, and day-neutral plants are the types of photoperiodism, while positive phototropism and negative phototropism are the two types of phototropism. 

Conclusion 

Photoperiodism is the response of plants to the length of light in a day. Based on that, it induces flowering. Moreover, it produces three types of flowering patterns in plants: short-day, long-day or day-neutral plants. On the other hand, phototropism is the directional movement of parts of plants in response to light. Therefore, the apex of the shoot shows positive phototropism, while the apex of the root shows negative phototropism. Therefore, the main difference between photoperiodism and phototropism is the type of response to light and their effect. 

References:

1. “Phototropism & Photoperiodism.” Khan Academy, Khan Academy, Available Here.

Image Courtesy:

1. “Photoperiodism in plants” By Giovnnni pastrami – Own work (CC BY-SA 4.0) via Commons Wikimedia   
2. “Phototropism Diagram” By MacKhayman – Own work (CC BY-SA 3.0) via Commons Wikimedia