What is the Difference Between Heterocyst and Vegetative Cell

The main difference between heterocyst and vegetative cell is that a heterocyst is a differentiation of a vegetative cell that occurs under nitrogen deprivation conditions, whereas a vegetative cell is a cell that undergoes photosynthesis.

Heterocyst and vegetative cell are two types of cell stages that occur in cyanobacteria. Both cells associate with each other symbiotically in filamentous cyanobacteria.

Key Areas Covered

1. What is Heterocyst
     – Definition, Structure, Function
2. What is Vegetative Cell
     – Definition, Structure, Function
3. Similarities Between Heterocyst and Vegetative Cell
     – Outline of Common Features
4. Difference Between Heterocyst and Vegetative Cell
     – Comparison of Key Differences

Key Terms

Heterocyst, Vegetative Cell

What is Heterocyst

Heterocyst is a specialized cell of multicellular cyanobacteria. It has the ability to undergo nitrogen fixation. Generally, in Anabaena, a single heterocyst occurs per 10 to 20 photosynthetic vegetative cells along the cyanobacterial filament. Heterocyst formation occurs during the diazotrophic growth of cyanobacteria. The structure, as well as the metabolic activity of the heterocyst, are in consonance with the oxygen-sensitive process of nitrogen fixation.

Figure 1: Heterocyst

Furthermore, cyanobacteria belong to a large group of Gram-negative prokaryotes. They perform oxygenic photosynthesis. Cyanobacteria evolve multiple types of specialized cells, including spore-like akinetes, nitrogen-fixing heterocysts, and motile hormogonia filaments. Among them, heterocysts are large, round-shaped cells with thicker cell envelopes. In addition, they contain cyanophycin granules at the poles adjacent to vegetative cells. However, the main function of a heterocyst is to provide a spatially-separating environment for the fixation of nitrogen.       

What is Vegetative Cell

The vegetative cell is an actively-growing cell of filamentous cyanobacteria. The main function of the vegetative cell in cyanobacteria is to undergo oxygenic photosynthesis. Moreover, the vegetative cell of cyanobacteria contains two distinct membranes. They are the plasma membrane and the outer membrane. In addition, there is a peptidoglycan layer between the two membranes. In general, photosynthesis occurs in the extensive internal thylakoid membranes.

Figure 2: Vegetative Cell

Moreover, vegetative cells differentiate into heterocysts under nitrogen-limiting conditions. The interior of these cells is micro-oxic due to the presence of a high respiration rate. In addition, the process of forming a heterocyst inactivates the oxygen-producing photosystems and forms a thickened envelope on the outside of the cell wall.       

Similarities Between Heterocyst and Vegetative Cell

• Heterocyst and vegetative cells are two types of cellular stages that occur in cyanobacteria.
• Moreover, both occur together and work symbiotically to fulfill the needs of cyanobacteria.

Difference Between Heterocyst and Vegetative Cell

Definition

Heterocyst refers to a large transparent thick-walled cell that is found in the filaments of some cyanobacteria and is the site of nitrogen fixation, while vegetative cell refers to a cell of a bacterium or unicellular alga that is actively growing rather than forming spores.

Importance

Heterocyst is a differentiation of the vegetative cell of cyanobacteria, while a vegetative cell is an actively-growing cell.

Structure

Moreover, heterocysts are large, round-shaped cells with thicker cell envelopes, while vegetative cells contain two cell membranes: plasma membrane and outer membrane.

Function

Heterocyst is responsible for nitrogen fixation, while a vegetative cell is responsible for undergoing photosynthesis.

Conclusion                                      

In brief, heterocyst and vegetative cells are two types of cellular stages in cyanobacteria. They occur together and have a symbiotic relationship between the two types of cells. Generally, a heterocyst is a large cell that is transparent and has a thick cell wall. It occurs in the filaments of cyanobacteria. It is also a differentiation of a vegetative cell of cyanobacteria. However, the main function of a heterocyst is to undergo nitrogen fixation. In contrast, a vegetative cell is an actively-growing cell of cyanobacteria. But, they do not form spores. In addition to that, their function is to undergo photosynthesis. Hence, the main difference between heterocyst and vegetative cell is their structure and function.                                                     

References:                

1. Kumar K, Mella-Herrera RA, Golden JW. Cyanobacterial heterocysts. Cold Spring Harb Perspect Biol. 2010 Apr;2(4):a000315. doi: 10.1101/cshperspect.a000315. Epub 2010 Feb 24. PMID: 20452939; PMCID: PMC2845205.
2. He H, Miao R, Huang L, Jiang H, Cheng Y. Vegetative cells may perform nitrogen fixation function under nitrogen deprivation in Anabaena sp. strain PCC 7120 based on genome-wide differential expression analysis. PLoS One. 2021 Mar 4;16(3):e0248155. doi: 10.1371/journal.pone.0248155. PMID: 33662009; PMCID: PMC7932525.

Image Courtesy:

1. “Anabaena sperica2” By Elapied – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Necklace of Mermaid” By Veryn4ik89 – Own Work (CC BY-SA 4.0) via Commons Wikimedia