Animation 27.1 Signaling between Plants and Pathogens

INTRODUCTION

Like animals, plants have a number of ways of protecting themselves against disease. Their first line of defense is their outer layer of tissue—the epidermis or cork—which is generally covered with a barrier of waxes, cutin, or suberin. However, if a pathogen, such as a virus, bacterium, or fungus, penetrates this barrier, the plant responds by producing other protective molecules. Plants and pathogens have evolved together such that pathogens have mechanisms to attack and penetrate plants, and plants have evolved mechanisms to kill the pathogens and limit the infection.

Video titled: Animation 27.1 Signaling between Plants and Pathogens

Transcript Area

Textbook Reference: Key Concept 29.4 Animals Have Biological Clocks Tuned to Cycles in Their Environment, p.725

CONCLUSION

The presence of a pathogen can trigger immune responses in plants. The pathogen produces molecules that serve as "elicitors." Within the plant, elicitors bind to plant receptors, and then the activated receptors initiate a cascade of events that culminates in changes in gene expression. These changes are protective to the plant.

In one protective response, the plant produces polysaccharides that plug the plasmodesmata between cells and prevent viral pathogens from moving freely from one cell to the next. The polysaccharides also enter plant cell walls and provide a foundation for the laying down of lignin, which enhances the mechanical barrier.

The plant also produces phytoalexins and PR proteins, both of which destroy a variety of pathogens.

The plant may also respond with a hypersensitive response, in which the infected region commits suicide and walls off the pathogen from infecting other parts of the plant. During this hypersensitive response, the infected region produces salicylic acid, a molecule that may then be transported throughout the plant. Salicylic acid triggers the widespread production of additional PR proteins, which provide the plant with systemic acquired immunity.

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