Plant defense proteins, particularly lectins, play a crucial role in plant defense against various organisms. Lectins are carbohydrate-binding proteins that can agglutinate cells or precipitate glycoconjugates. They are classified into three main types: merolectins, hololectins, and chimerolectins, based on their structure and function. While the original definition of lectins was based on their ability to agglutinate erythrocytes, the current understanding includes a broader range of proteins with carbohydrate-binding domains. Lectins are found in various plant species and are involved in plant defense against pathogens, insects, and animals. They can interfere with the normal functioning of these organisms by binding to their glycoconjugates. This binding can lead to various effects, such as cell death, inhibition of growth, or prevention of infection. For example, type 2 ribosome-inactivating proteins (RIPs) are highly toxic to eukaryotes, including insects and fungi, and are considered as a defense mechanism for plants. Plant lectins also exhibit antiviral, antibacterial, and antifungal activities. They can inhibit viral replication by binding to viral glycoproteins, prevent bacterial growth by interacting with cell wall carbohydrates, and inhibit fungal growth by binding to fungal cell wall components. Some lectins, such as those from stinging nettle and the potato lectin, have been shown to have antifungal properties. In addition, plant lectins can have toxic effects on higher animals, including humans. For example, the phytohemagglutinin (PHA) from soybeans is highly toxic to animals and can cause severe gastrointestinal symptoms. However, the toxicity of lectins is often due to their ability to bind to glycoconjugates in the digestive tract, leading to cellular damage. Overall, plant lectins are important components of the plant's defense system, helping to protect against a wide range of pathogens and pests. Their ability to bind to specific carbohydrates makes them effective in recognizing and neutralizing harmful organisms. Despite the lack of a complete understanding of all their functions, the evidence strongly suggests that plant lectins play a significant role in plant defense.Plant defense proteins, particularly lectins, play a crucial role in plant defense against various organisms. Lectins are carbohydrate-binding proteins that can agglutinate cells or precipitate glycoconjugates. They are classified into three main types: merolectins, hololectins, and chimerolectins, based on their structure and function. While the original definition of lectins was based on their ability to agglutinate erythrocytes, the current understanding includes a broader range of proteins with carbohydrate-binding domains. Lectins are found in various plant species and are involved in plant defense against pathogens, insects, and animals. They can interfere with the normal functioning of these organisms by binding to their glycoconjugates. This binding can lead to various effects, such as cell death, inhibition of growth, or prevention of infection. For example, type 2 ribosome-inactivating proteins (RIPs) are highly toxic to eukaryotes, including insects and fungi, and are considered as a defense mechanism for plants. Plant lectins also exhibit antiviral, antibacterial, and antifungal activities. They can inhibit viral replication by binding to viral glycoproteins, prevent bacterial growth by interacting with cell wall carbohydrates, and inhibit fungal growth by binding to fungal cell wall components. Some lectins, such as those from stinging nettle and the potato lectin, have been shown to have antifungal properties. In addition, plant lectins can have toxic effects on higher animals, including humans. For example, the phytohemagglutinin (PHA) from soybeans is highly toxic to animals and can cause severe gastrointestinal symptoms. However, the toxicity of lectins is often due to their ability to bind to glycoconjugates in the digestive tract, leading to cellular damage. Overall, plant lectins are important components of the plant's defense system, helping to protect against a wide range of pathogens and pests. Their ability to bind to specific carbohydrates makes them effective in recognizing and neutralizing harmful organisms. Despite the lack of a complete understanding of all their functions, the evidence strongly suggests that plant lectins play a significant role in plant defense.