Kranz Anatomy – An Overview
Kranz Anatomy is a distinctive arrangement found in C4 plants, characterized by mesophyll cells forming a ring around the bundle-sheath cells. Kranz Anatomy is found in angiosperms like sugarcane and grasses which undergo C4 photosynthesis. Plants growing in warm tropical or arid environments have developed this efficient photosynthetic pathway. Let us discuss Kranz’s anatomy in detail.
Table of Content
- What is Kranz Anatomy?
- Kranz Anatomy in C4 plants
- Kranz Anatomy Diagram
- Structure of C4 Plants
- Function of Kranz Anatomy
- Advantages of Kranz Anatomy
- Development of Kranz Anatomy
- Characteristic features of Kranz Anatomy
- What is the Difference Between C3 and C4 plants?
- Difference between Mesophyll Cells and Bundle Sheath Cells
What is Kranz Anatomy?
In this pathway, atmospheric carbon dioxide (CO2) is initially fixed into a four-carbon molecule (malic acid or malate), hence the name C4. Those plants typically exhibit a distinct leaf anatomy called Kranz anatomy, which involves two types of photosynthetic cells with separate morphological and functional characteristics. These are the bundle sheath cells surrounding the vascular centers and the mesophyll cells enveloping the bundle sheath cells beneath the leaf epidermis.
This distinctive wreath-like arrangement serves as a structural framework for the compartmentalization and functional segregation of the two sets of biochemical reactions necessary for this specialized CO2-assimilation pathway. Notably, the bundle-sheath cells contain a higher number of chloroplasts compared to the mesophyll cells.
Kranz Anatomy in C4 Plants
In C4 plants, Kranz anatomy refers to a specialized arrangement of leaf cells that enhances the efficiency of photosynthesis, particularly in hot and dry conditions. This anatomical adaptation is crucial for their ability to concentrate CO2 around the enzyme rubisco, thereby minimizing photorespiration and maximizing carbon fixation. C4 plants have two types of photosynthetic cells: mesophyll cells and bundle sheath cells. Mesophyll cells are typically arranged in a layer beneath the upper epidermis of the leaf.
These cells initially fix carbon dioxide into a four-carbon compound called oxaloacetate or malate, instead of the three-carbon compound, 3-phosphoglycerate (PGA), as in C3 plants. Surrounding the vascular bundles, which contain xylem and phloem, are specialized bundle sheath cells. These cells are characterized by having a high concentration of chloroplasts and are tightly packed. They form a protective layer around the vascular tissue.
Kranz Anatomy Diagram
The Kranz anatomy diagram is given below:
Structure of C4 Plants
The structure of C4 plants shows a distinctive Kranz Anatomy that includes:
- Mesophyll cells are uniform and arranged in concentric layers around the vascular bundles.
- Chloroplasts in mesophyll cells are fewer and do not contain starch. They possess the enzyme structure necessary for C4 photosynthesis.
- Chloroplasts in bundle sheath cells store starch and are larger. They have the enzyme structure required for C3 photosynthesis.
- Mesophyll cells and bundle sheath cells are connected through plasmodesmata, facilitating communication and exchange of materials between them.
Function of Kranz Anatomy
In most plants, carbon dioxide undergoes initial fixation into a compound with three carbon atoms (C3) through the photosynthetic enzyme ribulose bisphosphate carboxylase oxygenase, or RuBisCo, which is known as C3 photosynthesis and these plants are called C3 plants.
- However, Rubisco is inherently inefficient as it can also catalyze a reaction with oxygen, leading to an inefficient process called photorespiration instead of photosynthesis.
- To overcome this inefficiency, the C4 pathway strategically fixes atmospheric carbon dioxide into C4 acids using the enzyme phosphoenolpyruvate carboxylase, which is not responsive to oxygen.
- Subsequently, C4 acids release carbon dioxide for re-fixation by Rubisco. In many C4 plants, these two phases of the C4 pathway are spatially separated into morphologically distinct photosynthetic cell categories.
- This segregation allows for a high concentration of carbon dioxide to accumulate in the vicinity of Rubisco, promoting better photosynthetic efficiency.
Advantages of Kranz Anatomy
Kranz anatomy is advantageous because it enables plants to efficiently produce their food. This anatomical feature revolves around the veins in the leaves, forming a layer of cells that can absorb more light. This capability allows the plant to generate increased amounts of sugar and oxygen for its metabolic processes. Consequently, there are other advantages too. Some of these benefits are outlined below:
- It creates an optimal site for the concentration of carbon dioxide within the plants, particularly around the RuBisCO enzyme.
- It plays a role in preventing photorespiration, a process that can be detrimental to plant productivity.
- It facilitates the fixation of carbon dioxide twice within C4 plants, thanks to the involvement of bundle sheath cells in this specialized anatomical arrangement.
Development of Kranz Anatomy
The development of Kranz anatomy occurs in three distinct steps:
- Initiation of procambium
- Specification of bundle sheath and mesophyll cells
- Development of chloroplasts and integration of the C4 cycle
Characteristic Features of Kranz Anatomy
The features of Kranz Anatomy include:
- Mesophyll cells are uniform and arranged in concentric layers around the vascular bundles.
- Chloroplasts in mesophyll cells are fewer and do not contain starch. They possess the enzyme structure necessary for C4 photosynthesis.
- Chloroplasts in bundle sheath cells store starch and are larger. They have the enzyme structure required for C3 photosynthesis.
- Mesophyll cells and bundle sheath cells are connected through plasmodesmata, facilitating communication and exchange of materials between them.
What is the Difference Between C3 and C4 plants?
In the context of Kranz anatomy, it is worth noting the important differences between C3 and C4 plants.
Characteristic |
C3 Plants |
C4 Plants |
---|---|---|
Dark Reaction Pathway |
Calvin cycle |
Hatch-Slack pathway |
Season and Habitat |
Cold season, cool and wet areas |
Warm season, dry areas |
Environmental Conditions |
Temperate environments |
Tropical environments |
Product of Dark Reaction |
3-carbon compound (phosphoglyceric acid) |
4-carbon compound (oxaloacetic acid) |
Kranz Anatomy |
Absent |
Present |
Bundle Sheath Cells and Chloroplasts |
Bundle sheath cells lack chloroplasts |
Bundle sheath cells contain chloroplasts |
Photosynthesis in Closed Stomata |
Requires open stomata for photosynthesis |
Can complete photosynthesis with closed stomata |
CO2 Fixation Rate |
Slower CO2 fixation |
Relatively rapid CO2 fixation |
Location of Dark Reaction |
Mesophyll cells |
Mesophyll cells initiate, crucial steps in bundle sheath cells |
Photorespiration |
High rates of photorespiration |
Absence of photorespiration |
Temperature for Growth |
4-7 degrees soil temperature |
16-21 degrees soil temperature |
Global Presence |
95% of total green plants on Earth |
Approximately 5% of plants on Earth |
Examples |
Wheat, oats, rice, sunflower, cotton |
Maize, sugarcane, amaranthus |
Difference between Mesophyll Cells and Bundle Sheath Cells
Mesophyll cells are located in the leaf’s interior, and responsible for initial CO2 fixation in C4 plants, while bundle sheath cells surround vascular bundles, facilitating the Calvin cycle and minimizing photorespiration. Here are some key differences,
Characteristic |
Mesophyll Cells |
Bundle Sheath Cells |
---|---|---|
Location |
Interior tissue of the leaf (mesophyll layer) |
Surrounding vascular bundles within the leaf |
Chloroplast Density |
Contains chloroplasts, less densely packed |
High concentration of chloroplasts, densely packed |
Cell Arrangement |
Loosely packed, irregular shape |
Tightly packed, regular shape |
Function in Photosynthesis |
Initial fixation of CO2 into a four-carbon compound |
Site of the Calvin cycle, breakdown of four-carbon compound to release CO2 |
Metabolism |
Involved in C4 pathway and other metabolic processes |
Primarily involved in the Calvin cycle |
Adaptations to Environment |
Adapted for gas exchange and light absorption |
Adapted to minimize photorespiration and maximize carbon fixation efficiency |
Conclusion – What is Kranz Anatomy?
The specialized molecular processes underlying Kranz Anatomy in C4 plants enable high photosynthetic rates and increased glucose production. Expanding the use of C4 plant species in agriculture, like maize and sugarcane, or transferring C4-like CO2 fixation capabilities to C3 crops, such as rice, holds promise for enhancing agricultural productivity. Additionally, understanding C4 photosynthesis may help in developing biofuel sources like maize and switchgrass, contributing to green energy.
FAQs – Kranz Anatomy
What is Kranz Anatomy Class 11?
Kranz anatomy refers to a distinctive arrangement found in the leaves of C4 plants, wherein the tissue corresponding to spongy mesophyll cells forms a circular cluster around the leaf veins, situated outside the bundle sheath cells.
What is the Advantage of Double Carbon Fixation in C4 Plants?
In C3 plants, which experience significant water loss through stomatal diffusion in hot and dry climates, C4 plants exhibit reduced water vapor loss due to the occurrence of the C4 cycle within the bundle sheath cells.
Which Plants Show Krantz Anatomy?
Kranz anatomy is a characteristic feature observed in all C4 plants. Examples of such plants include sugarcane, sorghum, maize, millet, and switchgrass etc.
What is the Function of Vascular Bundles?
The primary function of vascular bundles is to serve as a crucial component of the transport system in vascular plants. Two essential types of vascular tissues are the xylem, and phloem.
Do C3 Plants have Kranz Anatomy?
Kranz anatomy is typically absent in C3 plants. Although chloroplasts are found in the bundle sheath cells of these plants, carbon dioxide fixation occurs only once in the mesophyll cells.
What is the Anatomy of a C4 Plant?
C4 leaves showcase a unique Kranz-type anatomy, with vascular bundles encased by organelle-rich bundle sheath cells, surrounded by radially arranged mesophyll cells.
What is the Difference Between Kranz Anatomy and C3 Anatomy?
Kranz anatomy in C4 plants enhances carbon fixation, unlike C3 anatomy, which lacks this specialized leaf structure, leading to less efficient photosynthesis.
Contact Us