Apoplast

[clarification needed] Similarly, all gaseous molecules emitted and received by plants such as oxygen must pass through the apoplast.

In nitrate poor soils, acidification of the apoplast increases cell wall extensibility and root growth rate.

During local oxidative stress, hydrogen peroxide and superoxide anions can diffuse through the apoplast and transport a warning signal to neighbouring cells.

In addition, a local alkalinization of the apoplast due to such stress can travel within minutes to the rest of the plant body via the xylem and trigger systemic acquired resistance.

[7] The concentration of solutes transported through the apoplast in aboveground organs is established through a combination of import from the xylem, absorption by cells, and export by the phloem.

One common apoplastic disease appearing in plants without restricted habitat or climate is black rot, caused by the gram-negative bacteria Xanthomonas campestris.

Entophytic bacteria can cause severe problems in agriculture by alkalizing the apoplast with their volatiles and therefore inhibiting plant growth.

One of the examples is the endophytic and phyllosphere microbes can indirectly promote plant growth and protect the plant from other pathogens by inducing salicylic acid (SA)and jasmonic acid (JA) signaling pathways, and they are both parts of the pathogen associated molecular patterns triggered immunity (PTI).

In conclusion, the apoplast acts as a crucial role in plants, involving in all kinds of regulations of hormone and transportation of nutrients, so once it has been colonized, the effect it brings cannot be neglected.