What is the Difference Between Chlorosis and Etiolation

The key difference between chlorosis and etiolation is that chlorosis is a physiological change in plants that takes place due to chlorophyll deficiency under light conditions, while etiolation is the physiological change that takes place in plants due to prolonged exposure to darkness.

Many plant diseases occur due to external conditions that are abiotic. Some of these conditions include nutrition deficiencies, soil compaction, salinity, high sunlight, and extremely cold weather. Chlorosis and etiolation are two conditions in which plant systems respond to the deficiencies and change in physical growth factors accordingly.

CONTENTS

1. Overview and Key Difference
2. What is Chlorosis 
3. What is Etiolation
4. Similarities – Chlorosis and Etiolation
5. Chlorosis vs Etiolation in Tabular Form
6. Summary – Chlorosis vs Etiolation

What is Chlorosis?

Chlorosis refers to the yellowing of green leaves due to chlorophyll deficiency. Many factors contribute to chlorosis. Plants affected with chlorosis have less or no ability to synthesize carbohydrates through photosynthesis. Hence, they usually die due to this condition unless the cause of chlorophyll deficiency is treated properly.

Figure 01: Chlorosis

Chlorosis is commonly caused when leaves do not have sufficient nutrients required to synthesize chlorophyll. Most causes of nutrient deficiency in plants are related to specific mineral deficiencies such as iron, magnesium, and zinc in soil. Nitrogen or protein deficiency also affects chlorosis. Unfavorable soil pH will disturb the absorption of essential nutrients by the roots. Poor drainage due to waterlogged roots, as well as damaged and compact roots, also disturb nutrient absorption. Certain pesticides and herbicides, exposure to sulfur dioxide, and ozone injuries are a few external factors that cause chlorosis. Additionally, bacterial pathogens such as some Pseudomonas sp. and fungal infections cause chlorosis.

Chlorosis varies from mild to severe. The initial indication of chlorosis is the paling of the green color of leaves. In mild chlorosis, the leaf turns pale green, leaving the veins green in color. In moderate cases, the tissue between veins becomes yellow. In severe cases, the leaf stunts and leaf tissues turn yellow, developing brown spots between veins. The main treatment for this condition is monitoring soil pH and supplying iron in the form of chelate or sulfate, magnesium, or nitrogen compounds in various combinations.

What is Etiolation?

Etiolation is a process that takes place in flowering plants grown in the absence of light. Plants show long, weak stems, smaller leaves due to long internodes, and yellowing as a result of etiolation. Etiolation increases when the plant grows under leaf litter, soil, or any shady place. The growing tips are attracted to light strongly and elongate towards it. Major changes due to etiolation include elongation of leaves and stems, cell wall weakening in leaves and stems, and longer internodes.

Figure 02: Etiolation

Etiolation is mainly controlled by the plant hormone auxin. It is synthesized in the growing tip and helps to maintain apical dominance. The process of etiolation takes place in plants that seek the activity of light in abundance. Thus, in order to stop such conditions, light should be given to the plant since plants require sunlight for growth and development.

What are the Similarities Between Chlorosis and Etiolation?

• Both scenarios show pale green or yellow color in leaves.
• They cause morphological changes in the plant.

What is the Difference Between Chlorosis and Etiolation?

Chlorosis is a physiological change in plants that takes place due to chlorophyll deficiency under light conditions, while etiolation is the physiological change that takes place in plants due to prolonged exposure to darkness. Thus, this is the key difference between chlorosis and etiolation. During chlorosis, the leaves become pale non-green, and yellow in color, while etiolation show features such as long and weak stems, long internodes, and yellowing of leaves. Moreover, chlorosis is mainly caused due to iron deficiency, whereas etiolation is not a process that is affected by nutrient deficiency.

The below infographic presents the differences between chlorosis and etiolation in tabular form for side by side comparison.

Summary – Chlorosis vs Etiolation

Chlorosis happens mainly due to chlorophyll deficiency under light conditions. On the other hand, etiolation happens mainly due to prolonged exposure to darkness. So, this is the key difference between chlorosis and etiolation. Chlorosis is commonly caused when leaves do not have sufficient nutrients to synthesize chlorophyll. Leaves show pale green or yellow color as a result of chlorosis. Following etiolation, the plants show long, weak stems and smaller leaves due to long internodes. Prevention methods may vary for the two conditions.

Reference:

1. “Chlorosis.” The Morton Arboretum.
2. “Why Does Etiolation Occur.” Gardening Know How.

Image Courtesy:

1. “Leaf-sunflower-leaf-sunflower” (CC0) via Pixabay
2. “Etiolation of plants” By சஞ்சீவி சிவகுமார் – Own work (CC BY-SA 4.0) via Commons Wikimedia

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