How do enzymes help plants fight off pathogens?

Enzymes help plants fight off pathogens by producing defensive chemicals and strengthening their physical barriers.

Enzymes play a crucial role in the plant's immune system. They are biological catalysts that speed up chemical reactions, including those involved in the plant's defence mechanisms. When a plant is attacked by a pathogen, such as a bacterium, virus, or fungus, it responds by producing a range of defensive chemicals. These chemicals, which include antimicrobial compounds and toxins, are designed to kill or inhibit the growth of the pathogen. The production of these defensive chemicals is controlled by enzymes.

For example, the enzyme phenylalanine ammonia-lyase (PAL) is involved in the synthesis of phenolic compounds, which are part of the plant's chemical defence arsenal. When a pathogen attacks, the activity of PAL increases, leading to a higher production of phenolic compounds. These compounds can directly kill pathogens, or they can strengthen the plant's cell walls, making it harder for the pathogen to penetrate.

Enzymes also play a role in the strengthening of the plant's physical barriers. The plant cell wall is a major line of defence against pathogens. Enzymes such as peroxidases and laccases are involved in the cross-linking of cell wall components, making the wall stronger and more resistant to pathogen attack.

In addition, some enzymes can trigger a process called 'programmed cell death' in the cells surrounding the infection site. This is a kind of 'scorched earth' strategy, where the plant sacrifices some of its own cells to prevent the pathogen from spreading. The enzymes involved in this process include proteases, which break down proteins, and nucleases, which break down nucleic acids.

In summary, enzymes are essential for the plant's defence against pathogens. They control the production of defensive chemicals, strengthen the plant's physical barriers, and can even trigger the death of infected cells to prevent the spread of the pathogen.