Wound response in plants

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Plants constantly face injuries from herbivores and harsh environments. To cope, they use local defenses at the wound and also whole-plant (systemic) defenses that spread signals to other tissues.

Physical barriers and early signals
- The plant’s outer layer, called the cuticle, and the cell wall help keep pathogens out. Lignin and other materials also strengthen damaged areas.
- When tissue is damaged, plants release internal signals (DAMPs) to warn themselves. They can also sense microbes (MAMPs) with special receptors to start defenses.

Hormones coordinate the response
- Jasmonic acid (JA), ethylene, and abscisic acid (ABA) are key hormones that control wound responses.
- JA rises after wounding or leaf bites and turns on defense genes and pathways that produce protective chemicals. JA can travel through the plant to alert other leaves to the danger.
- JA works together with ethylene and ABA to fine-tune the response.

Rapid and longer-term actions
- Wounding triggers quick signals such as changes in water pressure and electrical signals inside the plant.
- The phloem’s sieve elements carry sugars and other nutrients. When damaged, the plant first uses P-proteins to plug the damaged pores and stop sap loss.
- For a longer-term fix, plants deposit callose (a sugar-based substance) at the sieve pores to seal off the damaged parts. Callose is made by callose synthase and is removed again once the area heals. Callose also has roles during normal growth and stress.

JA and friends in action
- JA activates many defense genes and helps produce compounds that deter attackers.
- The JA signal moves to other parts of the plant, so distant leaves respond to the wound.
- Signals such as ethylene and salicylic acid can boost or modify JA’s effects through cross-talk.

Morphology and protective traits
- Plants can change their appearance to reduce stress. They may grow smaller leaves, tilt leaves away from the sun, roll leaves, or wilt to reduce water loss and heat exposure.
- Tiny hairs on leaves, called trichomes, can reflect light and keep the leaf cooler, lowering water loss. Dense trichomes are most effective, though they can sometimes limit photosynthesis.

Additional protection
- A thicker cuticle helps prevent water loss during drought and can reflect light to reduce heat.
- Beneficial root bacteria, called plant growth-promoting rhizobacteria (PGPRs), help plants cope with stress. They improve water and nutrient uptake, boost growth, and produce hormones such as auxins, gibberellins, cytokinins, ABA, and ethylene, along with other helpful compounds.

In short, plants defend themselves after wounds with a mix of physical barriers, rapid signaling, hormone-driven gene activation, and growth changes, often aided by helpful soil microbes.